, Draft: No'l; for Quotation

THE STRUCTURE OF SCIENTIFIC REVOWl'IONS

Thomas S. Kuhn

Contents

I. Introduction. . .. . . . . . . . • • • • • · .. • •• • • •

II. The Route to Normal Science •• • • • • • • • • • • • • • •

III. The Nature of Normal Science. • • • • • • • · . . • • •

IV. Normal Science as Rule-Determined • • • • · . . • • • • • •

V. Anomaly and the Emergence of Scientific Discoveries • • •

VI. Crisis as the Prelude to Scientific Theories. • • • • • •

VII. The Response to Crisis. • • • • • • • • • • • • • • • • •

VIII. The Nature and Necessity of Scientific Revolutions. •

IX. Revolutions as Changes of World View. · • • • • • • • • •

X. The Invisibility of Revolutions • · • • • • • · • • • · • XI. The Resolution of Revolutions • • • • • • • • • • · •

XII. Progress through Revolutions. • • • • • • • · • • • • •

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I. Introduction

The study of h1storYll.as not been's. u:iw source for the West's can-

ceptionof ｳｃＺｴｾｉｩｬｩ･Ｎ･ｍｩｴｩｮＱｳｨｴｵｳ･ＱＧ｜ｵｩｹ｢･｣ｯｭ･ｯｮ･Ｎ＠ Viewed&s a reposi-

tory for more. than anecdote orchronoloe;y. history cOUld proiluce a decisive

transformation in the image of science by wbich ve are ｮｾｑ＠ possessed. That

image has previously been I'lrawn. even by scientists themselves, mainly :?rom

the study of finished scientific achievements as these ere recOl'ded in the

claee1es and. more recently. in the textbooks from which each new scieu-

ｴＱＧＱＧＱ｣ｧ･ｮ･ｲ｡ｴＱＰｮＭｬ･｡Ｚｲｮｳｾｴｯｾｰｲ｡･ｴｩ｣･＠ ... ＺｩｴｳｴｲｴＡ､･Ｎｾ＠ .. "Inevitsbly •..... ｨｾｶ｣ｲ＠ •..... the

a1m ot such books is perS1.ll1sive and pedagogic; a conception ｯｴｾｳ･ｬ･ＡＱ｣･＠

than an image of a national. culture ､ｲ｡ｾｦｲｯｭ＠ ,a.tourist brochure or a lan-• " ,," "" / c· ＬｾＧ＠ ' ""

guage teJct;. This monograph attempt a to Bhow ｴｾｴＧｉｔ･＠ ha.vebeen micled by

them and in ｾ･ｮｴ｡ｬＢ＠ ways; Its airuis.s eketch of the quite different ',"

conception of eciencethat can emerge .. :?r0l)l thl! llistoriClll record of the re-

searcll ｾ｣ｴｩｶＱｴｹｩｴｦｬ･ｬｦＺ＠ .. ,'.

Even trOll! history> hOlfever, tbatnew C()!lCePt:l.on will not be ｦｑｩﾷｴｨ｣ｏｩｩｬｾ＠

ing if' h1storicalda.ta continue to bescught nnd scrutinized mainly "to t'.!l-

.lIver questionn pOGed by the .unhiatoriceJ. .Iltcrectype <b.'awn from flcience

teAts. Tholle texta. lw.ve •. for .. ･ｘｾｬ･＠ •. often seemed to imply that, the con-

t(lll-(; of Gcience ie uniquely exemplified by the observatioIla, la-.. ｳｾ＠ au:'!.

J.

\

2

together with the logical opers:tiolle cll!ploJ'-eU "hen rolE.tine; those data to

the textbook's theoretical generalizations. The result Me ｢Ａｾ･ｮ＠ e. con;:ep-

tion of science vith profound developmental ｩｾｬＱ｣｡ｴｩｯｮｂＮ＠

If science ie the constellation of facte, theories, and methods ｣ｯｬｾ＠

lected in current ｴ･ｸｾＸＬ＠ then scientists are the men uuo, successfully or

not, have striven to ｣｣ｮｴｲｩ｢＾ｾｴ･＠ one or another element to that particular

constellation. Scientific development becomes the piecemeal process by

which these items have been aclded, sin,gJ.y and in combina:l;ion, '';0 t.he ever-

growing stockpile tha·t constitutes scientific teclm:t.que o.:nd lmwlee.ge. ,W.a

history of science becomes the discipline uhich chronicles both these suc-

cees:l.ve increments end the obstacles that have inhibited their acc1J.lliUlation.

Concerned. vith scientific devel.opr.lent, the historian then appears to have

tl1C main taslts. On the one hs:ad, he muct de1;e..'"l/l1!1e bY whet man and at tlhat

point in time each contemporary ecientii'ic fact, law. and theory liaS dis-

covered or invented. On the other, he must describe and explain the ccn-

gel'ies of error, myth, and superstition which !leve 1.uh1bited the more rapid

･｣｣ｾｵｬ｡ｴｩｯｮ＠ of the constitucnt£ of the modern science ｴ･ｾｾＮ＠ Much recearch

Im!l been directed to these ends, and 1:J0lt-e still ill.

In recent yss.:t:a, h01r<lVer. II :few ｨｩｇｴｯｲｩｾＧＱｳ＠ of science h",ve been ｦｾＮｮ､Ｍ

lug it more a.,d more difficult to fulfill the funetions ｾｾ＠ the concept of

scientific develepment-by-accunmlatiun essigns to them. lw cUronicl(;T:' oJ.'

au incremental process they ､ｩｾ｣ｯｶ･ｲ＠ that additionnl research makes it

harecsr, net easier, 'co sumTer queatiOnfl like: When .>as O::ygen diecovsiO'ed?

truo ｦｾＺＮｲｳｴ＠ COl1.t::ei ved of emrgy cc·nser'li"ation7 . Incr;;aaingly> n few of them

3

cultiesin· diatil)gUishill5.the "scientific". comr.onent ofpaet ｏ｢ＡＱＰＱｾｶ｡ＮｴＺｩＮｯｮ＠

end belief i'rom 'tihll.ttheir predecessors had readily labelled Herror" and.

that those once current v1awse! ｮ｡ｴｵｲ･Ｎｾｾｲ･＾＠ as a whole, neither leao

scient1:t'ic nor more the product of human idiosyncrasy than ou:r.O\I!l. llone

of these notf disce..1:'dedbodies of theory &ldobservation ce-.!l,even in retl:O-

spect,.bed:l.v.l.de.d 1ntotwoparts,.Qne.belong1ngto 't.!le. scionti:f'ic stocl;pile

because it. is preserved .in eurrent.texts,.theother to mytholoBY because

torian had thought he.stu.d1cd .must include bodiel3of belief' incoIil.PGL'i;ibJ.e

lIith those current today .. or.1tmllst exclude views. of. nature v.!.thout 'Il'hich

olJr '(mn ll'ou1.d not have come ＱｴｩＧｾＰ＠ 'being. The llame hiztor1cal research th&t

displays the difi'icult:l.esin:!.eoJ.e.ting indiv:l.dmt.l. ｩｚｬ｜Ｇ･ｮｾＺｬＮｯｬｬｦｬ＠ E1.tlci. diSCOVel'-

iee gives g:r.ctind ·forprof'oUllddou'bta about .. the cumulative .procees thr0\1Olh

wien these ｾＬｮ､ｩｶＺｬＮ､ｵ｡ｬ＠ eont:r:!.but1olUl to science 'Were. thoue,ht '1;0 he,Ye been

revolution int.'ie study of eciEmce; th01.1gb one thetis still in its c,"-,.'J.y

4

they insist upon studying the OD:lniolls of t1;&t g;:ot-'l? fJ,i:W. ethel:' ailll:Uc.r

ones from the vie-dpoint--ucuslly very ､ｩｾｲ･ｲ･ｮｴ＠ froul thst of ｾｾｩ･ｬＢｮ＠

scienc:e--which g;ives ｴｨｾｭＺＺ＠ opiniolls the mm:im"um :lntert'.!ll cohe::euce /too.

the closest possible fit to nature. ｓ･ｾ＠ through the 'Ii'Ol'i!:C tllat l'OSUU,

varks perhaps bellt exell1J?lii'ied in the llritings of Alm:andre Koyrii, science

does not seem altogether the sume ･ｮｴ･ｾｩｂ･＠ as the one discussed by writ-

ers :1.n the older historiographic tradition. By implication. ct leest,

these historical studies suggest the possibility of a new ｾｾｺ･＠ of science.

This ｭｯｮｯｧｲ｡ｾｨ＠ aims to delineate that imase and to make it flLl1y explicit.

What aspects of science ｾｾｬｬ＠ emerge to prcm!nence from the ｶｩｾｾＱｬｯｩｮｴ＠

toward science here to be eleborated and ､･ｦ･ｮ･ｾ､Ｒ＠ Fixst. at least iu.Ol'-

der t,f' prellentat1on. is the in(lU:fi'iciencyof methodological ､ｩｲ･｣ｴｩｶ･ｾ［＠ by

themeelves. to dictate D. unique eubstallt:l.\re conclusion to l!lI?.!ly sorts of

eciellt1i'ic queot1ona. Inst..-ucted to examine electrical or cilemical phenom-

ena, the 1&'.0 ,ho ift ｩｧｵｯｾＺ｡ｮｴ＠ of these tields out '\rho lma.Hl l!h£t it ie to be

scientific lEay ｬＮ･ｧＱｴｩｭＸ［ｾ･ｬｹ＠ reach any one 01: a =ber 01: Ｑｮ｣｣ｲｾｽＭＺｬＮｕ｢ＱＰ＠ con-

clusions. Jlmong those leGitill!<,te po03s1·011:1.t1es, the :;:.articul2.r ccnclEsions

he docs arrive at are lU'obnbly determined by his prio:;;, e::q:·orieo.ce in other

fields. by tbo accidents of his investigation, ｾＮ＠ by his O"Jil iniiviQtcal

l!!8.li:ol,lJl. Hb2.t beliei'D a1Jout. Ga:j. the starn does be brillg to the nttte,y ｯｾ＠

chemistry or ･ｬ･｣ｴｲｩ｣Ｑｴｹｾ＠ "nieh of the many conceive.ble ･［Ｚｰ･ｲＺＡＮＺｬｬＭ＼ｾｮｴｳ＠ rele-

vu.nt to ""he r,:;,'.f fiola. dees he elect to pel'form f:l.rat? Ani ｾ［ｨ｡ｴ＠ e.ll'pects of

5

. ｣ｾｴｙｬｩｩｬｶ･ｬｬｓｩＺｩｓＧｴＱ･ｲｬｩｴＶｱｵ･ｳｴｬｏｩｩｳ＠ l:l.ltetheoeare oft.,nc'sriditial ｣Ｑ･ｾ＠

terminants of scientificde'Velo71ment •... ｾｬ･ＡｬｍＮｬｬ＠ note •. ｦＨｪＩＢｑ＿ＮｶＮｲｬｩｬｬｬｑＮ［｣ＭｩｴｌＮｓ［［ＺＬ｣｟ＢＭＮＺｾ＠ ..

tion II tbll.t the ･｡ｲｬｹ･ｴｾｳ＠ ofmoet aciences have been characterized by

cont1nua.1.· competi tionbetlleen a'number"of'd.1Btlnct-'V1:evs . of- nature, each

partially derived··i'rom· .. sndaU roughly, compatible,v1th,the,.d:l.ctll.tes of·

scient1fic observation and method. What differentiated 'I;hese variO'..tS

8choo16 wal!! not one ｯｲ｡ｮｯｴｨ･ｲｦＧ｡ｩｬｵｲ･ｏＢＮｲｬＺｬ･ｴｨｯ､Ｍｾｴｨ･ｹｶ･ｲ･＠ all "scien-

ti:l'icH--but whatve shs.Ucome to CIlJ.l the:l.r1ncamnenaurablev.ays of see-

inzthe w.rldand Of doing science in it. Observation ana' eXJ,>llxience can

drnatically restrict the range Of . admissible SCientific belief. else there

｣ｾ､ＮＮｾｮｯｓｃｩＨｬｉｬｃＨｬ＠ •. ·ll\1ttl:leY.C:SJlllot .. ｡ｬｾ､Ｈｬｴ･ｾｬｬ･ｅＡ＠ .. ーＡＡｬＢｴＱｾｊＮ｡ｲ＠ ... bqdy of

suchbel:l.et.An apparently arbitraryelement, compounded of'persontll'an:l

ｨＮｩ･ｴｯｲｩ･ｴ＾ｊＮ｡｣･ｩ､･ｮｴｾ＠ is a.lWllyt3&, tormative ingredient of the beliefs es·

:poused by a giVen scient1f1ccOmmlmity at a given time.

That element otarb1tr&'1neSB does ｵｯｴＮﾷｨｯｷ･ｶ･ｲｾｩｮ､Ｑ｣･Ｎｴ･＠ that any

scientit'.c group could in'acticelts trooe at an witliout SOllie set of ra-

ceived beliefs. Nor does 1t mekelees consequential the jport:l.c1.uar con-

stellation towl:l±ch the group, at agi·reu time, is in fact cOl:r.ll1tt.od. Ef-

fecti ve reeearch ecarcely beg1ne-bd'ore a ec1entif1c c=1 t.y thinke :i. t

has acquired :firm answcra toqv.est:l.one like: W'aat arc the t'lmClament;cl en-

tit.ies en: "hieh the uni·Jerae ie cO!llposed? nOlI do '.;heee in'tercGt with Cll.·;:h

other end with the senses? What questions may lezitimately bo csked about

such entities snd "What techniques employed in seeking Elolutiono'l At. leust

:tn the tr.c.ture GCienCCB, anr;wcrll (or full substitutes for ｣ＮｮＵＱＡＧＺ［ｾＧｳＩ＠ to que:;·,

t1,('lns like 'these ('-ol:"e firr::ly' ｇｾ｢ＧＤｴＱＮ､ｾ､＠ in "the ･､ｵ｣｡ｴＺｩｾｏｬＺＡＮｏｊＮ＠ :tr-.;it1.ation that

6

eo.uce.ticn 13 booth rigO!'ous end rigid, ｴｨｾ｡ＧＤｬ＠ aUfil:re:,."s c:omG' to ｾＮＺ｣･ｔｴ＠ ｾＮ＠ u.eel.:)

hold cn the scientific n1ind.. That they can do so dool} It''olch to t;cccun:i:,

both tor the peculiar efficiency of "l;!-.. 2 no!1'".At ree.cc,zoch ac'.;:\. \';c t.y ar.d. fCle'

·tohe direction in wich it p.-oceeda at any given t1.me. "''hen e;{e!"..:.tu:!.ng

n=l science in Section III, lie fiho.ll want finally to t',eaeribe ·the;t r·e-

search e.s a atrenuoU!3 ana. ､･ｶｯＧｾ･､＠ attelllpt to force nature into ﾷｾ｢Ｎ･＠ concep-

tual. boxes svp}?lied by professional education. S1.!i1UltrulCO'-'OJ.y; li'O oll",ll

wonder whether research could proceed without such boxes, ｾｨ｡ｴ･ｶ･ｲ＠ the

e.1elll0nt of arbitrariness in their ｨｩｅｲｾｯ［ﾷＺＡＮ｣＠ ｯｲｾＮｧｩｮｩｊ＠ end.. occaz;:l.o:ll1.l1y, in

their eubsequent ｾ･ｶ･ｬｾ･ｮｴＮ＠

Yet that element of arb! trarinc!ls ie prel'lent, i!.I'.!l it too l:ias 1m im-

portant ef:fect on z;cieutitic dcvelop!!len'G. one '1M.ell .. 'ill be e:mrnined in

detail in Sact5.ons V and VI. r,o=l ･｣Ｚｾ･ｮ｣ｯＮ＠ the a.ctiv:!.ty in uhieb. ＱＱｬＰＳＧｾ＠

scientists inevltebly epend aJr.oet ｾＱＱ＠ t.heix time, is predicated on the

assumption that the llc5.entUic collliIl1.lIdty km:n;ra l',hat the w,')l'ld 18 15.1;:.",.

Much of the en'l;erp-.t'"ioe 9 s success ､･ｲｾＮｶ･ｮ＠ fl'"O!J. the ｣ｏＧＢｾＢＢＢｊＧｩＮＺｩＺｴＮｹｾＮｳ＠ "t.t111il'igl:lens

to defend thet. tt!HI'llll!;ptl.on, it neceseary at consideruble corrh. No=l

aCi€llC!€, i'c:,r ey,.s.urple, au:ppreoscs ｩ｜ｴＮｾｭｯｮＮｴＮ［Ｎ｡ｬ＠ nevel t.ies becaur.re ｴｨｺｾＢ＠ ｾｔＧＨｊ＠

nCC:€'DE'-ar5.1y cubvercive of its beeic co-.auitmcnts. ｉｲ･ＧｬＮＺＬ｣ｬｾｨ･ｬ｣Ｕ｡［＠ flO l-:'):-:.g

aG ·those ccrotri ｴｲＮｬ･ｬｬﾷｴｾｄ＠ :retcin an clem\?ut of the m"bi trn.."7, the v'ery no:t.UX'0

of nOrlnnl re8earcb. encU!:>"',;c tha;'c novelty shall not .be E"r.1ppress&:l for. ｶｇＭｲｾｬ＠

ｬｯＺｮＮｧｾ＠ So.nretltnos e norlml p::'o'!Jlem; one ';;'ha't cugh:'\i to be solvable by ｬＺ［ｲｬｯｾｲｵ＠

ruleg and ｲＧｬＢｯ｣･､Ｚｾ･ｳ［＠ resistu the reiter:z.t8a onslnv,ght of thc cblGl;rfi mern-

7

'Which ｃｳＮｮｮｯｴｩ､･ＹｰＱｴ･ｲｾ｡ｴ･､･ｦＺｴｯｲｴｪ｢･ｮｬｩＵＱＱ･､ｵｩｴｨ＿ｬＮﾷｯＺｦＧ･･ＧｊｩｯＡｬ＼ＩＬｪＮ＠ e:l):ec-\

tatioo.. !D .. , these. and otller ;roys ｢［ｾｂＺｴ､･ｳｮｏｚＧＡＡｬＡｬＮｬｳ｣ｩ･ｲ［｣･Ｎ＠ doe" a'1d. Wlct go ＭＭＭＭＧＢｾ］ｾ］ｾ］Ｍ］］Ｍ］］ＺＮ｣ＮＮ］ｾ］ｾＺＺＺＮＺＺＺｾＺＺＺＺＺＺＺＺＺＺＺＺＮＮ｣ＮＺＺｾｾｾｾＬ｟ＢＢ｟ＢＢＢ｟ＢＮＬ＠

astray. And when it dooll--:vhen, tha'G is, the pro:fcs,,1cn can )10 101lscr

eva.de811omal1esthats'.1bvertthe e..':istiIl$tre.ditiOll- of (:cient:Lf'ic prs:::tice--

then" 'begin " th!l, . ｅＺｸｴｬ［Ｇ｡ｯｬ［ＧＴｩｐａａＧｙＺｩＬＷｬＬｹ･ｂｴｩｳﾧｴｾＹｮＡｬＬｴｨ｡ｴＮＬＫＨｬ･Ｎ｡ＬＮｴｨ･＠ ｊ＿ｬＺＨＩＺ［Ｇ･ｾ＠ sio!!.?, tIMt

to I!I. new set c£ cOIllrilitments and ｡ｮｾｭ＠ .. ;;;yo! l'I't1.Ct:tci!'.g science. T'ill1 extl'u-

ordinary episodes in vhich that shift ofprofess:ton&icommitments occurs ｾ･＠

the ones ｫｮｾｾ＠ in this monograph as acientific revolutions. T'ney are the

ｴｾＮｴｩｯｮＭｳｨ｡ｴｴ･ｲｩｄＸ＠ cOlllplements to ｴｨ･ｴｲｯＮ､ＱｴＱｯｮＭ｢ｯｾ＠ a.ctivity of normal

science.

The llIostobVious ｾＺ＼｡ｭｰｬ･ｳ＠ of scien'.ific revolutions exe those famoua

episodes in Bcient1f1cdevelopment tbb.t, have ｯｦＭｾ･ｮ＠ 'been labeled revolutions

before. There:f'ore.:tn Sections VII an.clVIII, where the ne.ture 01' scientific

revolutions i6 fir!!t directly scrutinized, 'Ire shall deal repe"tedly 1d,th the

episodes in the history 01' at lellat the physicnl science these display lrnat

all ｾ｣ｩ･ｮｴＱＮｩＧｩ｣＠ revolutions areaboui; •... Each of theIll necessi'uateu. the C0'U'':::U''

nity's rejection of ella time-honored lilcientifictheoryin favor or ＦＺｬｬｊＧｾｨｯＺｴ＠

illcompatible 'With. it. Each produced. 1:. COllGGguent shift in the go.'l.la of

ｯ･ｩｾｲＮＮ｣･Ｌ＠ in thelll'oble."Js avo.llnble for scientific ,scrutiny J and. :tn the

ste.'I'1dards by 1>-m.ch tr.e pro1'es::;:!.on 6.eternined what shol.',ld count o.S e.ll o.amis-

;mys tM;t 1f!'! shell uJ.t1ma.tely need to describe as a tranefol"'lll.'li;ion of the

acteriet.:i.cs of cc:i.eutii'ic ｾＢ｡Ｍｶｯｬｵｴｩ｣Ｚ［ｺＮ＠

8 .

These characteristics emerge with particular ｣Ｑｾｲｩｴｹ＠ frau a stu-iy of,

say, the Newtonisn or the ｃｨ･ｾＱＱ｣｡ｬ＠ Revolution. It is, h01lever, lJ. ＺｦＧＮｭ､Ｂ｟Ｂｬｬｯｮｾ＠

tal thesis of this monogra.ph that they can aleo be retrieved from the study

of meny other episodes which were not so obviously revolutiontlry. For the

far smaller professional group effected by them ｴｾ･ｬｬＧ＠ s equations were as

revolutionary as Einstein 's, and they Wl';'re resisted accordingly. The in.

vention of other new theories regularly, and appropriately, evokes the same

response from some 01' the specialists on ｷｾｯｳ･＠ are of special compatence

they impinge. For these men the ne-:-l' theory implies a chsIJge in the rules

governing the prior practice of normal science. ｉｮ･ｹｾｴ｡｢ｬｙｊ＠ therefore, it

reflects upon much scientific work they ha7e already ｇｕ｣｣･ｳｳｦＧｶｾｬｹ＠ ｣ｾｾｰｬ･ｴ･､Ｎ＠

That is why a new theory, however special its range of application, is sel-

dom or never just an increment to what is already k!lmm. I'GS sOBiml1at:!.on

requires the reconstruction of prior theorY and the reevaluation ot prior,

fact, an intrinsically revolutionary precess that is completed seldom by a

single man and naver overnight. No wonder historians have had difficulty

in precisely dating this extended ｰｲＮ｣ｾ･ｳｂ＠ that their vocabulary impels them

to view as an isole.tsd event.

Nor are nov inventions of theory the only scientific events which have

ｲ･ｶｯｬｵｴｩｾＧｙ＠ impact ｾｬＧＰｮ＠ the ｾ｣Ｑ｡Ｑｩｯｴｳ＠ in Ｎｾｯｅ･＠ ､ｾｩｮ＠ they occur. The

cOl!l1!litments 'Which govern ncl'1llc.l science speci;('y net only what sort6 (Yi: en-

tities the univorse does cOllt5.in, but alBO, by implication, those thnt it

does not. It follows, tbOU8h the point will ｲ･ｾＧＱＧ･＠ ext.ended diccu5s;l.on,

that n ､ｩｳ｣ｾＮ･ｲｹ＠ ｬｩｾＮ･＠ thst of, say: 07.ygen or X-Reys docs not ｳｾｾｬｹ＠ ndG

or:.e more it-2m to tbe PCIfJlat:i.on of the scientist; ｾ＠ S ,(-Tcrle.. tJl"'o-tJj'c·tely it

9

newark at theory thrOUGh lIh1ch it deala 'ldth the world. Sc:!.ent:t:!'ic :f'-sct

and theory are < not ｾ｣Ｒｴ･ｇｯｲｩ｣｡ｬｬｙｬｬ｡｝Ｎｬ｡ｲ｡｢ｬ･ＮＧ｣ｸ｣･ｰｴ＠ perhaps''lflthln a sillgle

«tradition atnormaJ.,..scient1fic. practice; The.t.is .. lilly ｴｨ･ｬＡｬｬ･ｾ｣ｴ･､＠ <iis'-

covery is not simply factual in ita import and why the scientist's world

is qualitatively tranaformed as well asqwmtitativel.y enriched. by :f\mda-

mentalnovelt1es 01' e1ther fact or theory.

This extended conception at the nature at scient;1flcrevolutiollS is

the one to be delineated in the pages \Thich tollow.';.dmittedly the exten-

sion stra.tnscu8tomary uea,se,];lerhapsbeyond the l1cenacallowed even to

metaphor. Newrtheless. I shllll. contiIl1!e to speak o;t'<e'l."en diecoveries.e.a

revoidtionary, because it is .1usttlieposslbility of relatii'l!!: their_Btruc-• "', __ M""_"'_'''' "" ,_''', •• ,_'''',,' __ '''' __ "'" '''_ "" • '" _" '"'''''' ''''''

tu..-e to tba:t &f •. say. the Ca,pernican Revolution that makes the extended

conception seem to me 60 important. Theprecedlng dicc1.!.ssioniniicates ... how

the· com,plementarY not.:!.onsaf normal ecienceWll.tofscientiticrevolut:to!1!l

will be developed in the eight eectiOllS immedia.tely t.o follm: • The oncs

that :1'01l0-W" them attempt to dispose of tbrea l·ema.1ning ｣･ＺｃＺｾｬＧ｡ｬ＠ quoetion:::.

Section X, by discussing the textbook tradition. coneidcr6'fby 6c:1.l'utific

revolutionahaveprevlcusly been so difficult to see •.. Section XI o.escribea

the revolutionary cO"'.P<'ltit:i_on bet ... -een the proponents of the 01(, nCrJ"..al-

5cienMflc tradition and the adherents of the new one. It thus conoidal'S

the process l!ilich lllUllt eomehC".;' replace-the coni'1rmat$.on or falsification

procedm'ea made femililll' 41' cur uaual in:3ge of acienco. COlIrpGtit:i_on b$tween

10

progress. For thnt question, hO'.-ever, thitl mouosrapll 'Will p:ro'l5.,1e no mOTe

than the main li-nes 01' answer, cne which depends 1-!pon ｃｨＢＮｬﾷｾ｣ＮＺｴ･ｔｩＺｳｴｩ｣ｳ＠ of

the scientific c0lil!llUll1ty that require llI'J.ch arld1tior..al o:qJlo;:ation em!;.

study.

IT"ne f1naJ. vereicn Yill x'equire one or 1:,,10 additional ps.rag;rapha at

this point. They ,.111 ｵＬｯｾＺ｣Ｚｲｩ｢･＠ footnote and bibliography polic;", ｾＮｮ､ｩ｣｡ｴＮ･＠

the relation of this :fon! ot the flCnogrli.ph to its i'ull<:!l:' v!)l'siou, JuotH'y

t181 acknowledgmente.]

or more past ec:l.entif'ic achievements tha.t have· CO'.:le to be accepted. as es-

tablished Paraa.:@i1sbY the ov'erimelfuingmaj6r1ty of thepr.ofessionalscien-

tif':!.c qommunity. Todaytheee parsdigmaareto be ｾｦｯｵｮ､ｾｩｮｾＮｳ｣ｩ･ｮ｣･ｴ･ｸｴ｢ｯｯｫｦｬｬ＠

elementary and. advanced. SUch texts Bll.-Pound the body of accepted theorYt

illustrate many or ell of its lluccessfulapp1:tca.tione.andcompare these 6.p-

plications wIth eltempllll'Y obsen'atians and el>.-periments. Betoreoooks111re

thelle became popuJ.arearly in the nineteenth century (a."!d. until even. mere

recently 1nthe more recently matured sciences),meny6f the ｩ｡ｭｾｾｂ＠ classics

of ecienCBserved.a similar !Unction. Aristotle's !hysics.,Ptolemy·s

ｾ･ｳｴＬ＠ llewton's Princ1l?ia and 9gt1c!tl!. Franklin's Electricity, Isvoisier's

Chemill:tr;y .•..... and .. ｉ［ｹ･ｊＮｬﾷｉｬｃＭ･ｯｬｯｾＧＺＭｴｬｬ･ｳ･＠ and m::,uy other ;rorks served tor a time

implic1tly to define the legitimate problema end methods afa research field

tor succeeding generations ot ーｲ｡｣ｴｩｴｩｯｾ･ｲｳＮ＠ They ｾｾ･＠ able to do so be-

cause they shared two essential cheracteristica. Theil' achievement ｾｾｳ＠ suf-

ficiently unprecedented to attract an enduring group of adherents ｡ｾｹ＠ from

open-ended to leave all sorts of problems for the ｮ･ｾ＠ practitioners to ｾ･ｳｯｬｶｯＮ＠

These character2stics of pnradisws reguire!urtller elaboration a.id ＮｾＱＱ＠

shortly recei v,," it. 1'1.-1; fir st the I'ole of paradigms must be cle.rified 'DY

noting a sense in \1hich i;hc.:e can be such a i:htn$ as scientific practice

11.

12

physical optics. Tcday's physicc ta:ttboo1::s tell Ｑ［ｨｾ＠ Btv.zlent th,at lii¥d;. 5.s

of \laves and. ｇＨＡＡｬＧＮｾ＠ of particles. ｒ･｡｣ｾｳｲ｣ｨ＠ prccee(ls accoz'dillgly, 01' ｲＨｩ［ｾｨ｣ｲ＠

according to the rom-e elabors;te end. Lw,themstic.,l cnaracteri"s.tion from "ilieh

this ｕＶｕｅｾ＠ verbalization is derived. That chr.racteri:!;a;l;:!.on of light is, h<:;!,-

ever. scarcely half a century old. Before it 'I.'aS dc-"eloped by P1e.nck, E:l.n-

stein, and. others early in this century, 11hysice texts tm:ght that light 'il8S

t.e.nsveree wave motion, a paradigm derived uJ.tiDately frCl'!l! the opticC'.l writ-

iDgB of YOtlllg and. Fresllel in the early nineteenth century clld. cmbG.o.ied 111

most physics teaching frClll about 1830 cu. Nor .'as ths l1'<lve theo!'Y the first

to be embraced by almost all pre.ct1.t:l.ollerz of optical adell.ce. DV.Z'ing the

eighteen'vn centu.."'Y the psradigm for this field '!>."as provided by ｬｬｾｬＮｩ［｣ｮＧ＠ s

ｾｩｃＡ［ＺｳＬ＠ which taught that light 'Ima lll9.terieJ. cOl"puaclcs. Jl.t that time pbya-

ic1.ats Bought, as the early '!lave thsol'j.ots did not, for ev:!.e.ence of the pres-

sure exerted. by light particle a impingiDE on solid bodies.

rmrolutione, and the success:!. ve trl1.!lci t5_OD from one peTli.d.i(!% to Imothsr via

be exrunining :I. t Il,S such in the next three sectiO'.ls. But ｬｩｨＬＺｾ＠ cC!r:.cerns uo

hel."e is only the contrast bet'htl9n that pattc..-m .C'wd the one chnrac-terizing

'.

13

ss· Ｚｰ｡ＮｲＱＱ､ＮＺＡＮｉＡＩｔ＼ｬｴｾ｣ＨＩＧｬｬｑＡ［ｦﾷｹｧＺｾＺｩＮｾｵＧｴＬＺＺＮｊ［ｬｩ･＠ .. :i;l8rilcUJ;ru.- cluster·cf·· OXrG ｩｃ･［ＡＮﾷｰｬｬｃｮｾＢＨＹｮ｡＠- "---------,,---.-.,,

which its own theory could domoet to ",::;plain.

dealt with by !l'! !.!££elaborations, or theyrellainc.(t as ｯｵｴｦｩＮｬＧｾｮ｡ｩｄｧ＠ problGfas

for further research.

At varioust'JUQ.s. e.ll toone schools ｾ･＠ significant contributions to

--'-______ Ｍ］ｴＦｬｨｬｬｩ･ｾ｢ｬｏｯ､ＨＮｬＬｃｊ＼ｬＱｦｲＭｑｯｩＭｦｬｅｭ･･ＺｐＧｴ［ｉｬＬ＠ phan=1ll£, WJd. techlligueo tra.n. 'lrilich liewton <Ire;, the

first nearly uniformly accepted paradigm for physical optics. Any defini-

tion of the scientist that excludes.st least. the more creative members of

these various schools i;illexclu.de their mod.e:rn IltlCCesaore as well. Those

men were scientists. Yetanycne ｾｩｵＱｮｧ＠ a survey of physical optics be-

fore Newton may well conclude that, though the field's practitioners were

scientists, the mit .resuJ,t or their activ.ltY'llllssomething leaothan ec1ence.

Baing able to take no cC!l!lllon body of belief tor grsnted,each -writer en phys-

ical optiCS Zelt forced to bUild his field a!lew from ita foundations. In

doing 80 his choice of l!UPPorting ｯ｢ｬＳ･ｲｶ｡ＺｾＺｴｯｮ＠ and e;-q>erimcnt ;'7ltl relatively ｾＬＺＮＬ＠ ,." "',, '

free, for there .Wlsno standard llet.oi'·methodeOl' of phenomena that every

ax>tical writer ＺｦＧ･ｾＮｴ＠ forced to employ and e:r.p1.s.in. Inevitably, Ullder these

d.rcumstances, thed:!.eJ.ogv.e o:f'thereaultingbooks ｾｉｬＺＡｓ＠ often directed as

ll"o'.,ch to the members of other flcho()ls,as it.Ull.s t·o .. nature. That pattern is

Lot unfamiliaz' :i.n a number of creative fields today,nor is it ｩｴＡ｣ＮｯＬｾｰ｡ｴＺｬＮ｢ｬ･＠

,rith sign:l.fictmt discovel'Y and in'.rent:!.on. It 16 not, ho-»ever. the l?at.tern

of develC1'ment toot phyeicsJ. optics acquired after Newton o.nd that other

natural sciences lila-!re f'smilim: today.

The histCl'""l.,! of elec-crice.l :cescnrcn in the fir£r!# ha1f 0'1 the eighteentb

,

All their numeroue concepts of electricity had sO:llcthlng ｾＬｮ＠ c=oll--they

were partially de .... ived. fran one or another version of the mechanico-corpl.lS-

culnr philosophy tlw.t guided a.1.1 scientific reseru'ch of the day. In addi-

t1oo, all were components of real scientific theories, 0-1 theories, that

is, which had been draw 1n part :£'rem experiment and observation and tthich

partially deter'Jl'n"a. their choice and in"OOl'llretat10n of ｡､､ｩｴｾＬｯｮ｡Ａ＠ problems

undertaken in research. Yet thov.gi:l all the experilll'ants ｬ＼ｾ･ｲ･＠ electrical end

though most of the ｃＲＮｾｲｩｭ･ｮｴ｣ｲｳ＠ l"ee.rl each other's works, their theories had.

no lllore then Il. family resemblance.

One early grcnip of theories ｩＧｯｕｯｾ［Ｍ･､Ｎ＠ se'li'Emteenth-century pre.ct:!.ce, re-

gar.ding attraction and frict:i.onaJ. generation as the tunda!!:0!:tll.l electrical

phencmena. This group tendec'!. to traat repulsion ao a fleccndm'y ei"l'ec·t; due

to scme sort of mec!J.s.::licaJ. rebounding v.no. also to pOfJtpalle fer 8S long e.s

pOl'lllible bo'ch discussion e.n.d syatemat:l.c :research or! ｇｲｴｾｹＧ＠ s ne'lrly discovered

･ｦｦ･｣ＧｾＬ＠ electrical conduction. (Jl;her ｾ･ｬ･｣ｴｬＧｩ｣ｩ･ＮｮｓＬ＠ tt the t01Ul io their crl11l,

took attraction and ｾ･Ｚｰｵｬｳｩｯｮ＠ to be equelly ･ｬ･ｭｾｮｴ｡ｲｹ＠ ｭｳｮｩｦ･｣ｴｲｾｴｩ｣ｮｳ＠ of

electricity end modified their theor:f.e!: end x'osearch accordingly. (Actw..lly,

this group is remarkably ｳｭｲｾＭＭ･ｶ｣ｮ＠ Franl:1in's 'cheory never gutte ecaounted

fa::- the lr.utual rCIlvJ.zioll of ＧｾＧ｜ｲｯ＠ n<:gs.t:t vely C;l."'Xged bcdies.) But they h,;(l as

15

Ｂ･ｦｩｬｵｶｩｵｭｩｩｾｴｨ｡ｴＭ･ｭ］ｴ･､Ｎｦｲｏｬｬｬﾷｮ｡ａ｣ｇｮ､ｵ｣ｴｯｲ｡ｾＭｔｨＺＡＺＶｓｴＧｯｴｲ［［［ｽ＠ ···initwtu.."U,

______ had diff'iculty:.'econ.::1ling its tb.eca'Y .. "ith a number ot' {;"tt;:'act:tvc w::d rc-

pulaive efi"ecta. Only through li'rantlin's wca'kd:l.datheo:ry srise which

couldaccov.nt with aomethitlg.like equal facUityforverynearly all theee

･ｦｦＧ･｣ＺＮＱ［｡ＬａａＨｌＺｷ｢Ｌｩ｣ｨＬｴｨ･ｲ･ｦｾ･＠ co\lldanddi4proviAeamws?;quent generation

of "electricians" withe. CCl!D!ilon :pa:t'adigm for ita. reaeexch.

Excluding thosefields,likemathelll8.t1cll ar,d. astronomy, "'hose t'irst

firm.paradigms date from.prehistca'y and: also those. like ｢ｩｯ｣ｨ･ｭｩｬｩｲｾｲｹＮ＠

which arosc by division .and. reccmb:l.zJation of apecia.J.tics. ab'ev.d.y matured.

the situations outline.d abovo are historically t:l'p1cah Though itinvclveo

my ｣ｯｮｴＺｬＮｮｕｩｾ＠ to em,ploy the tmfortunates1!llplif1cation 'Ghat tags an. extendeCl

hiator1ca1 episode with a single and somewhat·.a:ib1tlll.:t'iJ.y chosell r.ame (Ne'b-ton

or Franklin, above), I ｳｵｧｧ｣ｳﾷｾﾷ＠ t!l£l:'G awnSf'. tundamentaldiaagracments chsr-

acterize.d, far example, the study 01' motion before Aristotle and. of statics

before .llrch1medes,the .study ... ｯｦＮｨ･｡ｴＮｾ｢･ｦＧｯｲ･Ｎｬｬｬ｡｣ｫＬ＠ of ｣ｨ･ｭｩｳｴｾＢｹ＠ bai'ara Boyle

and.Boerhaave, and of' historical geology before Hutton. Inl>ar.te of b:l.ol().z;f;

the study of heredity, for example, the first ｵｮｩ［ｾｲｳ｡ｬｬｹ＠ received ps:radigms

6."e still more recent, and it relll!1.ins an open question 'Whutpsrts of EC-:::!.aJ.

science M'ile ;yet 8cqu1reil. I!Uch paradi@llllatall. Hi3tory. Busgellts thQ.'t; the

dic.atc for parE'..digm ell of the. facts ｴｾｴ＠ cc.Qu possibly PCl"t!:'.in to the de-

1.6

the:t lie ready-to-hand. The resultill3 pool of f!lc'ca cont .. ｾｩｮｳ＠ t,hoae ac.:!s:s-

sible to casua.l obaez"Ifl1:tion a.,d e.."qw.riMnt 'l;ozethe:r ,lith !lome ot the Illore

Illaltillg, and metel.J.urg;}'". It is psrtly because the craf'ts are t;he oue :::-000-

ily accessible source of facta wIu.ch ｣ｏｩｊｾ､＠ not have ooan cflsuulJ.y discovered.

that technology has so often ple.:>""d a v:I.tB1 :role in the emergence of new

!lciencos.

But though this BOllt of fact-collec'c:i.ng has been essential. to the

origin of many significant SCiences, anyone who ･ｾｾｩｮ｣ｳＬ＠ say. Pliny's ency-

clop.-.ed:l.c writings or the :flaccID.an nn:tural histories of the seventeenth

｣･ｮＧｾｵｲｹ＠ ,,'ill diseovGr that it :pro:;.ucea a morass. One sO!llehmr hesii;ates to

CI1.l1 the 1i terature that z·el'mJ.tl:l eeie'ltific. The Baconiml "histories" of

U<Slllt, color, wind., mining, and co on are filled "tI1th intOl:'lllaUCol:l, SOOle of

it reccmiUte. But they .1uxtepo::e facts (so.y, heating by m2Xtm:e; ths:t "\Jill

17

statics, dynamics, ll.!ld ｾｧ･｣ｭ･ｴｬＷｩ｣＠ Grlfcics,do:l:e.cts collected'l>r:tthsoUttle

be done in no other 'its:y.

This is thes1tua.tion1ibic:'b. creE,tea the schoolscharacte;:>i:;:tic of the

eerly stages of a science's de-.;elO.',}ment. UonaturaJ. h:!.s'(;oI"",f can. be inter-

Ilreted in the absence 01: at lee.at 80me ｾｬｩ｣ｩ＠ t body of intertv!ned thco-

;r·etica.l andmethodolog1cal belief that perm:l.ts selection, evru.uat:LCll, and

critii::iam. If,thntbQi;y'ofbeUefiEl notalrcl.l.dy implicit in the collection

of :f'ac:tB--in 'Which CCl.semore than Ｂｭ･ｲ･ｾ＠ facta" 'are ｡ｴｾ＠ hlmd--it must be ex-

ｴ･ｲｾｬｬｙＱｏｬＱＧｐｬｬｊＬｩＮＬ､ＬｐＨ［ｬｲｬｬ｡ｾｳ＠ bta.current metaphYsic, by another scienc:e, or

by personal and !iistoricsJ. accident. No lronder, tlwn, that in the early

st6,ges ｾｯｦｴｨ･､･ｩｩ･ｬｯｰｭ･ｮｴ＠ of ｾｾ＠ any sciellce different men. ccnfi-ont:Lng the seme

:;.leo un:l.que :i-a its degree to the fields we c!lll sCience, is 'Ghat eu,,!;. ... · .. 1_

tid ｾ＠ o.i vergenceilcrh(l"U:W. ever lareely diSF.J?.it'S!Il'.

Fox they do d.isa.ppeer to e. very considerable e;{tent ana th·:m. :;.p:;;e.rcn"c,J.y

tr:tl;u:rgh of one of the pre .... :;r..lXadigm schools. 't1hicn, because ot" its Qt.11 C!1C:::-SC-

18

fruit 01' their ci'torts ;ras ＧｾｩＱ･＠ wytl.;)n j!'.l', Go ck"rice ,inion ＱｬＡｾＮｧｨｴ＠ never have

been discovered by a man el:ploring llE.tlU'e carrua.l.ly O!.' at rsndom but which

lras in :fa.ct it:uiepandently dev(':lClled by Ii;!; least t\;O ill.'.reati5Gi;ora in t.hc

early 1740' s. Almost i'rom the lltm7t at: his electrical ree",a::'ches Fl"a:.1Uill

'liaS particularly concerned. to e:;,.-plain that strange !llld., in the event, p..'U'-

ticularly revealing piece of ｾｺ｣ｩｮｬ＠ ｡ｰｾ｡ｲ･ｴｵｳＮ＠ Eis success in doing so

provided the most effective of the ｡ｲｳｵｭ･ｾｴ･＠ that ma.de hie theory a paredigm,

though one which 'iias f)'cill tmeble '&0 a.cccunt for quite all t.ile !mmm. case a of

electrical repulsion. To be accep'Geo. a.s a perai!.igm a theory' l1IUOt seem bet-

ter than ita ｣ｾｴｩｴｯｲｳ＾＠ but it need not, and in tact neve:;:, does, explain

all the facts that ita proponeate feel it should.

What the fluid theory of electricity ､ｩｾ＠ for the ｳｵ｢･ｲｾｾｰ＠ which held

rected to secondary er to overly call1l1ex ｉｬｬｾｲ､Ｎｲ･｡ｴ･ＮｴＱｯｮｳ＠ of eJ.ectl."icity, 1 .. oul5.

li'reed from the concern ｾＢＧｩｴ［ｨ＠ ｾＺｮＮｹ＠ and all el€:ctr1ce.l phenomena, -the UJ"11ted g;t'ouy

19

"'!'rUth emerge a more readily from eloror tllanf'rCll'i collflauion."

based .. resea:rchin .. the ne:..":I; .. l:Iec'cion.. Oll1;fllUSi.; fil.'si.; note briefly ho;; the emer-

genee • of . a}laradigm· a.:ffects .. the structure· of the profession. Wilen, in the

development ofa natural science "anindj.vic1ua.lOl'" groupctiratproiuces Il.

synthesis able toattrsctl!lost of; the ne::tgenerat:!.on' s praci;itioncro, the

by the:l.l' members' convei'aion to the new paradigm. B1.ltthel:'e are all1a.;y-s soma

me.n ｾｬｬｯ＠ cling to one Ol'811other of the older views, alldthey e.l:'e. simply read

out Of the profession. vhj;chthereattel' :l.gnO::GS the:l.l' work; ｾ･＠ new :pm-a<li&,'Ill

implies a new Slld more r1giddefinition of the field. Those um::l.ll:l.ng or

unable to accOIll!!Iodate t!l.e:l.l' ｾｩｯｲｫｴｯ＠ .itmus·'prcceed in isolation or attach ,

themaelves to some other group •. Historically, they hIl."eoften simply stayed

in the depar'-uments Of philosophy by "hich Bomany of" the spec:!.f'-lsciences

have been ｳｰ｡ｾＧｮ･､Ｎ＠ This h:l.nte--wat could at lcast't'.e e.l:'gued.--tliat it io

just their reception of e ]}In'ad:l.gm that trallSfo:rins into S 1,lrofcosio!l a group

that had previously just been intoreflted. in theotuay of }w.tlll'e, L'l the

sciences (though'ilot in f:!.elds 1:1.100 medicine. technology, a..'1d. la17, ;lh050

:pri.ncilW-l ｾ｡ｩｳｯｬＩＮＱＱ＠ 'tltre is an external social need.), the fOl"Ill<Ltion of ｾｰ･Ｍ

cia1 journf'-ls, the Ａｯ｜ｕｬＺｬｺＺｾｩｯｮ＠ of' apscialis'.;s'. societies; an.o. the claim for

a special ｾｬ｡｣･＠ in the ｣ｕｬＧｲｾ｣ｵｬｵｭ＠ have ｵｳｾ｡ｬＱｹ＠ been ･ｓＹｾ｣ＺｬＮ｡ｴ･ｾ＠ with a ｧｲＮｕｾｐＧｂ＠

20

first principles ｾ＠ justifying the use of each ｣ｯｾ｣･ｰｴ＠ ｩｾｾｲ｣ｾｵ｣･､ｷ＠ ｔｾｴ＠

can be left to the ｷｾｩｴ･ｲ＠ of textbooks. Given a DUradiBP, th0 creative

scientist can beg"-Jl his research Ｇｾｨ･ｲ･＠ it lea.ves off ｾＬｮ､Ｎ＠ can thUD conceu-

trate exclua1 vely upon the llubtJ.Got rulll. most eaotel'i,c aspects ot the natural

phenomena that concern bis group. As h.e tlOO!l this. hmrever I h:!.s research

communiques begin to chmlge in ,rays ｾｲｨｯｳ･＠ evolution hall been too little

studied but yhose modern eoo-prlxh,.cts are obVious to all e.l1d. oppressive to

ﾣｾＮ＠ to anyone vho might be 1ntel'ected in tIle subject matter of the tield.

Instead they m.ll usually eppesr ao brief er'tic!es addresseel only to proi'ea-

ｳｵｾ･､＠ and ｾｩｬｏ＠ prove to be ｴｨｾ＠ only Cn0.8 able to read the payors aadre8sed to

them.

Todey in the sciences books are al""aya either texts Qr ｲ･ｴｲｯｳｰｾ｣ｴＮＺＱＮｶ･＠

reflectio!l5 tlpOl1. O!le c.*ct ox' anothe:- Cot: tb.e ecient1 .. 1':i.c life _ Tk.l.e sc:ten-

tiot wh.o writes one is .more 11.kely "co fine. bis profeaaioual reput .. ｾﾷｴｴｩｯｮ＠ im-

velopmcnt of the verioun ncicnccs did ＢＡｪｨｾ＠ book o:rdiniirily J}osseo3 the name

ｲ･ｬ｡ｩｾｩｯｮ＠ to profes2iollaJ. ＸＮｾｨｩ･ｹ｣ｲＮ［ｈｮｴ＠ that it still retains in other creative

/: ... -, "'" .... ＭＮｾＭ .....

21

educated a.udience. In dy-aamics research become 3imilarly esote::c-ic in the

later Middle .d.ges, and it . recaptured general intelligibility only briefly

which had guided medieval research. Electrical research began to require

translation-for the laymanbei'orethe end of the eighteenth century) and

most other fields of physical science ceased to be generally accessible in

the nineteenth. Duril'.g .the emne tvro. centuries silll:t1ar. trana5.tiol1s can be

ieol.ate.d in the various parts of. the biologi,cal sciences. j.n purts of the

social. sciences they may 'I>"'ellbe occurring today, Althov.gh it hac become

custoruary,end. issu.,:,ely prOJ:ler, to deplore the 'irideninsgLllf that ee1=tes

.the professional scientist.from his. ｣ｯｬｬｾ｡ｧｵ･ｳ＠ in othe.r fields, t.oo lit'Ue

. attention is paid to the essential relationsh1p bet-J'een that Gulf and 'ehe

mechanisms .int1;'i061c to ecientific.ad"snce.

Ever since prehistoric antiquity one field of tltudyafter another ha.s

crossed the divide bet"!reen lfhat the historitm might can its pre-history as

a ec::i.ence and it.shis'vory proper, These transitions tQlllatur1ty have aeld.om

been GO sudden 0.' so. unequ:l.vocalas mynecssflar:l.ly schellllatic dis.cussioll may

have implied.. llu.t neither oove they been histOrically f7!!.dutl.l, coe:rteno:!:'!c,

·that is to say. w.!.tu the ･ｵｴｩｲｾ＠ develo1ll1lsnt of the fields 'rlthin ｾｔｬＺｬｬＮ｣ｨ＠ ｴｨｾｹ＠

occu.rl"ed. ft:r:tters on electricity duril1g the r.irst four decac1.es of the. eigh-

ﾷｾ｣･ｮｴｨ＠ century ｰＡｊｳｳ･ｇｾ･､＠ ｾｲｯＺ＠ &!lore infoxl""t-S.tion ｡｢ｯＱＮｾｩＺＮ＠ elcctr1.cel ーｨ･ｮｃＦｬｾｮｾ＠

Cot.l.1omb I o.nli Volta in the lust ttird e·f the ｣ＺｾｮｴＮ＠ .... '1:;."Y ｩｾ［･ｩｬｬ＠ ZV..l'thel' l"2ilnO"';;·cd.

from those of GraY', Dll Fay: and. even ｅＧｉﾷｏｊＮｬｾＧＡＮ［Ｚｬｩｮ＠ 'chan ･ｾ･＠ the ｜ｻｩＮｾｩ＠ t:tn...;z of

these eru."ly eighteenth-century elecJ:;rical ｡Ｎｩｳ｣ｾｊＧ｣ｲ･ｲｇ＠ trots those of the

sixteenth century. ｓｏｔｾ･ｴｩｲ･･＠ ｢ｾｴｴｲ･･ｮ＠ 17'!.() aud 1780 electricians 'irere tor

the first time ene.bled to take the ｦｯｵｵｾｸｩｯｵ｡＠ of their field for granted.

From that point they pushed on to mcre concrete and ｾ･｣ｯｬｬ､ｩｴ･＠ problems, and

increasingly they then l'eported their results in articles addressed to

other electricians rather than in books addressed to the learned world at

large. As a group they achieved 'ilhc.t astronOlilers h::lil gained 1.11 alltiquity,

students of motion in the DI.1ddle Agee, of phYGical optice in the 1n.te seven-

teenth century, and of historical geology in tho e:>J."ly nineteenth. They had,

'chat is, achieved Co ｰ｡ＮＮｾｩｧｭ＠ that proved. able to gui.de the lmole group' [) re-

aea"t."ch. Except with the advantage of hindSight, it 1.s lo..ard to i'im], another

cr:!. ter:!.on that so clearly Pl"Oclaims Il. field a eCience.

ＧＭＭＭＭＭＭｾ｟｟ｷｮ｡ｴ＠ then is ·eo ｾｾＭｩｬｌ＾･Ｍｮ｡Ｍｴｾｴ［｢［･Ｍｲｮ｡ｲ･Ｍｾｬｦ･ﾣｾｲｭｬＭＭ --------

and esoteric research that it,p reception by the Groul? ll€rmits? For the

moment the second. of these questions :1.0 the mOl'e ｩｮｷｯＺｾＧ､ｮｴｽ＠ aid a BchelllUtic

anm.rer to the t'irat will permit us tcpi'oCried to it ; Bye. paradigm I mean

a :fundamentsi sCientific achievement that!J.as been a.cce:pted· as such by a

group concerned to explo!.t it further. Fund.!J.Dlentalheremee.ns tlmt the

paradigm bll.ildll i'l'om first principles to ｾＺＡＮ｣ｨ＠ group practice neea no'!;, 101"

some t:l.methereatter, return. Sc1entificmeans ,thoughthis is no defini-

tion Otthat vexing ter:n,that the paradigm inclUdes :l.l!lP1icitor explicit

.. la.mland pr:!.nciPleiabouttheelementsoftfuichnat\1remaybe conceived to

consist and about the ｾｾｳ＠ in which these ･ｬｾｮｴ｡＠ affect both observers . -.' . .. . ,

. ... ...- .. ·-and-each,othel".--.A-pm'adigm.,._ ... there:f'oro ..•... _is_ .. at .... ｟ｬ･･Ｎｳｴｩｬｬ｟ｰ｡ｬＧｴ｡ｴｬＺｵｾｯｲｹ＠ or, .

more loosely,. a conceptual Ilche!;1c. :Bu.,; and this ,,1.111ate1' prove oriti-

cally important, a. paradigm lmlst alr;o be SCl:1retbing more. It must. that is,

from its first enunc:!.a.tion be exhibited as givinG order to come concrete

rar.ge of natural phenomena. These phe1lomena are the theory's knmm Iil.:ppli··

cations, ani, v1 thin the p:rxadigm. they are Inver 'luite eep..'U's,ble from the

cepted as such. Hore :lJ:n:portaut; appl:tce.tiolllO azoc need.ed to s\.ll?ply at least

part of the P<!!'ad'.e.:Iil'E! llleaning. Stue.entG of Iiemon's 1'r1nci;pi8, like those

of any other scientific classic or tarot, learned the lll!lanings of concs!".s

like force, mass. rrpace, und time less f.rom the ｾｾ｡､ｾｾＧｳ＠ ･ｾＱＱＱＱ｣ｩｴ＠ ､･ｦｩｮｩｾ＠

23

auccess:ful than their competitor5 iu solvir,g a fe;, problEma that the grOt\)?

ot practitioners ｾｾＧｂ＠ ｣ｾｾ･＠ to recoenize ns acute. To be ｾｯｲ･＠ ｷｾ｣｣･ｂｇｦｵＱ＠ is

not, hO'lfever, to be either completely successful ,;'itt a single problem or

particularly successful 'il1th any lro:ge n'.lmber. The Bl,ccesa of Il. parae.ism--

'lfnether Aristotle's, Ptolemy's, Neilton's, ui'loiBier's, or Mex;;ell's--is

initially aJ:waya a potential success ､ｩｳ｣ｯｶ･ｲｾ｢ｬ･＠ in selected Slut still 1n-

complete examples. Normal science cooaiGtB in the actualization of that

potentiality, au ｡｣ｴｵ｡ＱＱ＿ｾｴｩｯｮ＠ achieved by ･ａｾ･ｮ､ｩｮｧ＠ the knowledge of those

i'actsthat th;;: ＡＱｾＺｲ･Ｎ､ＺｬＮｧｭ＠ dieplaya as l=ticula,ly l'evealing, by incl'eaoil1g

the e::rtent of the r.:atch ｢｡ｴｾ･｡ｮ＠ thoEle facts and the llaJ:uligm' s predi.ct1ons>

pOints need to ba una.sl·stccd. M(j!'ping-ull ｾｓｬＧ｡ｴｩｯｮｳ＠ Il.re wlmt eng::5e moot

ｬｬｏｬｾＦｬ＠ science. Closely examined.$ ｾＢＧｨ･ｩｴｨＮ･ｲ＠ ｨｩｳｴ｣ｲｾｃＭＧｊＮｊＮｬｹ＠ or ｾ｟ｮ＠ ＧＡｾｨ･＠ contenJlSc-

25

. ﾷﾷＭ｡ｲｴ［ｩ｣ｵｬｳｴｩｯｮｯｦＭｩ［ｨｯｳ･ﾷﾷｷｨｩ｣ｾﾷﾷｴｨ･ﾷｪＬｬＢＧＮｲ｡､ｴｧＡｬＡﾷ｣ｵ［ｰｬ＿Ｚｬ［ｩ･ＡｬＮＭﾷ＠ ............. .

ｐ･ｬＮＢｨ｡ｰｾＧ｟＠ these _ere def'e-cts, cuI; they have ｣｣｣ｯｾｹｩｬｬｧ＠ virtues. by

focusing a.ttention upon e smi:.ll rll.llgc of relatively ecc·teric problems the

. parad:!.gmf'orces ... Bcientista to illvestigate sOlile part of·rw.tUZ'ein a detail

.. and depth thatwouJ,g,otherw,tseba un1maZ:1!reblj:!, . The. arees i:wes·cigatoil.,

ｴｨｯｳ･ｾｩｃｨｰｲ･ｳ･ｮｴ＠ normal. science With ita problems, are, of' course,

rainisculejthe enterprise.now underdiscuGsion has drastically restricted

vision .. But that restriction tu...""nB out to dono harm"at least nc·t to the

development of science. Normal science. as we shall begin to see in the

next section. has abuilt,..iu mechanism 1.'hich.ensures ttsabandom.nent wen

its guiding paradigm ceases to function f'ruitfully, At that point scien-

tists begin to behave d1fferently. end the nature of their research prob-

le1l16 changes • <Satin the interim, during the period when the paradiglil is

euccesaful, the profession "!dUlle-ve solved. problems .they could scarcely

have iIP.agined and vouldnever .. have ."Mer"taken withcut. corlllll1tment to the

para.?igm.And at leas'l;pa..""taf that achievement:. always proves to be perma-

nent.

To displaj" rllOl.'e clearly. ,,'ha.t is meant by no.."'mal 0"' paradigm-baaed rc-

Il'illll'ch. let me nowat'csl1lpt to· classify snd illustrate the problems of which

normal science principslly COnB1sts. For convenience I. postpone theoretical

activity p.nd begin with fact gathering, that 19, with the experiments and

observations described in the technical journals throU3h Which SCientists

:!.nform their professional colleag'..lesof the results of' their con-tinuing re-

search. Cll ,;hia:t e.er.ects of nattl,l.'e do SCientists ol'di=ily rc;port'l '1hat

choice to Q ｣ｯｮ｣ｬｵｳｾｯｮ＿＠

V(.'7st:lgation, end they are neither elw--ays ncr ｰＧｾｲｭＦＮｮ･ｬｬｴｬｹ＠ di.Et:.hJ.ct.. ｆｩｲｲｾｴ＠

is that cle.sG of i'e.cts tlhich the )Jaradigm has sho;m to be Ｚｧ｡ｲｴｩ｣ｵｬｾﾷｬｹ＠ .e-

vee.1ing of the na',ure of things. :By eEPloying thei;! in salving problems the

paradigm has made them l10rth o.etel'lll1nii:lg both 'doth lilore precision an.'I. in a

larger variety of situations. At one ｴｾＮｭ･＠ or another tness significant fac-

tual determinations bF.ve included: in astroncmy--ete1.lar position and ＢｾＭ

nitude, the periods of eclipsing binaries and of planets; in physicB--the

specific gravities and compressib1litiee of materials, Ｇｾｶ･＠ lengths and

spectral intensities, electrical conductivities and contact potentials; end

ill chemietry--compoaition and cO!!lbining Wights, boiling points SIlo. Il.ci6.ity

of solutions, etructursl fOl>mlle.e SIlo. ｯｾｇｩ｣｡Ｑ＠ activities. Attempto to in-

crease the accuracy and scope vith which facts like these are known ｯｃｃ｜ｾｹ＠

a signii'ico.nt fraction of the literature of ･ｾ［Ｚｰ･ｲｩｭ｡ｮｴ｡ｬ＠ tnd. Observational

science. l\ga.in aLd again cotiplex Ilpzcial ap..=atus has been ､ｾｬＧｩｩｧｮ･､＠ for

such purposes, and. the invention, const.--uction, o.nel deplo;yment 01' '"hat ap-

paratuB ha.s demenO.ed first-rate talent I ｮｲｾ｣ｨ＠ time I and cCllsi<lerable tiILO'.u-

cial backing. Synchrotons end radio-telescopes are only tho moet recent

e:;:.aropleo of the lengths to lmich acientiata lI"ill go 13: a p:n,oo.igm aSGurea

thei!! that the facts they seek e.re ll.'llOl'to.nt. From Tycho B;:slle '(;0 E. O. Ｑ｡ｾ［Ｍ

renee a nunber of them have acquired great reputations not from ｾｾｹ＠ novelty

of their diacov"riea but frcr.:l the preci:::!.o!l, z'eliability, mil. ",cope of the

of fact.

t ... ·-t ｣ｾ＠ r • ... of ... ＮＬＭｾＮＮＮＬ＠ •• ｲＮｾＭ ＢＮＢＮＬＬＺＮＺＭＮｾ［ＺＮＧ＠ •.• '>' C.;:.?,·.:-.r.·· .. ·, ••.• ' •. , •.....••.. ,'.r. .. ' •. ' .• -,· .. ｾｊ｣ｬＢＬ＠ ｟Ｎ［ｾｾＺＭＬﾷＮＢＭＺ［｟Ｇ［Ｇ｟ｉ［ＮﾷﾷＺＮＺＭＮ＠ ｾＮｾｾｾﾷＮＨＮﾷﾷＭＮ｜ＮＮＭ［［｣ﾷＺﾷ＠ .• " :;'ec en. ·f.O 1:otl\)...:-;<;.: ::..<..- ...... ｾＭＺ［［ＧＮＬＧｾ＠ ..... ;.;., - ＭｾＭ｟＠ -- '- ｾＭ , -, - ..... --- .. Ｍｾ＠ ｾ＠

27

"'ce.n-be cOJJl!l1ll'ed:directlYl>"i tnJ.?l'ed±ct.:!:Olla from the':9$"adigm'.;!leory. AS1re

shall see ,when I shortly tl.lXn,i'rom'Ghe c;;""l,Wri'Jl$z(.;ruto Ｍｾｨｇ＠ theoreticalprob-

leme ot: normal science, there are Ilclda.n muny a.reas in ＭｲＮｭｾＬ｣ｨ＠ a scientific

theory,-pa.rticularly a mathemat:1cal theory, can be directly ｣ｾ･､＠ .In.th

theory 01' relativity •. li'u:rthel:'li1w-e, eVGn in those aroos uhGre 8J?j}lication is

possible, it often demilnde theoreUcal and 1.1strumental allproxima.tlo11!J ',;hat

severeJ.y.1.1mit -t;he agreement toea expected. ｾｲｯｶｩｮｳ＠ the..t ｾＧ･･ｌｊ･ｮｴ＠ or

findiDgnewareas in ｾｾ｣ｨ＠ agreement can bo demonstrated at ell presents n

constant challe!'..ge to the skill end :1JusginaMon of the experiment.alillt rmd

observer. Specialtelellcopell todell!lonstrate the Coparnicsn prediction of

annualperal.lax; Atwood' s machine. first invented. almost Q century aftei' the"

Pr1nc:!.1?ia, to g:l.vei the first uneqUivoetlldemonatrat:i.on of Newton's ｾ｣ｯｶＮ､＠

l".&l.w; Foueault' s appare.tuB to show the speed. 01" light greater :I.n air than in

lreter; or. the gigen'ticbubble .cilambel' designed to, del!l?l1strate theexis'.:€nce

oftheneutr:!.no;tl:tesc p:l.ecee of apeciaiallparatulil s.ndJilaIl .. y others like th\)m

illustrate Ｇｾｨ･＠ :imuensc etf'o..rt and ingenu:l.ty that have been required to ori.ne;

implicated directly in the design of £lr1pm'attl3 able to solve the problem.

i-Jithout the?rin:::ip,j&; for.0l'.!\l!lple, meaS'.l,;:'Cll!entG made ,lith the Atvrc"d. ma-

28

undertaken to ar'i;iculate the paradigm tileo-.L'Y, t.h"i.t ie, to ｲＰｳｯＱ｜Ｇｾ＠ some of

its'residusl ambiguities thus permitting the tlolution of problems to ｾ［ｨｩ｣ｨ＠

the paradigm h;:l.1l previously only drawn at'tenUon. Thill ｣ｬｾｳ･＠ proves to be

the most important of all, and its description ､ｾｬ､｡＠ its subdivision.

In the Dore mathemticlll sciences some of the experiments aimed at articu-

Jation are directed to the determination of physical constants. Newton's

ｾｲｯｲｫＮ＠ for er-=1?le. indir.e.ted that the force ｢･ｴｾｲ･･ｮ＠ ｾｲｯ＠ unit masses at unit

distance would be the same far all ｴｊｾｳ＠ of matter at all positions in the

\miveree. But his own problema could be solved without even eatimatix:g the ,

size of this attraction, the univerBal gravitational cOl1stan't, and for a

century attar the Principia appeared no one else vas able to devise appa-

l'stUB a.ble to determine it. N01' 1m9 Cavendish's famolls determiIIBtioll in

the 1790's the last. Because of its central position in physical theory,

',ll1pl'oved values of the sravitational coostant have been the object of re-

peated efforts ever since by a number of outstanding experimentalists.

Other examples of 'the seme sart of continuing work 'Would includ,e determina-

tj.olla of the astrollomical unit, JI,-;ogadro's nlSber, Joule's coefficient, the

electronic charge, and so on. Few of these elaborate efforto uould have

been conceived an,l none wculd have been cru:ried out v.ithout a paradigm

theory to defiuG the problem and to guarantee the existence of a stuble so-

l.utton.

Efforts to ｡ｲｴｾ｣ｵＺＡＮ｡ｴ･＠ fI, paredizm ere net, hmmvel', l-eetri,cted to the

29

isnotapparentth8.t aparadigmisprerequisite1;o-thediScovcl'ycf la'i,s

____ ＭＧＭＧｾｬＱｫｬｌｪ［ｨ･ｳ･Ｎ＠ - We ｯｦＧｾ･ｮ＠ hear that_theY_Il.:>:'e found by examiniU$ It-easuremen-ta un-

dertakeu_i'or theirotm sake Wld 'llithout theoretical commitment. But history

of'ferstlo'supporti'or-so excessively Be-coman a method. Boyle I s experiments

---wcrenot··conceivable -. (and- if. conceivecL'lould_'ha.ve __ ｲ･｣･ｩｶ･､Ｎ｡ｮｯＧｾ･ｲ｟ＺｬＮｮｴ･ｲｩ＾ｬＧ･｟＠

tat:l.on or none at allFuntil air lms recognized as' all elastic fluid _to "1hich

all the elaborate concepts of hydrostatics could be applied. Coulomb's L'lUC-

cess depended upon his constructing specialapparlltus to measure the force

oe'cl1e6n pOint charges. (!rhoae ,'mo had previously measured electrical:f'orces

using ordinary pen balemces, etc., had found no_ consistent or simple regular-

ity at all.) Buttl:ul.tdesign. ｩｮｴｵｲｬＱｾ＠ depe!lil£cl'lll!<?l1 Franluin's previOUS

recognition that every particle of electric fluide.cts upon every other at a

､ｩｳｴＡｬｴＺｬ＼ＺｾＮ＠ __ ｉｾＧ｜ｬｓｉｬＺｲｯｲ＠ the force betwensuch particles--the ouly for<:e v.hich

might safelY be assumed a simple function of dlstancethat Coulomb ,-ms look-

ing. - ｊｯｵｬ･ＧｳＧｾ｣ｰ･ｲｩｭ･ｮｴｳ＠ couldalsobe\lSedt;)illustre.te ｨｏｬｾ＠ Q.uantitative

JAWS emergethrClll&li parildigmarticulation. ' In fact; so general cnd close is

the relation ｢･ｾｲ･･ｬｬ＠ qualitative paradigm and Q.uantitative Ｑ｡ｾＭｲ＠ t$t, since

Galileo, such la..Tshave very otten been correctly and repeatedly guessed by

'choseii"lio held the paradigm for some ;real'S before apparatus could be designed

f.'or their experimental determino.t10n.

Finally, there is a thil'd sort of ezpel'iJne!1t -which aims to articulate a

pal.'ad1gm, one which is particularly prevalen', in those periods. end. sc:l.ence3

"hi,eh deal more "l-1ith the qualitative than'l.1.th the q"..tantits.'cive aspects of

nat.ure g s regule=:lty. Often a pnred.1e;m de<:.relCj?ed.. far O!'le set of phenomena is

30

to the lll'l,1 area ot intel·est. For example, 'the paradigm a:U:i?lications of: the

caloric theory of beat \lere to heating sn.d. cooling by mixtures and by change

of state. BUG heat could be released or absorbed in lJ'.aly other ｾＺ｡ｹｳ＠ beSides,

e.g., by chemical combination, by friction. ana. by comprcsoion or absorption

of a gG.s, and to each of these other phenOflCn!l. the theory could be applied

in several lrays. If '"he vacuum lw.d a hea'G cacpac1ty, for exe.mple, heating by

compression could be explained as the result of mLxiug gas ｾｲｩＮＮＧｴｨ＠ void. or it

might be due to a change in the specific heat·or gases ｾｴｨ＠ changing pres-

sure. lind there ,,>ere ueveral other explanations besides. MElny experiments

,rere undertaken to elaborate these various eJ.lllanstions and to distir.zu;!.sh

｢･ｾＮ＾･･ｮ＠ them; all these ･ａｾ･ｲｩｭ･ｮｴｳ＠ arise from the caloric theory sa paradigm,

and all exploit it in design of experiments ana in ｴｨ･ＧＱｮｴ･ｬｾ･ｴ｡ｴｩｯｮ＠ of re-

sults. Once the phenomenon or heating by ｣ｾｲ･ｂ･ｩｯｮ＠ had been established,

all fuJ.··cher ･ｊｾ･ｲｩｮ［･ｮｴｳ＠ in the area were paradigm-dependent in this vray.

Given the phenomenon hO'\l else could an expel."iil1cnt to elucida.te it have been

elloaen?

Raving discussed the empirical problems of normal scientific reseerch

at 'Ghis length ｾ､ｬｬ＠ permit an abridged examination of Ｇｾｨ･Ｑｲ＠ ｴ｢Ｎ･ｯｲ･ＧＬ［ｾＮ｣ｮｬ＠ COU11-

terparts. The theoretical problems of normal f.'cicnce fe.ll into Ve;,'Y r:.CB.,;:J.y

'the sane classes as the e):perimental ana Observational. A llurt of no.';)""l

'(;ooo1'e'(;1co.l ,{ork, but ｾＮｮ＠ this case a vcry smeJ.l part, ｣ｯｮｂｩＮＺＩＧｾｳ＠ simply in the.

use of ex:i.oti!'..g them·y to pred:i.ct factual ini'o::.'mation of ｾＮｮｴｲｩｮｳｩ｣＠ vl:.lue.

Ths ｭｓｊＮｾＮｵｦ｣｣ｴｕｉﾷ･＠ of ast:::,"onr:mj ｃＸＮＧｾ＠ ･ｲ＾ｨｾｉｃＮ｣ｲｩ､･ｳ＾＠ the ｣ｯｲｲｾｵｴ｡ｴｩｯｮ＠ of. lens ch,&'ac-

tsx'iGt:1cs, 0= the ｰｬＧｯＵｾｵ｣ﾷｴ［ｩｯｮ＠ of radiO :propsgation cm"vcz: are ･ｾｘＳｐｬ･ｯ＠ of ·uo:'k

31

tain /l. greatwmy theerstic:?.! ･ＬｾＮｳ｣ｵＡＮｈｬｩｯｮ｡＠ ot: problelC8 !l'hieD., ＮｾＨＩ＠ the nCll-ｾ｟ｾＲＮＮＭ］Ｎｾ｟ｾｾｾｾｾＭＬＭＭｾｾｾｾＭＭＭＧＭＭＭＧｾｾｾｾｾｾｾｾｾ｟ｾ＠ ___ .. _._. ____ .... _ .....

tr:!.ns:tcally T&1ua.ble bu;t becauGc they can be confx'onted directly vith ClC-

-------'pe-r...J:!!ne""· .. ﾷＢＧ｡＾ＪＭｴ］ＮＭＭＧｉＧｬｭｬＭｰｾｂ･＠ 1eta clieplay ('. nell ｮｰｰｬＺｴ｣｡ｾｬｯｮ＠ of ｴＧｾ＠

to incres,ee the precision or an c.pplicatlon tile.t llalLall'eady been sade.

T"ne need for trol'k of this sort a.-r1ses from 'l1l1!;:t I previously caned the

illllllQnee diffiCl.'.ltiee oftenencot'.ntered in developing points of contact be-

'tween atheol'Y aIld. ns.tllre. The.se difficulties can be b:defly illustrated by

an examination w: the hiotory ot: dynamics after lie-Jton. By the early eigh-

.teerith centu.--y those scientists '\/ho Mceptedthe ｐｲｩｮ｣ＺｬＮｾ＠ as ーｳＮＧｴＧｾ､ＮｩｧｲｲＡ＠ took

the generaUty oi' its conclusions 1:1»:' granted, and. they had every reason to

do eo. No other 'Work lm0\'1l1 to the hietcry of science has permi t"(;ed so large

a eimultansous increase. in ｾＢｨ･＠ scope m!.7. );ll'ecie1011 of reeearch. F:ll' th'l!

Ｂｩｯｾｾ＠ on "l'IA ..... A .. '1i.".,WI ... , ﾷｴＢＢＧＯＢＺＢｩｮｾ､＠ ＧＢＢｴｾＢＢＧＧＧＧＧＧＱｬ＠ ｮｾＢ＠ ｴｨｾ＠ t";.:1r.. r ' l·J-T+.h ｴｬＧＮＧＢｾ＠ ｾＧＬｩｲｩ＠ 0'2 r. .... 1 .;·.1._ u ＮＮ｜ＮＴｾＮＬ＠ .... ｺＺｾＢＮｉＮＮＧ｟ｾＢＢＢＢＧｯｏｉｾ＠ ｾ＠ ... .1. .... ,,,J. ...... ｾＮｉｉｯｊＮｾ＠ " 4,.t.lJ.l.4 """' oloU.;.g. 1 .... _ __ .......... ｾ＠ .'. ;.:c.v.. .....

tiOll£.l end ad hoc ｣･ｓｾｬｾｮｴＺＡＮｯｮｳ＠ he had elEo been ｾ｢ｬ･＠ to lie:d-,c Eeyle' s rr." -- -and an ill1porte.n:!; fOl'lrr'.lle. fo:r the opesd of c01.llld in air. Given the f;w.te of

science at the time, ｾｇｨ･＠ r.lUCCCIlS of these ､･ｭｾｮｅｴＡＬＳｴｩｯｮｳ＠ '!;as il;.tencdy im-

quired in order to pI'o\'ide the epeci&l dI1.',,;a that the conCl'etc ｡ＡＧｐｬｩ｣ｴｶｾＺｬＮｯｮｳ＠

of Newton' B paradigm dell'.anded. Similar di:fi'icultie!1 in obtaining agreement

existed on the side of theory. To apply h:1.a ｌ･Ｎｾｲ｡＠ to pendulumCl J fGr ｾｾ･Ｚｭｰｬ･＠ I

Neilton .. -as forced to treat the bob as a. masfl-point in order to prolride a

unique dei'ini tiOD of pendulum length; most of his theorems J the few eJ>cep-

tiona being hypothetical and preliminary. aleo ignored the effect of air

resistance. These vere sound j?hysical. approximations. ｎ･Ｇｾ･ｲｴｨ･ｬ･ｳｳＬ＠ as

apprOX:i.matlon they restricted the agreement to be eJ:pected bet,reen Newton's

p:edictiona GIld. actual experiments. The !1ame dUi'icultles a:pr,ear even ｭｾＧ･＠

clearly in the application of rJelf!;on's theory to the heavens. SillWle guan-

titative ｴ･ｬ･ｂ｣ｾｧｩ｣＠ observations indicate that the plcnets do not qUite cbey

lillpler's la'fS, and N5mtou's theory indicate a tw.t they ohoulc1110'I;, To de-

l'ive thoBe laws i{e-.n;on had been forced to neglect all gl',witational attrac-

'\;ion except thai; betv.een indiv'.dual p1al2ets alld the sun. Since the plw..eta

also ｡ｴＧｾｲ｡｣ｴ＠ each other, only apprmtimate agl.'cemsnt bet,,-een the Cl)lllied

ｴｨ･ｯｾｹ＠ end telescopic obee.-vation cOttld be eA1?ected,

All in the case of;' pendulums the aw.eCilWllt Obta.:!.l'lcd was more tlmn satis-

zactory to those "ilo cb'Gained it. No other theory could do nem-ly 50 ,.ell.

ｬｾｯｮ･＠ of those ,T£20 questioned the validity at He.lton' Il ,.,ork dia GO bec(">Uee

33

ｷ･ｲ･Ｂｴ･｣ｨｬＧｬｩｱｵ･ｳＧｩＧｯｲＢﾷｴｲ･｡ｴＱｮｧＢｴｨ･ＭＹＱｬＱＡＧｊＮｾｴ｡ｮ･ＨＩｵ｡ﾷﾷｭｯｴＱｯｕＵﾷﾷ＠ Ｐｦｾｭｏｬ［･ＺﾷｴｬｊｊｩＮｮﾷﾷﾷｴＬｲｯ＠

Jilutue.J.lyai:i:ract:tngbcdies. These ;pz'oblcms and.lllSllyothers like themcc-

eupied many ot ｾｏ｝Ｎｬ･＠ 'Il best ms.thema;i;:l.c:io.ns au."t'ingthe e:i.ghteenth andesrly

nineteenth· centuries • The Bornoullisj,EuJ.er,LP.grenge. lE.plece, ·ana. Gause,

aU .. d.ilisome of .the1rmos,!;bri,111antvork !')nproblemlll!.).lllCd to :tm.prove the

match betlreenl.'ie1f,1;on's parad1gm.lJludnature. Manyoftlieso same fl.gures

s1!1ru1taneO'J.slyworked to develop the mathemll.ticareqUired' for <lPlllicatiorul

that Nemon had not even attempted, producing, ｦｯｲ･ｾｬ･Ｎ＠ en ii1lll!eDSe

literature and sOliWvery l'cwer1'1llrnathell'at1caJ. techniques for ｨｙＧｩＷＮＧｾＧｬＧＮＮＡＡＮＷＡｬｩ｣ｳ＠

and for the problem of vibrating strings. These pro·Dlems of e;pplicat:lon a.c-

count 'for whatisprobablythemo£.ltbl·:tlliant end conauming scientific wOrk

of the eighteenth century. And they could rl/la.diJ.y be d\tplicated by 1m

examlbat:l.ono:f'·· thepoBt":paredigm periottinthe developmento!" thetmod.yne.mics.

the_Vi! theory of ligiit,eJ.ectromsgnetic theory,or any other bra:::lch of

science whose fundtillnental le.i'S EIl'e. tully quanti tati ve. At least in the more

mathemstical" sciences moe1;theoret:l.cal,vork isof.thio sort .•

ll'<lt it is not all oi'this scrt.E,,-cninthe ｭ｡ｴｨ･ｭ｡ｴｩ｣ｾ＠ sCiencee

there are alaotlieorErf,:!.cal'problemo'oi'pa7.'a.d.:lgm articuiation,a.uci In the

periods of mm'o q:ml:l.tative sc:tcntif.'ict'.e.el"l>l"ilnt thelle. pl'oblelEs ､ＮｯｯｩｵｾＬｴ･Ｎ＠

ｓｏｾｬ･ｯｦﾷｴｨ･＠ p::'oilJ.ems, in both ',he more quantitative Emd mor-s ｱｵ･ｊＮｩｴＺ［ｲｾｬﾷｾＬｾ＠

cc.ienceUt e.1!11 61nrjilly t.t cll3rific<1.tion by reforl!lUlation. 'ra.e E:2:.n.ciJliq. fo"!!

exa.::lpJ.e. did n,jt al"lmys !!l'ove en eesy \;c.r!( to a.pply pa..""'tly bec:ml3e it l'e-

tfdnee. some of. the C1V.!llBines!.I inevitable in a first v(mture s.nd because S'.)

1'[;t.lch ｣ｾｦＺ＠ 1:'(#9 metil'd.ng waG only :i.mpliei t in ｾＺＮ＠ ｩｾｇ＠ ｾＺＮｲＮｰｬｩ｣ｾＮｴｩｯｮｳＮＮ＠ ｩＱｨｾｦＮＺＧ･ｦｯｲ･Ｌ＠ ｦｾｯｭ＠

brilliant mathematical Ａ＾ｨｹｂｩ｣ｾＮ･ｴｳ＠ ｲｾｰ･｡ｴ･､ｬｹ＠ et:d.cnvored t.o l:*c:i:'crmu.lc:te

leflBons of. the Prin.cip:ta in a log1c&11y more coherent vel"s:i.o!l., Dill) 'Gha.t

lIculd 'he less eqtrl.,'ocal in its applications to the nC;,ily els'borate problems

Similar reforlllulat:!.oll3 of. a pm:>ail.igm have occu...-re.d. repeatedly in all

of: the sCiences, but most of' them have lll:'oduced wore :mlnrt3lltial cb.e.ngas in

the p.'l.l'ai.'!.igm than the reformulatiollS of the Principia oi ted above. Such

changes rellUl.t frOll! the empirical • .'ork prev.1ously (lescrib€d as ailted a',; para.-

digm articulAtion. Indeed, to cll:>seify that ･ｏｬＧＢＢＧｾ＠ of work a9 <;l!(iliricaJ. we.a

arbitrary. ｾＡｯｲ･＠ than any other sort of normel research the problems of

paradigm artic1.1.1e.t1on are simultlmeously theoretical a.."ld. exr."crimentaJ.; the

e,mmples given previously mll serve equally ... -ell here. ＱＳ･ｦｯｲｾ＠ he could

construct h:1.e egui:p:nent and make measurements ［ｾｴｨ＠ i'C Coulomb had to c!!I:p1oy

electrical theory in determining how his ･ｾｵｩｰｭ･ｮｴ＠ should be bUilt, ｾｾ､＠ the

｣ｯｮｳ･ｾｬｬ･ｮ｣･＠ of hit; meaouren:ents lI'aS a refinement in that theory. O:r ['.sam,

Ｑｲｾｲｫ＠ is of this sort.

{", ... 4-_,,;' ... V;

35

·theUterat1iriFof-norlt:aracience'-15otliempiricar:::n<rtlleCi'etical;-. - ｾｨＺ･ｹ＠ do

not. of cauree. quite exhaust the entire ｬＺｴｴ･ｲ｡［ｾｴＱｲ･＠ ofm:ience. There aJ:e

also extraordinary problems, and1t may lTell 00 their resolution that "'"kes

the scientific enterprise -as eo whole lIopa..--t:1c:u1e.r ly W()rth while. ｂｉｘｾ＠ ex-

trll.ord1nm:y.problems.are not to be.h&dfor the aI3K1:ng. Theyemeree only on-

special occasions preparlld by tlw advance of normal l"eaearch. Inevitably,

therefore, theovennelmine; majority of the problems under.takenbYeyeu the

very best scientists usuallY falls into one of the three categories out-

lined above. Work under the pa:t'eil.igm can be conducted in no other way. and

to desert the paradigm iato cease practicing the sc1ence it defines. We

shall shortly discover that such desertions do occur. They are the pivots

about vhichscient1fic revolutions turn; But betore beginning the study of

such revoiut:!.ono,letuiihave one lasta.ti!l morepanore.rnic looket the normal

scientifj.c purSUits l>'hich prepare the ... -ay.

have Just considered is hov little they aim to produce ｾｪｯｾ＠ ｮｾｶ･ｬｴｩ･Ｖ＾＠

eithel' conceptua.l or pnenomenal. The elaborate projects that scientists

have repeatedly ｵｮ､･ｲＧｾＮｫ･ｮ＠ to ｾｲｯｶ･＠ the ･ｾｰｩｲｩ｣｡ｬ＠ ､･ｴ･ｾｾｩｮ｡ｴｩｯｮ＠ or theo-

retical prediction of, say, v.svelengths or planetary motions increase the

ｱｴｾｴｩｴｹ＠ and precision of the Ｑｮｦｯｲｮｾｴｩｯｮ＠ available to science. But be-

cauce directed so ･ｾ｣ｬｵｳｩｶ･ｬｹ＠ to phenomena already known, they are partic-

ul8xly unlikely to disclose ｾｾｹ＠ new order in nature or to add a new sort

of fact to the liet with which science deals. Every&hing but the mont eso-

ter:lc detail o£ the result (e.g., the lest t.ro decimal. ;places to the right

in a mm ·"e.vel.ength meo,surellWllt) is knC1<m it! ad'lranee. An el'.p-erimeut 0):

theoretical manipulation whose outcome does not closely coinciQe ｾｴｨ＠ ex-

I19c'o;at1on tells nothil'.g about nature but s:!.lllply rei'lec';;a upon the zkill and

aometirees even upon the ｣ｯｾ｡ｴ･ｮ｣｣＠ of the man ｾｾｯ＠ ｜ｌｾ､･ｬＧｴｯｯｴ＠ it.

Advance e7.p6c·tations are not, of COUTee, often so :preciSE as in the

･ﾥｾＮｭｬｬｬ･＠ or v.svelength detel'miua.tio-A. Particularly in work v.hoee aim is

ｰｾ｡､［ＧｧｭＭ｡ｲｴｩ｣ｵｬ｡ｴｩｯｮ＠ there is usually genuine latitU:;1e of e:::pectution, and.

e Bort of factual llovd' .. ,- can then emerge. The Z"cllUltf: of Coulor:;1J' fJ meas-

urementa need ｮｯＧｾＬ＠ perhaps; heve :I:'i tted just an invel'sc egnare lal;; the men

perea. for S.l1y one of sevez-el different results. Nevertheless, the ral1fJe of

anticip&.ted, (E'.rul ｴｨｾ｜･＠ aei!imiJ.eble) ｬＧｾ｡Ｇｕｬｴｺ＠ is al1!aYO smal.l, ｡ｾ｡Ｎ＠ the PTCjcct.

,. -l-' ' .... ,. '.t ,',;. ' .. )...; ••.. ＭｾＩＺＮＭｾｾ＠ '.-.• ('.' -:-:.r:-,:-:." •.•• '.-.,." •. -:-•• ｾｩＮＮＬＮＧｾｾﾷＮﾷＬＮＧﾷﾷｾＮ｣ﾷ＠ •.. ,.'_, ＺｾＮﾷｾﾷＬＧ｟ﾷＮＬ＠ .• ﾷＮｾ＠ .. ,,:>.:.:_'o;':.:.· ,., .. : •. ;-•. ｟ｾＬ＠un.;.":! ｃＺＢｩＺＮＺＺｾＺＺＺＧＺＧＺＧＺＮｾＺＺＢＧＮＧＺｖＺＺＺ＠ \ .. ＬｾＮＢＢＬ＠ ｣ＮＬ［ｾ＠ .... ; •.. .:.v\";I..-. _._,' r. --"'-' • - ｾ＠ ｾ＠ • ｾｾＢＮＧ＠ >

which they derived: Ther-sfo:re they rer.15.ined mere facta I unrelo.ted &'110.. u.n-.. --,

relatable to the continuing progress of electrical resecrch. Only in retl'o-

. about, whatcharacteristlcs Of electrical phenolll('::ila they display. C01l1cmiJ

and his contemporaries" of course, also posl3essed this later paradigm or one

that, ｬｾ･ｮ＠ appUed to the problem of attraction, yieldB the same el.-:pecta.-

tiona. ｔｩｾｴ＠ is 'Why Coulcmb _e able.todG-sign ｡ｰｾｴｴｴｳ＠ 'l;hat gave a result

assimilable by paradigm articulation, But it is also ,illy that result sur-

prlsed no one and lItIy several of Coulomb.' II cOl1temporaries had been able to --- ｾＭＭ ＭｾＭ ｯｾ＠ ____ ＧＢＧＮｾｾＬ＠ ｟ＮＬｾｾ＠ ｟ｾ｟Ｌ＠ .. __

predict it 1ri ad"-rulce. Even the project whose goo.l is p3radigm-al't:l.culaUon

does not a5.m at the unex.pected novelty. •. ............ c ....... _ ....... ,:............................................................................. . •...•.................

But i:( the a.im of: n.o:t'I!lal science is not major I!1lbets.\'lti ve nmrel ties--i£, /

failure to come near theant:l.c:!.pat.ed result is Usually failure a.s a scien-

tist--then why are these problen1s ul1i!.ertali:eu. at a.ll'l Part of the answer has

a1rel1.Qy ｢･ｾｮ＠ developed •. To scientists. &t least, the results gail1ed in no!'-

ms1 research are significant because '.:hey e.adto theacope end precis:1.on

vith liniel:! the ｾｉｬＮ､ｩｧｭ｣･Ｎｮ＠ be ap,pl:!.ed. Thatanm;er. hom:lVer, CImll.crG accouut

fez' the enthusiasill and devotion th"..-\;. scientists (,d.splay fer the ;probler;s of

nO'.cml?l reaearch. No OIl.e <l.evotee yee:rs to. flay, the a.e,,<:'J.opment of s. ｢･Ｈ［Ｇｾ･ｲ＠

spectrometer or the production of an ilJl.prcveil solution to the !ll:oblem 0;:

38

so lII1lch of it is repetition of ｰＺｲｯ｣ｾ｣ｬＮｭＺ･ｳ＠ that have been ce.rdcd otyl; bci'cro.

That, I ·think, is the key of fascina'Gion of the norms.1 research problco.

Though its outcome can be anticipated, often in detail so Ｆｾ･｡ｴ＠ that whE.t re-

mains to be known is in itself ｵｮｩｮｴ･ｲ･ｳＧｾｩｮｧＺ＠ the way to achieve 'i;hat ｯｕＧｾ｣ｯｭ･＠

remains very much in doubt. :Bringing a norme.l research }?::'oblem to a conclu-

sion is achieving the antiCipated in a neUl,>ay, ana. it requires the solution

of all sorts -of complex instrumental, ｣ｯｮ｣･ｰｴｕＤｾＺ＠ and mathematical puzzles.

The roan liho succeeds proves hill!seJ.:f an expert pu:::zle-solver.

The problems ot ｮｭｾｭ｡ｬ＠ research are puzzles, and their fascination is

largely that of the puzzle. The psradigm from which they derive defines

both the natUl'e of the solution ｡Ｎｾ､＠ the rules under which the search for

that solU'l;ion nmst be unl'.ertaken. Wi'thout the paraa.igm there would be no

problem (or puzzle) at all. Eq1:al1y important, it is the scientist's COl1ll:li'l;-

ment to the ptJ.re.digw which assures him that the problems it poses ｾ［ｩｬｬ＠ have a

eolu-(;ion. Without that felt guarantee the problems of normal resesrch,

Hoother conceived. or not, would ecarcely be v.nclertr;:ken. Perhaps all this

ｉｄＸｾ･Ｓ＠ normal research eeem uninteresting, but it ought not do so. Any chess

player w-lll testify that to knOl{ the rules and the sl:istence of a solution

dec3 not deprive a chess prOblem of challenge end fascination. On the con-

ｴＬｾ｡ｲｹＬ＠ wi·thout that knO'.>'leo.ge there ll01.1ld be neither puzzle to solve nor game

to play.

This reference to chen:: can, ho,:O'i'$1', introduce no more th<:" a me'Gs.llhor.

Ae a rr.etaphor it ca',chee, ! beHove, the ｂｊ＿ｩＩｾｾＮｴ＠ ::.nii fc.scination of normal

science" Jvhcu,5h probably not the iU'l;ensiJIi:r of th;;. addiction g.sna:,;-c:'::;ea. by the

.. t· ＭＧＮＡｾＧＭｬＢ＠ ＬＮｾ＠ ....... ｾ＠ ﾷｾｉ｟＠ ... ,· ... ·.:_ .... ｾＬｊ｟＠ ::".:;.. .. ,., .•. ;' ... :,:,.. •.. ', .... Ｈｾ＠ ••.. " .• ＺＮｾｾＮＺＮＬＧＮＬＮｾＮ＠ C".,..r .f-." •••••• ＨＧｾ＠ ｾ＠ ••• <: ..• : .•.•.••. ＺＺＺＭｾ＠ •••..••• ｾＮｊＮ＠ ＢＨＬＢＧＬ［ｾＬＮｾＮＢｾｾ＠'C::.0 ｬｬｬｾ＠ ﾷｃｾＡＱＮＰｲ＠ (;, ..... .;:0\...:;. ... ;...-; ... ｾ＠ .• 1 Ｎ［ＮｾＢＮｬＺＮ［ＭＮ＠ ... -' ｉｴＮ［ＧＺＺｩｾ＠ .... -- - - - - ｾ＠ .... ｾ＠ - - ｾ＠ - -- .... _.. .._"-

39

is .conducted. Chess ba.a Ｎｾ･･＠ that can bew.:.a.ee:r;plicit: thl1.t is "'hy the

same can be played by machine. lire there equivalent rulea for tl:.e ｰｲｳＮ｣ｴｾＮ｣･＠

to do normal science?

let me say at once that I am not altogether sure of the anlTh"r to

these questions. For some j<!are I took it tor ｳｲ｡ｮｾｴ･､＠ tliat a. seto! rulea

eui'ficient to detemine normal 8c1enti:f'1c practice was implicit in the text-

books and the training procedures that ＱｮＱｴｩｾｴ･＠ the student to the profes-

sion. During that time my discu6s1ous.of norl!lal sCience made no reference

to pIlIlldigme. Inatead they referred to the speci:t'ic ｣ｯｮ･Ｇｾ･ｬｬ｡ｴｩｯｮ＠ of COln-

mitments--methodolog:lcal, theoretical, and ｯｮｴｯｬｯｧｩ｣｡ｬＭｾｖＯｨｩ｣ｨ＠ n:eJl:e a pm"tic-

ular problem"solViilgtr8.ditionpol3S1ble. on that view periods of normal

science w"re periods of consensua, during which the entire scientific com-

mun1ty···agreed·aboutthe·rules····ofthe·game.·······Al!d··scienti.fie·revolutions ··were

then the episodes through l,hich the rules of the game were changed. That is

the position implied, for the salce of preliminary ｓｩｾｬｩｦｩ｣｡ｴＱｯｮＬｩｮ＠ the in-

troduction to this monogra.ph, and I st111 tind it extraordinarily tempting.

But it is very probably wrong, and we can learn something more ebout both

normal science and. revo1utiol16 by exploring first ',he position's temptati.ona

and then the reasons for reSisting them.

Anyone ｾｲｨｯ＠ bas tB.lked much with contemporary SOcial SCientists is

111tely ﾷｾｯ＠ have observed their frequent and deep concern &'001.11; the <lefini··

tions of their various fields and I).bout the problesa, methods; end stel1'J£,rc'.s

of solution legitlme;(;{; 1'01' their specialties. Among many of' them ｴｯｰｾＮ｣ｳ＠ of

this sort ｡ｾ･＠ repeatedly discussed, aud the discussiousproduce little or no

40

They were, for example. particularly ilUport&nt in tha ＬＱ｣｜ｩ･ｬｏＢＧｬＮｭ･ｮｾ＠ cf GeV(l!l-

teenth-century chemistry and of late Gigh-te:enth- ,r..nd. ee.l"ly ｮｩｮｾｲｩ［･･ｮＺｴｨＭ｣ｴＺｬｬｴｵｲｹ＠

geology. Furthermore, they recur ｲ･ｴｲｾｬｦｕＢｬｹ＠ duriug periods of sc:l,entific

revolutions. the tiMes t;hen para-diems Chllnge. ＧｬＧ｢ＮＧｾ＠ transi tio!'! f.'om Ne,,-'.;onlv.n

to relativistic and quantum mechanics evoked mauy deba'"es about 'ene nature

and standards of physics, some of wich still continu,e. There are people

alive today lTho can remember the simila.r argumento engendered by l<a:,mell's

electromagnetic theory and by otatistical mechanics. PJii earlier still the

assimilation of Newtonianiem gave rise to a particularly famous series of de-

bates vith Aristotelians, Cartesians. and I.eibnitzia.ne about the standards

legitimate to science. Contro-.ereiee of this sort, though not ｡ｬｴｾｹ･＠ on this

scale. are a consistent feature of scientific revolutions and a v,sual :feature

of pre-paradigm scientific development. But they seldom occur dvring periods

of normal science, and it is therefore very temptil".g to suppose that normal

science depends upon a consensus among practitioners about the nature of

their field, i'l;s problems; aml its methods. Appal'ently, if scientists do not

d1.sagree about the nature of their field, that must be bacause they s;;ree

about :Lt.

Yet tha't cOnclueioll is Ilurely not neCCfllml"Y and is very ;pxobo.bly lllis-

'taken. Certainly there are a great many th:!.:ngs about ,mich all scientis'Gs

do agree, and Ｇｾｨ･｡･＠ probably could be explica.ted and tranetormed to l'u1eE.

In the first ｰｬｾＮ｣･Ｌ＠ there are at least a fe\Ol endurir,g cOll!lllitmenta withou'c

Which no man is a scientist. The sc:tentist must, for eXaILple, be concerned

to underctand the 1;orld end to demonstrate previously unno'l;;l.ce(1. aspects of

41

····of ﾷ｡Ｇｰｰ｡ｲ･ｮｴﾷ｡Ｚｴｳｯｲ｡Ｎ･ｩＧｩｾｴｬｩ･ｮＧｴｬｩ･ｳ･ﾷｩｩｩｕ｡ｴﾷ｣ｮ｡ｲｲＶｮｧ･ｬｩｩｦＮｩＧＦｏﾷ｡＠ ·uei,i· ｾﾷ･ＺｴＺＡＮｬｬ･ｬｕ･ｮｻ［＠ .. ' 'of

his observational ｴ･｣ｨｮｩｾ･ｳ＠ or to ｩ｜ｬＺｦｴｨ･ＮＺｴＺ｟ｭｩｊＺｵｬｾｴＬＱｑｮｉｌｯａｊｩｊｉ＠ .. ｴｨＢＬＮｯｲｾ･ｬｬｾＢＮ＠

There must be other l'Ules like these that hold for a.llscientiots. In ad-

axid.thatthusdist1l'1guishit frOlJl its predecessors axidS'.lccessQJ;·s can be

made explicit. NS1;ton'sI.awswere l'Ulesfor the Nemonislls .. but not for

the .Aristotelians or Einsteinians. Mass was a fundamental ontolog1cal oat-

egory forprerelativiBticphysiCsji though it is no .longer that today. Or

i:tgaill,thoUghChemietsbelieved1nelemertts b6thbefore and after I.avois1er,

the Chemical Revolut10n:traJisformed the chemist's convictions about what an

" ........... , ....... , ... ｟･ｬ･ＡｬＡ･ｲｩｴｾＮｅＡＮＡｬ＠ .. ＬＴｦＺＡ＼･ｲＬＺｴＡｬＮＮｙＮＲｮＺｴＮ･ｲＧｦｌＡＧＡｑｲｋｾｬｧｬｬｬ･ｮＮｴｾＬｾｲ･ＮＬｾＡｬＮＱＡＮ｢ｳ･ｴＨＩｾＮｪ［ｬＱ･＼Ｚｲ･ＬＮｓＡｬＮＬＮ＠

purele.boratbry suDstIlrices. Before that timetheyhSdbeen conceived as sub-

stances which lnprinCiple could not be isolated for laboratory .investiga-

tion •. TheaeeXrimples illustrate the sorts of rules that ce.n be made e:i:plicit

and that 'help todistingu1shone trad1tion of normal reEearch practice from

ｴｨ･ｮ･ｸｴｾ＠

Undoubtedly other such l'Ules would be discloeedby the study of pv.rticn-

lar normal-scientific traditions. We shall, in fact, be ･＾ｾｩｮｩｮｧ＠ many rnor.e

'Of thamin tlie'pageathat follow. . Nevertheless,thenumber'O:f: rules ths.t

call be educed. by suchatudy never seems su:f'ficient to.define .the puzzles the',

sc:1.entists ·normally undertake or to rcstrictscient11'ic .attention to their

pursuit. Furthsl'more, it is by no means cleG,!' that scientists l10uld or even

could agree aboute.ny set of r'.:!lee su:f'fic:!.entlylnrgep..ud prec:i.se to have

that effec'i;. Asl, ellY rand-om group of physicists; ｣ｨ･ｭＺｴｳＧｾｯＬ＠ aotrollomcrs, or

get almost as =y different ImlTh-el:'S Coil there Ul"e scientists in YG\J_'7 r.;,'.!';n2c_ - -. and. -none of theil: &llSwcrs is likely to fit prec1.3cly til", iull range vi: ccn-

tinuing professional reaearch. Or Oxam:tUe the texts tllrO"<lZll ,lhich at-:.zdents

learn to practice normal science and the ClaGB1cs through which an older

generation was ｩｮｴｲｯ､ｾＱ｣･､＠ to its professioilll.l :?ield. l,gain you "ill :rind

many explicit rules, laws, and principles, but again they will collectively

fail to dei':tne the traditional problems and procedures of the profession.

If' a BUi'i'icieni; body of roes is to be found at all, it ｾｮｬｬ＠ not be retrieved

simply from a textbook's discussion of ｬ｡ｾｔｳＬ＠ dci'in:l.tiona, and theories. That

disC"<lseiion ".oilJ. y .... oYiu.e same rules for noml science, but ｏＧｾｨ･ｲｳ＠ must be

sought implicit in the semple problems that bulk so large both in science

texts end laboratories ｡ｲｾ＠ in the ｾｬ･＠ app11ce.tionsthat are en integral

part of every scientific cla.ssic. That is wy, at the start ol this aectiCll,

I insisted so strongly that its applications are a ｾﾷｴ＠ ot every parsdigru.

But if sampl.e problems and applicaticns m'e pext of uhat =);;es possible

e. tradition of UOl'r:lel reaec::ch, then that trs.dition need. not be entirely de-

'Germined by discoverable rules. Applications end problems need ｮｯＧｾ＠ im!?ly

rules in order to deterwine nOl'1l1$.l science.' Rather than learn r.ulea the

scientist can, and. in some part clearly does, learn by pr<:;ctic1ng on paradigm

problema. In contcmpore.:ry scientific education thin process of educ:;rc:!.on

through ーｲｯ｢ｬ･ｭＭ･ｯｬｶｩｾｧ＠ bezins in high achool or in the first ｾｾ｡ｲ＠ of college

ｾｾｭＺｴ＠ con.tinUetl s"i:;et'..d:i.ly to" or more often ｴｨｲ｣ｲｾｨＬ＠ the c.O'..;to::.:'al dissertation.

Subsequant prof'ee3ioMl l'e3earcn. is no I'!hsrp and r,il!dd0n depal'ture. Its

ＬＭＭＮＭＭＮＭＬＭｾ＠

43

- ---. -

･ｘｩｳｴＱｊ｝ｧﾷﾷﾷ｡Ｎｰｰｵ｣｡ｴｩｯｮ･ｏｴｾｴｨ･ｰ｡ｲ｡､ＱｧｭＬＬﾷ｡ＮＭｰ･ｲ｡､ＱｧｭﾷｾＢｨｩ｣ｨＮｩＸｴｬＺｩｕｩＳｾ｢ｏｴｨｭｯｲ･＠

and less than a set. of rules .tor .the co!lduct. of .the ... scientific life. It is

because they learn in this vay thatscientista can so regularly agree in

'.'their·evaluations··of·part.1cular-problems·.and •. particular.solutions without

manifesting anysimil.eragre"ment ｡｢ｯｵｾ＠ thefu1laet of rules that apl?3ar

to underlie their Judgments. One can model lfork upon.aparlidigm or recog-

nize work mOdeledoncne 'ifithoutbe1ng entirely able to say what it ie tOO.t

gives the model its status.'

This view. of the ｾ＠ ... y in which parad:tgms determine. normal science seems

to me ;particularly plausible because of' 'Ghe assistance it gives nth ｴｾＬｯ＠

__ ..... ｾＮＮＮＮＮＮ＠ problems that we shall ellCounter below •.... Hot all the debates that are evoked _ .. ".,,- ＭｾＢＢ＠ ｟ﾷＢ｟Ｂ｟ｾ｟ｾ｟Ｂ｟Ｂ｟ＧＢｾＧｾＧ＠ __ Ｇ｟ＢＢＢＧＧＧｾ＠ __ Ｇ｟ｭ｟ＧＧｾＢ｟ＬＢＢ＠ •• ,, __ ,,_.,."_,,'_." __ ._"""_ .... _ ••• _. _____ ... ｟ｾＬＬｾＬＮ｟ｾＢ｟ＬＮ＠ _____ ＢＧ｟ｾＬ＠ __ ｾ｟ｾＬ＠ __ "." __ ..:.....""" ___ ＢＮｾＮＬ＠ ___ ｾ｟ＮＬＬ＠ __ ,_ ... ""' ___ ••• ,,

bye. proposal for 8. revolutionarycbange in 8c1enti:f1ctheory are defini-

ｴｩｶ･ｬｾ｡･ｴｴｬ･､＠ by the profession' saEsim11at1on of the new paradigm. Some

are, of course, ;particularly those' that revol"/e around the. choice between

tlro cOl!l1}eting setsoi' Bc1ent1:f'1c lawliorsometbing .else of the sort. But

other debates" part1cu18rlysome .of ·thoflewh1ch:attempt· to define .the proper ,

suoject ma.tter of a particular science, seem rather to die out Ol' to go 00-

Clergl'01l!ld 'Without any consensus . having. been reached. Though .relewnt to a

sc:timce irl't<:l1' thefpllrOOigmhasbeen chocell... Problems can be selected 14'10.

solutions evaluated m.thout sareement about ﾷｾｨ･ｭＮＮ＠ During p!:)l'iods of ncr-.ral

science' they are therel'O" ... e silnplynot often nor seriouaJ.y diccucsed, Ins'Gcad.

they renain as lo.tent srsaa of d:l.sagreamer;.t until b;,'ought to light by a

philosopher or by a new flcien'Gif:i.c revolution. The absence of disagreernent

A second and more important problem about flcielltii'ic rcYol1.\ticns is

even more sierJificantly affected by recognizing that a nor-wal ｳ｣ｩｮｴｩｾｬ｣＠

trac.ition may be deteTlllined by moo.el.:i.ng sa well as by Tolles. E,rery physi-

cal scientist today learns the 1&'Irs of:. say, quantum IlWchar;icB and mos'l;

emv1.oy them at ｓｏｬｬｊ［ｾ＠ point in their reeeerch or tee-ciling. But they do net

all J.e&'n the same applications of theee lalrs, m:ld. they ere not therefore

aU af:fected in the S8!o.'C ways by changes in Quantl!lll-mecillm1caJ. ·practice.

On the I'cad to professional specialization a fe'\l' physical scientists en-

counter only the basic principles c:t.e q1.1lm·tUl!l mechanics. o-thers s·t,my in

detail the paradigm applicatione of these principles to chemistry, still

others to the physics of' the solid state, and 80 on. Wast gw::.ntUl!l meche.nics

means to each of them depends upon what cour13es he has had., what te:dis he:

has read, and which journals he studies. It follows tbat, though a change

in qm1.ntum mechaD.1cal. law will be revolutl=y fur all of these groups, a

change that reflecto only on one or another of the pm:adigm s)?plice.tions of

quantUl!l lrechanics need be revolutionsry orJ.y for the me:nbere of a perticular

professional Bub-specielt7. For the rest of the profession and for those

who prac';;ice other physical sciences that cheuge need DO'!; be revolu.Uo:anry

at all. In short, though quantum ll'.echanic:s (or }Jewl;onian dynClllic:n, or e lec-

ｴｲｾ･ｴｩ｣＠ theory) is a paradigm for many SCientists, itl> role as pe.radigm

is not the same for all of them. It can, there1'ore, siur<l.l:..al1.eously ､･ｴＬＬｾＭｭｬｮ･＠

several traditiolW of normal science ｾｔｨｩ｣ｨ＠ ovsl"lap without beive; coextensi 1{<:).

Ae a resu.lt, a revolution proo.uced ,ritl"dn one of these trruli',;ions 1nll not

l1ecessE'xily e::;:teno. to the ot.h.era e.s ｾｬ･ｬｬＮＮ＠ In the sectioZl that follol:a im1!le-

ｏｾｬ･ｳ＠ .

a highly cumulativeenterpr:!.ae, e1ll1.!'..entlystlccessful 1:0. its a1m, t.he steady

･ｸｴ･Ｇｩｩ･ＱＰｩｬｾｯｦＧｴｬｬＨｦＢＢＶ･ｯｰ･ｦｾｗ｡ｰｲ･Ｚ［ｪｩｳｩｯｮｾｯｴﾷﾷｳ､･ｮＺｴＱｦｪｊＺＺｫｉｦｃＧ＿ｬ･､ｧ･［＠ ··In all these

reapectsit fitswithgree,i; prec:i.ilionthemost usuelima,ge oi"acientific

ｬｬＧｯｲｫｾｙ･ｴｶ･ｭ｡［ｙＧＧｬｩ･ｬｬ＠ hesitate to equate this scirt of science wlth the

vhole, for one standard productotthe scientific enterprise isstillm1.s-

ｳｩｨｧＮｾｉｏｲｭ｡ｬ＠ science s'*Iksno noveltiea of factortheol'Y, and" Ｑｾｨ･ｮ＠ IlUC-

cessfUl,f:l.nds none. New Wld'unsuepected.phenClllena are, however: repea.tedly

uncovered'bt sc:!.elltif':1.c rellearch, ･ＮＮＮｾ｡ｲ｡､Ｑ｣｡ｬ＠ nelf theories h:J.ve ega1.nand

_ .. ｟ｾ＠ ...... ｾ＠ __ .......... ._._l'.gain.beelLin;rented.'tiy_sc:l.elltistl ... ｟ｬｉｩｬｬｴｯｲｹｾＮｙ･ｮｉｬｊｾｧｻｾ･ｦＮｬｴＡＧＡｴｬ［ｬＺＡＺＡ［＠ ... tlle .... ｳ｣Ｎｩｅｭｾ＠

tiftc enterpriSe has Cl.evelopedauniquely pooerful techniquei'or produc1.1'.g

llUl"pl'isks ofth1,ssort. If this ｣ｨｾＸＮ｣ｴ･ｲＺｴｳｴｩｃＺ＠ ofedence is to be recon-

｣ｩｬｾ､＠ mth ｾｔｬｬ｡ｴ＠ has already been said,then research under a paradigm must

bea particularly ･ｦｦ･｣ｴｩｶ･ｾ＠ .. e.yof inducing lla.rad:Lgmchalige. The.tiswhat

funilaInentalno·"relt:l.es of fact e.ndtheory do. PrOduced inadvertently by a

game playedund,eI' one set of ruies, theirassilllilatiou requires the elabora-

tion of Ｆｮ｣ｲｾｨ･ｲ＠ set. After theybave beCCllleparts of science, tbeenter-

pl":!.se, at least ·of'thoscspecialtsts:l.n'lihoee perticula.r field the novelties

lie, is never quite i;lie same again.

We !:Just now ask am; cha,\1gea of thio sort can come b-,"oout: ｣｣ｮ､ｯＮＰｉＧｾ＼ｵＮＺＧＡ＠

t:irst discoveries,· 01' novelties of tact, e.ml then inventions, ox'nov0:ltieo

1;5

fincl that \lJ.scover:l.eo are not ieo1ated' evento but ex'tenC'.oc. e;giso:l.es Hi',;h

a l'egu.larly recurrent structure. Discovery conmencea Ｌ［Ｚ｣Ｂｾｨ＠ the miu!'eUGSS

of an0ll!3.1y, i.e., with the l'ecognition that nature han somehow v5.oJ.atcd

the paradigm-induced expectationo that govern normal ｇ｣ｾ･ｮ｣･Ｎ＠ It then

｣ｯｮｴｩｮｵｩｾ｡＠ .71th a more err less extended eJ..'Plare:tion of 'Ghe area of ancrualy.

And it closes only"ilen the paradigm theory bas been adJueted so that the

anroalous has become the expected. AElsim1lat1ng a netf sort at fact d.emands

a merre-thlln-additive adjUBtmellt of theory, and until that adjustment is com-

pleted--until the scientist has learned to see nature in a differeflt way--

the new fact 1a not quite a scientific fact at all. That conception of

dil1co-;rery as a process :I.Ilitiated by ano:aaly and completed. by a simultaneous

adJ1.,stment r:tf: fact and theory is the one to be discussed in this Election.

In those that foL1ow we shall explore the rather similar'structure of the

episoo.es that eventuate in the prcduct10n of JD3.jor theories. There too 'We

shall note the VIa;{ in which tact and theory are cntengled lfithin the expec-

tations induced by a. paradigm. In particular, .re shall then .;ant to say

that one important function of a new ｴｨ･｡Ｎｾ＠ is the cre&tion of new facta.

With a ｮｾｾ＠ theory scientists can see ｾｦ｡｣ｴ｡＠ phenomena tPJat they had pre-

viously sCen in another 'my. Only in the textbooks written after recogni-

'cion haa occurred are fact and theory once again firmly separated.

'1'0 see hOI. closely factual end theoretical novelty are intert.rined in

scientific discovery examine a pru.-ticulerly :tamous erJample 1 the disco"ery

of ｯｸｾ･ｮＮ＠ At ｬ･｡ｦｪＧｾ＠ three different reen have a J.eg:l:timate claim to it, and

Ilcvel'al other che::!liat.s ｴｬｕｾｴＬ＠ in the early 1870' s, have had enriched air in

ﾷｴｨｯｲｯｵｧｨｬ［ｙﾷｾＺＺﾥｩｬ･Ｍ･｡ｲｩｩ･･ｴｯｴＮｩｨ･｣ｩｂＮｩｦｲｬｊ｡ｮｴｓ＠ .. toPl'e)fiU'e .C1r.rok,tively purG

. of'. the ;me the . Swedish 5,pothcc:;,ry, C. tl, Scheele. We !mY, ｢ＺＷＮｾＢＮ＠

ever, ignorahis ｾＮＬｯｲｫｳＱｮ｣･＠ it .mSllot. published until ozygen' c di,scovery

had,·repeatedly ... been,announcedelsevhere ..•. an,d .• ;thus .. had .. no .... eft.ect .... ullon .the

:. historical. pattern that most concGI'nl3 us her.e...The second. in time to ea-

.. tablisha. claim '!raG. the British Bcient1.st .. ¥d ... di-vine, Joseph ｐｲＺｌ＼ＧＡｬ＾ｴＢｴｬＢＧ･ＢＧｹｾＮＭＭＭＭＭﾭ

wo colle¢ted the gas released. by hes.ted.reO;.oxide o:f'!llercury e.s ena item

in aprolonged>nOrmaJ.invest:!.ge.tion' of. the "e.irs" evolved by a la:r.·ge. number

of solid subatanees.· In lTI4 he identified theg&s . thus. llrcdueed as ni-

trous oxide and in 17'75. led by f'urthertests, as camnonair w.!.th less than

i'1;6 usue.l··· quantity of phlogiston. •. The chiI'd Cla.:i.ma.nt, . Lavoisier , started

theworkWich led him to'OXygen after Priestley's experiments of 17'74 and

pcssibly"asthe'result of 'e.hintfrom: Priestley. Early in lTI5 wvoiflier

reported that the gas obtainedbY'heatingtheredoxide of mercury ws "ail'

itself euttio ,lii;houtaJ.terai;ion [e:l':cept the;t] • • • it ccmes out more pure>

l!!orereap1rable." By lTI7,probably ;i1iththee.saiatlmce ot a second hint

'fr()l!l l'r1es-t;ley, Lavoisier had concluded", thai; Ｇｾｨ･ＮｧｳＮｳ＠ ,,;as a d:i.stincts]fscies;

one of the ｴｗｏｬｬｬＸＮｩｮ｣｣ｭＮｪｪｴｩｴｵ･ｬＱｴｳｏｦｴｾ･＠ .a.tmcrlphere .. a ccnclurJion that

Prieatley. .. :was .. ·.I!.eVel· .able.i;o ... e.ccept"

Thisr.attern ot:d:!.scoveryraiaes a,.queBtion .'hich, at ｬ･｡｡Ｇｾ＠ in its

seconiiand more fund.ame.:ltal:f'orm. can be asked about every no .... el phenomenon

that has e .... er entered the consciousness, of scientists. Was it. Priestley or

Lavois:!.er. ifeii;her. dlo first'ctiscoveredoxygcn'l In either C3IlS--a form of

i;he q'<lsationthat could. be asked.. even if only the man proclaimed discovGrcr

0.0 SO precisely becau.e€l there ie no 2.!!S'4'C:':- oi' th0 tind Ｍ｣｢ＮｾＧＡ［＠ io sought. ｄｩｳｾ＠

been contested since the 1780' a--is e. eYlllptcm of lloL:ethlng aske1'; in the inlllge

of science that ｾＱｶ･ｳ＠ cl,iecovery GO fun&l.mente.l a role. Look once moroat our

ezample. Priestley's claim to the discovery of ｾｾｧ･ｮ＠ is bused ｾＱｬｯｮ＠ his pri-

01'1 ty in iaolating a gas that 1ms later recognized as a ､ｾＢ･ｴｩｬＮＱ｣ｴ＠ species.

But Priestley's sample ,raa not pure. and. > i:t' hcl<Uug impure ＼ﾻｾＢｭ＠ in 000' s

hands is to d..tscover it, that b(ltd been done by cw:ryone who ever lJo'GUer1 a"t-

moephel'ic air. Bes:!.des) if ?.cieat1ey was the discoverer, when was the dis-

co"ery i!'£.de'i' In 1774 he thought he bad obtained nitrous oxide, a species he

eJ.ready ｫｮ･ｾｔ［＠ in 1775 he eaw the gas as (lephlogisticated n:!x, ... "hich ie stHl

not Ol:Jlgen nor even, fOT phlogistic chemists I a quite ulle:.-pacted sort of go.s.

ｊｾＡｬＮｶｯＺＡＮｳｩ･［｣Ｇ＠ e claim !!lay 00 strQ<l-{£cr, but it prec.:zuts the S9.!ilO p7:cbler:,s. If ,Ie

ref1..l.ae the paJ.l11 to Pricctley J l-re C2Jlnot ｡Ｚｲｲ･ｾﾷ､＠ i:ti to L3vo:'i.sier fer the ｾｲｯｲｫ＠ of

IT{5 lfh:!.ch led him to iif:!ntify the gas as the uair itself ell·tiro." P!.-(,)!l1.\!iKlbly

uo waU fOT the work of. 1 if6 and 1 Tn "Hhich led IE-'IO:!. sicr to S:€ ;(!'Yi; merel y

i.n 1777 e.nd to the end of his life Is.Yoicier iU;:!ioted ｴ｢Ｎ･ＺＧｾ＠ O:'Jrgen ,:aG ｾｮ＠

Hr .. ::inciple" m:dtGd.. ir'lth calor:tc, t.he Ｚｵ｡ｴｴｾｲ＠ of reat. Shall 'tIe therefore

like the discovery of oxygen. Though ,llldoubtedlycorrectthe ｮＢ＼ｬｮｴ･ｬｬ｣Ｌｾ＠ >

"OXygen was disco"ered, II mislenda by 5U(Ogest:l.ng that discove:d.!lg SCJ!lletl.d.ug

isa"singleosimpleoactoasslml1a.bletooouroutrual ... (and alllo ... questionable)

｣ｏｪＺｬＬ｣･ｰｾｩｯｬＱＮＹｦＧ＠ ｳｾﾥＡｧＺＮ＠ Ｇｒｬｬ｡ＬＧｴｩＡＳｾｙｾ＠ Il0 readily assume. that disco\>-ering,

like fleeing or touching; should be unequivocally at""..ributiible to an i!i.di-

vidualandtoa moment '.n time •. :But the latter attribution is aJ:IIS.Ys im-

possible and the fOl'lllel' often is as .. well. Ignoring Scheele. we . can sai'ely

say that oxygen .had not been discovered.before lT74 and we would probably

also say that it. had been d1scoveredby l7T7or shortly thereai'ter. But

wUhin limits or others lilte. them sny attem;pt to date the. discovln'Y

mustinevit.ably be arbitrary. Furthermore •. itl!lust be arbitrary Just be-

cause diacoverillS "a newsOl'tof phenO!lJenonis necessarily a com,pJ.ex event

which involves recogniz1ng. both that someth:l.ngis.and what it is. Note, - .-. for example ,that:tfoxygenwereac'!;W:illy,dePhlogistlca'csd. air 1 we shou.ld

ｩｮｳｩｳｴｭＮｴｨｯｵｴｨ･ｳＱｴ｡ｴＱｯｮｴｨ｡ｴＮｾｩ･ｬＧｬｴｬ･ｹ＠ hsd discovered it thoughw-e w9u1d"

. still notknawquitewhen. BItt if bothobserva'cion and conceptualization,

fllct Wldassimllation to theory , are inseparably linked in theproceao of

conceptual ca.'.;egoriesarepreparedinll.dvance, in lihich cane the phenomenon

"would not be ofa new sort, can discovering that and discovering voot occur

eff()rtlesSly, together, and in an instant.

BItt, granting that discovery involves an ehtended, thoue¢l not neccssar-

ily long, procesa of conceptual assimilation, can ｾＭ･＠ say that it involves a

his paJ?""l'S froo lIT{ on *,s lJ.Qt £0 much the discovery of OlWi},Ci:Z!. as the ｏ［Ｈｹｾ＠

g,en theory of canbuation" and. th.a.t theory 'V;-as the keystone for: a ｲＧＷＺｩＧｏｊＮｲｑｵｬ｡ｾ＠

Uon or chemistry so vast Ｇｾｨ｡ｴ＠ it is usually called the Chemical Revolu'Gion.

Indeed, if' the discovery ot rurygen llsd ｈｏｾＧ［＠ been = intim:,.te part of the

emergence of e new paradigm for chemifJtry, the question of priOl·1ty from

which ｗｾ＠ began would never have s"omeil. so iPl)?ol't:m:t. In this ct'.se fiG in

o'chera the value :placed u);lon a new pilenomenon and th'(l.s upon its a.iocovoloer

varies 'IIi th our estimate of the extent to which the phcmcmenon yicla't\:1d

p.'U'sdigm·,:tndtlced &nt1cipations. Hoticl;l, however, since it will be ｾ｣ｲＮＮＢｐｯｬＧｴＮＮＢｮｴ＠

J.a.tel", that the d1acov0::-y of oJ::yj!;en *'3 not by itself the ce:llse of the change

in chemical theory. Long before he ;Played any ps;rt in the discovery of the

new gas, Lavoisier liaS convinced both that s01ll!;lthing .ms 'If.t'ong 'With the

ｰｨｾｯｧｩｳｴｯｮ＠ theory and 'w.s:t burning bodies l1.baorbed some ー｡ｲＧｾ＠ of th<l etmoll-

phere. That much he had recorded in a eeF.led note deposited v1'c.h the Secre-

tary of the French Academy in lT72. What the ;Tcrk on oxygen did *'!) to give

much ｾ､､ｩｴＺＡＮｯｮ｡ｬ＠ form aud structure to Lavoisier's earlier sense that some-

thing '1m!) amiss. It told bim s. thing he WE alrelJ.dy ｐｉＧ･ｾＢＧＮＱＮＧＬｾ､＠ to diacever--

the nature of the ,substance that combustion removes f:-cm the at.!Uo!f,k'ihe!Oe. ,

ThEt advance l:'l.iiSl'eness of <liff:tculties in the ･ｾｾｩ･ｴｩｮｺ＠ phlOZis'i;cll ｴｨ･ｴＺＺＺｾＺﾷｹ＠ of

cO!1:lbust:J.on Iu"Uct be $. significa.nt purt of "t-That enabled I.e.:VOiDl.C:C "'';0 sr;:a :tn

･ｾｱＺ･ｬｾｩｭ･ｮｴＳ＠ m-a.ch like Priestley4 a n gas t:'hs.t ｆｩＺＱｾ｣ＵＺＺＧＱ･ｹ＠ hf!..d be04 ul1c.1.blc "co

sce there himself. Conversely 1 the fact that a. maja;; psr(migm rCYiaion ,*,,""aO

ｮｾ［･､･ｩ＠ to sse \fhat ｉﾣＢｬｲｾ､Ｎｄｩ･ｲ＠ Sa'l:T r:!"uct be Ｎｊｾｨ･＠ pr:tnc::':psl r;;;iUSo-n yhy ｐｸﾷｾＮ｣ｳｴｬ･ｹＬ＠

51

coverieocan come abou.t,these Elxa",plea ｡ｲ･ｾ｣ｨｏｂ･ｵＧ＠ to be di.:I.'ferent ｢ｏＧｾｨ＠

ｦｲｯｭ･｡｣ｨｯｴｨ･ｲｾ｡ｮ､ＧｦｲｃｩｬｬｬＬｴｨ･､ｩｳ｣ｯｶ･ｲｹﾷｯｦＬｯｸ［ｬｧ･ｮＮｾＢ＠ The:1'irst,X-rays,:L1i! a.

clAss,10"case., of ､ｩｳ｣ｯｾｲｹｴｨｲｯｹｧｨＬ｡｣｣ｩ｡･ｬｬｴ＠ , a type '\,hiob occurs mCl'e fre-

quentlytha.n the impersonal ｉｊｴ｡ｾ､ｂ＠ of eCien:t:!.f'icrcporting e.1l0l! us

easily to realize. ｉﾷｾｓ＠ story opens on the dey that the physicist Roentgen

interrupted a nor:malinvestigat:!.onof cathodersys because he had. not:1.ced.

that e. 'barium platinocyanide screenst some dis·tanee from hiezhielded F-.p-

paratus glOtTed when thedisclliirge WEi in proeMS. ll'urthel:' inverrtigatious--

theyretjuiTedseven hectic;reeksdu.Tillg which Roentgen rarelyle:ft the

laboretory--in::1icated that the cause ot the glO1f came in ctraight lines from

the cathoo.e ray tube,that the radiation 'cast shadows, c(mld !lot be de-

fleeted by a msgnet, and l!lilch elSe besides. BsforellllZlcuncing his discovery

"Roentgenbndconv:l,nced • himBel:f''thai; ｨｩｳＬ･ｦＺｦＧ･｣ｴｾ＠ ",""Ss not due to cathode l7aye

but to an'agentmthat least some sill!ilar'ltyto light.

EVen so brief' an epitome reveals striking resemblances to thed:l.r;covel"¥

the pll.J;og:l.S·COll parad:i.gm: Roentgen '0 d1.scovery c,omr.enced 'ldt.h the l'ecogni-

1;1011 that his screan gl(f"ed "hen it' should not..!n both cases the pcrc'=p-

Uon of anomaly , that:!.!'.: > of a :phenOmenon for "'hich t.he parad5.r,m lw.d nat;

prepared. the investigator: plv..yed. an essential role in prepa."t'ing the l-re::

52

aSllimilation. At 'I.-hat. point in Roentgen's invostigl'!:tiollJ for e::liLlplo,

ought 'Ire say that ｘｾｲＡＩＮｹ｡＠ lllld actl1£21.1y been discovered.? ｎ｣ＬＬｾ＠ > ｾＮｮ＠ cony c;;:,ss 1

at the first instant, '\!hen all t.hat hl:.d been noted was a clewinG nCl'cen.

At least one othel" investigator had. Been that 6101/ sud, to hie Ｓｵｨｾ･ｱｵ＼［ｬｬｴ＠

chagrin, disco;rered nothing at ell. llor, it is almost es clero:, can the

moment of discovery be pushed back to Il. point during the last lo-cek of in-

vestigation; by which time Roentgen '!.'nll exploring the properties of the

:new radiation he had alread,v discovered. We CI.Ul say only that X-ra.ys

emerged in ｦｦｴｬｲｾ｢ｵｲｧ＠ between November 8th ｡Ｎｾ＠ Decembc1' 28th of 1895.

In a third nrea, hOl.'ever 1 the existence of cignificant r.a:rallels be-'

tween the discoveries of oxygen ana of X-rays is far less apparent. Unlike

the discovery of oxygen, that of X-rays n'tl8 not, at least fer a decade

after the event, implicated in any obvious upheaval in scientific theory.

In wat sense then can the assimilation of that discovery be auid to have

necessitated. :paradigm ｣ｨｳｮｧ･ｾ＠ The ca£e 1'01' denyir.g euch a cr..c..nge is very

strong. To be sure the paradigms subecribed to by Roentgen e.Jli his coa-

temporaries could not have been used to predict X-rays. (!<!a.lrnell'" elGc-

troosgnetic theory had not yet been generally accep',;ed, and. the electron

theory of cathode ra:ys hed net even ｢ｾ･ｮ＠ !l.Il.-1ounced..) But neither did those

paradigms, at J.east in fIily ob"liC'.ls senee. prohibit the exis'cence of X-rays

as the phlogiston theory b£d prohibited laVOisier's interpretation of

Priestley' e gso. On the contrary, :!.n 1895 acccpt,ed ･｣ｾＮ･ｮｴＺｈﾷｩ｣＠ theory P,J::d

practice admi'.;'.;ed e. ｮｕｬｾ｢･ｲ＠ of 1'O::-dl9 of rr..dis.tioll--visible, infrared, end

53

New elements-;!erestillbeiDgfi tted ｴｯｴｨ･ｾ｣ｨ･ｭｴ｣｡ＱＢｰ｡ｲ｡､ｩｳｭｩｮ＠ Roent,,"Cll' B

____ day. Theil'. ｾｳｵｩｴ＠ had become a stWldard pro.ioct for normal scienc:e " __________ _

Ult us first be clear that X-rays '\:lere not BO received. Though

Roentgen had previoulllY'eetablished a fine reputation an an "expcriJlw,ntalist.

_ his_ .announcement:lnDece1llber, 1895. W.II. ｷＱｾＱＩＺｧＺｲ･ｾｲｬ［ｾ｣ｬＬ＾ｰｾｴＺＡＮ｣ｵｬ･ＮｲｬＬｹ｢ｹ＠

those most concerned, w1ththe incredulity and.skepticism 'Which we shall

henceforth repeatedly encounter as· Signs: of· resistance to paradigm char>l)e.

IDrd Kelvin, to c1teonly an especially prominent example, immediately pro-

nounced X-rays the product oi'an elaborate hoax, Even without benefit of

Freud, one m1ghtguess from theee circumstances that to some scientistll the

ass1milation of X-rays meant the surrender of sanethiDg else. Furthermore,

only one more step is needed to recognize that what. had to be. given up, or

at least strenuously reexamined. was the current Ｚｉｮｾｴ｡ｴＱｯｮ＠ BUd design

of a numbel" of paradigm laboratory procedures. If Roentgen's apparatus had

produced X-rays, then a .number .. ofother European. experimentaliatS ... lllUst. for

sCIlletime have been prodUCing those rays in-their ow laboratories but 1.-11th-

out knowing it. Perhaps those rays,'Illrl.ch me-ht well have. other unackuowl-

edged sourcea too,wre implicated :In behavior previouoly explained 'lfi'Ghout

reference to them. At thevl'ryle:::.Gt, ecveral.sorts oi'loDg faml.lw· o.:ppa-

ratuB often deployed on experiments quite unrelated to X-rays 'lfould in the

future have to be shielded with lead. Some previously completed scientific

work· on normnl paradi&''lll projects might now have to be done over becauoe

earlier scientists bad tailed to recognize and control a relevant variable.

X-rsyu, ｾＮｴ＠ is true, opened up n neY field end 'GtU!l adc1.ed to the potential

clC'".k"lain of ｮｯｲｭｾｬ＠ sciel:,ce. B"' .. 1.t ｾﾷ｣ｨ･ｹ＠ also, end. th:ts is i"lm! the more important

previously parCldigmatic appUcationc of theor.y tbeu' :t'ight to th&t tit.!.",.

In ShOl-t, if" a pro:adigm incluiies e'...pplicattonll, aEi ! hs.v," alre::Cl.y in-

sisted. that it IllUst, then mere failu.r-e to tuke an ｵｮ･Ｚｾ｣Ｇ｜［･､Ｎ＠ flo,,'t of phe-

nomenon into account may often imply that that sort of phenC:ll<::Doll cannot

exist. Even when it violates no explicit theoretical preo.ict1on, the

emergence of a nefT sort of phenomenon can necessita·te pe.,'s(liem chsnge.

There is even, for example, some evidence that so readily assimilable a

discovery as that of Neptune evoked resistance that may ｲｾＧｴｬｹ＠ have been

due to its destructive impact upon previouelyparadigmatic astronomical

tools. Neptune's existence end approximate position and motion lTere first

predicted from Newtonian theory to account for observed d:!.screpanc1.eB be-

tween the predicted and observed motions of Uranus. (Note, again, the role

of observed anomaly.) A felT astronomers uere skeptical even about Neptune's

existence, and all but a very fev displayed a remarknble reluctance to

search for the neii' planet even 1/'herr told just linere to look. Some of tha.t

resistance was very probably due to their recognition, corwci= O!' ur.con-

scious, that previously paradigmatic tnbles for the motien of Satu::'n t,nd

perhaps aleo of Mars 'ITouId have t.o be recomputed. if the unp:c€lcedented :flTe-

diction of Adams end. Le Verrter produced a planet. Only if. 11'," U!1licrata.'1il

haw a par::il.igm can, partly by ,1.irect statement a.'1d :partly tlll'oue;h :l.ts appli-

cations, restrict the field of phenomena acce!!sible to Bcienti.i'ic invcl'!t:1,ga-

t10n, shall 'We realize hOt-T the discovery of X-rays, for exauwle, couJ.d open

a strange nelr 'World to 60 many scientists. And if X-rays had not had that

effect, they could sco'::.:"cely he.v£: :paxt1cipated ｾｾＬＧＩ＠ ef:i"ect1 vely in generating

ｴｨｾ＠ crisis th=:\.t leO. to the tv;er;.tleth-cent.u::y rcYolution :tn ph.yaic;s.

55

Ｍｾｏｕｲｾｾｦｩｮ｡ｊＮｾ･ｸ｡ｭｰｬ･ｾｯｦ＠ ｂ｣ｩ･ｮｴｩｦｩ｣､ＱＮｂ｣ｯｶ･ｲｬｩｾｴｨ｡ｴ｣ｯｦｾｴｨ･ＭｩＮ･ｹ､･ｮｾｪ｡ｲＺﾷ｢･＠ ..

longs to a class that may be dCBcril;led .all theory-induced. Initially, the

term may seem paradoxical. because everything said eo flU' muatindicate that

discoverieslihose outcome ｣｡ｮＮ｢･ｰｬﾷ･､ｩ｣ｴＮ･､ｾ｢ｹＮｴｨ･ｯｲｹｩｮ｡､ｶ｡ｮ｣･＠ 'Ill"e.perts

of' ＱＡｾｾ＠ ... ｳ｣ｾｬｬ＼Ｚ･Ｎ｡ｮ､ｸ･ｂｕｬＧｴＮ＠ .. inno ｾｾｯｩＧｦ｡｣ｴＮ＠ I ll£,ve,f'or example,

preViouslyref'erredto the discoveries ... of' new chemigal elements during the

second half of the ninet.eenthcentury as proceedingfrOlll,normal sCience in

this way. But, as we shall see. in the next section, not all theories. are

paradigm theories .•.. Both during the. pre-p&radig1ll periods descr5.bed in Sec-

tion U,and during the erise8that lead to. lerge-Bcale chaIlges of paradigm,

sCientist.susually develop many quite flpeculative and unartigulated theories ,

which call themselves point. the way to discovery. Usually. however. that dis-

covery-is not quite the one anticipated by the speculative and tentative

hypothesis. (Yukaw' s meson theory of nuclear forces provides one ･ｾｰｬ･＠ •

. It. helped scientists to.lloe meson .. ｾ｣ｫｳ＠ .. inphot()8l'aphs.theyhad repaated.ly

examined ｢･ｦｯｲ･ｾ＠ But that ｭ･ｳｯｮｾｷ｡ｬｩｬｩ＠ not the one .. predictedby Yuka'1a. It

was not found until later.) Only as both experiment and tentative theory

are articulated to II. match. does the discovery emerge and the '.;heory .become

a .. parad1gm.

Thediecovery ot: the Leyden jar diSi?lays all these features as well as

the others we have observed before. When 1t begen, there w"as no paracligrn

tor electrical research. L'lotcad, a number of theories, aU derived £'rom

crelatively.accessible phenomena, were .in competition, and. none of'these

theories seemed to handle the whole variety of electrical phenomena very

;lcll. Thllt failure is the first of several.e.no:.aliea that provlo.e bacJ;erounc1.

f{1r ""he ､ｩｇ｣ｯｶｾｲｹ＠ of the 1.e:ruell jc;r. One of Ｎｲｾｨ｜ｚＡ＠ conwsting schools of

electr:\.c1£,ne took electricity to be a fluid, aud that cOIlcuption led. s.

n<llDber of men to attempt bottling the flu1d by holding a ,mtor-filled

glass v1al in their handa end touching the wter to a cond,1.'.ct.or (mspended.

from an active electroetat:\.c generator. On removing tho jar from the tna-

chine and to"o1Ching the water (or iii conductor connected. with it.) ,.'1th his

free hand: each 01' these investigators experienced a severe shock. ThODe

first experiments did not, however. provide electriCians with the Leyden

jar. That device emerged more slowly, and it is agll.i.n :l.mpocoible to say

.just when its discovery vas completed. The initial. nttempte to store

electrical. fluid worked only because investigators held the vial in their

handa while standing upon the ground. Electricians had still to learn

that the jar required an outer as veIl as an inner conducting coating and \

that the fluid is not really stored in the jar at all. SOUle"llnere in the

course of the investigatlons that showed them this and that introduced them

to several other anomu.lous et'fectll, the device which we call the Leyden jar

emerged. Furthermore, the e:cper1ments which led to i ts ･ｾｬ･ｲｧ･ｮ｣･Ｌ＠ many

of them perfoI'med by Franklin, Ｇｾ･ｲ･＠ elso the ones which necessitated the

drastic revision of the fluid theory and ?hich thus ーｲｯｶｩ､ｾ､＠ the ｦｩｲｾｴ＠ ｾＧ｡Ｍ

digm for electricity.

To e. greater or lesser extent (cc=esponding to the ccnt;tnuUlll frOD

the shocking to the tmt1dP'ltod reault) the characteristics COEmOll to the

three el;amplcll ebove s.re charac'i;eristle of all diBcoveriea frO!!! ullich 1le"""

sorts of llhenomsDlJ. elnerge. Thoee ohsractel·'.atico are: the prior awareness

of anO'J:cly, the sradu.u ano. Ilizml teneous Elll!ergence of bo·th observational

and ｣ｏＺｬ｣･ｉＩｴｾｯＮｬ＠ l"ecosn:l.ticn, s.nd. the ccnnt;;Cr: .. ;ent change of perao.igl!l categorien

57

process itself' • In .. ｡ｬＧｾＧｃｨｯｬｯｧｩ｣｡ｬ＠ experiment ﾷｾｨ｡ｴＮ＠ deseryea to be ｢･ｴＮﾷｾ･ｲ＠ _____ . __

kuO'"rIn outside ｴｨ･ｴｲ｡､･ｾｂｲｵｺｬ･ｲ＠ end Postman asked experimental ｳｵ｢ｪ･｣ｊｾＶ＠ to

identify; on short ana. controlled exposure· a series of'"play1ngcards. Hoot

of' thecardsyere ZlOrma],il>utafC\i' 'iTereme,de anOJilalo.\ls ,e.g. , .. £1. red .. fi va

of clubs and. a black seven of dismonda. Each experimental run .. /sa consti-

tuted by the. display. of a single. card to a single' subject in a .. series of

gradually. increased exposures. After. each exposure the subject ws aslted

what he had seen,< 8lld therun1l83 terminated on correct ictentii'ication. ,

On the shortest exposures, of ｣ｏＧＢｾｳ･Ｎ＠ no. identifications, correct or

incorrect, were produced. But; ""ithe. small increase of'expoaure (the amount

varying from subJect ｾｯ＠ subject) identifications vere regularly produced for

all cardS".·Por thenormaJ. cerds these identifications wre usually correct,

but the ano:nalousclll'da were un1formly1dent1fied .. lv"ithoutapparent hSllita-

tion. or puz1.lement, as. normal... The red ... five 01'. clubs. might, fOl" cXfi.ll!J?le, be

identii'iedas a five ·ofclubs ... of hstl..'"'tsror ofdiamonG.a. WithO"llt awareness

of trOUble it .ra.a1mmed1ately fitted to one of the available cOZlce:ptual.

ca.tegoriea for plnying cards. One vould. not even like to say tOOt the} sub-

jectll had seeu something different from l."ht<.i:. they identified. With a fur-

ther :!.ncreaae of exposu..--e to the 8nooaloUll cards subjects did begin to heei-

tate and. to diaplo.y !l'lr-areness of aIlOlllaly. Exposed, for e:l'.ample to the reel.

five of clubs aame ｾｾｯｵｬ､＠ .say: tlw.t's the five of hearts, but there's some-

thing 1o/l'Ong with it"-thered seems alli'ully purple. Further increase of: e}:-

posure resulted in stUl more hesitation and. confufJio!l until finally, and.

58

anomalous cards they would have no fur-cher difficult.iea uith the ot;h"rs.

A few subjects, however, were never able to make this tronsition. Ｎｾｇ＠ their

awareness of anomaly and. of their inability to reflolve it increas:;d, they

became so confused that they felt forced to v.lthdralf :!.'rOll! the eA'jy.:riment

elltirely. In the next section we slmll occasionally see scientists behav-

ing this way too.

Eitherae a metaphor or because it reflects the nature 01' the mind,

tlmt psychological experiment provides a wonderfully simple and cogent

schema for the process of scientific discovery. In SCience, as in the play-

ing card experiment, novelty emerges onlyvith difficulty manifested by re-

sistance-against a background provided by expectation. Initially, only the

anticipated and. usual is experienced even under circ1llllstances where anomaly

:l:s later to be oboerved. Further acquaintance, however I does result in

n=eness of something wrong or does relate the effect to somthing that has

gone wrong before. That awarenees of anomaly opens a pariod in .... hich con-

cep-tual categories are adJusted and the ｡ｮｾｬｯｵｇ＠ is seen for '\/bat it is.

At that po:!.nt t.he discovery has been completed. I have already urged that

that proceas or one very web like it is involved in the eUlergcnce of all

fundamental scientific novelties. Let me now point out that, recognizing

the proceoe, 'Ire can at last begin to see 'Why normal SCience, a purouit not

directed to no,clties and tending at first to suppress them, should never-

thelesa be quite 130 effect:!. ve ill cau£ling them to lU'ise.

In the ､･｜ｾｬｱｰｭ･ｮｴ＠ of any science the first received paradigm is uau-

ally felt t.o account quj.te succes:::fully tor most of the oba0r'J'J.t;ions and

59

equipmentithedevelopment-ofcan-esoteric,-voc:e.bUililry-eru:iskiJoJ.s,-alld-·a···;ce-

fi.nement. of concepts. tbat-1ncreasinslylessens their resemblance to. their

usual commonsense ｰｲｯｴｯｴｾｳＮ＠ Conce1vablythatsort of elaboration could

be accomp11shedby-the.relat:l.'Ielyrandom.fact"collect1ngand.theor1z1ng of

ｴｨ･ｰｾｾｰｴｮＧ｡､ｩｧｭＺｰ･ＱＧＱｯｩｬ［｢ｵｴ＠ euc:hal'levelOImlent 1Gun:Likely, In any case,

even ｴ･ｮｾＺｧｴｄＮｮ｣･＠ ｾｴｯ＠ Ｇ｣ｷｾ＠ hao a use that lYill be ･ｸｰｬｯＺｾＺＧ･､＠ more tully in t.he

60

surrendered, reaistance. e;um-an"teee that Ilcientill'ts will not be lightly

distracted and that tae anomalies that lead to ー｡ｲ｡､ｩｾ＠ ｣｢･ｾ･＠ will peu€-

trate existing knowledge to the core. The very fact that a significant

scientific novelty so often emerges simultl).Ucouely fron several labora-

tories is an index both to the strongly traditional nature of normal

science and to the ｣ｏＡＡＡｰｬ･ｴ･ｮｾｳｳ＠ with 'fhich that traditional purllUit pre-

pares the way for its !Tan change.

All !;he discovex lee c:onetdm"ed 11. S<:lc: tlonV1rere-cau8e3\li'-or-corr"---. ....:u--

'tributors to psra.d1gJJl change. Furthermore, the ｣ｾ･ｳ＠ in 'Which thelle

discoveries were implicated were all destruc:tive all veil ae constructive.

Atter'lille . disc6,ferylladbJen aririiiDlrated, reed ｾ･､ｰＮｩｬｲＸ､Ｑ･［ＮｊＡｳ＠ ·l .. :ereable to

｡｣｣Ｚｯｵｮｾ＠ for atrl.der range oti'laturai phenomena erto account :for. some of

those previously known with greater prec1sion. But that gain vas achieved

only bi declsrlDg scme previous paradigm beliefs or procedures no lOI18er

paradigmatic and, simUltaneously, by replac1ng those components of the pre-

vious paradigm vith o1;hers. Shiits of thiB sort are, I have argued, asso-

ciated vithall dis.coveries·· achieved· throushnOl'lllal·· science excepting only

the tmsurprising ones that had been antici:pated in all but their details.

Bu'tcdiscoveriesarenot··the···onlysources.of .. theaedestructive-eollst-"'Uctive

paradigm changes. In this section we shal1besin to consider those simi-

lar but usually ｦｾｲ＠ larger shifts that result from the invent10n of new

theories.

Having argued already that in the sciences fllct and theory, a,ieeo,e:::r

and invention, are not ca'tcegorically and pennanently dist.inct, <re ｃｴｾ＠ an-

ticipate overlap between this section and the last. (The impossible SUZ-

gelltion that Prientley first discovered oxygen and. w-voisier then invented

it haa its attractions. Oxygen naB encountel'ed as discovery, above; ve

shall meet it again as theory, below.) In taking up the emergence of new

theories ｾＱ･＠ shall inevitably extend our understanding of discovery as well.

Still, ave:;.-In]? is not id€:ttity. The aOl'to of d:i.l':covcl'ies considered i.,'). the

61

aa the Cqpernican, Nevtonian. Chemical, and ｅｩｮ｡ｴ･ｩｲｾ｡ｮ＠ Revolutions. Ner

\/ere they responsible for the flome"ilat smaller, ｢･｣ｾｾｵｳ･＠ more excluoively

professional, changes in paradigm prod.uced by the ",-ave theory 01' light,

the dynamical theory of heat. or ｾＢ･ｬｬＧｳ＠ electromagnetic theory. Hew

can theories like these arise from normal science. an activity ｯ｢｜ｾｯｵｳｬｹ＠

even less directe« to their pursuit than to that of discoveries?

If allsreness of anomaly plays a role in the emergence of all new

sarts of phenomena, it should surprise no one that a similar but more pro-

found awareness is prerequisite to all changes in theory. On this point

historical evidence is, I think, entirely unequivocal. The state of

Ptolemaic astronomy "'as a scandal before Copernicus' announcement. Gali-

leo's contributions to the study of motion depended closely upon difficul- •

ties discovered in Ariatotle's theory by scholastic critics. ｎ･ｾｾｯｮＧｳ＠ new

theory of ligbt and color originated in the discovery that none of the

ej:isting pre-paradigm theories would account for the length of the spec-

tru.m, and the wave theory that replaced Nevtoll' s ",-as announced in the ;:lidst

of gt'OIdng concern about anomalies in the relation of diffraction and :polar-

ization effects to ｉｱｾｲｴＮｯｮﾷｳ＠ theory. Thermodyn!u:!1cs was born from the col-

lision of two existing nineteenth-centuryphya1cal theories; and quantum

mechanics from a ｜ｾｩ･ｴｾ＠ of difficulties surrounding black-boay radiation.

specific heats, and the photoelectric effect. Furthermore, in all these

cases except that of' Nel.<ton the aimreneGS of anomaly had lasi;ed so long

and ーｾｮ･ｴｊＺＧ｡ｴ･､＠ so deep that one can apl?l"oprilltely describe the :f'ielda ai'-

ｦ･｣ｴｾ､＠ by it as :I.n a a'.;o.te of gI'm:ing cri,r.:is. Be::auoe it demands lerge-,

Gcc:l0 ｰＳＮＺｾＺﾷｯＮＨｬｩｺｭ＠ dcctruct:tn::l ｯＮｾ､Ｎ＠ mr.jo:c ｂｨｩＺｲＧｾｅ＠ in the ＺＹＡＮｾｯ｢ｬ･ｬＡＱｳ＠ ｲＭｾＺＱ｡＠ ｴ･｣ｨｲ､ＮｾＧｩＮＮＧ｟･Ｓ＠

ｾ＠ ________ ｾｾｴｾ＠ 1nnecurity is generated by the Fer3iotenttailure ｯｾ＠ thepuzzlca of

nOl'llll!l science. to come out as they should. Failure of exist:i.::lg rules is

the prelude to. a. search for new ones.

emergence of Copernice.nl1stronomy. When its ーｲ･､ｾ｣･ｳｳｯｲＬｴｨ･＠ Ptolemaic

system, was tirBtde\'Clopeddur:Lng the .lasttwo centuries before Christ

I1nd. the first two ｡ｦｴ･ｲｾ＠ it lms ad!n:l.rably succesef'ul inpredict1ng the

changing posit10naof' both stars and planets •. !lo other.S!l..cient eyste:m

had performed. so .well; for the stare Ptolemaic astl'onomy i8. still widely

ｾ＠ ... :uned,today .. ｡Ｎｬｴ｡ｮｾ･ｮｧＱｮｾｊＺｪＬｉｬｧｾ･ＮｰｰｲＮｾｩｾＱＱＡｾｴＮｦＰＷＺ＠ ＮＺｬＺｊＺＡ･ｬｬﾱｾ･ｾｴｂ＠ ... ｾＲﾱｅＡｉＧｉｙｾＱＡ＠ .pre-

dictions were as good aoCopex'nicus'. But to be admirably successful is

never, for a scientifictheory,to be completely successful. Withrespect " """ ,,_n<_'M Ｎｾ｟ｾ｟＠ ｾＧＧＧＧＧ｟Ｌ＠ ••• ,_, ....... " '"'''' ｟ｾＬＬＬ＠ __ , n,,,_,,, ''''',.,'''' ________ ,, __ ''' __ ""' __ ''" .,,"'_""'" .,,'"'''_''''' ____ ._""'''''' ",_ .. '''''' "" ____ '" _____ "" """ ＮＬｾＬＬ｟ＢＢＧＮＢＢＢＧ｟＠ ,_ .,. "" "."_,, __ "'" _" .,,"" ＬｾＢＧＢＧＧ＠

both to lllaneta:ry position and to precession of the eqm,noxes predictions

ｾ､･ｷＱｴｨ＠ Ptolemy's 'system never qu1teconformed with the beat .a;r&i1able

observations. Further reduction otthose minor discrepano::iesconctituteci

many oftbe principal problems of normal astronomical reeearch for ｾｾｹ＠ of

Ptolemy's succesoors JUDt as a similaJ:" attempttobrinS celestial observe."

·t1oD.andNewtonian theorytogetherpro.vided normal reeearch problema ·fOl·

Newton's e1ghteen'.;h-century successors. For some time astronomers had

every reason to. Bup:p0lle that 1;hese attempts WOUld. be as successful as those

which had led to Ptolemy's system. Given a particular diecrepancy: aatron-

omara wereinv-n;riubly able to eliminate it by me.ltillg come particular adjust-

mant 1nPtolemy' s system of comp;:rv.nded circl()ll. B-..:t as time mmt on 0. mru1

then its accuracy and tha.t a diGcl"elle.ncy ca:!"Z'ccted. in ｯ［ｾＮ･＠ plo.ce ｬＺ｣ｾｮ＠ lil':cly

to ｡ｨｯｾ＠ up in another.

Because the astronomical tradition lIUC ｲ･ｰ･ｓＧｾ･Ｈｕｹ＠ intel'r1T.),lted from

outside and becauoe, in the absence of pI'illting, cOlllllllmication between ｡･ｾ＠

tronomers ws restricted, these difi'icultiea were ollly alcnrly rec052lized.

But awareness did came. By the thirteenth century Alfonso X could prcdaim

tllet, if God had consulted him when cl'eating the universe, He would hllve l"e-,

ceived good advice. In the siXteenth celltury Copernicus' C0'I1Orker, Domenico

as Novara, held that no system so cumbersome and inaccurate ao the ｐｴｯｬ･Ｂｾｩ｣＠

had become could possibly ba tnm of uature. And. Copernicus h:l.mself ,;.rote

in his Preface to the ｾｒ･ｶｯｬｵｴｩｯｮｩ｢ｵｳ＠ that the astronomical ＧｾｲｕＨｬｩｴｩｯｮ＠ he

inherited had finally created only a. monster. By the early sixteenth century

en increa.sing number of Europc' fl best astrono;ners ｾｲ･ｲ･＠ recogn:tzir.g tns.t the

aat!'onomical paradigm tras failing in application to ita m:n i;rllditionai. prob-

lems, That l'ecognition was prerequ.1.e:l.t.e to Copernicus' rejection ot the

Ptolemaic paradigm and Me search for a new one, His famous preface still

ｰｲｏ｜ｾ､･ｂ＠ one of the classic dcacr1ptions of a crisis ｳＧｾｩ［･Ｌ＠

only ingl'edient of the astronomical crisis that faced Cope?nicu8. An ･ｸｾ＠

tended treatment would also dil3CUflS the social pressure for calendn.r ref:czm,

." pressure which l1l1'..a.e the puzzle of precession particulE.rJ.y u:q:;ent.. In ad-

clition, D. fuller e.cco:4"1t ,,"(Jul!l COIloider medieval c!'iticism of /;risi;otlc, the

rise of Henaias£.nce Ncopl&tonl.mn, e.v.d other s:tell1i'icant hillto!'l.cnl ＨｾｊＮＢＧ［ＢＰｬ｜ｴＸ＠

beside(·:, Blxt technical brcwiOlm '\f:luJ.d still remain th" core of the ｣ｲｾＮＢｩｳＮ＠

s:t'ea -in .mich, because e;:l.ven pm:ticul!i.r ｡ｴｴ･ＬｲｾｩｯｮＬ＠ thebl'e&l;.·io!1n first oc-

curs. Though 1mmeneely important, issues of that sort are out-of-bounds

for this monograph. -. Particularly,tlleyare out-or-bounds-in·, this section

whOseob,1ect ill Only to show. that ,a recQ'gtdzable techni.cal breakdown :1nthe

practice or normal science precedes the emergence ot a nell theory.

If' that, much is cltlar in the case or the Copernican Revolution, let us

tlirnfrom it toa seCOm and rather different eJci.mple', the crisis which pre-

ceded the emergence of IavoisieX" s oxygen theory of combustion. In the

18'70' s many factors canbined to generate acriais inchemiatry, and hi.Btor-

18.llB are, not altogether agreed about either the:l.rnature or their relative

imPortance. But two ot them are generally accepted as of first-rate signif-

:!.ce.nce:the rise ofpIieUmiitic chemistry ana'" the ques1;iOl1 of weightrele.tions. " ., ., __ ",.' _____ '" '" __ "". ____ '''''_, ""'" -,,,-,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,-,,,,,,,,,,,,,,,,,,,-,,,,,,.,,1,,,,,,,,,,,,,,,,,,

The history of the first beginG in the seventeenth century with development

of the air pump and 1ts deployment inchemice.1 e:'lle:r1lnentetion. During the

follOl.'1ng century, us:J.nt that putnpalld 8: nUll!ber of· other pneutatil:: devicee,

chemists came increasingly to real:tzethat air must be an active ingredient

in cilel!>icl).]. reactions. But, 'With a few excepiionsBo equivoCEll the.t they

mo,y not be e):ceptions a.t 1).].1, chsmiflts continued to believe that a1.1' ,!U.s the

only sort of gas. until 1756, when Joeeph Ble.ckshcwed tont tuea sir (C02)

>Jas conSistently distingu:l.eb.able from normoJ. air ,. t'.o I3elllplee of· ear. m.;re

thought to be distinct only in their impurit.ies.

lli'ter Ble.cl;:· B work the investiga.tion of eaaBe )?l'oceeded r&pldly, most

notab:ty in the hende of Os-vents.ish, Fr5.:?:stley, and. S-:ueele, \o,.Tho tcgether de-

66

the phlogiston theory li'm often el!Jployed. 11; ill their design a.!ld iril:el']?l"e-

tation of ･ｸＺｰ･ｽｾｩｉｮ･ｮｴｳＮ＠ Scheele actually til"at produced. oJ,"Ygen 'by an elabo-

rate chain of experiments de£igned to dephlogbticate h,"at" Yet the net

result of their exper1m':=nts lias a .... ariety of. gas samples a.nd gas proper·ties

so elaborate that the phlogiaton theory proved increasingly little able to

cope with laboratory experience. Though none of these chemists suggested

that the theory should be replaced, they were unable to apply it consis-

tently. By the time Lavoisier began his experimento on airs in the early

1770's, there were almost as many versions of the phlogiston theory as

there were pneumatic chemists. Thnt proliferation of veraione of a theory

is a very usual symptom of crisis. In his Preface Copernicus complained of

it as well.

The increasing ｶｳｾ･ｮ･ｳｳ＠ and decreasing utility of the phlogiston

theory for pneUlUatic chemistry ""ere not, hm.-ever. the only source of the

criGin that confronted Lavoisier. He i<"Ba also much cOllcerne,d to explain

the gain in '!>'eight ths.t moat bodies experience when burned or roasted, and

that e.gain 1e a problem tlith e. long prehiBtory. At leaat a few Islamic

chemis' .. s had lmOlm that some met&ls gain wight when ro"llted. In the seven-

teenth century several investigators had concluded. :from this f)1l.mc fact that

a roasteo. metal takes up some ｩｮｧＮｾ･､ＺＡＮ･ｮｴ＠ :from the ntJnosphere. But ｾＮＱＱ＠ Ｇｾｨ･＠

seventeenth century that concluSion seer::-ed UIllleCGOSory to mO:3t cue:nir:r'cs.

It chemical l'cacticns could alt.er the volume, color, and. toxture of the :tn-

gredients, why sl:lO'.11d. th(,y not E'.1ter Height as we1l1 He:l.£;ht VT"-S no'c ahT.Ys

talten to be the" ｭ･ＤＮｓＱｴＮｾ･＠ of q'J,antity of ｾＩ､［･ｬＧＮ＠ Eceidea,. -YJ'2:1.g:l:rt-gain on

BpOlll:lee. to the J.1!:9blem or weight-ge.in beceme inCl'easingly dii'f'icul t ﾷｾｯ＠ main-

tain. Partly because the bals71ce _e increasingly ueed as a stalld.ord chemi-

cal tool and partly because the developmcntofpneums:ticchemiatxymade it

... ﾷﾷｰｯｳｳｩ｢ｬ･ｾｂｩｬ､､･ｳＱｲ｡｢ｬ･＠ . to retain. the .. gaseous pt:od.Ucts· ot reactions.· chern-

lets discovered more and more cases in which Wight-gaj.n accOJn1laIlied roact-

lng.S:!.multaneously,tb.e gradual aso1mllatloIi of Newton's gravitational

theory led chemists tOinsiat tilnte;ain in wa1ght must mean gain in quantity

of matter. Those conclusions did not reeultinreJecticn of thephlcg:f.ston

theory, for that theory cOUld be adjusted in many ways. l-'ert.aptl. phlogiston

imdnegativewes.ght,or llerhalls fire particles or something else entered the .

roosted body as phlosiston left it. There ,rere other ･ｾＺｰｬ｡ｮ｡ｴｩｯｮＸ＠ beeio.ee.

ｂｵｴＬｩｦｴｨ･ｰｲＰＧ｢ｬｾ＿ＱＧｖｉｬｪＮｧｨｴＧ［［ｧＦＱｮ＠ did IiOt lead to rejection, it did lead

to an increaa:!.ng numooroi'special etudieain-wilich thiS problem bulked

large. One of them, "On phlogiston conSidered as lLsubatance uith weight

9.1ld.[SrialYzed)in termsoi' theveightcllE'.ngcs it produces in bodies with

which it uIiites," was read to the French Academy early in 1772, the year at

whcaeclose Lavoisier deposited his famous eealednotewith the Academy's

. Secretary. Before that note lr.;l,9 written a problem that had been a:tthe edge

of the chemist's conecioUsnessfor many years had become an outstanding lxn-

solved puzzle. Many different versions of the phlogiston theory "ere being

els.borated to meet it. Like the problemlJ of pneumatic chemist!".! tho .. e of

theory "'tre-n. 'I'hough still ｢･ｬｩ･ｶｅｾ､＠ Cll0. truoted. a.s Co vOXk-t"lg ｩｾｯｯｬＬ＠ e. j,)CtJ:'ud.igra

66

"the competing schools of the ーｲ･ｾｰ｡ＺｮＮ､ｩ･ｭ＠ period, ｡ＮｵｯＧｾｨ･ｲ＠ ｊｾｪＢｊ＿ｩ｣｡ｬ＠ ･ｩＧｦ･ｾｴ＠

of crisis.

Consider now, as a third and final ･ｾｬ･Ｌ＠ the late ｲＮｩｮ･ｴ･｣ｮｴｨｾ＠

century crisis in physics that :preparea the way for the emerGence of ｲ･ｬ｡ｾ＠

tiv1ty theory. One root of that ｣ｲｾ｟ｳｩｳ＠ can be traced to the late seven-

teenth century when a number of natural ーｨｩｬｯｳｾｨ･ｲｳＬ＠ moat notably Leibnitz,

criticized Neaten's retention of an up-dated version of the classic concep-

tion of absolute space. They wre very nearly, 'though never quite, able to

show that absolute positions and absolute motions were vlthout any function

at all in Nctltcm' s system, and they did succeed in at least hinting at the

considerable aesthetic appeal which a fUlly relativisitic conception of -

space and motion would later come to display.- But their critique ;;as purely

logical. Like the early Copernicaos who criticized Aristctle's proofs of

the earth's stability, they did not dream that tran£ition to a relativisitic

system could be directly justified by observation. At no :point did they

relate their ... 'ie-.rs to any problems that arose when applying Neutonitm theory

to nature. As a result, their views died'TUh them during tbe early decades

of the eighteenth century to be resurrected ｾｾｹ＠ in the last decades of the

nineteenth "hen they had 11 very different rela·tion to the :practice of l?b¥o1cs.

The technical problems to .bieh a relativistic ph:i.lozo1?hy of space waD

ultlmately to be related began to enter normal science ｷｾｴｨ＠ the ｂ｣｣･ｰｴｾｾ･＠

of the ;re,ve theory of light ef-i;er about 1815 though they evoked no crisis

until the 1890's. It light 10 .. -ave !notion prop&Sated in a ｭ･｣ｨｯＮＮｮｩｾ｡ｬ＠ aether

69

. accuracy 'tiO';pl'cw1iiti-relevant· informaUon.'andthec'detection···ofsether-dxifi;

_____ ＭＢ｢ＺｊｹＬＭＧ･Ｎｾ｢ＮＮＬ･ｾｲｲｾ｡ｾｴｩｾｯＢＧｮＺＡＺＭＺＺＡＡｭｾ･ｾ｡｣ＡＡｳｵｲｾ･ｾｭｾ･ｾｮｾｴｾｳ｟ｌｾＢ｢Ｎ･ｾＱﾷｾ｣ｾｦＺ］ｏｩｾﾷＺ･ｾ｢･ｾ｣［Ｚｾ｡ｾｭ･ｾ｡ｾｲｾ･Ｚｾ｣ＺＺＺＺｯｧｮＺＡｬＡＺＺＱＺＺｺｾ･ｾ､ｾｰＺＺＮｲｾｯ｢ｾｬｾ･ＺＺｲｮＺＺＮｦｾｯｲＺＮﾷﾷＮＺｮＺＬｯｾｲｾｄＺ｡ｾｬ｟＠

research. Much special equipment was built to reaolve it. That equipment.

however ,detected noobservabledrl1't, and the problem wBtheretore trans-

. f'erred· from the elcper1mental1stst;ndobseryers to thetheoret1c1ans who had

no great difficulty with It. .During the· central decades at the century

Fresnel, Stokes, and otbersdevised n\linerousertlculi1.tlons ot theaether

theory deaigned to expla1l1thefalluretoobllerve drift. Each of' these ar-

ticulatiOns assumed that amov11l8 body draga somefract10n of theaether

mthlt, and each "as sufficiently successful 'to explain not only the nega-

tiVCl .. re.su1ts of celest1a,lobserw.tion but also those· of terrestrial experi-

mentation includ1l1g the fl1lllousexper1ment of Michelllon fUld Morley. There

waS still no confl1ct exceptinSthlitbet'ifeenthe various srticulauons. and,

in the absence of relevant experimental techniques, that conflict never be-

cMleacute.

The situation clui.ilged asain only l."iththe g:.oadualacceptsnce of' Max-

well's electrOllll!gnetic theory of light lnthe last t'ifOdecades of the nine-

. teenth century. Though Maxwell hillleelfbel1eved in the aether, he made no

use of its mechan1cal properties in hiefiiIeJ. theory. In particular. hie

discussion of theelectranagnetic behavior ofbod1es 1n motion made no

reference to any sether's l>e1!l8 dragged with them.. BIlt, in the absence of:

aether drag, a 'Iofuole series of earlier obser\'8.',ione to detect motion through

the e.ether beCm!1e anomalous. The years after 1890 therefore ""itDessed a

long aeries of brilliant ･ｸｰ･ｲｌｾ･ｮｴ｡ｬ＠ ar,Cl theoretical attempts both to de-

.. __ ._ ..•...••.....

70

results eguivccaJ.. The latter proO.uced a nWdler 01' prO!:liSing cta:cts, par-

ｴｩｾｷｬ｡ｲｬｹ＠ those of Lorenz and Fitzgerald, ｾｾｴ＠ they also disclosed still

other puzzles and finally resulted in Juct that proliferation of competing

theories 1Ih1ch we bave previously found to be the conc01ll1te.nt of crisis.

It is against tbat historical settina tbat Einstein's special theory of

relativity emerged in 1905.

These three examples are almost entirely t;ypical. In each case a novel

theory emerged only after 8 pronounced fs.llure in the normal problem-solving

activity. ·Furthermore, except in the case of ｃｾｲｮｩｃｕｂＬ＠ where factors ex-

ternal to science played 8 particularly large role, that breakdol!ll and the

proliferation of theories Which is its sign occurred within a decade or at

most two of the new theory's enunciation. The novel theory seems a direct

response to crisis. Rote also though th1s may not be quite so typicaJ., that

the problems w-lth respect to 1Ihich breakdown occurred wre all of a type

tbat bad long been recognized. Previous practice of normal science hQd

given every reason to consider them solved or all but solved, which helps to

explain why the sense of failure, when it came, could be quite so acute.

Failure with a new sort of problem is often disappointing but never surpris-

ing. ｴｾ･ｩｴｨ･ｲ＠ problems nor puzzles often yield to the first attack. Finally,

these ･ｾｬ･ｳ＠ share another characteristic which may help to make the case - .

for the role of crisis impressive. The solution to each of them had been at

least partially antiCipated during a period when there vas no crisis in the

correoponeling science. and, 5.n the absence of criois, thODe ll.!lticipationfl roel

been ignored.

The only cOnT.Qlete cntiicip&tion iD c,lso the nor·t feJIJot!.!J) tha.t of Co-pern:t-

71

ﾷﾷｾ｡｣ｩ･ｮ｣･ｨｳ､｢･･ｮｾﾷｬ･｡ｳ､･､Ｎｬｬ｣ｴＮｩｶ･＠ ﾷﾷﾷ｡ｮ､ｾｩ･･ｩｩｾｾｲｩ､､･ｩｩＺ｢ＧｙＭ､ｯｧｭ｡ｲｨ･［Ｑｩｯ｣･ｮｴｲｩ｣ｾｳＮｂ｟＠

troIlOmy IIl1ght have bego.lnits' developillent' eighteen centuries earlier than

it did. But that is to ignore all. histOrical conte:&t. 'rlhenAristurchus'

suggestion··'l/as·made ,., ·the .. ,yastlY·cmore .. reasonable,geocentric ,system, had. no

needs that a hel,i()Centr1c system might evenc:ollceivably have :L'ul.filled.

The whole development of. Ptolemaic astronomy, bOth its triumphs and ita

breakd6wn,'falls in thecentur1es'after'Aristarchus·'proposal. BeSides,

there were no obvious reasons for taking'.l\ristarchus seriously. E'ren Co-

pernicus' moreelal;lorate proposal was neither Simpler nor more accurate

than PtoJ.ellly·ssystem.Ave1lable observational tests,jas we shall see

more clearlybelow,providedno',basis for a cho1ee.betw-een them. . Under

those c1l'cUDlstances onsot the factors' the.t'led astronomers to Copernicus

(and one that ciSUldnct"have"ledthemto'Ar1stllrchus) was the recognized

crisisthat'lll'idbeen'respousiblefor innovation in the tirs't place. Ptole-

maic astronomy he.d failed. tosolve.itsproblemlJ;.:tne .time had come to give ,

.acomp:e't.itor;a chance. our other tlro examples provide no similarly ·full

anticipations. nut eilrely one reason, why the theories of combustion-by-

Il.tmosplleric-e.bsorpt:1ondevefopeo.ln theseVeIlteenth century by Rey , Hooke,

and Mayow fe:tled to get a suf'f1c1ent heerl.ngllaS that they m!<,cle no cont!l.ct

ｾｮｴｨ｡Ｎ＠ recbgnizedtroubJ.espotin normal scientific ーｲ｡｣ｴｩ｣ｾＮ＠ And the long

neglect by ･ｩｧｨｴ･･ｮｴｨｾ＠ and nineteenth-century scientists 01' ｎ･ｾｯｮＧｳ＠ rcla-

tivisticcriticli must largely have been due, aSlzaS arll;ued above, to a sitl-

ilar :failure in confrontat1on •.

Philosophers of science bave repeatedly delllonctrated. that more than

one theoreticnlconstruct:!.on canalHayabe pl!lccd upon a Biven collection

ci' <le-ta.. History of science indicates tha:t, p:E:t'tiCW.Ul"ly in. t.he early

72

develoJ,)lllental stages of a new perad.igm, it ie not eyen supremely ... ifficult

to invent BUch alternates. ｌｾｴ＠ that invention of ･ｬｴ･ｲｮ｡ｴｾｳ＠ is just ｶｨｾｴ＠

scientists do not and probably ought not undert!!ke except (i.uz'ins the prc-

ｾｾ､ｩｧｭ＠ stage of their science's development and at very npecial occasions

during its subsequent evolution. While the tools a paradigm supplies con-

tinue to prove capable of solving the problems it defines, acience moves

fastest and penetrates most deeply through coni'ident employment of thoHe

tools. As in manufacture so in science. retooling is Illl ･ｸＭｾ｡ｶ｡ｧ｡ｮ｣･＠ to be

reserved far Ｇｾｨ･＠ occao1on that demands i't. The significance of crises is

the indication they provide that au occasion for retooling has arrived.

emergence of I),ovel theories and ask mmt hew scientists respond to thei;:

existence. Part ot the auswerl as obvious us it. is importent, can be rc-

ｴｲＺＡＮ･ｶ･､ｾ｢ｹ＠ not:l.ngfirst what scient:1.sta ne ... erdoHhen collfronted. by even

eevereand prolongedanon:-e.l1es. Though they may begin toloee faith und ,

then to consider alternatives, they do not pronounce ｴｨ･ｰ｡ｲ｡､ｾＮｧｭ＠ that

has led them into crisis invalid. In part that generalization is simply

a statement from historic fact, baaed upon ･ｸ｡ｾｬ･ｳ＠ like those given above

and, more extens:!.Yely, below. These hint ,rhat our la.ter examination 01'

:pa.radigm;;;rejectionvilld1sc!osemore:f'Ully:onceithas achieved thesta-

tus of paradiem, a scien'cific theory is declared invalid only if an ulteI'-

by the historiccd study of scientific development ･Ｚｾ＠ all resembles the

methodolog5.cal Dtereotype of falsification by direct compeJ.'ison u:tth na-

tuxe. That remark does not mean that scientists do not reject scientific

theories, nor that experience and e:<periment are not essential to t.he proc-

ess in which they do so. But it docs mean--what iYill ｵｊＮｊｾｩｬｬＹＬｴ･ｬｹ＠ bE! a ＬＺｾ［Ｚ｜Ｍ

tX'al point--that the act of judgment \'Thich lead.s scientists to reject a

paradizm '.;heory is alw-ays baaed upon more than· a cCh."Iparison of that theory

"ith the world. The decision '1;0 reject one pnradigro if! ullmyo nirr.l),ltan:;-

ously the deci.sion to accept ano'.;her J and the judgment leading to that; de-

cis2.0n ｩｮｶｯｊＮｶｾｳ＠ the ｣｣ｭＧｰｾＮｲＺｴｳｯｮ＠ of' ｾ＠ parL4dignw lrl th ｮ｣ｾＮｴｾｩＮＬＧＡＮＺｩＮＺＧ･＠ nile!. Ｇｲｴｴｾｨ＠ c<?,ch

other ..

73

developing it my argument ,rill itself begin occauionally to ｦＨｊＩＺｯＢＧＭＧｊｯｃ､ｯｾＱ＠

this monog-!'aph' s main theses. The reasons :ror do;;.bt sketch"", aboye Ｂ･ｾＧ･＠

purely factual.; they ｾｲ･ｲ･Ｌ＠ that is, mere cQunterina'.;al,ces to D. prevllle)"!t

epistemological theory. As such; if my present pOint is correct; ';;hey

can at best help to creat a crisi.s or, mOl"e accurately, to reinfoZ'ce one

that is already very much in existence. By themselves they cannot 1:U10-

.Till not falsify that theory, for its defenders Will do> what He have al-

ready seen scientists doing llhen confronted. With criSiS. They u:I.J.l de.,

vise numerous articulations and ｾ＠ ｾＬｭｯ､ｩｦｩ｣｡ｴｩｯｮｳ＠ of their theory in

order to eliminate any apparent coni'l1ct. In fact, many of the relevant

modifications and qualifications are alread.y in the literature. J£, ｴｨｾｲ･Ｍ

fore, my counter',nstances, are to constitute more than a minOI' '.rritant,

that nill be because they help to :permit the emer8ence of a ne'.; theory

within which they nre no longer a sourco of trouble. Furthermore, if a

typical pattern uhich ue shall later observe in scientific revolutions is

applicable here, they ,,111 then no longer seem to be oimply facts. Prom

.. 'ithin the theOl"y they may instead. seem to be something very much like

tautologies, representable by statements '!;hich could not have been othCl'-

It haa often been observed, for example, that 1'Io"ton's Second 1m.; of

motion, though it took centuries of difficult factual and theoretical rc-

search to achieve, behaves for those committed to l!cW".;on· B thecr;r 'lory

ouch like a purely logical stllter.;(mt that no amount of obzel'vation could

ｲｾｦｵｴ･Ｎ＠ In ｓ･ｾｴｩｯｮ＠ IX vIe shall ｣Ｎｾ･＠ that the chemic;;..l lB.1-' of ｣ｯｾｾｮｴ｡ｬＱｴ＠ pro-

Co; ｾＮ＠ ｾ＠ ,,' 0"'" ｾＢ＠ ... - ｾＬＬＬＬＬＬＬＬ＠ ｾＬ＠ .- ., .• ｾ＠ r ＢＢｾＺ＠ ::::::: ＢＧＢｾＨＧＺＺ＠ :1,,',,-,' ｾＧＮＬＢＢＢ＠ :,.' '_' ＧＬＺｾＢｊＬＧＺｾｲＧＮＧＢＬ＠ ,', ｾＺＮＮ＠ 1"">'"'-'"'.''' ", '.",', ｾＺＢＢＬｾＱＺ＠ ','" Ｍｾ＠ -,'., .',',,:":. •• ＬＧ［ｾＢ＠ ＬＧ［ＧｾＢＧＢ＠ ｾＮ＠ :.' ｾＬＮ＠ＬＧＮＮｾｌﾷＧＺｾ＠ ;...", ｌ［ＮｾＧＺＧＭＮＧｾＭ .. q ..... ｾＬＺＬＭ［＠ _. __ ._ _ _._ .-_ __ - • , - - - -- • - v ..

75

gestthat :f'rom the vie'iPoint to.;arCls science beiI1-8 developed in this mono-

graph, scientists tail to reject paradigms l;hen :faced. H:l.th coimterinstances

simplyllece.use they could not do so and stili remain scientists.

Though history 10 ｡ｮｕｮｬｩｬｾ･ｬｹｳｯｵｲ｣･＠ of eX!l.!llples, some men have un-

doubte:ily 'beendxiven to desert science because of their inability toaup-

port crisis. Like art:l.sts, creative scientists must occasionally be able

to live in a world 'out ofjo1nt'. I have elselrheredescribed '.;hat !"..ecessity

as "the essential tension" implicit in 'much scientific research, and a psy-

'chologistwhoinvestigates artistic creativity has ,since""taken, Q"fJ'cr the

term. But that rejection of' science m,taver of another,occtlpation is, I

Ｌｴｨｩｮｫｾｾｴｨ･＠ ｯｮｬｹＺｳ･ｲｴｾｯＺｦＧＢＬｰ｡ｲ｡､ＱｧｭＢｬﾷ･ｪ･｣ｴｩＨｬｮｴｯｶｨｩ｣ｨ｣ＨｬｴｬｮｴｬｲＺＺｬＮｉｬｦｬｴＺ｡ｮ｣･ｳ＠ by them-

Delves ca.'l lead. 'Once e. firstperadigm through uhichto view natu=e has been

1ouna.:;there iEi'I'li!riPlynoSUchthirtgaareseO.Tchuithout a para.dl.gm. To re-

ject one paradigm Hithout simultaneously substituting another is therefore

to reject science itself. NrJ.O. that act reflects not on the paradigm ｢ｵＧｾ＠ en.

Ｇｾｨ･＠ lna.'1.. Irtevi.tablyhem.ll be seen by hia colleagues as, "the carpenter ,':10

blames his tools."

The same :point csn be tlade at least equally effectively in revel'se:

there is no auchthing as research ｾｲｩｴｨｯｵｴ＠ counterinataI'..ces,. For what is , .

it that di:f'ferent:l.a.tcs nonta1 science !rom science in a cr:i.sio state? Hot,

sv.rely, that the former confronts no' couuterinstanceEl. On the ｃｏＡｉｾｲｬＮＧＮｲｹＬ＠

to do that, e .3., geometric optics, have ehorUy ceased trJ yield research

problems at all and have instead become toolo for engineering. F.:Xce:;::>t:i.ng

those that are exclusively instrmnental, every problem that normal science

sees as a )?Uzzle can be seen, from another viewpOint, as a counterinstance

and thus as a source of crisis. Copernicul; sa1f as counter instances ,That

mest of Ptolemy's other successors had seen as puzzles in the ｾｴ｣ｨ＠ be-

tween observation and theory. Iavoisier sa" as a ｣ｯｵｮＧｾ･ｲｩｮｳｴ｡ｮ｣･＠ what

Priestley had seen as a successfully solved puzzle in the articulation of

the phlogiston theory. And Einstein ea,! as countcrinotances .mat Lorentz,

Fitzgerald, and others had -seen as puzzles in the articulation of Newton's

and MaJ(well' s theories. Furthel-nlOre, eYen the_existence 0:>: crisis does

not by itself -transform a puzzle into a counterinstance. There is no ouch

sharp dividing line. Instead, by proliferating versions of the paradigm,

crisis loosens the rules of normal puzzle-solving in ways that ultimately

permit a ne,; paradigm to emerge. There are, I think, only t"10 v.lterna.tiv-es: ,

either no ccientif'ic theory ever confronts a counterinstance, or t.U ouch

theories cor.front counterinsta.nces at all times.

How can i-G ever l>.e.ve seemed otheruise2 That quention tr-.lct ｮ｣｣･ＵＺＺ［ｲｵＮＧｩｬｾＧ＠

lead to thp ｨｩ｣Ｇｾｯｲｩ｣｡ｬ＠ and critical elucidation of philocophy, ano. those:

topics are here barred. But 'ie can at lea.:;t note t,l'O reaGons 1;hy science

haG seemed to provide so apt an illustration 0:>: the eeneralization that

truth and falsity are uniquely a.'l.d unequivocally determined by the eonfron-

'.;ut:1.on of ｳＧｾ｡ｴ･ｭ･ｮｴ＠ "lith :fact. Normal science docs and must contimmlly

ｮｴｾ＠ .. i vc to b:::-ing theory (4'1(1 fact into clOSer und closer agrec:aent, end. that

e.ct:tv:U::y curl c7,;::ily be

77

a puzzle for v.hose very existence the vaU<l1tyof thoparadiQU ,".lot be a:;··

ＭＭＭＭＬｂｆＡＱｵｭ･ＢＢＢＮｮｾ｟［Ｇ｟ｆ｡Ｑｬｴｬｉ＠ e· to· achieve a· ｡ｯｬｵｾ｣ｍＺｴＡｬ＠ ｾｹｴｨ｣＠ ec:'.cnt;J,s-G u:1I1· ｂｾＱｲＭﾷＭＭ ....

the theory. Here even more than above the proverb applieo: "It is a 1'00:-

carpenter 'who blames his tools. II In addition. them=cr ｩｮｾ［ｨｩＮ｣ｨ＠ Ucicilce

pedaScgyente!rigleifctiscusslon ··ofa"theory wltlircmrtrlts··· ont ts"exemple.ry ap-

plications bas hel:petlto·rew.forcee. cOnfii'mation-'thcorydra""Ilpred.ominantly

from other SMCCO;;· Given the slightest reason for dciing so. the man ,rho

rea.d.s a sCience text can easily take the applications to be the evidence

1'01' the theory,thereasonswhy ito1.lghtto be believed. But science stu-

dents accept theories on the authorit.yof teacher and te:f:t I not because of

･ｶｩ､･ｮ｣･ｾ＠ ···Whatalt.ernattves havethey,orlThat COlllJ.letence'l-Theaplllica.

tiona given in to)..-1;s are not there as evIdence butbecaullc learning them is

·llartof-rearning·the::paredi.gmat.the .. base .... ofcurl'ent ... :practice .•..... !f..applies . .,

tions .rereeducedasevidencEl, then the very failure of te)(ts to suggest al-

ternative interpretations or ·todisc;u.Ss problEims:;f'orlrhich sc:ientists have

t'ailed to produce plIl'f.ul.:!.gmsolutions would convictthe:trauthors ot' eX'';l'eme

bias. There is not the slightest reason for such an :tniictr,;e:lt.

Row then: to ret1.U'tl to the in! tial question, do scientis'ts rcsp::m.o. to

the a,m:rcnescofan anomaly in the fit between theory ll..'ldncture? ｾＺｨＺＺＮｴ＠ has

just been sa.:i,d indicates that even a discrepa.ilcy u,lflccountably larger t.':lan

that experienced in other ap:pl:tcatiol1s of the theory need not dra .. ? any very

llrofouild reopcnse. There are always some discrepanc'.es. Even the most

stubborn ones usually rert}?ond at laet to normal 'Il1'D.ctice. Vel'y often seien-

78

of that observed. As Europe's best mathell'.atica.l physicists continued to

westle unsuccessfully ... '1th tho \Joll-knoul2 discrepancy, there "Wero occa-

sional proposals tor a modification of Nouton's inverse squaxo laW'. But

no one took these proposals VOl'Y seriously ano.l in practice, this patience

ｾ［ｩｴｨ＠ major anomaly proved justified. Cls.:traut in 1750 \.'l11l r;ble to ShOll

. that only the mathematiCS of the application had been ｾｔｏｮｧ＠ and that New-

tonian theory could stand as before. Even in· eases 1{hore no mere lllistcl{e

seems quite possible (perhaps because the mathematics involved is simpler

or of a familiar and elsewhere succesaful sort). persistent and recognized.

anomaly does not always induce crisis. No one seriously questioned Ne\T-

tonian theory because ot the long-recognized discrepanCies between prediC-

tions from that theory and both the speed of sOl.'m and the motion of Mer-

cury. The first discrepancy _'l1S ultimately and quite une:l'pectedly resolved

by experiments on heat undertaken for a very different purposej the second

vanished with the general theory of relativity after a crisis which it had

had. no role in creating. Apparently neither had seemed eufficienUy funda-

meu·;;a.l to evoke the malaise that goes ,lith crisis. They could be recog-

nized. as counterinstancea and stin be set aside for later ;rork.

It fo11o'l1'B that if .an allOm!lly is to evoke crisis i t ｭｵｳＧｾ＠ \lsu<;lly be

more 'Ghan just an anomaly. There are aluayo difficulties aor.:e;{hel'e in the

paradigm-nature fit; most of them are set right soonel· or la.ter, often by

processes that could not have been foreseenj the scientist ,mo pauses to

e:t:"llline every anomaly he notes \/ill seldom get any s1g11if'.cant 17ori, done.

He have to as}: ,;hat it io that mokec an anomaly seem llorth concerteD. scru-

t:i.ny, an£. to tho;:; ＨｲｾＱ｣ｇｴｩｯｮ＠ thc:r;; is proba.bly no fully genc:::-cl G.!lB1f0r. The

79

alizat10ne 01' the paradigm as thepl"oblem of ＢＢＧｩＧＺｨｾＢ＠ .. diet for th.ose lfltO

accepted Maxvrell' Btheory •. Or. aI3 in the Copernj,can Rovolu'.;ioll, an allO:mly

.. vi ｴｨｾｵｴ＠ apparent .... f'undamental.,importmay.evoke .crisis, .ifthe.applications

ｷｨｴｾｽｬＱｴ＠ .. 1nhibits ha'V'e ｡ＮｾＬｺＺｾｾ｣ｵｾｾｾｦｬＺＬＱ［ｩｾｦｊＡＺＮＱｾｊｲＱ［ｾ｣ＮＡｌＬｩｅＺｴｨｾｉＳＮｾＮ｡ｬＳ｡＠ for

calendar des1€!l'1-. and astrology. or,. as in eiit1lteollth .. century chemistry 1 the

development of .. normal Ｘ｣ｾ･ｬＱ｣･＠ may transform an anomaly tiliat hrulprev.l.cuflly

been only a .vexation into a source 01' crisis: .the. problem of weight reln-

tions had avery different status a:f'ter the evolution of pneumo:l;ic chemical

techniques •. Presumably there. are still other circUID.stances that can make an

anomalyparticularly .. pressing. and ordinarily .sevel'a! of 1;hese w111 combine.

We have alz:eady noted, for example. that one source of the. crisis that con-

fronted Copern1cuswas the.Dlere length of time during ,,'bich astronomere had

wrestled llnsuccesstully.uith the reduction(jf the residual diGcrepouciea in

• Ptolemy'. s syst",m.

Hhen; ·.for···these. reasons or.others ·lil;:ethem,. an anomaly comes to seem

more than jus'.; another puzzle of normal sCience, the ·transition t.o crisis , , . -' .

and to e;ctraore.d1nary science .ha.s begun. Thq anoml.lyitself DOlt COines to be

11I0regeIlerallyrecognizedas GUchbythe ·PI'o:r",e.sion. More ... and more ｣ＮｴﾷｾＢＧｮｴＩＮｯｲ［＠

is devoted to it by more end more of. the :field I S moat eainent men. If it

still continues to resiEt, as .it usually does not, Illany of them may cOr:!e to

view its l-esolution as the subject metter of their discipline. Ii'or then: tho -..... .

fj.eld ｾﾷｲＮｩＮｬｬ＠ no longer look qu1tethe !lame as it hadeal'1ier. Part of its dif-

ferent ｡ｬＧｐｾ｡ｲ｡ｮ｣･＠ results simply fror.l the new fixation point of ncient:ific

80

tnade availa.ble. The ea.rly a:'taclto upon the reo:i.c.t2.nt pre-blen ,,:";'11 have

tollol-red the paradigm rtllea quite clonely. ｂｵＧｾ＠ with contint:ircg rocista.l1ce

more .and more of the attacks upon it unl have inyolved £lome minor or not

DO minor articulation of the para:iigm. no tlTO of them quit\! alike, each

partially BuccesB1'ul. but none sufficiently so to be accepted as paradiGP.l

by the group. ThrQugh this prolii'cI'ution of divergent srticulat;ions (they

'1,'111 come to be iocree.eingly dcscrib",d aa ｾＡＡﾣﾣ＠ adJustments). the rules

of normal science become increasingly bl1.1l"I'cd. Though '.:here still ia u

pal'e.dlBID •. fev practitioners prove to be en'.::h'ely agreed abO'.1t ｾｲｨ｡ｴ＠ it is,

Even formerly paradigm ｂｯｬｵＧｾｩｯｮｬｬ＠ of solved probler:lo are calleel in quest:ton.

Copernicus complained that in his day e.stronomers vere so "j,ncollsicterl't; in

these [astronomical] investigations • • • "that theY' cannot eYen e';pls.in 01'

observe ';;he COllstant length of the seaconal year. rr "Kith them," he ｣ｯｮｾ＠

tinued, "it is all though an artist lIere to gcther the hs.nO.s, feet, heau. and

other members for his images from divol'se mcx1.els, each part cxcelJ.cn>.;l,;

eh-e:IlIl, but not related to a SiiJ.i!;lc body, uno. since they in no ,my [Latch

each other, the result "Would be monstel' rather than man." ｅｾｊＺＺＮＶＢｾ･ｩｮＬ＠ 1'0-

ｇｴＺｾｩ｣ｴ･､＠ by current uoage to less florid language, l!rote only, "It ｾＷｃ［Ｎｳ＠ co

if the ground had been pulled fl'om wder one, with no firm fOU11O..s.ticn to

be seen any'(;uere on \7hich one could have built."

Such explicit recognit1.ol1a of ｢ｬＧｾ｡ｫ､ｭｭ＠ m'e ｅＺＩＺｴｬＢ･ｲＮｾ･ｬｹ＠ rc.:::c" bUG the

effec,.l.;.o of crisis do uot en-"irely ､ｃｬＧｾｾｮ｣ｬ＠ upon ito conscious Ａﾷ｣｣ｯｺｮＱＺｾｩｯｮ＠ ....

'\f'1ut call ,\;'I"G say tha.t these efi'cctG c,l:e? Only ttro of them Gccm to 'bG un:t-

81

. ･ｾＺ｣･ｰｴｴｨ｡ｴｴｨ･ｬｯ･｜ｬＮｯｯｦＧ､ｩｦＺｲ･ｲ･ｮ｣･＠ Ｇｩ｡｢ｏｴｨＧ｣ｭ｡ｬｬ･ｲｾ＠ and'lllol'e'cleaHyde;;"

fined.incrisis. And all crises close ,.;itt the emergence of a roSY'clll'ldi- . ___ ._._

date for paradigm and with the subsequent battle over ito acceptance.

Thesearesubjects·tobe considered in later sections. but "tTe 1I!Uatantici-

pate .. a .. bit,of ... :wbat .. l1111 .there ... h.e .• Baid.in:.order toccnnplete .theacrems.rl;:s .

about the evolution and anatomy of the crisis state.

The transition from a paradigmllhich has evoke"- crisis to a ne,' one

from which ti. nel; tradition of normal' science can emerge iafar from a

cumulative process. one achieved by an articulation or extension of the

old paradigm. Rather it is a reconstruction of the field from new t'unda-

men:ta.ls. a recolllltruction which cho.nges some of the field I a moat elementary

theoretical generalizatiollll as well as many of its paradigm methods and ap-

plications. ｄｵＺｴＺｩ｟ｾｴＮｨ･ｴｲ｡ｮｳｩｴｩｯｮＮｰ･ｲｩｯ､ｴｨ･ｲ･＠ .lill bea laree but never

complete everlapbetween the problems l1hicncanbe solved by the old and

by the mmparadigm.BIl:1; there ｾｲｩｬｬ＠ all10be a decisive dii'ferencein. the

mod.es of solution. When the traneition 1scomplete, the profession ,rill

have changed its view of the field,its methods,and i'.;s goals. One l)cr-

ceptiveh:!.storian, vievin€\ a classic case of a science's reorientation by

l?1J,radigmchange, recently described it as "picking up the ｯﾷｾｨ･ｲＮ＠ end 0:(' Ｇｾｨｯ＠

s'.;ick, tf a process which involves "he.mUng theaame bundle of Ｇ､ｄＺｾ｡＠ as be·-

fore, but placing them in a nl1m system of relations lr.i:th one another by

giving them a dil'i'erent frer,ie.forl<;." Others who have noted this aspect of

scientific advance have et:11'hasized ito similarity to tl change in ｶｊＮ｣ｲＧＮｾ｡ｬ＠

g'"stnl t. Tho mw,ka on llSper which were first aeen as e. 1;'ird arc ｮｏｾＧＷ＠ seen

82

\le have already examined some of the prchlatls ｣ｲ｣ｾｴ･Ｐ｟＠ by nc.ying ﾷｩ［｢Ｎ｡Ｚｾ＠

Priestley saw oxygen ｾ＠ dephlogist:l.cated a:tr. In ｡､､ｩｾｾｩｇｬｬＬ＠ the sCientist

does not preserve the gestalt subject IS f'reedo:. to ｂｷＭＺｩＮＮｾｇ｣ｬｬ＠ bacl: and forth

between ways of seeing. Nevertheless, the IlWitch of 6(ostalt; pru:ticl.llarly

because it is today so familiar, is a useful ･ｬ･ｾ･ｮｴ｡ｲｹ＠ ｰｲｯｴｯｴｾｔ･＠ for what

occurs in full-scale paradigm shift. Until. Section rt we can go no 1'u:r-

ther.

The precei'.ing antiCipation rne.y help us see crisis as I':'.n appro]?!':l.ste

prelude to the emergence of new theories, particu.l.arly since we have al-

ready eXlllllined a smaller scale version of the Ilame process iu dj.l3cullsing

the emergence of discoveries. Just becaulle the emel'e'mce of a new theory

breaks with one tradition of scientific pl'o,ctice and introduces a new oue

conducted under different rules and within a different universe of ､ｩｇ｣｣ｾｳ･Ｌ＠

it is only: likely to occur ,·then the first tradition is felt to haye gone

badly astray. That remark is, hem'ever, no Incre than a prelua.e ',;0 the in-

vestigation of the cl.'inis-state, and, \.!Ilfor',;une.te1.y, ｾｇｨ･＠ questions to ,,111c11

it leaiJ.B demand the co.mpetence of the psychologist even mOY'e than that of

the historian. "mat is ･ｾＭｴｲ｡ｯｲ､ｩｮｇＮｬｾｹ＠ research like! IIOVi is e.norco.ly made

lm;-like? How do Gcientiste proceed "hen anare only that soneth:'.ng has

gO'"e t'und£Jricntally wrong at a level '.1 til vhien their trc:in:i.:ng he,s not

I equi!>,Pcd them to deal? Those qucaticns need fer more ｩｮＧｬｊｃｾｲｴｩＺｴｧ｣Ｎｴｩ｣ｮＬ＠ c.l1d

it. ought not. all be historical. \,;'hat ｦｯｬｬｏｩｾｳ＠ 1·1il1 ncc(-;sso.ril;r be norc ten-

Ｂｾ｡ｴｩ｜Ｂ･＠ und. J.esn complete than l .. hnt 112.5 gone befot'c ..

83

full extent of the crisis 1n pneuma.ticchemistry •. Or again, Thomas

Young's .f1rstaccountsof thetlave theory of light appeared at a very

･｡ＮＺｲｬｹｳｴ｡ｧ･ｾｯｦ｡､･ｾｬｑｰｩｮｧ｣ｲｩｳｩｳＮ＠ ｾＮｩｮｯｰｴｩ｣ｬｬＮ｣＾ｲｩ･＠ ... that .. would .be almost ...

unnoticeable. except that, w1th no assistance from Young, it had grOlm

to an international scientific scanaAl within a decade of the time he

first wrote. In cases like these one censay.only that a m1nor breFlk·

dOlmof thepal:adigm and the very:t'trstblurrillgofits. rule 11 for normal

science 'tlere sufficient to induce a new way of looking at the field.

Uhat . intervened between the firet Bense of trouble and the recognition

of an available alternate must.havebeen largely unconscious. Hith the

techniques apprapriatetothiB monogrephwe cannot even suggest t1hat .may

have transpired.

In other cases,· hmrever,for example those of Copernicue,Einstein,

and contemporary nuclear theory, considerable time elapses betlreenthe

i'irstconsciousnessofbreakdown and the emergence of a ne-..r paradigm.

When that occurs, the historian may capture at least a fe., hints of yThat

extl'aordinaryscience is like. Faced f:ith··an admittedly funiiamen'"al

anomaly in theory, the scientist's first effort w1lll often be to isolate

it more precisely and to give it structure. On the. one hand, though nmi

a:m,..x'e that they emmot be quite right, he will push the rules of normal

science harder than ever to see, in tho area ofdif'ficulty, jUGt whel"e and

ho../ far they can be mcUe to lTork. On the other hand, ｾｲＮｩＮｴｨｩｮ＠ the ",:::ec of

had been ,rilsn dis:played in experiments whoae outco:ne m.lS ｴｨｏＢｾ｣［ｨｴ＠ to be

kno,m' in auva!Jce. And in 'che letter effort, ma;.·e than iT.! 14<;( ot)ler pm't

of the post-paradigm development of science, he will J.ook aJ.n:ollt like our

most prevalent image of the scientist. He vill, in the first place, often I

seem a man searching at random, trying experim€nta ;lust to [lee wtJ.at trill

happen, looking for an effect whose nature he cannot qu1.te gueas. S1mul-

taneausly, since no experiment can be conceived without &ome sort ot

thet'l'Y, the scientist in crisis '1."111 constantly t):y to genel'ate specule.-

ti'1e theories (e.g., Yuka;.'S's meson) \,h1ch lll!lY, if successful, 6.:1.oc10se

the road to a new paradigm and which, if unsuccessful, can. be surrenil.ered

with relative ease.

The noteboolts lm1ch reCord Newton's optical researches CJr. the rema;,?2s

of Dalton's notes on his lTork with Dlixed sases provide classic e:;;am1?len of

ttc more l.'G.m1.o111 sort of research proclucea by the awareness of e.nomv.ly.

Bu·t; probably the best illuetra.tions ofaJ.l come from contcr.rvore.ry research

in field theor:r and on fundamental particles. In the absence of a crisis

"h:l.ch has !!!!W.e it nececae.ry to see JUDt hOll far Ｇｾｨ･＠ rules of n.ormal science

-carl. stretch, would the immenae effor'G rcqu:f.red. to detect the netltrino h.l-;oVe

£leemed ,1U:Jtj.:!.'ied'l Or, if the rules had not ｏｾｖｩｏｕＶＱｹ＠ br.oken dmm nt sa":€:

l.:md:l.scloGeo. 1')o1nt, Hould the radical hypothesis or. pari ty ｮｯｮ｣｣ｮｳ･ｲｾｾｾｇＮｴＺｴｯｮ＠

h!'.ve bc,,:m either llUU..,gost,oj. or ｣ｯｮｦＵＮｲｭ･､Ｎｾ＠

Th:ts sort of cx"t;raox'dina1:Y l'eseEXch is cftect thOl'.gil by no I:l2nnD

'1:0 the extent that normaJ.research l10rk can be conrl.ucted by using the

paradigm aa a model, rules and 8.sIlUlllpticna, need not be mae.e e;,:.plicit. In

Section . III we notedtha.t the full eet of rules ｾｧｨｴ＠ by philosophical

analysis ' need not even exist •.. But.tha.t1s notto .. say,that"the search:for

aesumptions (even for nonexistent ODes) can not be., an effective w.y.to

weaken the grip of a trad1tion upon the mind and to suggest the basis :for

a new ODe. It is no. accident that the emergence of Newtonian physics in

the seventeenth century and. of' relativity and quantum mechanics in. the

twentieth should have been both preceded and accompanied by fundamental

philosophical analyses of . the contemporary :research ｴｲ｡ｩｴｾｴ［ＬＱＬｯｮＮ＠ Nor is it

an accident that in both the.se periods the so-called "though'l; ･ＺＱｃｰ･ｬＧｾＮｭ･ｮｴＢ＠

ＱＡＱＱｃｬｬｬｬ､ｬｬ｡ＧｬｅＡｰｬｾｹ･､＠ eo critical a .role in the prClgl"ese 0:1' resecn·,:ll. As I ｟ｾＬ＠ ,_ ""'" ,. , •• , '" ,_'"'' ＧＢＢｾＧＧＧＧＧＬ＠ "'''".,,'' .. ｾＬ｟ＬＬＢＧＮＢ＠ _"_""" •• ,, ＢＢ｟ＬＬｾＬＮＧＧＧＧ＠ ""'''''''''''''''''''' _""" ＢＬＬＧＬＬＢＬＬＧｾＢＧＢ＠ •• , .. m,. ＢＢｾＧＧＧ｟ＧＧ｟ＧＧＧＧＧＧＧＧＧＧＧＧＧＧＧＧＧ｟ＧＧ｟ＧＧＧＧＧＧＧＧ＠ ,C ＧＧＧＧＧｾ＠ ._'_,.''_"" '" .' __ ,," • __ " _.'_." ,

have sho-.m elsewhere, the aualyticalthought ex.per1l!!entat:l.on that bulks so

larGe in the ＢｲＮ［ｾｩｴｩｮｧｳ＠ of' Galileo,Einstein,Bobr, and others a.,·e psrfectly

ce.lculated to expose the old paradigm to exis·ting knowledge in ｾｬｬｬｹｳ＠ that

isolate the root· of crisis ｾ､ｴｨ｡＠ clarity unattainable in the laboratory.

With the deployment, singly or together. of . these extraordinary pI'O-

cedures, one otherthill3 may occur. By concentrating scientific ｡ｴＧｾ･ｮｴｩｯｮ＠

unon a narrow area of trouble end by p.reparing the llcient1fic mind to rccog-- .

nize e;:pel'imcnUl-l anomalies :for lihat they are, crisis often prOliferates . .

new discoveries. We have ･ｾ･｡､ｹ＠ noted haw. the al?areneasof crisis dls-

ting1l1ahes !.?voisier' s ｾ［ｯＭＮ｣ｊｴ＠ on ｯｸｾＧｕ･ｮ＠ from· PrIestley's I and. ｯＺｾｹｧｯｮ＠ viaS not

86

like polarization by reflection, wel'e a l'O(l1lJ:c of tho ｡｣｣ｩ＼ｬＮｅｉｔｾｇ＠ that con-

centl'ated work in an ares of trO'.lble makeD likely. (!.1:lJ.us> lfho reeia the

discovery, was just starting work for the Academy's prize oesey on double

refraction, a subJect widely knOhll to be in 'an unsatisfectory state).

Others, like the light spot at the centor of the shadow of a circular disc,

were predictions from the new hypothesis and ones whose success helped. to

transform it to a paradigm for later work. And still others, like the

colors of scratches and of thick plates, were effects that had often been

seen end occasionally remarked before but which, like Priestley's oxygen,

had been assimilated to well-known effects in ways that prevented their

being Eeen for lrhat they uere. A similar account could be given of the

multiple discoveries which, from about 18515, "IIere a constant concooi'l;ant

of the emergence of quantum mechanics.

Extraordinary research must have still other ｭｾｮｩｦ･ｳｴ｡ｴｩｯｮｳ＠ end cf-

fecte, but in this area ue have scarcely begun to discover the queotlons

that n"ed '.;0 be asked. Perhaps, hmrever, no more are needed at this pain',;.

The preceding remarks should suffice to chow how crisio simultaneously

lcoaens the stereotypes &nd provides the incremental data necessary for a

fundamenta). paradigm shift. Sometimes the shape of the nell :;>aradj.gm is

foreshadO'Jed in the structure which elttrao:rdinary resc2.rch ha:3 given ',;0 the

anomaly. Eins'.;ein ;11'0te that before he had any oupstitute for classical

mocilenicG he ｣ｾｵｊＮ､＠ see the interrelation bet\reen the knmm anO"JiaHcs of

black-body radiation, the photoelectric effect, ｶｾ＠ specific heats. More

often no such structuz'c ｾＮｺ＠ consciously seen in atlvo.nce.. ｉｮ｡ｴｾｊＮＮ＠ tte ne-VT

. . ｾ＠ '.'., l-'-" Ｍｾ＠ .. - ｾ＠ ..... -'.' '"' r. ..... ＢＬＮｾＮ＠ ."'.',', -v····,·,.·.'·· .·,··.·,·,.w· ＢＮＭｾ［＠ (" .. ｟Ｎｾ＠ t"-•. ＧＬＧ｟ＧＮｾＧｲ［＠ ,; •.. -... ｾ｟＠ .• :..-,:,.:.,-• c ... ,.. .. ( .... ﾷｾｾＭﾷﾷﾷﾷﾷﾷＬＮｾｦＮＮＮＭＬＮＮＮＬﾷ＠ h, ,-l •. ﾷ｟Ｇ｟ﾷ｟Ｂ｟ＺｾＢ＠ '".l ,- .......... , Ｎｾ｟［＠ •. ,,'., - - -u,::. -.1",'..: J .;-.; __ : .... ＮＬＮＧ｣ｯＧ［ＮＬＮｾ＠ ｾｾｾ＠ ＮＮＬＮＮｾＧ［ＺＮ＠ - ｾ＠ - - ｾ＠ ｾＮＭ ＮＭｾＭＮ＠

ｩｭｩｩｩ･ｲＵ･ｩｉＭＺｬＮｮ［｣ｲＱｳＺｬＮｳｾ＠ --WbattlieIiature Ｖｾｴｬｦ｡ｴＺｲｬｬｩ｡ｲＭｳｴ｡ｧＨｦｔｳｾｾｉｉ｢ｷＭＭ｡ｬＱＭ ind::t;;;

_____ ｾａｵ｡ｬ＠ invents (or find-she lias invented) a nelr liay of givin,,'1 o:rderto data

now all aesembled;.;..musthere remain inscrutable and may be perillilnently 00.

Let 'UsherenoteOIllyone' th1ng about ｩｴＭＮａｬｮｩｯｂｴＭ｡ｬｾＢ｡ｹｳｴｨ･＠ menuho aChieve

·.tbese--t'Undamental-inventionoof tl,: new; parad.:!.gm . havs_been eithel' .. very·young

(unaer28) or very new to the field whose pe.:radigm they change. And. per-

haps that point need not have beenma.deexpl1cit. For. obviously these are

the men who, being little committed by prior practice to the traditional

rules of normal science, are particularly l1kelytossethat those ruies no

longer define a playable game and to conceive another set that can replace

them •. '

VIII. The Nature and Necessity of Scientific Revolutions

These remarks permit us at last to turn to the problems 1fhich provide

this monograph with its title. WhAt are scientific revolutions, and what

is their function in scientific development? Much of the an61fSr to these

questions has been anticipated in earlier sections. In ー｡ｲｴｩ｣ｵｬ｡ｾＬ＠ the

preceding discussion bas indicated that sCientific revolutions are here

taken to be those noncumulative developmental episodes in which an older

parad18Jl1 is replaced in whole or in part by an incompatible new one. Only

through such epiSodes, I have suggested, do :t'Unds!llental novelties usually

enter the sciences. There is more to be said, ｨｯｷ･ＮｾｲＬ＠ and an essential

part of it can be introduced by asking one further question. Why, even in

metaphor, should a change of paradi8Jll be called a revolution? In the face

of the vast and essential differences betMeen political and SCientific de-

velopment, can the metaphor much finds revolutions in both disclose ar.ry

significant parallelism?

I believe that it can and that one part of the parallelism must al-

ready be apparent. Political revolutions are inaugurated by a grmnng

sense, often restricted to a segment of the political community, that ex-

isting institutions have ceased adequately to meet the problema posed by

an environment that they have in part created., In much 'ehe same ｾｲｯＮｹ＠ scien-

tific revolutiOns are inaugurated by a growing sense, again often restricted

to a narrow professional subdivision of the scientific COmmunity, that an

existing parad18Jll has ceased to function adequately in tile exploration of

an asooct of nature to llhich that "ps.r&digm itself had pl'evi01.1s2y led the - -way. In booth political and scientific develcllmeut the sense oi: mo.lf"1nction

llhich can lead to crisis ie prerequisite to revolution. Furthermore,

88

89

though it aamittedly_stra,1ns the metaphor, that ｾ｡ｬｬ･ｬｩｳｄｬ＠ holds not only

far the majar paradigm .. changes, like. those due to COp1lrnicutl e!!d lavoio1er.

but also .far the far smaller ones associated. with the assimilation of Ii. new

sort ofllhenolilenon. ｬｬｫ･ＮＮｾｾ･ｮＮ｡ｲ＠ X,.rays. ScientifiC reVOlutions. as we

--------.,noteci at the end of ｓ･｣ｴｩｏｬｬＮｾＮ＠ Deed seem revollltio-aery only to those lihofle __ _

paradigms are a1.'f'ectea, by them. Toou'\;siders they .may •. like the Balkan

revolutions of the ｾｬｹ＠ twentieth century. seem ｮｾｭ｡ｬ＠ parts of the devel-

opmental-process. Astronomers, for example, could accept X-rays as a mere

addition to knowledge, far their paradigms ｾｲ･ｲ･＠ unat'fected by the existence

of the newradiation •. But for men like Kelvin, Crookes, and Roentgen,

. vlioseresearchdealt wlthradiat10n theory or with cathode ray tubes, the

emergence of X-raylinecessar1lY vi()lated one ー｡ｲｾＱｳｭ＠ as it created another.

!Ilbat 18 whY . ｴｨ･ｳ･ｲ｡ｾ｣ＺＺｏｩｩｩ､｢･､Ｚｦｂ｣ｯｶ･ｲ･､ｏｩｩｩｙｴＱｩｩＧｯｩｩｓｨ＠ sowitlilng's first

going wrong With normal research.

This genetic aspect of the parallelism between political and scien-

tific development has already been developed quite fully. Though its 81g-

ｮＱｦＱ｣｡ｮｾ･ｭ｡ｹｳｴＱＱＱ｢･＠ questionable, its . existence should no longer be open

to. doubt. The parallelism has, however, a second and more profound e.spect,

. and thes1gn1ficance of the first depends upon it. folitical revolutions

aim to. change political institutions. in l>"ays that those institutions them-

selves ｰｾﾷｯｨＱ｢ｩｴＮ＠ Their success. therefore n.ecessitates the partial relin-

quishment of one set Of institutions in favor of another, and in the interim

society is. not fully governec. by i.nstitutions at all. Initially it is cri-

sis alone that attenuates the role of political institutions as we have al-

ready eeenit attenuate.therole at llI3Xadigms. In incl.'easi1lg llumbe,,'s indi-

viduals become .. 1ncreas:!.ngly estra.'lged from political life 8.3ld behave more

90

and more eccentrically within it. Then, as the crisis deepens, many of

these individuals commit themselves to some concrete proposal for the re-

construction of society in a new institutional framework. At that pOint

the society is divided into competing camps or parties, one seeking to

defend the old institutional constellation, the others (usually only one)

seeking to institute some new one. And, once that polarization has oc-

curred, political recourse fails. Because they dii'fer about the institu-

tional matrix within which political change is to be achieved and evalu-

ated, becauae they acknowledge no supra-institutional framework for the

adJudication of revolutionary difference, the parties to a revolutionary

conflict must finally resort to the techniques of mass persuaSion, often

including force. Though revolutions have had a vital role in the evolu-

tion of political institutions, that role depends upon their being par-

tially extra-political or extra-institutional events.

The remainder of this monograph aims to demonstrate that the histor-

ical study of paradi@D change reveals very similar characteristics in the

evolution of the sciences. Like the choice between competing political

institutions, that between competing paradigms proves to be a chOice be-

tween incompetible modes of communtty life. Because it has that character,

the choice is not and can not be determined merely by the evaluative pro-

cedures characteristic of normal science, for these depend in part upon II

particular paradigm, and that paradi@D is at issue. When parediSDIs enter,

as they must,into a debate about the choice of a paradigm, their role is

necessarily circular. Each group uses its mm pa.."'8digm to argue in that

paradigm's defense.

,

91

The .. resul t1ng circularity does· not',ot course, . render the arguments

. ineftectuaJ, or evenlYTong. The man who premises a paradigm uhen arguing

in its detense csn,nonethelessprovide a clea.r· exhibit of what scientific

. practice willbe.l1ketor those.who .. adopt the new view of'nature, and that

exhibit can.be :lmmensely persU8stue,oftencompelltngl;y eo. Yet, whateve'''z---

its.torce, the.statusot the circular 8l'gument, is, only ｴｨ｡ｴｯｴｰ･ｲｳｵ｡ｳｩｯｮｾ＠

It cannot, as we shall ... discover in. the pages ,to tollaw, be made logically

rorevenprobabilistically compelling tor those who refuse to step into the

circle. The prem1ses and values shared.bythetwo parties to a debate

over paradigms are not sutticientlyextensive to make logic the sale arbi-

ter of choice. As· iii poll tical revolutions ,so iii paradigm choice--there

is no s'Mn!!erd .. higher .. than .. the ... assent .. ot. the .. relevant,.cOlllllJUllity. To dis-

cover haw scientifiC'revolutions are. eftected,.. lie .. shall therefore have to

examine not only the impact of , nature and ot logic but also the techniques

ot persuasive 8l'gIl1I1entation eUec:t1ve w1,1;hinthequite'spccial groups that

conetitute the community .of scientists .•

'To,discover'Wy this;·issuc· of'parad1gmchoicecsn naverOO ·settled by

logic alone, we must.shortlY.exaIIIlnethe nature·of the differences that

separate the proponents of a. traditi.onal paradigm from their revolutionary

successore. That examination iethe ーｲｩｮ｣ｩｾｬ＠ object otthie section and

the next. We have, however,already noted numerous. examples of: such dU-

ferenc:es, and no one .will doubt that history can SUpply many others. ｾＧｨ｡ｴ＠

is more likely to be doubted than. their eXistence .. and llhat must therefore

be .cons1dered fir.st., is. tblit .. Buch exwrrDle.s pl'O'.rideessential ini'ormation

about the natu-"6 of science. Granting that parad1gmreject5.on has been an

historic fact, does it illuminate more than human credulity and confusion?

Are there intrinsic reasons why the assimilation of either e new sort of

phenomenon or a new sCientific theory must demand the rejection of an

older paradigJD.?

let us first notice that, if there are such reasons, they cannot be

merely logical. In principle, a new phenomenon might emerge tdthout re-, :rJ.ect1Xlg destructively upon any part of past scientific practice. ｾｯｵｧ｢Ｎ＠

discover1Dg life on the moon would today be. destructive of existing para_

digms (these tell us things about the moon that seem incompatible with

life's existence there), discover1Dg life in some less well known part of

the galaxy would not. By the same token, a new theory does not ｾ＠ to

conflict with any of its predecessors. It might deal exclusively vith

phenomena not previously known, as the quantum theory deals (but, signif-

icantly, not exclusively) with subatomic phenomena unknown before the

twentieth century. Or, again, the new theory might be simply a higher

level theory than those known before, one which linked together a whole

group of lower level theories without substantially chaDging any. Today,

the theory of energy conservation provides just such links between dynam-

iCs, chemiStry, electricity, ｾｴｩ｣ｳＬ＠ thermal theory, and so on. Still

other com.patible relationships betlleen old and new theories can be con-

ceived. ｾｧｩ｣｡ｬｬｹ＠ any and all of them might be exemplified by the historic

process through which science has developed. And, if they ｾｬ･ｲ･Ｎ＠ scientific

development would be genuinely cumuJ.ative. New sorts of phenomena would

simply disclose order in an aspect of nature where none had been seen be-

fore. In the evolution of science new knowledge lrould replace ignorance

rather than replacing knowledge of another and ｩｮ｣｡ｲｲｾ｡ｴｩ｢ｬ･＠ sort.

93

Ofcoursecscience(Orsome"otherenterprise; perhaps less eff'ect.ive)

.' might have develaped in that. fully cIlmulative manner. !/.any people have

believed. that it did. so, and 1II0st still seem to BUPi,lPSlfthatcuimuation

.... ｾｳ｡ｴｬ･｡ｳｴＮｴｨ･＠ ideal which historical development would display if only

it had not so·(otten' been distoi Wil by ho.man :td1osytlcrasy. There ace im-

lIortimt rell.sons·i'Or that·bel1ef .... ·In Sec.tion'IX·we shall discover how

closely,the ·View. of. science..;as-'cUmulativeis entaDgledwitha dominant

ep:l.stemologythat.takes;kJiowleage'lio beacenatriictionplaced.directly

upon raw sense' data; by ｴｨ･［ｭｩｮ､ｾ＠ And in Section X we shall examine the

... "sti-ong·sUppol't provided to the sSllle histOriographicsclmaby the ·tech-...................... ·c.

n:l.ques OfetfectiVe sciencepede.gogy. Nevertheless , despite the immense

plausibil:ttY'of 'thIlt'[ideal1ma.ge, there" is increasiDg reason ,to wonder

Whethi!ritC:an})CIssibly bean 1IDage £! science •. ' After the. pre-paradigm

period theass1:mulationOf all new-theOries and9f. almost all nev sorts

ofphenomerie.;'hBs ti1rnedoutto:deman(Lparad1gm. destruction and. a. conse-

quentcOrifJ.:l.etb'Ertwee:d'competiDgi.schools .. of, scientific .thought. Cumula-

t:1ve;a.cqiilis:l.'Ii:l.cm of'tfrlBb.t:f.cipated'hoveltiesproves to be an·.almost nonex-

. istentexceptiOh'tCf the rule of .. sc1ent:L:f'icdevelC)pl!lent. The man who takes

. historici'act se:riOusly·lnust suspect that science. does not tend tOlrord the

:l.dell.l Whicib.6ur1.Ill8Se, of its cUIinllati veness has. suggested • Perhaps:l. t is

atlotlierI'lOrtofehter:p:rise.

ti',however'.ii,e·sistant facts· ｣｡ｮﾷｾ＠ us ·that. far, then a second

lOOk. a.tthlil·!?;i-OUDd we have' alreadycoVereil may. suggest that cumulative

acquisition'ot ·noVeltyis not only. rare in fa.c'\; but impro'bsole in pI'i.n-

cipie.Normal bas:l.c research,which !!!.cUIinIla.tive. owes its succpas to

the ability of scientists regularly to select problems that can be solved'

)

with conceptual and instrumental techniques close to "!;hose already in ex-

istence. (That is why an excessive concern 'tdth useful problems, regard-·

less of their relation to existing knovledge and technique, can so easily

inhibit scientifiC development.) The ｭ｡ｮｾｩＱｯ＠ is striving to solve a prob-

lem defined by existing knowledge and technique is not, hOlrever, just

looking around. He knows lIhat he wants to achieve, and he designs his in-

stuments and directs th1s thoughts accordingly. Unanticipated novelty,

the new discovery, can emerge only to the extent that his antiCipations

about nature and his instruments prove wrong. Often the ill\po,l·tance of the

resulting discovery will itself be propOZ'tional to the extent and stubborn-

ness of the anomaly which foreshadOlred it. ObViOUSly, then, there must be

a conflict between the paradigm that disclosed anomaly and the one that

later renders the anOlllaly lavlike. And, since the older paradigm had pre-

v10usly been constitutive of some part of SCience, the cOlllll!1.Ulity concerned

resists the new one while it can. Paradigm destruction is, to a greater

or lesser extent, characteristic of each of the discoveries examined in

Section V, and I nO'l1 suggest that it had to be. Those examples did not

confront un with mere h1storical accident. There is no other effective

way in wbich discoverles might be genel.'ated.

The same argument applies even more clearly to the invention of new

theories. There are, in principle, only three types of phenomena about

which a new theory might be developed. The first consists of phenomem

already well explained by existing parad:l.gms, and thase seldom provide

either motive or point of departure for theory construction. When they do,

as with the three fsmoun anticipatiOns discuilsed at the end of Sec'cion VI,

the theories that result are not accepted because nature provides no ｧｲｯｶｾ＠

95

for dis.c:r:l.mine.tion.A.secondclass· of phenomena. con81$1;s of those ｾｔｨｯｳ･＠

nature is indicated by existing paradigms but whose details can be under-

stood only· through furthertlleory articulation. '!I!Ilese iUoe the phenomena

. upon which scientists do do researchifltichoftlletime,·llut that research

aims at the ｡ｲｴＱ｣ｵｬ｡ｴＭＺｬＮ･ｮｏｦ･ｸｾｯｯｴ･Ｎｴﾷｴｬｩ･＠ iri1Iention of

new OlIeS. Only when these attempts at articulation fail do scientists

enc:.ounterthe. third type of phenomena, the·· rec08l1izedenomal1eswose

characteristic·feature· is ｴｨ･ｩｲｬｬｴｵ｢｢ｯｲｮｲ･ｩＧｩＱｳ｡ｬｴｯ｢･＼ｾｳｳＺＱｭＱｬｬｬＮｴ･､＠ to ex-

isting paradigms. This type alone gives rise to new ｴｨ･ｯｲｩ･ｳｾ＠ As the

next sectionw111 disclose more fully, paradigms provide all phenomena

except. anomalies ·mth a theory;;.Cietierillinedplaceu"theaclent1st"s field

of nslon. . ...

But ifI .. newtheories are called'forth to resolve anomalies in the re-

lation of an existing theory to nature, then thellucceesful new theory

must somewhere permit predictions that aredi£'ferent from those derived

from. its predecessor. That difference could riot occur if the two wre

logically caupatiblei 'Intheprocessof·beingasaimiJ..il.tedthesecond must

displace the first •. Even a theorylikeeneret:! conservation, wich today

seems a logical superstructure that rel.8.tes to 'nature only through iIlde-

pendently established theories,did not develop historicallY't>"ithout :p!U'D.-

digm destruction. Instead, it emerged frOlll a c:risisone of wose essen-

tial ingredients w.stheincom;patlbllitybetween Newtonian ｾ｣ｳ＠ and

some recently formulated consequences of the caloric theory of heat. Only

after the caloric theor:rhsd been rejected could energy conservation be-

come part of science. And only after it l!ad·been:part of science fer some

time could it come to seem a theory of a logically higher type, one not in

\

confl1ct with its predecessors. It is bard to see how new theories could

arise without these destructive challges in beliefs about ns.t14"'e. Though

reductionism remains a log1cally permissible view of. the relation between

successive sc1entific theories, 'it is en historical ｾｬ｡ｵｳｩ｢ｩｬｩｴｹＮ＠

A century ago it would, I think, have been possible 'to let the ease

tor the necessity of revolutions rest at this pOint. But today, unfortu-

.nately, that cannot be done because the view of the subject developed

above cannot be maintained :I.i' the most prevalent contemporary interpreta.

tion of the nature and function of scientific theory 1s accepted. That

interpretation, closely associated with logical pOSitivism, would restrict

the range and meaning of an accepted theory so that it could not possibly

conflict with any later theOl"Y that made predictions about Bome of the

same natural phenomena. The best known and the strongest case for this

restricted conception of a scientific theory emerges in discussions of the

relation between contemporary Einsteinian dynamics and the older dynamical

equations that descend from Newton' s Principia. From the viewpoint of

this monograph these two theoriee are tundBmentally incom,patible in the

sense illustrated by the relation of Copernican to Ptolemaic aGtronomy;

Einstein's theory can be accepted only ｷＱＮＧｾｨ＠ the recogn1tion that Newton's

ws wrong. TOday this remains a minor1ty view. We must therefore e;:....,.,'!ne

the most prevalent objections to it.

The sist ot these objections can be developed as follows. Relativis-

tic dynamics C8Jl1lot have shown ｎ｡ｾｲｴｯｮｩ｡ｮ＠ dynamics to be wrong, for Nelf-

tonian dynam1cs is sti:ll used '!.i. th great success by most engineers and, in

selected applications, by me.ny phySicists. Fu..»thermore, the propriety of

this use of the older theory can be proved :f'rO!ll the very theo.."'Y that has,

in'otherappl1cations,'replaced it. Einswin'stheory can be used to

shaw that pred1ctions1'l'OlIf Newton'seq1lations will be as good as our meas-

ﾷｵｲＱＱＧｉｧＮＱｮｳｾｴｩｦ＠ in. au·' a;p;pl1cationB'jjat1sfy1ntf'iFsmallnumberof re-

strl.ct1veconditions •. ' For.ex.il.m.Ple.,1fNMoniantheory is to provide a

gooa: ｡ｾｴ･＠ So1.ut1On, '. tberelattve veloCities of tbe "ood:1es consid-

eredlllU8tbe smalli' com,pared l11ththevelocityof'.light.SUbject to this

cO!ld1tionand aifew otherB,Newtonian theory seems.tobe derivable from

,l!lI.Ds1;eintanOf' Whicb.it is therefareaspei::iU'case; .'. (Actually ;no one

bas yet produced Bucb.a derivation, atleasttor.E1nstein t e general theory.

'1'heassUiDI>ti'on tha.tone exists seems to be;an·act oftaithbased· upon the

.veryphilosophice.l. position tha.t .. thederivation is used to support. The

exietenceof ｴｨ･［､･ｲＱｶ｡ｴｩｯｮＢｷｯｵｬ､ＮｬＱｯｴｩ｢Ｎｯｷ･ｶ･ｲｾ＠ affectm;yp6int. and I

shall therel'ore assume tha.tone Vill Ult1mately.:beprovided.)

. But,theob'jectioncontiiiuesjno the017 can possibly confl1ct with

oDe of its Special:c:cases., If: Einsteinian science: seems 'to lIBkeNewtonian

ｾｩ｣ｳ＠ w:t'CIll!:,tbatisonlY because" some: Newtonians \rere so "incautious

'affto'cJJHm:thit'Newt(ifilMtheory'ytelded'elltirely precise'resUlts or that

it Was. WJ.id at wry high relative velocities. ,. Since they coUld not' have

. ha4:aut eVidence tor sueb. clB.1ms,theybetrayed the standards of science

. when they mBae them. Insotar'aB Newtontantheory .was ever a trUly scien-

t1fic theory supported by valid. evid.ence,1tstlll is. Only e;ttravagant

elaims 1'ilrthe theory-.i.elaims that were never. properly parts of science--

canhe.ve beenshOil'liby. E1nstein to be. 'i/1'Cli.'Ig. Purged 01'. these merely h1l!llall

extravaSances Ｎｎ･ｾｔｴｯｲｩｩ｡ｮｴｨ･ｯＺＧｙｨ｡ｳｮ･ｶ･ｲ＠ .. been challenged and. cannot be.

Some ve;r-fiili'tof this argUment 1squi teSufficient "to make any theory

ever ulled by a significant group 01' eom.petent scientists :!.mmul.1eto attack:.

98

!rhe much-maligned phlogiston theory, for example. gave order to a large

number of physic:aJ. and chemical phenomena. It explained why bodies

burned--they were rich in phlogiston--and why the metals had so many more

properties in comon than did their ores. The metals were all compounded

from d1i'f'erent elementary earths combined with phlogiston, and the latter,

common to all metals, produced comon pro:perties. ｾ＠ addition, the phlo-

giston theory accounted for a number of: reactiOns in which acids were

formed by the combustion of aubstances like carbon and sulphur. Also, it

explained the decrease Q:f' volume when combustion occurs in a confined vol-

ume of air--the phlogiston released by combustion "spoils" the elasticity

of the air that absorbed it Just as fire "spoils" the elasticity of: a

steel spring. If these were the only phenomena that the phlOgiston theo-

rists had claimed for their theory I that theory could never have been

challenged. A similar argument will suffice for any tlleory that has ever

been successfully applied to any l'8lIge of phenomena at all.

But to save theories in this way their range of application must be

restricted to those phenomena and to that precision of observation with

wich the experimental evidence in hand already deals. Carried just a

step further (and the step can scarcely be avoided once the first is taken)

such a limitation prohibits the scientist from claiming to speak "scien-

tifically" about any phenomenon not already observed. Even in its present

form the restriction forbids the scientist to rely upon a theory in his

own research whenever that research enters an area or seeks a degree of

precision for which past practice with the theory offers no precedent.

Logically these prOhibitions are unaxceptionable. But the result of ac-

cepting them would be the end of the research through which SCience may

develo:p further.

99

By now that point too is virtually a tautology. Without commitment ＭＭＭＭＭＭＭＭＭＭＭｾＭｾＭＺＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭ ..• - .•••....

to a paradigmtherecou.1dbe. no normal science. Furthermore, that cOllllllit-

ment muet -extend to'areaeand to degreellotprecision:l;orwhich . there is

no full precedent. If it did not, theparadigmcouldprovide.no puzzles

thi£thad;·.notalread;y been solved. Besides, it; is not only XlO1'IlI!d science

that depends upon· commitmenttoaparsdigm. If. eJl:ietingtheory.binds the

scientist ollly with respect. to existing applications, then there can be no

8u1.'Pffses,anomal.1es, or<d:'isea.But these. are just the signposts that

point thewaytoextraord1naryscience. If positivistic res'l;rictions on

. the raDgeota theory's legit:1mate al'Plicabil1ty.are .. taken literally, the

meC::bairl.emtba.tte'ils the sc1ent1f'ic cOlll!lllin1ty wl:la.1: problems may lead to

. fimdamentalchange mustcea.se4otunction.·And when that· occurs, the com-

IIIUIlit'y Willinev1tablyreturh. to. something very like its pre-paradigm

state,s. collditiou'in which "all practitioners do science b.ut in which

their gross product "sc::arcelyresembles. science at. all. Is .it really a:ny

woMer that the price of eign1tics.nt scienUficadvance isa commitment

whii:liZ'fme ｴｨ･ｲＱＧｳｫｏｦＢ｢ｾＱｮｧｷｲｯｮｧＧｬＧ＠

ｾｲ･＠ importantj"there is a revealing logical lacuna in the positiv-

ist's argUment and one that Will reintroduce us immediately. to the nature

of revolut:l.onaryc:ballgEl; . Can Newtonian. dynamics really be derived from

relativistic clynamics'l What would such a derivation look like? Imagine

"a set cif stateinen.ts, ｅｬＧｾＧ＠ .' •• !:ar'which'together embody the lawa of

relativity theory. These statements contain:va.riables. andpll.rameters rep-

resenting spat:l.al position, time, rest mas, etc.:, and from ﾷｾｨ･ｭＮ＠ together

With the a;pparatus 'of logicano.mathemattcs, .is deducible a ;;ihole set of

further sta:tements including some that can be checked by obaer-rotion. To

100

prove the adequacy of Newtonian ｾｩ｣ｳ＠ as a special case, we must add

to the El 's additional statements, like (V/C)2 « 1, restricting the range

of the parameters and variables. This enlarged set of statements is then

manipulated to yield a new set, NlI N2 , ••• lim, which is identical in

form 'With Newton's laws ot Motion, the law of gravity, etc. Apparently

Newtonian dynamics has been derived from Einsteinian subject to a few lim-

iting conditions.

Yet the derivation is spurious. Though the Ni's are a special case

of the laws of relativistic mechaniCS, they are not Newton's laws. Or at

least they are not unless those laws are reinterpreted in a way that would

have been impossible until after Einstein's work. The variables and param-

eters which in the Einsteinian Et's represented spatial position, time,

mass, ete., still occur in the Ni's, and they there still represent Ein-

steinian space, time, and mass. But the physical referents of these Ein-

steinian concepts are by no means identical with those of the Newtonian

concepts that bear the same name. (Newtonian mass is conserved,; Einstein-

ian is convertible 'With energy,; only at lOW' relative velocities may the

two be measured in the same way, and even then they IlIUst not be conceived

to be the same.) unless we change the definitions of the variables in the

Ni's, the statements we have derived are not NewtOnian. Ii' we do change

them, we cannot properly be said to have derived Newton's laws, at least

not in any sense of "derive" nOW' generally recognized. Is not this need

to change the meaning of established and familiar concepts central to the

revolutionary impact of Einstein's theory1 Though subtler than the changes

from geocentrism to heliocentrism, from phlogiston to ｾｾ･ｮＬ＠ or from cor-

puscles to waves, this transformation of established concepts is no less

101

decislvelydestrllctive of a prevlouely esteblished paradigm. Wernay even

.. ' cometoeeelt .. aSa ｰｲｯｴｯｴｾＺｦＧｯｲ＠ revolutionary reorientations in the

sciences •.. Juet.becauselt· .. did .. not ·invo.1vethe·.introduction of new objects

or.concepts,. the transition frOlll Newtonian to Einsteinian mechanics illus-

trates With part1CUlai' Cia1'ltyt1leeCieD.t1flc revoJ:ut1Oh as a displacemen""t

o.f theconceptuaJ:.'network throughwhich.csc1ent1ste view: the world.

These remarks should suffice to. show wat might, in another philosoph-

:l.c:8l cJ.:l.mate,bI'I.VeheeJita1tenforgranted.. At least for scientists most

ｯｴｴｨ･｡ﾧＸＱＧ･ｮｴ､Ｑｦｦ･ｲ･ｾ｣･ｳ＠ between a d1scarded.scientific theory and its

iiucc:essorerereal.:!rhoughanout-o.f-date theo.ry can always be viewed as

'a special case of lts,;up-tc-date.iiuccessor,it must be transformed. for the

. ｰｵｲｰｯ･･ｾＧａｮ､ｴｨ･ｴｲ｡ｮｳｦ｣ｲｭ｡ｴｬｯｮｬｳ＠ one.tbat.canbe undertaken" only with

the advantages ofliindelght,the explicit guidance of the more recent the-

ory.Furthermore, evenlfthat.transformatlonvere a legitimate device to.

employ'in;interPretilig the cIder theory, "the result o:f'1tsappl1cat1on

would be a theo.ry so restricted that;lt could onlyree1;ate lIhat was already

mow; 'Becauseof.itseconOlilythat zoestatement would.have utility, but it

could. not Suftlced'or,·the .. gul4,ance.Clfresearch.

; let us, therefore,now takeltforgre.ntedthat,the differences be-

tweeneu.ccees1Ve;Parlidigms;ereboth necessary and irreconcilable. can "Ire

then say moreaxpl1c1t1ywhattsort.,of,d1fferencesthese are? The mest ap-

pII1"enttY,ile has ,already been.1llustrated ｲ･ｰ･｡ｴｴｬ､ｬｹｾ＠ SUccessive paradigms

tell'us differentthil18sabcut. thepopulat1onof. the universe and abeut

that poplllatlen' sbehavior. ;!rhey di:f':f'er" tbat is, about . such questions sa

tb.e'ex:l.stellce of subatomic particles,the.lll!l.:teriaJ.ity ef light, and the

. coIlservation>of heat 'or ct energy. These are the Dubstantive differences

102

between successive paradigllls, and they require no further illustration.

But paradigms differ in more than substance, for they are directed not

only to nature but also back upon the science that produced them. They

are the source of the methods, problem-field, and IltandardS of solution

accepted by any mature scientific community at any given ｴｾＮ＠ As a re-

sult the reception of a new paradiglll often nece.ssitates a redefinition of

the corresponding science. Some old problems may be relegs.ted to another

science or declared entirely "unscientific." Others that were· previously

nonexistent or trivial maYi with a new paradiglll, become the very arche-

tY,Pes of significant scientific achievement. And. as the problems change.

so. often. does the standard tbs.t distinguishes a ｾ＠ scientific solu-

tion fram a mere metaphysical speculation, word game. or mathematical

play. ｾ＠ normal scientific tradition that emerges from a scientific rev-

olution is not only incompatible but often actually incommensurable with

that which has gone before.

The ｾ｣ｴ＠ of Newton's work upon the normal seventeenth-century tra-

dition of scientifiC practice provides a striking example of these subtler

effects of paradiglll shift. Before Newton was born the "new science" of

the century had at last succeeded in rejecting Aristotelian end scholastic

explanations conducted ｾ＠ terms of the essences of material bodies. To

say that a stone, fell because its "nature" drove it toward the center of the

universe had been made to look, what it had not previously been. a mere

tautological word-play. Henceforth the entire flux of sensorya.ppearances.

including color. taste. and even weiglIl;. were to be explained in terma of

the size. shape. pOSition, -and motion of the elementary corpuscles of base

matter. The attribution of other qualities to the elementary atoms 'Was a

103

resort to the occult aDd. theref'ore out-of'-bounds f'orscience. ｍｯｬｩｾｲ･＠

caught the new spirit precisely when he ridiculed the doctor who. explained

opium's ef'f'icacy as a soporif'icby attributiDgtoit a dormativepotency.

During the lasthalf' of' the seventeenth century I!laIIYscientistspref'erred

ＭＭＭＭＧＭＢＭＧＭＭｾｴｯｏＭＭｬｳＡＦ［｡ｩ｜ＧＭｴｨ｡ｴｴｨ･＠ 1'ollnel shapeo:r·the opillmparticles enabledthelll--toO--.lSKOIOO'l;;thD.-----

the nerves about which they moved.

In an earl1erperiod explanations in terms of occult qualities had

been an integral part of' productive scientif'ic work •. Nevertheless, the

seventeenth century' s new commitment to mechanico-corpuscular explaDation

proved immensely frUitful f'or a.number of' sCiences,riddiDg them'of' prob-

lelliS that had 'def'ied ﾷｧ･ｮ･ｲ･ｊＮｬｹ｡｣･･ｰｴ･､ﾷﾷｳｯｬｵｴｩｯｮ･Ｎｮ､ｳｵｧｧ･ｳＧｾｩｮｧ＠ others to

replace them. In dynamics, f'or example, Newton's three Laws of' Motion are

iEu';saprOduct of' novefexper1meiits ih!l.Dofthe attempt to r!id.iiterPret

well-known observations in terms of' the motions e.nd interactions of' pri-

mary neutreJ. corpuscles. Consider just one concrete illustration. Since

nelltreJ.· corpuscles cOUld act on each other only. by contact, the mechanico-

corpuscularviev of'···ne.turedirected scientific .. attention to a.brand new

subject of' study, the alterationof'particulate motiOns by collisions.

Descartes announced the problem aDd provided its f'irst ｰｵｴ｡Ｇｾｩｶ･＠ solution.

Huyghens, Wren, e.ndwaUis carried it still further, partly by experiment-

ingwith colliding pendulum bobs but mosUy by applying previOUSly well-

known" characteristics of motion to the new problem. And Newton embedded

. their results in his Laws of Motion. The equal "action" aDd "reaction"

of' the Third Law are the changes in quantity of' motion experienced by the

two parties to a collision., The same c!1ange-of."motion.ll1lPplies the defi-

nition of' dynamical force implicit in the Second law. In this case as in

,.

104

many others during the seventeenth century, the corpuscular paradigm bred

both a new problem and a large part of that problem's solution.

Yet, though much of Newton' s work ;ms directed to problems and em-

bodied standards derived from the mechanico-corpuacular vorld view, the

effect of the paradigm that resulted. from his work was a further and par-

tially destructive change in the problems and standarda legitimate for

science. Gravity, interpreted as an innate attraction between every pair

of particles of matter, was an occult qua.lity in the same sense as the

scholastic's tendancy-to-1'all had been. Therefore,wh1le the standards

of cor;puscularism remained in effect, the search for a mecba.1:lical explana-

tion of gravity was one of the most challensing problems for those who ac-

cepted the Principia as paradigm. Newton devoted much attention to it and

so did many 01' his eighteenth-century successors. The only apparent option

was to reject Newton's theory for its failure to explain gravity, and that

alterlUl.tive, too, vas widely adopted. Yet neither of these views ulti-

mately triumphed. Unable either to practice science without the PrinCipia

or to make that work conform to the corpuscular standards of the seven-

teellth century, SCientists gradually accepted the view that gravity was in-

deed innate. By the mid-eighteenth celltury that interpretation had been

'almost universally accepted, and the result was a genuine reversion (which

is not the same as a retrogression) to a scholastic standard. Innate at-

tractions and repulsions joined size, shape, pOSition, and motion a.s physi-

cally irreducible primary properties of matter.

The resulting change in the standards and problem-field of physical

science was once again consequential. By the 1740's, for ｾｬ･Ｌ＠ elec-

tricians could speak of the attractive "virtue" of the electric fluid

105

a century before. Astheyd1d so. electrical phenomena increasii!gly dis-

played' anorder'd11'ferent"frOlll the 'one''the:lha:diiliawwhenVie'iTed as the

ef1'ectsOf amechail1caJ.effluviumtllatcOuld act onlYby·contact. In par_

·'ti1Ctilar.'whetieleetdeal aetion';at-a-cl:tstanee bEicame a subject for stuay

uitSOlrlt r1ght.thephenoinenonwe nO'lfcallcllarg1l:!g by induction could

'be'recOgnized as one Ofi'ts effects. PreviouSlY, when seen at all, they

lI.!iifbeen attriliUted'to'theleak8gea iIieVItable"'1ifeny electiii:allabora-

tOiy.Thatnew vietf ofinlluctive effeets l.'as,u tUrn, the key to Frank-

lin'saUalysis Of the Leyden .1arantl thus 'to the emergence Of a new and

NMOntan parMigm for electricity. Nor were dyilamics and. Eilectricity

the onlY'scient:tficf1e1.ds affected by the legit1mizat1onofthe search

for forces inhate to matter. Tilelal'ge bOdy of eighteenth";century liter-

atureon cme'micaJ. affinities and. replacementsEiriesalso der:l.ves from this

supra:"mec:haiiical agpect OtNewt0n1anism.Chemists . who . bel1evedin these

'. duferential attractions between the various chemicaJ.species setup pre-

viouilly'jm'imaginelfeX,per1ments and searched'for'nevsorts"of reactions.

ｗｩｴｨｯｵｴＧｴｾ＠ oata and the, Chemical.concepts develaped in that process the

later 'work OtIavoisierand" moreparticularlYiOfIlaltonwould be incom-

prehensible.Changesin the standards ｧＨＩｖ･ｲｮｩｾ＠ permissible problems,

concepts, and.ex;planations can transform a science. In the next section

I ｳｾｬｬ＠ ･ｖ･ｮｾｳｴＧ｡＠ sentle in which' they transform the world.

Other examples of these nonsubstantivedifi'erences betn-een successive

parad1gmscan'be retr:l.eved from the history of .. ,anyscience in almoet s:tJ.Y

periodofiistlevelOpliient. ｆｯｲｴｬｩ･ＱｬｬＶｭ･ｮＧｾ＠ let us. be content with just two

other and far briefer illustrations. Before the Chemical Revolu'.;ion one

106

of the acknowledged taske of chemistry lres to account for the qualities

of chemical substances and for the changes these underwent during chemical

reactioils. With the aid of a small number of elementary "principles"--of

which phlogiston 'liaS one--the chemist 'liaS to explain why some substances

are acidic, others metall1ne, combustible, and so forth. Some success in

this direction had been achieved: we have already noted that phlogiston

explained why the metals were so much alike. and we could have developed

a simila:r argument for the acids. lavoisier's ref'orm, however, ultimately

did a'WlI¥ nth chemical "principles," and thus ended by deprivilfS chemistry

. of' some actual and much potential explanatory power. To com.pensate for

this loss the search for an explanation of qualities and. their changes '!laS

widely declared unscientific. During much of the nineteenth century scien-

tists took such explanatiOns to be no part of' their function.

Or again, Clerk Maxwell shared with other nineteenth-century propo-

nents of the wave theory of light the conviction that light waves must be

propagated through a material aether. Designing a mechanical medium to

support such waves W8 a standard problem for lDBIlY of hia ablest contempo-

raries. H:l.s own theory, however, the electromagnetic theory of light,

gave no account at all of' a medium able to support light waves, and it

clearly made such an account harder to provide than it had seemed before.

Initially Maxwell's theory was widely rejected for those reaSOllB. But,

like Newton's theory, Maxwell's proved difficult to dispense with, and as

it achieved the status of a pare.d1@!l in the last decades of the nineteenth

century, the community's attitude tovard it changed. li!.axwell's insistence

upon the existence of a mechanical sether looked more and more like lip-

service, which it emphatically had.not been, and the attemptn to de6ign

107

suchan aetherial medium were aba1ldoned.Sc1entistsnolouger thought it

uIlscient11'icto speak of an electrical "displacement" mthou·tspecifyiug

What was beingd18p18ced. 'Theresult,' again. was a new' sdt of problems

8JId ｳｴ｡ｮ､｡ｾｳＬｯｮ･ｗ｢ＱＺｃｨＬ＠ lnthe event, had much to de with the emergence

"Of ｩＧ･Ｚｨ｜｜ｴｬｶｦｴＮ｡ｌｨ･ｏＺｴＩｾ＠

Thesecbaracteristic shifts intbe scient:l.fic cOlllllllUlity' s concept:l.on

of itsleg1timate problellisand litandards wouJ.dbeve lessslgnificance to

'thilimonograph' sthesi:S '11' 'one' COUld ｳｵｰｰｯｳ･ｴ｢･ｴｴｨ･ｹｾ｡ｬｬ｜Ｇ｡ｙｂｯ｣｣ｵｲｲ･､＠

frOm some'methodologiCally lower to BOme hiSher type. In thatcaee their

. - - , - .' -- "" .' ' effects, too,Would seem cumulative. No wOXiderthat some histor:l.allS have

arPa'tbat tbe Mstory of'science 'reco:rds 'Ii 'continuing' increase in the

matUrity and refinement of man'sc:onceptioJl. of ,the ,nature of science • Yet

the case for CUIII1ll8.t1ve development of science's problems and. standards :l.s

even hardertomakethaJI. the case for cumuIation,of theories. The attempt

to eXplain gravity, though:fruitfUlly abandoned bymoste:l.ghteenth-century

sCient:l.sts, w,snet directed to all. intr:l.ns:l.cally,:l.llegi t1mateproblem; the

obJec:t1OJ1.sto:l.nnateforces werenei ther :iJ:lherently'unsc:l.entific nor msta-

pllYSiCe.J.<:I.Ji some pejoratiVe sense. There are rio extern8.l standards to

permit a ｾＢ｡ｧｭ･ｮｴ＠ i::itthat sort. what occurred wsneither a decline nor a

rais1ilgof standards but s:Lmply e. change demanded by the adoption of a ｮｾＮ＠

paradism. Furthermore,that change has since been reversed and. could be

aga:I.n. In tl1etwent:i.eth centuryEinsteinbesBUcceeded in explaining

gravitational attractions, and that eXplanation has returned science to a

set of canons andprobleIl!B that are;inthispsrticular respect, more like

those of Newton's lli'edecessors than of hie succesS'ora. -Oraga:l.n. the de-

velopment of quantum mechanics has reversed the methodolcg1calprohibiticn

108

that originated in the Chemical Revolution. Chemists nO',/" do a.ttempt, and

with great success, to explain the color, state of azgregat10n, and other

qualities of the substances used and produced in their laboratories. A

similar reversal may even be underlro.Y in electromagnetic theory. Space,

in contemporary physics, is not the inert and homogeneous substratum em-

ployed in both Newton's and Maxwell's theories,; some of its ｮ･ｾｲ＠ properties

are not unlike those once attributed to the aether; we may someday come to

know what an electric displacement is.

B.1 shifting ｾｨ｡ｳｩｳ＠ from the cognitive tQ the normative functions of

paradigms, the preceding examples enlarge our understanding of the ways in

which paradigms give form to the scientific 11fe. Previously lre had prin-

cipally examined the paradigm's role as a vehicle for scientific theory.

In that role it functions by telling the scientist about the entities lihich

nature does and does not contain and about the 'lIBya in 'ihich those entities

behave. That information provides the map wose details mat'.1re scientific

research elucidates. And, since nature is too complex and varied to be ex-

plored at random, that map is as essential as observation and experiment

to science's continuing development. Through the theories theyembody,

paradigms prove to be constitutive of the research activity. They are also,

however, constitutive of science in other respects, and that is nOW' t.lJ.e

pOint. In particular, our most recent examples show that p&'a.digms provide

scientists not only with a map but also with some of the directions essen-

tial for map-making. In learning a paradigm the scientist acquires theory,

methods, and standa,:us together, usually in en inextricable miXture. There-

fore, wen paradigms change, there a."'E! usually aignific6.J-:;t shifts in the

criteria determining the legitimacy both of problems and of ｷｲｾｰｯｳ･､＠ solu-

tions.

109

.. That observation returns us tothe:,pointfrom.wh1chthis section be-

gan,'foritprovidesourf:!.rst explicit indication of why the choice between

·competing·patiI!.dlgms regularlyra:l.sesql1estionsthat cannot be . resolved by

the cr:!.teria O:tnormaJ. science •. To the: extent,as ｳｩｧｮｩＺｦＱ｣｡ｮｾ｡ｳ＠ :!.t is in-

ＭＭＭＭＭＧＲＭＢＧＧＭＧｴ｣ｩｾｏｭｉｬｩｬﾷﾷ［ＮＮ＠ .. ｱＧｬｩﾷｾＮＬｌｬＺｅ･ｴｩＬＺＧＧﾷﾷ＠ ·i:1that"tw()scfent1:f'1c schools disagxeea'bout-wha;tis eo problellHlIld----.. .

what a solution; they w:i.llinev1tably talltthrough. each other when debating

thereJ.ativemeritsaf tbeir respective paradigms. In the circular argu-

ments that regularly result eaclrparadigmwillbe'shown: to:eat:l.si'y the cr:!.-

tEiriathat it d:l.ctatesfor:l. tselfand t()fallshort . of a' fev of those dic-

tated by its opponent. There are other reasons, tool.for the failure of

logiCe.l contact that coIiSlsttmtlycli8.racitEidZes Paz'8d:l.gmd.ebates. For ex-

8ni.Ple;:since rio paradigmeversolvesallcthe. problems.:!.t.def:l.nesand since

notw()'parad1gms leave all thesameproblemsunsolved, .. paradigm debates al-

ways :l.rivolve thequeBtion:which problems is it more significant to have

'solved? L:l.kEitheissueot competing standai'ds, that question can be an-·

sweredol1ly in terms ()tcl'iter:l.athat lie outside ofnorma.1scie!lce alto-

gether, arid there a:reothersuch·:!.saueS'lles:l.des. ·Ultimately,in Section XI,

they w.l.ll dri va us to conclude that there is no cri tel'ionsorelevant to

p8.rsdiSJII selection as persuas:!.venessin the competition for the .. allegie.nce

of thEl ecientific community. That is amain reason for describing parad:l.gm

sh1ftsas revolutions. But before.taltingthatstepwe must examine one more

l-esPectin which paradigms Eil'e. necessarily self-justifying. To this point

I have argued only that paradigms arecons1;itutive of science. Now I wish

to display a sense in llhichthey a:reconstitutive of nature as well.

IX. Revolutions as Changes of I10rld View

Examining the record of past rel3earch from the '11'!mte.ge of contemporary

historiography, the historian of science may be tempted to exclaim that . . I

'When paradigms change the world itself changes with them. led by a new

ｾ＠ scientists adopt new instruments and look in new places. Even

more important, during revolutions scientists see new and different things

'When looking with familiar instruments in places they have looked before.

It is rather as if the professional COmmunity had been suddenly transported

to another planet where familiar objects are seen in a different light and

'Where they are joined by many unfamiliar ones as well. I need not say that

nothing of quite that sort does occur: there is no geographical transplan-

tation; outside the laboratory everyday affairs usually continue as before.

Nevertheless, ｾ＠ changes do cause scientists to see the vorld of

their research-engagement differently. Insofar as their only recourse to

that 'World is through what they see, we may want to say that, after a revo-

lution, scientists live in a different world.

It is as elementary prototypes for these transformations of the scien-

tist's world that the familiar demonstrations of a .switch in visual gestalt

prove so suggestive. What were ducks in the scientist's world before the

revolutiou are rabbits afterwards. The man wo firl3t Baw the exterior of

the box from above later sees its interior from below. Transformations

like these, though usually more gradual and almost always iI'".!'eversible, are

common concomitants of scientific training. Looking at a contour map 'che

student sees lines on paper, the cartographer a picture of a terrain. Look-

ing at a bubble-chamber ｰｨｯｴｯｧｲ｡ｾｨ＠ the student sees confV,sed and broken

lines, the physicist a record of familiar subnuclei'll' events. Only after a

no

111

number of such transformations of vision. does .. the stUd.entbecome an in-

habitant of the. scientist's world, seeing.what the scientist seGS and

responding as the scientist. does. The world which the student· then enters

is not , hCJWever I fixed once and for. all by the nature of the environment,

on the one bend, endot sCience,on-the-Gthel'.Rathel' .. it is determine.tid-----

.1ointlyby thE! en:v1rolllllent.and the. particular normal scientific .tradition

which the stUdenthes been trained to.pursue. Therefore, at times of revo-

lution,when the .normal SCientific .. tradit10ncbanges,.thescientist' s per-

ception of his envirOlllllent mustbereeducated--in acme familiar situations

.he must learn to see a new gestalt. ADd. afterhe.he.s.c done so .. the world of

-his research Will seem, here and there,incammensurablewiththeone he had

inhabited before.. That iSaDother.reasonwhy schools guidedbyd1fferent

paradigms are alwayssl1gb.tly at ｣ｲｯｳｳｾｰｵｲｰｯｳ･ｳＮ＠

In their most usual form, of course, gestalt experiments illustrate

only the. nature of perceptual transformations. They tell us nothing about " <, .«" , ＧＢＧｾＢＢ＠ ., - ",,, _." ,_ ".. ',0 """ " ,

the role of paradigms or of prev1. .. OUB. ly assimilated experience in. the proc-"" " --" ' ,,--

ess of .. perception. ··But onthatpoint.thereis.a.richbcdy of psychological

literature,.much.of it stemming from thepioneer1ng work of the Dartmouth

Eye Institute. An experimental sub.1ect who puts on goggles fitted .:ith in-

verting prisms initially sees the. entire world upside down. At .the sta...-t

his percElptual apparatus functions Bsit had been trained to function in

the absence. of the. prisms, and· the result. is extreme disorientation, an

acute personal crisis. . But ai'terthesub.1ect has begun to learn .to deal

with his new world,1 his .. ･ｮｴｾｲ･＠ visual field "flips over, It sometimes after

an intervening pericdin vhicbvis:!'oD is simply obscure.. Thereafter cb-

.1ects are again seen right side up as they had .been before the prislII3 were

112

put on. The assimilation of previously anomalous visual data. has reacted

ｾｯｮ＠ and changed those data themselves. In the most literal sense imagin-

able the man accustomed to inverting prisms has undergone a revolutionary

transformation of vision. r

The sub3ects of the anomalous playiDg card eJ.."per1n:-ent. discussed in

Section V experienced a quite similar transformation. Until taught by pro-

longed exposure that the universe contained anomalous cards, they saw only

the types of cards for which previous experience had equipped them. Yet

once ,experience had provided the requisite additional categories, they were

able to see all anomalous cards on the first inspection long enough to per-

, mit any identification at all. still other exper1lllents demonstrate that

the perceived size, color, and so on of experimentally displayed objects

also varies with the subject's previous training and ｾｾｲｩ･ｮ｣･Ｎ＠ SUrvey-

ing the rich exper1lllental literature from which these eT.amples are drawn

makes one suspect that something like a paradigm is prerequisite to per-

ception itself. What a man sees depends both upon what he looks at and

also upon what his previous visual-conceptual experience has taught him to

see. In the absence of such training there can only be. in William JameD'

phrese, "a bloomin' buzzin', coDfusion."

In recent years several of those concerned with the history of science

have found the sorts of experiments descl'1bed above immensely suggesti \'e.

N. R. Hanson, in particular, has made brilliant use of gestalt demonstra-

tions to elaborate some of the same aspects of scientifiC theories that

concern me here. other colleagues bave repeatedly noted that his'Gory of

science would make better and more coherent sense if one ｣ｯｾ､＠ suppose that

scientists occasionally experienced shifts of perception like those described

113

. above.YetFthoughpsychological expei'iments ere suggestive" they C9.lll1ot,

1nthe D8tureofthe case, be more than that. ··Theydod1splay character-

:f.stfcs'ofpereeption'thatcould .becentral to. scientific . development, but

they do not demonstrate that the careful and controlleaobservation exer-

cisedb1 _research· sc1entfstatallpartake" of those ｣ｨｬｬｩＺ｡｣ｬ［･ｲｩｮｩＢＧ｣ｳｯＺｲＮＮｾＭＭＭ

Furthermore • the very D8ture of these exper1ments makes anyd1rect demon-

stration of that po1nt1mposlJ1ble. It histOri<:aJ. example is to make these

.psychOlOg1CeJ.exper1Dliffits .. seelll relevant'Wemustffrst notice the sorts of

evidence that We may and may not expect . history to provide.

Thesub.1ectofa gestalt,delllonstrationlmows that his perception has

shiftedbecal1se.hecan make.:!.t i3hifi bacIt and forth repeatedly while he

holds the'SSIIIC''bOok·Or'piece, of'paper1n his"hands. Aware that nothing 1n ,....... ... ............•................

. his'envfroni1lenthas 'cllarlgedmth . his ". perception, he' directs. his attention

1Jlcrea.singly nottothiffigure(duck or rabbit) but to the lines on the

:PaPer he is ｬｯｯｫｩｮｧｾ＠ at. Ultimately, hEf may even learn. to see .those lines

w1'thoutseeing either of the figUres;, and he may. then say (what he could

·nOtlegitiirilitelY'haweai"d"·ea.rlier»that>itts'these'lines which he reallY

sees but that he sees them alternately!! as duck and !! a rabbit. By the

same token the sub.1ect of the anomalous card experiment knows (or, more

accurateiy,c:anbepeisuaded) that his perception must have shifted. because

a. h1gherau'thor:LtYi theexper1menter,'assures .him that,rega.rdless of what

he saw, be. was looking ata black five of. hearts all the. time. In both

these cases, as 1n all similar psychological experiments, .the effectiveness

ofthedemonstrat1ondependBupon .. i ts ... being. analyzable in. th:l.S way. UnJ.eaa

therewere'anexrernalBtandAl'd with reapect1;o vrhich a Il'.ntch of vision

coUld be demonstrated, no conclusion about alternate perceptual possibili-

ties could be drawn.

114

With scientific observation, however, the situation is exactly re-

versed. The scientist can have no recourse above or beyond 1tant he sees

with his eyes and instruments. If there were some higher authority by

recourse to which his vision might be show to have shifted, then that

authority would itsel1' become the source of his data, and the behavior of

his vision would become a source of problems as that of the el>.-perimental

subJect has for the psychologist. The same sorts of problems would arise

if the scientist could switch back and forth like the subJect o:f the ges-

talt experiments. The period during which light 'WaS "sometimes a wave

and sometimes a particle" was a period of crisis--a period when something

was wrong--and it ended only with the development of wave mechanics and

the realization that light was a self-consistent entity different from

both waves and particles. In the SCiences, therefore. if perceptual

switches accompany paradigm challges, ve may not ｾ･｣ｴ＠ scientists to at-

test to these challges directly. Looking at the moon, the convert to

Copernica.nism does not say, "I used to see a planet but now see a satel-

lite." That locution would imply a sense in which the PtoleU!Aic system

had once been correct. Instead a convert to the new astronomy says, "I

once took the moon to be (or, saw the moon as) a planet, but I was mis-

taken. " That sort of statement does recur in the aftermath of sc:!.entific

revolutions. If, as I suspect, it ordinarily disguises a shift of scien-

tific vision or some other mental transformation with the same effect, we

may not expect direct testimony to that effect. Rather ve must look for

indirect and behavioral evidence that the scientist with a new:paradigm

sees differently from the way he had seen before.

115

Let us then return to history e.nd.s,sk whai;sorts oftrensformat1ons

in the scientist's world the man who believes there may be !r.lch things can

. retrievefrom.it.Si1-William ｈ･ｲｳ｣ｨ･Ｑｾｳ＠ discovery. of Uranusprpvides a

. first example and one. that closely parallels the anomalous card experiment.

On at J east seventeen d1 f'fCrt!nt occasions between 1690 Ang 1781. a number

of astronomers, ｩｮ｣ＺｊＬｾｬＳ･ｶ･ｲ｡ｬ＠ of Europe's most eminent. Observers, had

ｳ･ｾ＠ a star in positions that. we nmr s1lpIlose must have been occupied at

the time by Uranus.. 0lIe. of ｴｨ･｢･Ｓｾ＠ observers-in .this .. group had actually

seen the star on four successive. nights in 1769 without noting the motion

which would have. suggested another identification. Herschel, when he first

observed the sameob.1ec1;tweive>years later,Ma. so W11;iia IIl1ich-impro'led

te1escopeot his awn manufacture. As a result hews able to notice an ap-. /' ,'" ＢＢＢＢＧＢＧＮＬｾＬＬＬ＠ "," "--".,,, ,-, ＬＧＢＢＬＭｾＢＬ［ＢＧＢＮ＠ ＢＢＢｾ＠ '"

parentdiiic:':'iiizetbiitwsatleastunusU8.l.for ｳｴ｡ｩＧｳｾＵｯｭ･ｴｨｩｮｧｗｳＧ＠ aWry,

and he therefore postponed identification pending further scrutiny. That

scrutiny disclosed Uranus' motion amoDg the stars, and Herschel therefore

announced that he had seen a new comet! Only several months later; after

.fru1tless.attempts .. to fit .. the.observed motiC!Jltoa cometEiry or1l1.t. did

Lexell suggest that. the orbit .. was probably planetary. When. that suggestion

was accepted there were s.evera! fever stars and one more planet in the

world of the professional astronomer. Acelest1al body that had been ob-

served .ofi'-end-on for almost. a century WB seen d11':f'erenUy after 1781 be-

cause, like ananomalouB playing card. it could. no longer be fitted to the

perceptU8.l. categories (star.or comet) provided by the pa-"'adigm that had

previously prevailed.

The shift of vision that enabled •. 8stronomers to see Uranus, the plaret,

does not, .however, seem to have affected only the perception of that .; ..

u6

previously observed object. Its consequences ｾＱ･ｲ･＠ more far-reaching.

Probably, though the evidence is equivocal, the minor paradigm cbenge

forced ｾ＠ Herschel helped to prepare astronomers for the rapid discovery,

after 1801, of the nlllllerous minor planets or asteroids. Because of their

BJDall siZe, these did not display the anomalous magnification that had

alerted Herschel. Nevertheless, astronomers ｰｲ･ｾｾ､＠ to fini additional

planets were able, with standard instruments, to identify thirteen of

them in the first fifty years of the nineteenth century ｾ＠ The history of

astronOlllY provides IIlaIlY other examples of J.lIU"8digm-:l.nduced changes in

scientific perception, SOllIe of them even less equivocal. Can it, :for ex-

ample, conceivably be an accident that Western astronomers first saw

change in the previously immutable heavens during the half-century after

Copernicus' new pa.'"8.digm was first proposed? The Chinese, 'Whose COSIllO-

logical beliefs did not preclude celestial change, had recorded the ap-

pearance of new stars in the heavens at a much earlier date. Also, even

without the aid ot a telescope, the Chinese had occasionally reported the

appearance of sunspots centuries before these were seen by Galileo. Nor

were sunspots and a nelf star the only exmnples of celestial chsnge to

emerge in the heavens of Western astronomy immediately ｡Ｚｦﾷｾ･ｲ＠ Cor:ernicus.

Using traditional instruments, some as simple as a piece of thread, late

sixteenth century astronomers repeatedly discovered that comets wandered

at will through the space previously reserved for the immutable planets

and stars. The very ease and rapidity with lIhich astronomers BaW new

things lIhen looking at old objects with old instruments may make us ,,"ish

to say that, after Copernicus, astronomers lived in a different lmrld. In

any case, their research responded as though that were the case.

ll7

The.preced1Dg eX8Jll.Ples are selected froD!· astronomy beca.use· reports

of celest1aJ. observation are frequently delivered in a vocabulery con-

s1Btingof relatively pure observation terms. "Orilyfromsuch reports can

we hope to retrieve anyth1ng like a f'ull parallelism between the observa-

tionsof' se1entiatiHiM those Of thep!l1ellologist' sexper:i:loontBl subJects.

But we need not 1nsiston so :fUll aparallel1sDi, and we have much: to gain

byrelax1Dg om. standard. If we can be content with the everyday (as

. ··againstthephllosophieal)·.use·of the verb "to·seei"ws'ma.y quickly recog-

nize that· wei1S.ve· already encountered . many other' examples of these shifts

mseientific perceptionwh1ch accompany paradigm cbsnge. T'nat extended

Use 'Of""perceptiOll" a!ld'of'''iieeing'' Will' shortlyi'eqU1re expliCit • defense.

but let me ·first illustrate its usein.practice.

:Wok Bga1n for a moment at two of our. previous examples .tram this

history Ｖｦ･ｬ･｣ｴｲｩ｣ｩｴｹｾｄｵｲＱｮｧ＠ the seventeenth century, when their re-

search was guided byene or another effluvium theory, electricians re-

peatedly saw chaff perticles' rebound from, or fall off of, the,electrified

'bodies that had attracted them. Atlesstthat'iswhatseventeenth-century

observers' said, they saw, and we 'have no.' more· reason to doubt their reports

Of percept:!.en than our own. Placed before the.same apparatull a modern ob-

server would see electrostatic repulsion (rather than ｭ･｣ｨｾＢ｣｡ｬ＠ or gravi-

tational rebounding), but historically, with one universally ignored ex-

ception; electrostatic ｲ･ｰｵｬｾｩｯｄＮｷ｡ｳ＠ not seen '. at all until Hauksbee' s

J..arge"sealeapparatUShadgreatlymagnified 1tseffects. Once he had

learn.ed to see the repulsion produced by contact electrification, hm,rever,

. Hauksbee"was rapidly able to recognize ,a number of other repulsive effects

as well. TheelectricaJ. phenomena visible in,!;he early eighteenth century.

118

vere both subtler and more varied than those seen by observers in the sev-

enteenth century had been. Or again, after the assimilation of Fre.nklints

paradigm, the electrician looking at a Layden jar saw something different

from what he had seen before. The device had become a condenser. for

which neither the ｾ｡ｲＭｳｨ｡ｰ･＠ nor glass was required. Instead, the two con-

ducting coatings--one of which had been no part of the original device--

emerged to prominence. As both written discussions end pictorial represen-

tations gradually attest, two metal plates with a nonconductor betwEen

them had become the protot:me for the class. Simultaneously, other induc-

tive effects received new descriptions end still others were noted for the

first time.

Shifts of this sort are not restricted to astronomy and electricity.

We have already remarked some of the similar transformations of vision

that can be drawn from the history of chemistry. lavoisier, we said, saw

oxygen 'Where Priestley had seen phlogisticated air and where others had

seen nothing at all. In learning to see oxygen, however, lavoisier also

had to chsnge his viev of many other more femiliar substances. He had,

for example. to see a cOlllJ?ound ore where Priestley end his contemporaries

had seen an elementar,r earth, end there were other such changes besides.

At the very least, as a result of discoveriIlg oxygen, lavoisier saw nature

differently. And. in the absence of some recourse to .thath;i'Pothetical

fiXed nature which he "saw differently, n the principle of' economy will

urge us to say that, after discovering oxygen, laVOisier worked in a dif-

ferent world.

I shall inquire in a moment about the possibility of avoiding this

strange locution, but we first require an additional example of its use,

119

this,. one. deriving. from one of thebeBt ｫｮｏｬｭｾｓ＠ of· the 'W"Ork of Galileo.

Since remote. EIlltiqu1 ty most people have seen one or another heavy body

Mng1ngbackand .fo..-thon a string or chain UIltil.i t: fiD8.lly comes to

rest.'lo the Aristotelians, who believed that a heavy body is moved by

its OlIn JIat'1l!e from a higher position to s ststeot natural restst a

lower one, the swinging bOdy wassiDIply falling with difficulty. Con-

strained by the chain. it could achieve rest at its lowpoint only after

.. a tortuous· motion and a considerable t1me. Ge.J.ileoron the other hand,

look:i.Jlg at the sv1ng1ng bOdy. lava pendulum, a body which almost succeeded

in repeating the same motion over.EIlld over again !!!!: infinitum. And, hav-

ing seen that much. Ge.J.ileoobserved other properties of the pendulum as

well and constructed many of .the most significant end original parts of his

new ｾ｣ｳ＠ around them. Froathe properties of the pendulum. for exWnple.

Galileo derived his only. full and sound arguments for the independence of

we:l.glltand rate-of-fall as well as for the relationship between vertical

height and termiilal velocity of motions dovn incl1nedplanes. All these

·natural phenomenahe.8aw" dU'f'erently.from. the. way. they. had been. seen before.

Why did that shift of. vision occur?fhrough Galileo's individual

genius, of course. But note. that genius does not here manifeBt itself in

more accurate or ob.1e.ct:l.ve observation of the mringing body. Descrip-

tively the P.ristotel1an perceptionis.1ustas accurate. .When Galileo re-

ported that the pendulum'sper:l.odwas1ndependentof amplitude for ampli-

tudes as great as 90°, his view of .the pendulum led hiDI to see far more

regularity than we can now discover there. Bather, what. seems to heaG

been involved was the exploitBtionby.geniuB of· perceptual possibilities

made ava1lableby a medieval paradigm ｳｨｩＱＧｴＮｃｾｬＱｬ･ｯ＠ .1.'aS no-" raised quite

120

an Aristotelian. On the contrary, he 'llS.S trained to analyze motions in

terms of the ｾ･ｴｵｳ＠ theory, a late medieval paradigm which held that the

cont1nu1ng motion of a heavy body is due to an internal pOm!r implanted

in it by the projector which initiated its motion. Jean Buridan, the

fourteenth-century scholastic who brought the ｾ･ｴｵｳ＠ theory to perhaps

its most perfect formulation, is the first man known to have seen in a

mrillg1ng body any part of what GeJ.ileo saw there. He described that mo-

tion as cme in which increasing 1DJ.petus is 1DrGlanted in the bob by its

gravity during the downswing; that impetus is next consumed in raising

the body against gravity on the upsving; then gravity again carries the

body down, 1DrGlanting increasing impetus until the low point of the mng

is reached; end so on in a process "'hich repeats itself symmetrically again

and again. Clearly that is very close to the view of the pendulUlli from

which Galileo started. At least in Buride.n's case, and almost certainly

in Galileo's as well, it was a view made possible by the transition from

the original Aristotelian to the scholastic impetus paradigm for motion.

Unt:l.l that scholastic paradigm ws invented, there were no pendulUllis, but

only S'I11nging stones, for the SCientist to see. Pendulums were brought

into existence by something very like a paradigm-induced gestalt switch.

Do we, however, really need to describe what separates Galileo from

Aristotle, or lavoiSier from Priestley, as a transformation of vision?

Did these men really ｾ､Ｑｦｦ･ｲ･ｮｴ＠ things when looking at the same sorts

of ob3ects? Is there any legitimate sense in which we can say that Ｇｾｨ･ｹ＠

pursued their research in different worlds? Those questions can no longer

be postponed, for there is obviously another and far more usual 'loIay to

describe all of the historical examples outlined above. SUrely most

,

121

readers will want to say tlle.tl>1hatchailges 1dth a paradigmirtorily the

scientist's interpretation of observations which themselves are fiXed

·once:imd· for 8.l1 by 'the nature :oftlieeiiv:l;rOxnnent'and'of'the:perceptual

ap;pa.ratlis.On this VieW, Priestley-'aildIavo1sier b6tlisawoxygen. but

they:lDterpretfldiiheu ooseHaiiCnff 4ifferefttlyj1lr:!:stotle Slid· 68111eo.-----

both aawpe;du1uma, but they differed in their interpretations of what

thElybothhad seen •.

Iatmeaayat once·'that·this very usUaJ. viewofwhe.t occursl1hen

'scientists· change .. their minds· about 1'undamental ,·matterscanbe neither

all wrong nora mere mistake. Rather it is an essential. part ofa philo-

ﾷﾷﾷﾷｳｯｐｨｩ｣｡ｲｰＺ｡ｲｩ､ｩｧｭｾ､･ｶ･ｬｯｰ･Ｈｆ｡ｴﾷｴｨ･ｃＧｂ｡ｭｴｩｩｲｩ･ﾷ｡ｳｎｭｯｮｩ｡ｲｬﾷﾷﾷ､ｙｮｷｲｩＺｬＮ｣ｳ＠ and

with DesCSrtesin the role played. for dynamics by Newton. Thatparad.:l.gm

ｮ｡ｳｬｬｾｲｶ［［［､｢｣ｩｴｨｬｬ｣ｩｾｘｬ｣･｡ｮ｡Ｎﾷ＠ philosophy· well. lteeJqlloi tation, like that

of dyJ'lamicsitseJ.f. l:ui.s been fruitful of a fundamental understanding that

perhaps could not .havebeen achieved in another way. But. as: the example

of NeWton18n a.yD.amics aJ.so:l.nd1.cates. even the most striking past success

prov:l.desno guare,uteetliatcris1s can·be indefinitely postponed. and to-

day-research tn partsofphilosopny. ·psycholosy, linguistics. and even

afth:l.story. e.nconverge to sUggest that the traditional paradigm is

somehow askew. That failure to fit ·:l.s Iilso made increasingly apparent by

'. the . historical. stud;\' of science to which I necessarily direct most of my

atteritionhere. :'

Nonear these crisis-promoting subjects has yet produced a Viable

al.ternate tothEitraditional epistemologiCal. paradigm, but they do beg:ln

to sUggest what some of that parad:l.gm'livcharacteristicswi:t1be. I am,

for example,scutelyawre of the difficulties inherent in saying that,

-.

122

when Aristotle and Galileo looked at swinging stones, the firs·t sail con-- --strained fall, the second a pendulum. The same d1i'i'icuJ.i;iea sre pre-

sented in an even more fundamental form by the opening sentences of this

section: though the world does not change with a change of paradigm. the

scientist afterwards ttOrks in a different world. Nevertheless, I am con-

vinced that we must learn to make sense of statements that at least re-

semble these. What occurs during a scientific revolution is not fully

reducible to a reinterpretation of indJ.Vidual and stable data. In the

first place, the data are' not unequivocally stable. A pendulum is not a

fa]Jing stODe, nor is oxygen dephlogisticated air. Consequently, the

data which scientists collect from these diverse objects are, as ｾｾ＠ shall

shortly see, themselves d1ff'erent. Furthermore, and perhaps more impor-

tant, the revolutionary process by which either the individual or the com-

munity makes the transition from constrained fall to the pendulum or from

dephlogistice.ted air to oxygen is not one that at all resembles interpre-

tation. How could it do so in the absence of fiXed data for the scientist

to interpret? Rather than being an interpreter, the scientis·l; who em-

braces a new paradigm is like the m&n1itl!U'ing inverting pr:l.sms. SUddenly

he confronts a world which, ·though indubitably the same in i·l;s totality,

has been transformed through-and-through :l.n its details.

None of these remarks is intended to indicate that scientists do not

characterist:l.cally interpret observat:l.ons and data. On the contrary,

Galileo interpreted observa"tions on the pendulum, Aristo-cle observatiolls

on falling stones, Musschenbroek obBervat:l.ons on a charge-filled bottle,

and Franklin observations on a condenser. But each of these int.erpreta-

t:l.ons presupposed a pa:t'.adigm. They were parts of normal SCience, an

123

.. enterprise which, .as.we .. have already. seen,a:l.ms to 'refine ,cextend, and

articulate a paradigm that is ,already in existence. Section III pro-

,videdmany elr8IIIples in which interpretation played a central role, and

tht!seexample.s., typify, theoverwhelmiDgmajorityofresearch. In each of

ｾＭＭＭＬＭＭＭｾｾＱ［ｨ･ｳ･Ｑ･ｮｴｩｳｴｪＮ｢ｹ＠ v1l'tueef,.an ae<lepted pa.ra.digmjllmeu ,met ｡ＭＭ､｡ｴｗｬｬｾＭＭＭﾭ

was, .1dlat ... instruments miSht be used to,retrieve it, .andwhat concepts were

,relevant .. to its inter,pretation. Given a paradigm, interpretation of d.e.ta

',is central to the enter,prise.that' explores. it.

BUt that interpretive enterprise--endthisvasthe burden of the

· paragraph before l.a.st--can only.articulate a paradigm, not correct it.

· ParidigJIIs arenotcorrig:tble by'normal scien-deat.all.. Instead, as we

, have already. seen, .. nm:maJ; .. science ... ultimatelyleads .. ,.onlY.tothe .. recognition

· of, anomalies and to . crises. And the.se are terminated .. not by de.liberation

and interpretation, but by a relatively sudden and una.tructUl"ed. event like

· the gestalt switch. Scientists then of1;en speak of the "scales falling

.·fran the eyes" or of the ,"l1Shtning flash" that "inundates" a previously

obscurepuszlerenabling ,its components to be seen in ane\i';1Bythat for

the first t1mepermits ｩｴ｡Ｎｳｯｬｵｴｩｯｮｾ＠ On other occasions. the relevant il-

luminationcomes'in sleep. No ordinary sense of " the. terminterpreta'i;ion

fits these fl.a.shes of intutti.on through which a new paradigm is born.

Thougil such intuitions depend.upon,the experience, both anomalous and con-

gruent,gained with the' old paradigm .. they are not logically or, piecemeal

linked to particular items of that experience as en.interpretation would

be. Instead, they gather up large porUons of that experience 'cogether

'endtranstorm, it to the rather. different bundle of ex:periencethat .,-ill

thereafter link piecemeal to the new paradigm but not to the old.

124

To learn more about what these di:t':f'erences in eXllerien(!e can be, re-

turn for a moment to Aristotle, Galileo, and the pendulum. 1<lhat data did

the interaction of their different paradigms' and their common environment

make accessible to each of them? Seeing constra.1ned i'all, t·he P.risto-

telian would measure (or at least discuss--the Aristotelian seldom meas-

ured) the weight of the stone, the vertical height to llhicn it had been

raised, and the time required for it to achieve rest. Together With the

resistance of the medium, these were the conceptual categories deployed

by Aristotelian science when dealing With a falling body, and normal re-

search guided by them could not possibly have produced the 1 .. io7ll that C.aU-

leo discovered. It could anly--and by another route it did--lead to the

series of crises from which Galileo's view of the swinging stone emerged.

AS,a result of those crises and of other intellectual changes beSides,

Galileo saw the sWinging stone quite differently. Archimedes' w"Ol'k on

floating bodies made the medium nonessential. the impetus theory ;rendered

the motion symmetrical and enduring. and Neoplatonism directed Galileo' s

attention to the motion's circular form. He therefore measured only

weight, radius, angular displacement, and time per swing, which were pre-

cisely the data that could be interpreted to yield Galileo's laws for the

pendulum. In the event, interpretation proved almost unnecessary. Given

Galileo's paradisms, pendulum-like regularities were very ｮ･ｾｸｬｹ＠ accessi-

ble to inspection. How elee are we to account for Galileo's discovery

that the bob's period is entirely independent of amplitude, a discovery

Yhich the normal science that stems fron Galileo had to eradicate and which

we are quite unable to document today. Reb'Ularities that could not have

existed for an Aristotelian (and that are, in fact, nOiIhere precisely

125

exemplified by uature}.were _ consequences of 1mmediate experience for the

. man who saw theswing1ng stone as Galileo diii.

<Perhaps that example istoo·fanciful since the Aristotelians re-

corded no discussions of swinging stones. On their paradigm it lms an

the simpler case,. stones.falling without. uncommon constraints, and the

same differences of visionshoir there. Contemplating stalling stone

J\ristotle,Baw a change of state rather thana process. For him the rele,.

vant parameters.ofa motion .. were. therefore total distance. covered and

.total elapsedt1mewh1ch yield what we should now call not speed .but aver-

e.gespeed. ｓＱｭｩｊＮ｡ｲｾＮ｢･｣｡ｕｳｾ＠ the stone was.:l.mpelledby its nature to

reach·its·final. resting pOint, Arist.otlesaw .the relevant.,distance param-

eter at any instant. during the. motion as the. distal'l.ce to'tllef:iriii.J. end

point rather than as ｴｨ｡ｴｾｴｨ･＠ origin of motion. Those conceptual

parameters.underlie aDd. ｧｩｶｾ＠ sense to most of his ｷ･ｬｬＭｫｮｾ＠ "laws of mo-

•.. tion." .Pal:tly through the. impetus paradigm, however ,and pertly through

a doctrine known as the latitude:.of forms, scholastic cr:l:ticiam cha.."lged

this way ofView1ng motion. A stone moved by impetus, gained more and

... more of it while receding from its starting point; distance ｾ＠ rather

than ､ｩｳｴ｡ｮ｣･Ｎｾ＠ therefore became the relevant parameter. In addition,

Aristotle's notion of speed was ·bifUrcated by the scholasti.CB into con-

cepts that soon after Galileo. become our average speed and. instantaneous

speed. But when seenthroush_the paradigm of whichthafJecc·nceptioIls

were a part, the falling stone, like the pendulum, exhibiteo, its govern-

"'iog laws almost' ort·inspection.· . Ga1ileo··was not. ons.ot.the first men to

suggest uniform acceleration. Furthermore, he had developed that theorem

126

together With many of its consequences before he experimented ｷｾｴｨ＠ an in-

clined plane. That theorem 'WaS another one of the network of new regular-

ities accessible to genius in the world determined jointly by nature and

by the paradigms upon which Galileo and his contemporaries had been rained.

Living in that world Galileo could still, when he chose, eJ..1}lain why Aris-

totle had seen what he did. Nevertheless, the immediate content of Gali-

leo's ｾｲｩ･ｮ｣･Ｎｗｩｴｨ＠ falling stones was not what Aristotle's had been.

It is, of course, by no means clear that lie need be so concerned With

"immediate ｾｲｩ･ｮ｣･ＢＭＭｷｩｴｨＬ＠ that ie, the perceptual features which a

paradigm so highlights that they surrender their regularities almost upon

inspection. Those features must obviously change With the scientist's com-

mitments to paradigms, but they are far from llbat we ordinarily have in

mind when lre speak of the raw data or the brute experience f::oom which

scientific research is reputed to Ill·oceed. Perhaps immediate experience

should be set aside as fluid, and lre should discuss instead. the concrete

qperations and measurements that the scientist performs in his laboratory.

Or perhaps the analysis should be carried further still from the immedi-

ately given. It might, for example, be conducted in terms of aome neutral

sense-datum language designed to conform to the retinsl imprints which

mediate What the scientist sees. only in one of these 'Ways can 'We hope

to retrieve a realm in which experience is again stable, once and for all--

in which the pendulum and constrained fall are not different perceptions

but rather di:i.'f'erent interpretations of the unequivocal data proVided by

observation of a ew1ng:l.ng stone.

But is sensory experience fixed and neutral? Are theories ｂｾｬｹ＠ man-

made interpretations of given data? The epistemological paradigm that has

dom1nated WesternphUosopby· for· three centurles·dlctateslm 1mmed1ate and

ｵｮ･ｱｕＱｶｯ｣｡ｊＮＺＮｙ･ｳｾ＠ In the absence ofa develapedalternatlvei I find it

ＱｭｰｯｂｬｬｬｬＡｬ･ｱｕＱｴ･ｴｯｧｩｶ･ｴ｢｡ｴﾷｰ｡ｲＸ､ｩｧｭｵｰｾｙ･ｴ＠ I th1Dk ltno lODger func-

.. tloils .. effectlvely,and thee atteroPtsto makelt.do so through the introduc-

ttonOfan opGlat1cmal or of a sense-aatumlanguage now seem t;ome entire"'lny..----

hopeless.

!he operatlonsaDdmeasurementstbi1.t e. sclentlstUndertakes ln the

J.81'iorator;yarenot"thegiveii" of expenence btit rather "the collected-with-

difflculty." !hey are not ybatthe IIcientll1tsees,;;.;;at leallt not before hls

researChlsYell ad:vanced aDd hlsattentlon focused. Rather they are con-

｣ｲ･ｴ･Ｑｮ､Ｑ｣･ｾｴｯｴｨ･｣ｯｮｴ･ｮｴｏｴｭｯｲ･＠ elementazoyperceptlOUS, aDd as suCh

. they are selected,forthe close scrutlny ofnormsl research only because

. they ＺｰｲｯｭＱｳ･ｯｰｰｯｲｴｵｮＱｴｹｦ｡ｲｴｨ･ｾＺｉＮＧｩｕＱｴＺｦＧｵｊＮ･ｬ｡｢ｯｲ｡ｴｬｯｮ＠ of an accepted para-

digm.Far m6reclearly than the immediate experlence from wD.1ch they in

. part derive , •. aperatlonsand.D!euurements. are .ps.r8dlgm-determ1ned. SClence

doss not deal in allposslblelaboratory.msn1pulations •. Ins'tead lt selects

those ·relevalittothe.juxtapositlonofaps.r8dlgm with the·1llImediate expe-

dence tbat tbatps.r8digm bas partially determined. As a result, scientlsts

with .. differentparailieps engage indifferent concrete laboratory manipula-

tions. ··Themeasuiements to be· performed on a pendulum are not the ones

relevant to a . case of . constrained .fall..Nor .. are .. the operatious relevant

for the elucidatlon of oxygen' s properties .. uniformly the same as those re-

quiredYheliinvestigating thecbi1.racterlstlcs of dephlogistlcated n1r.

As for a sense-datum language, ... perhaps .. one will yej;pe d.evlsed. But

three centuries after Descartes our hope for .suchan eventuality still de-

psnds excluslvelyupon.a theory of perception and of the mind. And modern

128

psychological ｾｲｩｭ･ｮｴ｡ｴｩｯｮ＠ is rapidly proliferating phenomena ｾｾｴｨ＠ which

that theory can scarcely deal. The duck-rabbit shows that two men 'ldth the

same retinal impressions can see different things; the ｩｮＧｾｲｴＱｮｧ＠ prisms

show that two men with different retinal impressions can see the same thing.

Psychology supplies a great deal of other evidence to the seJne effect and

the doubts that derive from it are readily reinforced by the history of at-

ｾｴｂ＠ to exhibit an actual sense-datum languase. No current attempt to

achieve that end has yet come close to a generally applicable language of

pure percepts. Alld those attempts which come closest share one character-

istic that is likelY to render them functionless for the acquisition of

knowledge. They presuppose a paradigm, taken either trom a current scien-

tific theory or from some traction ot everyday discourse, and they then try

to eliminate from it all nonlogical and non perceptual terms. 'l'he.t effort ,

my, of course, ultimately be success1'ul. In a few realms of diacO'.l%'se

Carnap and Goodman have already carried it very far. But there is no rea-

son to suppose that a language derived by the purification of anyone para-

digm will prove transportable to another. It ever developed and deployed,

a sense-datum language derived in that way will probably tend to the Game

r1gidification of experience as the paradigm through whose ーｾｩｦｩ｣｡ｴｩｯｮ＠ it

was derived. It it is to be serviceable for research, a sen3e-datum lan-

guage must be capable of describing experiences which violate current the-

ory as wall as those which conform to it. Philosophical ｩｮｶＬｾｳｴｩｧｳｴｾｯｮ＠ has

to date failed to provide even a hint of what such a language would be like.

Under those circumstances we may at least suspect ｴｾ｡ｴ＠ ocientists are

right in principle as well as in practice when they treat oxygen and pendu-

lums (and perhaps also atoms and electrons) as the fundamental ｩｮＦｾ･､ｩ･ｮｴＳ＠

129

of their i1lllDediate· experience. As "11. result of: the paradigm-embodied expe-

dence 01' the race, tile culture, and, tinally, the profession, the world

ｏｦｴｨ･ｾｂ｣ｩ･ｮｴＱｳｴｾｨ｡ｅｲ｣ｯｩｄ･ｴｯＧ｢･＠ populated m thplanets 'andpendll1ums, con-

､･ｮｳ･ｲｳ｡ｮ､Ｎ｣ｯｭｰｯｵｮ､ｾｯｲ･ＹＬ＠ and othersuchbocHes besides. Compared With

····these ob3ects otper.eept:l:ou, both meter st1ck teadlngs and retinal ＱｵｴＭｾＭＭＭＭ

': pr1nts are elaborate constructs to:which.experiElUcehas direct access only

when the sc1entist,tor··the: special purposes·of his research, 'arranges

tbAt one or: the other should do so. .. Th"8.t is not to suggest that pendulums ,

say,. are the only th1ngs.ascientist couldposs1bly see .. ｾＷｨ･ｮｬｯｯｫＱｮｧ＠ at a

sw1ng1Dgstone. We have already noted that members of another scientific

cOllllllimity coUld see constrained fall. But 11; is t() suggesttbAtthe

ｳ｣ｩ･ｮｴｩｳｴｷｨｯﾷｬｯｯｫｳ｡ｴｾ｡ＺｳｷＱＺｮｧＱｮｧｳｴｯｮ･Ｎ｣｡ｮｨ｡ｶ･Ｎｮｯ･ｸｰ･ｲｩ･ｮ｣･ｴｨ｡ｴ＠ is in

pr1nciplemoreelementarythan see1ng.a.peildulum.'The alternative is not

some lIypothetical"t1xed"· vision but vision through another paradigm, one

• whichmakesthesw1.ng1ng stone something . else •.

All of 'this may seem .more reasonable it we now reemphasize a charac-

·teristicot:perception.thathas most recently been noted only in passing.

Neither scientists rior la;ymen learn to seethe .. world piecemeal or item-by-

ｩｴ･ｭｾｅｘ｣･ｰｴ＠ when all the. conceptual and manipulative categories are pre-

pared in advance".e ;g. ,for the discovery of an additional trans-Uranic

element orfortlle sight of anell'.house--both.scientists and laymen sort

out whole areas from the flux 01' experience together. The chUd who trans-

fers the word "Mama" from all humans, to all females, and then to his

motller is not Just learning what Ｇｾｍ｡ｭ｡Ｂｭ･｡ｮｳ＠ or .who his mother is. Simul-

te.ne()usly he is.learning some of the differences between males and females

as well as something about the ways in which all but one feme.ls ,Till behave

130

toward him. His reactions, expectations, and beliefs--indeed much of his

perceived world--changes accordingly. :By the same token, the Copernicana

who denied its traditional title "planet" to the sun were not only learn-

ing What "planet" meant or what the sun was. Instead they were changing

the meaning of "planet" so that it could continue to meke useful. distinc-

tions in-a world where all celestial bodies, not Just the s;m, were seen

differently from the way they had been· seen before. The same point could

be made about any of our earlier examples. To see oxygen instead of de-

phlogist1cated air, the condenser instead of the Leyden jar, or the pendu-

lum instead of constrained fall was only one part of' an integrated shift

in the scientis.t's Vision of a great many related chemical, electrical, or

dynamical phenomena. Paradigms determine large areas of experienoe to-

gether.

It is, however, only after experience has been thus determined that

the search for an operational definition or a sense-datum language can be-

gin. The scientist or philosopher who asIts what measurements or retinal

imprints make the pendulum What it is must already be able to ｲ･｣ｯｧｮｩｾ･＠ a

pendulum when he sees one. If he saw constrained fall instead, his ques-

tion could not even be asked. And if he saw a pendulum, but saw it in the

same way he saw a tuning fork or an oscillating balance, his question

could not be answered. Or at least it could not be anm.-ered in the srune

way, because it would not be the same question. Therefore, though they

are always legitimate and are occasionally extraordinarily ｦｾＧＱｬｩｴｦｵｬＬ＠ ques-

tions about retinal imprints or about the consequences of ｾｾｴｩ｣ｵｬ｡ｲ＠ labo-

ratory manipulations presuppose a lTorld already llerceptuelly and concep-

tually subdivided in a certain lTay. In a senee such questions are parts

131

of normal sCience, for they depend upon the eilstence of a paradigm and.

they receive dii'1'erent answers as a result of paradigm change •

. To c()%lc1Ude . this seCtiOll let UB henceforth neSlect retin8.J. impl'es-

sl()D8 and agaiJI.., restrlct attentlon' to the laboratory' operations that

prOVide the sc1ent;1st w1th concrete thOugbf:ragmentary1nalces to what

he has already seen.. One way in which such laboratory operations change

With parad1gms has. already been observed repeatedly • "After a sCientific

revolutlQ11 .. ｭ｡ｮｹｯｬ､Ｇｭ･｡ｳｵｲ･ｭ･ｮｴｳ｡ｄ､ＭｾＺｐｕｬＮｉｬｴＱｯｮｬｩﾷ＠ Decome "1rrelErvant and

are replaced .by others instead.OIIedoesnOtapply all the same teste . .

. to oxygen as .todephlogisticated air. But c:hSllges of this sort are never

tot!1.,l.. lIhateverhe may then see, thsscient1st 81'tera revolution is

stilliooldngat •. the same -world. Furthermore,though he ay previously

have ･ｭｰｬｯｾ＠ them differently, much of his language and most of his lab-

. oratory instruments are still the samess they vere before. As a result,

pt:!st1'evolutionary sclence invariably includes .'JiIaDy of the same manipula-

tions, performed With the same instruments and. described in the . same terms, \ .

as Its prerevolutionary predecessor .I1'thoseenduringmanipulations have

.been c:haDged at" all, the Change mustl1ee1ther in their relation to the

paradlgmorin their concrete results. I now eusgest, by the introduction

"01' one. lastnevexam,ple ,that both these . sorts 01' c::hanges CSZl be observed

to occur. Examining. the work of Dalton and hisccntelllpOra.ries we shall

discover that one and the same operation, when it attaches to nature

through a different paradigm, can become an index to a quite different as-

.pect.of nature's regularity. In addition, we shall see that occasionally

the old manipulation ln its D.ewrole will yield di1'1'erentconcl'ete results.

132

Throughout much of the eighteenth century and into Ｇｾｨ･＠ nineteentb

European chemists almost universally believed that the ･Ｑ･ｭｾｮｴ｡ｲｹ＠ atoms

of which all chemical ｾ｣ｩ･ｳ＠ consisted were held together by forces of

mutual affinity. ThUB a lump of silver cohered because of the forces of

affinity between silver corpuscles (until after lavoisier these corpus-

cles were themsleves thought of as compounded from still more elementary

particles). On the same theory silver dissolved in acid (or salt in

. water) because the particles of acid attracted those of Silver (or the

particles of water attracted those of salt) more strongly than particles ,

of these solutes attracted each other. Or again, copper would dissolve

in the silver solution and precipitate silver, because the copper-acid

affinity was greater than the affinity of acid for silver. A great many

other phenomena were explained in the same way. In the eighteenth cen-

tury the theory of elective affinity was an admirable chemical paradigm,

ｾ､･ｬｹ＠ and ｦｲｵＱｴｾｬｹ＠ deployed in the design and analysis of chemical ex-

perimentation.

Affinity theory, however. drew the line separating ｰｨｹｳｾｌ｣｡ｬ＠ mixtures

from chemical compounds in a way.that has become unfamiliar aince the as-

similation of Dalton's work. Eighteenth-century chemists did recognize

two sorts of processes. When mix.ins produced heat, light, effervescence

or something else of the sort, chemiCal union was seen to hEtve taken place.

If, on the other hand, the particles in the mixture could be distinguished

by eye or mechanically separated, there \laS only physical mb;ture. But in

the very large number of intermediate cases--salt in ｾＢ｡ｴ･ｲＬ＠ alloys, glags,

oxygen in the atmosphere, and so on--theee crude criteria were of little

use. Guided by their paradigm, most chemists viey)"ed this entire'

133

'intermed1aterange'aschemicaJ.';becausethe processes 01' which it con-

slsted1iereaUgovernedby 1'orceso1'thesSme sort. Salt in ｾｬ｡ｴ･ｲ＠ or

· ,oxygen Ｌｩｮｾｮｩｴｲｯｧ･ｮ＠ .were.1ustasmuchexampleso:f''chem1cal· combination as

'" . was;thecombinatlonproducedby. OJCidi;1ngcopper. ;·ThearguJ!ents 1'or

VifiW1ng .solutions as compounds were very strong. . A1'1'ini ty theory i tsel1'

· was 'welrattested., Besld:es, the' 1'ormatiolio1'e.com.PoUnd accOUnted fora

solutton'sobserVea.homagenelty. If/'rbr·examplei'oxygen and riitrogen

were ol'llymiXed· and.· notcolllbined' ill theaas;pHe:t;&, .. ｴｨ･ｮｴｾ＠ heavier gas,

oxygen, should settle to the bottom. . Dalton,who took the atmosphere to

be a mixture,·· liaS never ·aatis1'actorily able to ' expJ.a1l?i oxygen' sfailure

to do so. Theass1milatlon 01' hlsatomic'theoryult:l.mately created an

'·anomaiy; where.'there'had beennone'beforeC;;"

one is temPted 'to sayth8t thechemistri who viewed solutions as com-

pOuxlds d11'1'eredtrom·1;heir successors oniy over e. matter of definition.

In one sense that may 'have been the case. But that sense is not the one

which makes definitions mere conventional conveniences. In the eighteenth

centtiryin:lxtureswerencitfli1J.y cl1stinS\11shed:1'rom·com.Pounds by opera-

ttonal tests., and;perhaps they could not have been. Even if' chemists had

looked for such tests,they wouldhaVesifught Criteria thatlDade the so-

lution a compound. Themixture-colllp0und distinction vas part of their

· p8ra.dism--partot the way they v1ewedtheir wliole field· 01' research--and

as such it'waspr:l.ortoanyparticular.laboratory test, though not to the

acculllUlated experience 01' cheinistryasa whole.

But while Chemistry liaS viewed in this way , chemical phenomena exam-

· pUfied laws ､ｩｦＺｬＮＧ･ｾｮｴ＠ from those which emerged with the assimilation of

Dalton's newpe.radiSin;· III particular{while solutions remained compounds,

ｮｾ＠ amount of chemical experimentation could by itself have produced the

law of fixed proportions. At the end of the eighteenth century it was

widely known that !!.2!!!! compounds ordinarily contained fixed proportions

by weight of their constituents. For some categories of reactions the

German chemist Richter. bad even noted the further regularities now em-

braced by the law of chemical equivalents. But no chemist made use of

these regularities except in recipes, and no one until almost the end of

the century thought of generalizing them. Given the obvious counter-

instances, like glass or like salt in water. no generalization was pos-

sible without an abandonment of affinity theory and a reconceptualization

of the boundaries of the chemist I s domain. That consequence became ex-plicit at the very em of the century in a famous debate between the

French chemists Proust and Berthollet. The first claimed that all chemi-

cal reactions occurred in fixed proportion, the latter that they did not.

and each collected impressive experimental evidence for his View. Never-

theless. the two men necessarily talked through each other, and their de-

bate was entirely inconclusive. Where Berthollet saw a compound that

could vary in proportion. Proust saw only a physical mixture. To that

issue neither experiment nor a change of definitional convention could be

. relevant. The two were as fundamentally at cross-purposes as Galileo and

Aristotle bad been.

This was the situation during the years when John Dalton undertook

the investigations that led finally to his famous chemical atomic theory.

But until the very last stages of those investigations, Dalton ｾｾ＠ neither

a chemist nor interested. in chemistry. Instead he was a meteorologist in-

vestigating the, for him, physical problems of the absorption of gases by

" .. ;: .. '

, 135

vater andot.vaterbythe-atmosphere. Partlybecauseh1str8.irliDg was in

.a d1t1'erent. ｳｰ･｣ｩ｡ｬｴｹ｡ｮ､ＮｾｴｬｹＮ｢･｣｡ｵ｡･ｯｦｨｩｳ＼ｮＮＧｚｬ＠ '!fOr1tin that specialty,

.J:1e •... ｡ｰｰＡｾｱ｢Ｎ･ｾ｣ＱＬ＠ ＬｾｾＮＡｬｾｰｬ［ＧＡｬＮｑｬｾｉｉＱｉｬＺｗＱＮ＠ th ... a.parad1gm .... different ·ti-om . iha.i·· ot COlltem-

porary chelll1sts •... ｉｮｾｩ｣ｵｬＮ｡ｲＬｨ･ｶＱ･ｷ･､ｴｨ･＠ niixture oisa-ses or the ab-;, .: ,'.,,". ,,' -- , , - -",',' -- - , -

sor;pl;lou of a gas in water as a p1IySicaI .process, one iii wbiCh forces ot

ai't1nity ｬｬｬ｡ｹ･､ｮｯＮｾＮｔｯ＠ him, theretore,theobserved homoseneity ot

.solutious. vas a.problem,but. one which he.thOll8ht he coUld solve if' he

cOUld determine the :l;"elative sizes and. weights or the variOUII atomic parti-

cles 1n.hisex,per1mentsl mixtures. It was todeterm1lle theEe sizes and

ｷ･ｩｧｨｴｳｴｨ｡ｴｊＩ｡ｬｴｾ＠ tirlally .. turnedtochemistrY, BUP.PoS1ns tromthe start

that,.1n .. the . restricted range .. otreactious which he took to be chemical,

. atoms·coulcl OIllycombirle·one-to-OIle. or.in some other "simple'lfhole number

ratio. That physically. natural ass1llllPtlO1l didenablebimto detel'!ll1ne the

SizeS. and veights of elementary ｰ｡ｲｴｩ｣ｬ･ｳｾ＠ but it also mdethelaw of con-

stan'!;. prpportiOll.a.·t!;Lutology. ForDalton,anyreactionin'which the ingre-

dien'!;s didllOtenter 1nt1Xed .. ;proportion W2sipso ｾ＠ not a purely chemi-

cal proceSS. A lawWhlchEilq?er1ment cOUld not have establiSlied before Dal-

ton's .. wC)l,"k .l:leCli!llle, ... ｯｮｾ＠ that work vas accepted" a cOllstituti ve principle

whichnCl sinsle set of. chemical measurements could have upset. As a result

. of wbe.t is perhaps our fullest example of asclenttticrevolution, the same

chemical manipulations assumed a relationship to. chemical generalization

vel"Y d11'1'erent .. from the one they had had betore.

Needless to say I DaltOll' fl cOllclusiClns were widely attacked when first

8III10unced. Berthollet, in particular,was never convinced. Considering

the nature of' .. theissue, he need not .. have been,B'.1t tor most chemists .

DaltOll'Snew parad1gmproved conv1ncirlgwhereProust'.shad not been, for . ,.,

136

that paradigm bad 1IqpJ.:l.cations far m.der and more important than a new cri-

terion for distiDguiahing a mixture from a compound. Ii', for ･ｾｬ･Ｌ＠

atoms,cOUld combine chemically only in simple whole number ratios, then a

reexamination of existing chemical data should disclose examples of mul-

tiple as well as of fixed proportions. Chemistll stopped writing that the

two oxides of, say, carbon contained 5fi1, and 72$ of oxygen by weight; in-

stead they wrote that one we1ght of carbon wOUld combine either wit/ll.3

or with 2,6 weights of oxygen. When the results of old manipulations were

recorded in this way, a 2:1 ratio leaped to the eye, and this occurred in

the analysis of many weU-known reactions and of new ones besides. In ad-

dition, Dalton's paradigm made it possible to assimilate Richter' a WO!'k

and to see its full generality. Also, it suggested new experiments, par-

ticularly those of Gay :Wssac on combining volumes, and these yielded

still other regularities, ones that chemists bad not previously dreamed of.

What chemists took from Dalton was not new ex,per1mental laws but a new way

of practicing chemistry (he himself called it the "new system of chemical

philosophy"), and this proved so rapidly fruitful that only a few of the

older chemists in France and Britain were able to resist it. As a result,

chemists came to live in a world Where reactions behaved quite differently

fram the way they had before.

And as all this went on, one other tn,>:l.cal and very 1mpor"'-..ant challge

occurred. Here and there the very :nUlller ical data of chemiatry began to

shitt. When Dalton first searched the chemical literature for data to

support his PhYsical theory, he found some records of reactions that fitted,

but he can scarcely have avoided finding others that did not. Proust's ｾ＠

measurements on the ｾＱＰ＠ oxides of copper yielded, for ｾｬ･Ｌ＠ an ｾｊｧ･ｮ＠

,

137

,weight-ratio of 1.47:1 rather th8n the 2:1 demanded by the atomic theory, ＭＮｾＭＭＭＮＭＭ ----

and ｾｯｵｳｴ＠ -is just the man vilo m1ght have beenex.pected to achieve the

Daltonianra,tiO. He w.s,. 'tliatis, a f1neexper1iilentaJ.:J.st, and his view

ｯｴＬｾ＠ relation betweenlrdXtu:res aDd caDpouD.cle was ve;:rclose to Dalton's.

BUt 1t1Bhai'a ·tb III!Ike nat'i.l:i'e fit a. Paradigm. That 1s 'Wl'I.Y the puzzles of

ｾｏｬＧｬｬｬｂｬ＠ science are sochtl.lleng1nge.nd aJ.so why ｭ･｡ｳｵｲ･ｭ･ｾｴｳ＠ undertaken

v1thoutaparadigmso seldCimlelld to arri conclusions at all •. Cheinists

'. ｃｃｬｬＱＱ､ｬｬＮｯｴ［ｴｬｩ･ｲ･ｦＧｯｲ･ｾＧｳｦｩｬｩＮｐｬｩ｡Ｎ｣｣･ｰｴＧｄ｡ｩｴｯｲｩｾｳｴｾｯＺｲｙ＠ on the . evidence, for , '- " - - -'," -,','-, - - \ - -' , ,

.muchof·thB.tvas still negative. Instead, they had to beat nature into

.. line, aprocessWhich,in theevell.t;,took 1Wn0st another generation to

canplete.W1ienit wasdoll.e, even the percentage CanPoSition of well-known

compOunds·wasd1tterent.· bt is the lalltofthe senlles in which we may

'illmt.te> say that a1'tera revolutioxi sc:ientilltllli've in a: d:l.fferent world.

x. The Inv1s1bilityof Revolutions

We have by no means finished our discussion of scientific revolutions.

In part1cular, if science does resemble the process sketched to this point

in this ｭｯｮｯｾｰｨＬ＠ there are two pressing questions that we must still ask

about them. First, how are scientific revolutions ｲ･ｳｯｬｶ･､ｾ＠ What argu-

ments can persuade a scientific cOll!lDUllity to abandon one time-honored way

of pract1cing science in favor of another? Row is the conversion to a new

world-view tranBlllitted from the individual who invents it to his group?

fbat is the problem ord1nar1ly described as the nature of proof or of veri-

ficat10n in the SCiences, and we shall consider it in the section that fol-

10IIII this one. As we do so, a second problem will come to seem very urgent

indeed. We have already seen that, given -a scientific revolution, the pre-

and post-revolutionary generations must be slightly at cross-purposes. The

worlds in which they live and practice science are not everywhere quite the

same, nor are the rules identical which govern the normal practice of the

two cOll!lDUllities. It follOllll that, though either community may hope to per-

suade the other, neither can hope to prove its case. Proof can al'WaYs be

evaded by insisting that the world is not that way (the sample, is e. com-

pound not a miXture) or that some of the procedures involved in the proof

are themselves not scientific. If, however, scientific revolutions are re-

solved by persuasion rather than by proof, we shall have to ask how persua-

sion in the sciences can function as it does. Why, if there is no such

thing as scientific proof, should scientific development seem quite so dif-

ferent from that of, say, art or religion? Can the image of science de-

veloped to this point in the monograph be reconciled with what is generally

called the fact of scientific progress?

138

139

I think it can and shall. therefore shortlY. begin to ｴＮｾ･･ｴｨ･＠ path

alcmgwhich. that. reconclliation.is to be effected. But 1'U'8t one last at-

ＮｴＬｾｉｉｉＮｐＺＡ＼［＠ ... ［ＢＹＱ［ｬｾｾＧＧＧＡ＾ｰＮｮｃｴＱＮｰｮＮａＧｉＺｬｑｕｴＮ＠ the .existence and nature ···01' revolutions ie

caUedfor. ｬｨ｡ｾｳｯＮＡｦｬＮｲｴｲＬｩ･､Ｎｴｯ＠ display revolutions simply by iUus-

txatlon,lI.pdHtllE!!lei:U;ustrijjlive .. examples could be multiplied ｾ＠ =na::u:::s::;:e:::BIII::: .

. ｾｴ＠ clearly ｭｯｳｴｯｾ＠ these examples , which were deliberately selected for

ＮｾｩｲＮｦ｡ｭＱｬＱ｡ｲｩＺＡ＼ｹＬｨ｡ｶ･＠ customarily ｢･･ｮｶｩｾ･､＠ not.as revolution,- out as

CIIIIIUl.ativ'eadditi6lls tosc1ent11'i" knowledge. That ｳ｡ｭ･ＢＧ［ｾｶ＠ could equally

1IeU be <taken of any additionalillustrationa, anr'.. these would probably be

ineffective. I suggest. that there. is,exceUe:tt reason for the usual view ", '." "',, , " ',0 ,,"' "-,, "

.that.lllllkes revolutions. so J1e!ll'ly invisible. :,oth scientists and laymen

te.kemuch of.their·1mageofcreat1vescientif;,c activity from an: authori-

tative source that systematically ､ｩｬｬｧｵＱｳ･ｳＭＭｾ｜ｲｴｬｹＮｦｯｲＱｭｰｯｲｴ｡ｮｴ＠ func-

. Only when, the nature of.1;hatauthorit.y1s rer.:ogn1zed and analyzed, can one

hOReto.make,h1,storica+ examplej,'ullya.f'fective. Furthermore, though the

point. can be j,'ully developed only ir. my concluding section, the analysis

llCM,reqll4'ecin:P •. begin to •. indicat.e.oneofthe.aspects. of SCientific york

which most . clearly distinsuishes .itfromevery other creative pursuit ex-

cept perhaps theology •.

As .. the.llource of authority .. I. have in mind pr1ncipally textbooks of

science. together with. both thepnpularizations and. the philosophical works

modelled on them. All three of these categories"';.until recently nc other

significant sources of information about science have been available except

:through . the pract:l.ce of research--have one thing in common. They address

themselves to an already articulated body of problems, data, and theol".I',

140

most often to the particular set of paradigms to which the scientific com-

munity is committed at the time they are vritten. ｾｸｴ｢ｯｯｫｳ＠ themselves

aim to communicate the vocabulary and syntax of a contemporary scientific

language. Popularizations attempt to describe these same applications in

a language closer to that of everyday life. And philosophy of SCience,

particularly that of the English-speaking vorld, analyzes the logical

structure of the same completed body of scientific knowledge. '.rhough a

fuller treatment would necessarily deal vith the very real distinctions •

between these three geD1'es, it is their similarities which most concern

us here. All three record the stable outcome of past revolutions and thus

display the bases of the current normal scientifiC tradition. To fulfill

their function they need not provide authentic ini'Qrmation about the way

in which those bases were first recognized and then secured to the profes-

sion. In the case of textbooks, at least, there are even good reasons

why, in these matters, they should be systematically misleading.

We noted in Section II that an increasiDg reliance on textbooks or

their equivalent was an invariable concomitant of the emergence of a first

paradigm in any field of science. Tbe concluding section of this mono-

graph vill argue that the dom1nation of a mature science by such texts sig-

nificantly differentiates its developmental pattern from that of other

fields. For the moment let us simply take it for granted that, to an sx-

tent unprecedented in other fields, both the layman's and the pl'acti-

tioner's knowledge of science is based on textbooks and a few other types

of literature derivative from them. Textbooks, hO".rever, being pedagogic

vehicles for the perpetuation of n01"_1 science, bave to be ｲｇＢｾＢｬＢｩｴｴ･ＡｬＮ＠ in

whole or in part whenever the language, prOblem-structure J or standards of

141

normal science ,change. Inc short, they have to be rewritten in the si'ter-

math of each scientific revolution, and, once rewr1tten,they ine\"itably

disguise not'only the role but . the .very'.existence·of·therevolution that

. ,producedthem •. UDless he.has persoIial.ly experienced a revolution in his

own.l1fet1me,thehistor:I:Cal sense of. the. working scientist and of ｴｉｄｲｊＺ｡ｾＮＮＮＮＭＭＭﾭ

·reader of textbook.l1teratureextexids<only to the outcome of the most re-

cent revolution 'in the field. ,.

'l'extbooksthus beginbytrunca.t1ng the scientist's senseot his dis-

cipline' shistOl7', and they thenproceed.to supply a substitute for What

theyhave.el1m1.nated. Characteristically, textbooks. of Ilcience .. do contain

JUst a bit Of h1storr,eitherinanintroductOrychapter or, more often,

in·.scattered.referencesto·.the·.:great ··heroes· •. of·an earlier age. From such

references···both··· stUdents ··and.prof'essiOna1s.do come to ,feel like partici-

pants :lna.long-standing historical tradition. Yet the textbook-derived

tradition in which scientists come .. to sense.their.participation is one

that, in 1'act;neverexisted.F<irreasons.that. are.both obvious and highly

tunctional,sciancetextbooks (axidtoomany of the older histories of'

science) refer only to that part of the work of past scientists that can

be made to seem contrlbutions to the statement and solution of .. the text's

paradismproblems.Partly by'selection and partly by distortion, the

scientists otearl1er ages are ... implicitly represented. as having worked upon

tbesame set of fixed problems and in accordance with.thesame set of fixed

canons' that the most recant revolution in . scientific theory and method has

made to seem sciel'!tific .No vonder-tAAt jtjJCtPooks an,dthe historical tro.-

ditiontheyimplyhave .to 'b.e rewrittensi'ter eachscienUi'1c revolution.

And no.'Wonderthat, 8s·theyarerewrit'cen, ｳ｣ｩｾｮ｣･＠ once again comes to seem

entirely cumulative.

Scientists are not, of course, the only group that tends to see its

discipline's past developing linearly tOliard its present vantage. The

temptation to write history backwards is both omnipresent and perennial.

But scientists are more affected by the temptation to rewrite history,

partly because the results of scientific rese8.l·ch show no obvious de-

pendence upon the historical context of the inquiry, and partly because,

at any given time, the scientist's vantage seems so secure. More his-

torical detail, whether of science's present or of its past, or more re-

sponsibility to the historical details that are presented, could only

give artificial status to human idiosyncrasy, error, and confusion. Why

dignify what science's best and most persistent efforts have made it pos-

sible to discard! ｾ･＠ depreciation of historical fact is deeply, and I

think functionally, ingrained in the ideology of the scientific profession,

the same profession that places the highest of all values upon factual de-

tails of other sorts. Whitehead caught the unhistorical spirit of the

scientific community when he wrote, itA science that hesitates to forget

its founders is lost." Yet he was not quite right, for the SCiences, like

other professional enterprises, do need their heroes and do preserve their

names. Fortunately, instead of forgetting these heroes, scientists have

been able to forget or revise their works.

The result is a persistent tendency to make the history of science

look linear or cumulative, a tendency that even affects scientists looking

back at their own research. For example, all three of Dalton's incompat-

ible accounts of the development of his chemical atomism make it appear

that he was interested from an early date in just thOse chemical problems

of combining proportiOns that he WEI later famous for having solved.

Actually thoseproplemsseemonly.to .. ha.ve. occurred to him with their solu-

tions and then notuntll his awn creative vork'ifas very nearly complete.

What all of Dalton's accounts omit 8l"E!the r:eyolutionsry effects of apply-

ing to chemistry a set of questions and concepts previously.restr1cted to ｾＢ＠ , .. ｾ＠ ｾＬ＠ .", . . " - -, "".

physics and meteorology •. That is what Dalten-tid. and. the result 1M! a

reorientationtowarcithefield. a reorientation that taught chem1sts to

ask new questions about and to draw !leW, C:()IIclusions frODl old data •.

Or asain.. Newton wrote that Gallleohaddiscovered that. the constant .. . force of gravity produces uniform acceleration. . In fact. Galileo' s kine-

mat1c theorem does take that form·.when embed\ied in the ma1;rix of Newton's . .

awn dyzIam1cal cOllCepts.ButGalileo.se.1d nClthingofthe sClZ't. l:T1s diSCUB-

ｳｾｏｉＱｰｦ＠ falling bodies ｾ･ｬｹＮ＠ al,lnde.sto forces".lDUchll'lfJstoa uniform

grartta.tiOiiai forcethBtcauses bodies .to, fall •.. By. crediting . to Galileo

the. answer to a quest10n that Galileo' s paradigms did not permit to be

asked. Newton' s account hides the, effect ofa small .but rev()lut10nary re-, .,',', 'M",,"""''''_ ,_" ,,,,-. __ ." ,,, ,-"" , , ,

formulat1on in the quest10ns that sc1entists. asked .. about. motion as well as

in the .ansvers .they felt able to accept. But1tis just th1s sort of

change in the. formulation of quest10ns and answers that accounts. far lIIore . - , : ._," -'" ..

thannovel.emp1rical discover1es. f()r. ｾＱ［ｲ｡ｮｳｩｩ［ｩｯｮ＠ from Aristotelian to

Galilean and fran Galilean to ｎ･ｷｴｯｮＱｾＮ､ｹｮ｡ｭＱ｣ｳＮ＠ By disguising such

change!!. the textb.ook's tendengy to,lIIakethe development of science linear

h1des a process that lies at the, . heart of the.lllost sigm.ticant ep1sodes of

scientific development.

ｔｨｾｰｲ･｣･､Ｑｮｧ＠ examples display, eachwii;llin the context of a single

revolution, the beginnings ota ｲ･ｴＺＰｬｬ｡ｴｲｵ｣ｴｩｯｮｯｦｨＱｦｊｾｏｬＧｙ＠ that is regularly

completed by poatrevolutioD8l'Y science texts. But in. toot completion more

ie involved than a l!IUl.tiplication of the histol:'ical ｬｬｬｩｳ｣ｯｮｳｴＡＧｵ｣Ｇｾｩｯｮｳ＠ il-

lustrated above. Those misconetrwctiona render revolution£: invisible; ,

the arrangement of the still visible material in s.ciencs tEl:t:l ilnplies <.

process which, if it existed, would deny revolution!! a function. Because

they aim quickly to acquaint the student w.!.th 'What the contempol'al'Y Gcienn

tific community thiDks it know, textbooks treat '"he various e:x;r>eriments,

concepts, laws, and theoriee of the current normal science just as sepa-

rately and as nearly seriatim as possible. As pede.gogy this technique of

presentation is unexceptionable. But when combined w.!.th the gene:t-eJ.ly un-

histOrical air of SCience ｾｩｴＱｮｧ＠ and w.!.th the occasional systematic mis-

constructiOns discussed above, one strong 1Jllpression is ovel"imelm1ngly

likely to follow: science has developed to its present point by a series

of individual discoveries and inventions which, ,taen gatherod together

constitute the modern body of technical knowledge. Frro the begiiming of

the scientific enterprise. a textbook presentation ｾｬｩ･ｳＮ＠ acientiets

have striven for the particular objectives that are the paJ.'<ldiS1l! achieve-

ments today. One by one, in a process often compared to the addition of

bricks to a building, scientists have added one more fact, concept, 1&.;;,

or theory to the body of information supplied in the ｣ｯｮｴ･ｾｯｲｾｾ＠ science

text.

llerbaps I need no longer insist that this is not the way a sciene·;,

does develop. Many of the puzzles 01' ｣ｯｮｴ･ｾｯｲ｡ｲｹ＠ normal science did not

exist until after the most recent scientific revolution. Very tew of

them can be traced back to the historic beginning of the sc:l.cuce w'lthin

which they now occur. Earlier generatiolls :pursued thei:" OH'"" ＩＩＺＧｯｾＱＱ･ｭｳ＠

.nth their awn instruments and their 0'\IIl canons of !!olut:Lon. n.:>:!:, is i1;

just the problems tb2.thavechanged.-Ratherthewllole ｮｩＺＡｴｴｾ｣ＡＧｬｬＺ＠ of fact

and theory which the textbook puradigm fits to natm'a has shifted.

Viewed.tbrOUghanolder paradigm llIlt)lfe' itsel1'was notqu1 te <the same

aDd could not be studied1D. gUtte tilflssme ;;,my. Is the cOnstancy of

chemical ｣ｯｭｬＧｯｳＱｴｬＶｮｾﾷﾷｦｯｲ＠ example; amen fact ofei:PeriencetJlat chelll-

lstscould have discovered by exper1ment v.l.thin anyone of' th(:l'worlds

withinwh:l.ch chemistshavepracticed'lOi':f.s it rather one element--and

. an iiidubitabliFone; atthai:-'-'fiia iiewfii.ll:r:f.cO'tassoc:latedfact and 'che-

orythat Dalton flt1;ed . to the earllerexper:f.ence· of . chemists as a "mole,

chaDgingthatexperlencein the'prcicess'lOi', by the same token. is the

constani: accelerai:lon prOduced byacollstant force a mere f'actthat stu-

dents of dynam1cs have always sollgll'br ｯｲｾＺｦＮｳｩｴ＠ 'rather theamrwer to a

questlonthatfirstaroseonlY·i,iUhfii Net1'tcm:l.ari.·theory aruf\1hicn that

theory could anSwerirom the body of infoX'lll!ltion availablebefOl'e the

question was asked? These questions are here askedaoout ｾＱｨ｡ｴ＠ appear as

the piecemeal-discovered facts of atenbook presentation. But obviously

they have iDi;pl1catloD8 asw·llforwhatthetextpreaents astheol'ies.

Those theories, of coUrse , do "fit the facts,," but only by 1;J;·e.us:f'orming

prevlouslyaccessible informa.t:f.onintofacts·that.·for the· preceding

paradigm, had not exis1;ed at all. And that means, as we have by now al-

ready seen, that thebriestoo do not evolve piecemeal to t'it facta that

were there all the time. Rather they emerge togethervl th the facts they

fit fram a revolutionary reformulation of the preceding scientific tradi-

tion, s. tradition within wllich the lmcniledge-mediatedrela.ticnship bet\1eer:.

the sCientist and n!l.ture wes not qti! te the same.

146

One last example may clarify this account of the imT-act ot textbcok

presentation upon our 1mage of scientific development. Every elementl:J:'Y

chemistry text must discuss the concept of acllemlcal clement. Almost

always, when that notion is introduced, its origin is attributed to the

seventeenth-century chemist, Robert Boyle. in whose Sceptical Cllyeist the

attentive reader will find a definition of "element" quite close to that

in use today. Reference to Boyle's contribution helps to make "l;he neo-

phyte aware that chemistry did not begin with the sulpha drugs; in addi-

tion, it tells him that one of the scientist's traditional tasks is to

invent concepts of this sort. As a part of the pedagog:l.c arsenal that

makes a man a SCientist. the attribution is immeneely successful. Never-

theless. it illustrates once more the pattern of historical mistakes that

misleads both students and laymen about the nature of the scientific en-

terpriee.

According to Boyle, who was quite right, his "definition" of an ele-

ment was no more tll&n a paraphrase of a traditional chemical concept;

Boyle offered it only in order to argue that no such things as chemical

elements existj as history," the textbook version of Boyle's contribu"!;ion

is quite mistaken. 'l'hat mistake, of course, is trivial, thoue-I} no ｭｯｬＢｾ＠

so, I inSist, than any other misrepresentation of data. Wnat is not triv-

ial, however, is the impression of SCience fostarcd unen this s.).'t of mili-

take is first compounded and then built into the technical atruc'GUre of

the text. Like "time," "energy," "force," or "particle," tha concept of

an element is not the sort of textbook ingredient that is often "illVen"l;ed."

or "diacovered" at all. Boyle's det'inition, in particuk"r, ｾｯＮｮ＠ ｢･ｴｲｾ｣ＧＳ､＠

back at least to Aristotle and ｦｯｲＭｾｲ､＠ ｴｨｲｾｵｧｨ＠ Lavoisier into modern texts,

·Yet .thatls" not .to .. E!ay. that E!cience. has .. possessed. the modeI'Il concept of

an element since antiquity. Verbal definitionB'likelloyle' s have little

scientlflccontentwhen.considered by themselves.'TheY's->-e not full

logict+l spec:l,1'1catlons otmeanirjg(if there are such}, but more nearly

ＭＭＭＭＭＬＭＭＭＭＭｩｰ･､ｉ･ｑｪｂＢｬｧｾｏ＾ｬｩｧｩｰＬＮｾ｣ｾ｡ｾｬｬＮＱｬ､ｌｓｳｾ＠ • ＮＮＬＭＭｔｨ･Ｍｳ｣Ｑ･ｮｴｩＮｦｾｾ｣ｬＡｴｩｬｩｩｹ＠ point gain .full

ｳｬｧｮＱｦｬｾ｣･Ｎｑｬｬｬｹ＠ Jlhen related. within a text or other syStematic presen-

tat10n, to .other.sclent1fic concepts, to IIIEIl11pulat:!.veprocedures, and. to

paradigmappl1cat1onE!. It tollow!lthat concepts l:l.ke that o;t"sn element

can scarcely be invented 1ndep$ndent '01' context. 'Fu.."rthermore, given the.

context ,they,1"8l'ely requirelnventlon because they are already at hand.

Bo.thBoyle and lavoisler c:lUIIfged the.'cheri11cal signii'icanceof "element"

ln :1mportantways." But theydld.not.invant the notion or even change

thevel'bal:·formula that serves as. lts "definitlon. n Nor, as we have

seen, d1d Elnateln have to invent or even expllc:!.tly redet1heepace and

time ln order to give them.new mean1ng within the ｾｯｮｴ･ｸｴ＠ of his work.

What then wsBoyle' s hlstoric.al functlon in that part 01' his work

that 1ncludes··the···1'amous "definition"?· ·Hews the leader ota sclen-

. tl1'lc revolut1on that,. by cha:og:lngthe.relatlon 01' "element," to chemi-

cal IlI!l!l1pulatlon and chemical theory, transtormed the notion into a tool

quite different trom what it had been before.·and tranatormad both chem-

istry and. the chemist's world in the process. other revolutions , in-

cluding the one that centers aro1.1I!.d lavoisier, were required to give the

concept lts modern ':t'orm and function. But Boyle provldes a typical exam-

ple both of the.process lnvolved.ateacho:t' these stages and.of what hap-

pens to that process when existing knowledge is embodied :!.na textbook.

148

More than any other sitlgle aspect of science 1 that :pedagogic form has, I

think, determined our image of the nature of science and of the role of

discovery and invention in its advance.

If the description ot sCielltif1cdevelopment; so far achariced has been

at all persuasive I 'it ｭｵｳｴｲ｡ｩｩｩ･ｾＧ＠ f6rmost'readersla:i'Uiid8lDental problem.

What is the process bywh1cha new candidate tor paradigm replaces its

predecessor? TO this po1lit we !lave seen iIOIf a paradigtD preViously suc(fellll""----

tul in gll1d1ng pro1'essional research encounters first anomaly and thenl it

the anomaly enduresl crisis. In add1tionl we have examined at least a tew

occasional characteristics of the extraordinary' research 'I!b1ch is engen-

dered by the recoSDition ot crisis and which precedes the rapid emergence

at a new candidate tor paradigm. Fin&llYI we have compared the new para-

d1gm with the oldl noting part1cularly the incommensurability ot the new

and oldl an.'1ncommensurab111tyman1test in changed rules tor scientific be-

havior and, in the new entities and regularities which scientists can see in

the world. But clearly in tollowing this path we have mieced a step. The

new candidate tor paradigm that emerges :from a crisis, emergeD tirst in the

mind of a single 1IId1v1dual. It 1s he who tirst learns to see SCience and

the world d11'f'erentlyl and usually his ability to make the transition is

tacilitated by two circumstances Which. ere not common to most other mem-

bers at his protession. Invariably his attention has been intensely con-

centrated upon the crisis-provoking problems; usually, in add1t1on, he is

a man so young or so new to the crisis-ridden tield that practice has com-

mitted h1m less deeply than most of his contem,poraries to the world-view

and rules determined by the old paradigm. ROlf is he a,ble, 'What must he do,

to convert the entire profession or ｴＮｾ･＠ relevant professional sub-group to

his way ot seeing science and the world? What persuades the group to aban-

don one tradition of normal research in favor of another?

150

In the present state of the literature on scientific method one point

requires emphasis at the start: the preceding questions represent the

only formulation which the historian can ｳｾｬｹ＠ for the philosopher's in-

quiry about the testing, verification, or falsification of established

scientific theories. Insofar as he is engaged in norrual SCience, the re-

search worker is a solver of puzzles, not a tester of paradigms. Thougn

he may, during the search for a particular puzzle's solution, try out a

number of alternative approaches to the solution, rejecting those that

fail to yield the desired result, he is not testing the paradigm when he

does so. Instead he is like the chess player who, with a problem stated

and the board l1terally or mentally before him, tries out various alterna-

tive moves in the search for a solution. These trial attempts, whether by

the chess player or by the SCientist, are trials only of themselves, not

of the rules of the game. The pa. .. 'ad1gm itself is never at issue: it is

not being tested, end, in the puzzle-solving Situation, could not be.

Puzzle-solving can continue only so long as the paradigm itself is taken

for granted. Therefore, as we have already seen, paradigm-testing occurs

only after perSistent failure to solve a noteworthy puzzle has given rise

to crisis. And even then it occurs only after the sense of crisis has

evoked an alternate candidate for paradigm. In the sciences the testing

situation never consists, as puzzle-solving does, ｳｾｾｬｹ＠ in the ｣ｾｩﾭ

son of a single paradigm with Datura. Instead testing occurs as part of

the competition between two rival paradigms for the allegiance of the

scientific community.

If closely examined, this formulation displays tUlexpected and, I

think, significant parallels to the ｾｦｏ＠ most popular contemporary

151

"phUosophicaltheories about ,verification. ,Few: philosophers of sCience

ＭＭＭＭＭＭｾＭＭｾＭＭＭＭＭＭＭＭＭＧＭＭＭＭＭ］ＭＭ］ＭＭＭＭＭＭＢＧＭＭＢＭＭＢ＠ stills.eek ｡ｰｳｯｬｵｾ＠ criteria ｦｯｾ＠ the verification of sCientific theories.

ｎｑｴｾＱＡｊＺｬＦ＠ .. t"JlQ ,\;llE!or'l.!=!1J! ｾＡｾＬｾ･Ｎ｜ＺｬｾＬｳＬ･､＠ .. to, allposBible relevant teats, ',. . ＬｾＢＮＬｾＬＮＬＢＬＬｾＬ＠ ＭｾＧ＼ＢＢ＠ ,- Ｍ＾ｾＢＭＬＬ＠ ... ｾ＠

. they., ask not:wbether:the theQry bas been verified .but rather about :Lts

prObab:tltty hi thel:l;ght of theevideneethat-aetually exists •. ｾｬＧＭＭＭＭﾭ

that quest:Lonons'1mportant : sChool is driven, as .1 am llere, to compare

, theabil1tyof a number oi'.different theor:Lestoexpla;Ln the evidence at

:hand. Tl:i8.tiris:LstenceonCompa1'ing ·theQr1es points one. of .the directions

inwh1Ch;t belie-v:e . future discussiQ1l8 of verification must go. In the1r

ｭｯｳｴｵｾｬ＠ fOl"lllS,:however,.probapilisticverification theorles demand the

cOlII,(iBrisonof all theories,thatcouJ,d possibly be. constructed for. the ex-

::plaDation"of a given body ｯｦＺｳ･ｮｳｯｲｹｾ･ｮ｣･Ｎ＠ And. the very concept of

suCh a construction.be8iris by raising all the problems. discussed previ-

ously. in connection With ｾ･ｊｕｬ･Ｍ､｡Ｇ｜［ＱＡｄｉＱｾｾｳ＠ and then gives rise to

others besides .• , S1nc:e,J:may .. ｮｯｴｨ･ｲ･ＺＮｾ＠ spaqe to eJ!al!l1ne those diffi-

culties,letme only urge that the ｴｨ･ｯｲＺｌ･ｾＮｷｨｩ｣ｨ｡ｲ･｣ｯｭｰ｡ｲ･､＠ by sc1en-

tists concernedWithver1fication are al'llllYB actual proposals of whiCh

there,areseldommore,tban tW!l •. 1 can discover neither a need for nor a

route to theconstructiono:t ｡ｬｬｰｯｳｳｩ｢ｬ･Ｌｴｨ･ｯｲＱｾｳＮ＠ Verification is like

natural selection: 'it picks out the most viable emong a number of' actual

alternat1ve9in a ｰ｡ｲｴｩ｣ｾ＠ ｨｩｳｴｯｲｩ｣｡ｬｳｩｴｵ｡ｴｩｯｮｾ＠ Whether thet choice is

the best that could have been made. ifst1l1.other alternatives bad been

., available is e. question that can not usefully be ･Ｎｳｫ･ｾＮ＠

Karl Popper, 'Io.l1ose news are obviously far c:lose1' to mine than are

those of the probabilists, appears to.av01d,the problems of all-poBsible-

theories by denying the existence of any ｶ･ｾ｣｡ｴｩｯｮ＠ procedures at all.

152

Instead he emphasizes the ｾｯｲｴ｡ｮ｣･＠ of falsification, i.e., of the test

whose outcome is negative and vhich therefore necessitates the rejection

of an estabrished theory. Like myself he sees science as progressing

from one theory to another incampatible one, the pOints of transition be-

inS,the falsification episodes which demand abandonment of the theory

which had previously prevailed. Clearly the role that Popper and his fol-

lowers attribute to falsification is very like the one I have here been

assigning to anomalous experiences, i.e., to experiences which, by evoking

crisiS, prepare the way for a new theory. Nevertheless, anomalous expe-

riences must not be identified with falSifying ones, indeed, I doubt that

the latter exist. As was em,phasized repeatedly in Section VII, no theory

ever solves all the puzzles with vhich it is confronted at a given time,

nor are the solutions already achieved often perfect. On the contrary,

it is .1ust the incompleteness and imperfection of the existing data-theol"".)'

fit which, at any time, defines IIW.llY of the puzzles 'I1hich characterize

normal science. If any and every failure-to .. fit were ground for theory

re.1ection, all theories ought to be rejected at all times. On the other

hand, if only severe failure-to-fit Justifies theory-rejection, then the

Popperians will require same criterion of "improbability" or of "degree of

falsification. " In developing one they will almost certainly encounter

the same network of difficulties -..>hich have haunted the advocates of prob-

abilistic verification theories.

Many of the preceding difficulties can be avoided by recognizing that

both of these prevalent and opposed views about the underlying logic of

scientific inquiry have tried to compress two sellm-ate processeo into one.

Popper's anomalous experience is ｾｯｲｴ｡ｮｴ＠ to science because it evokes

153

...•. ne,l candidates fOrparad1sili.B'.1t falsification, . thcni,gh it· surely exists,

does not occ:urw:Lth nor simply because of' the emergence of' anomaly. In-

stead '1t1s' a subseqttent"and separate process Wll,ichm1ght equally well be

Caul!d verification smce it cOnsists m the triumph of a new paradigm

. JiJezthE:01dcme:FuxthermOre,,ic Ｑｳｾｴｨ｡ＮｴＳｯｩｮｴﾷＢ･ｲＱ［ＡＡＧＱｾｾＱＡｉｬｲｬｦＮｪ［ｾＭｾＮ＠ ---

cation process that the probabilist' s C:Ompa.riSOD-of'-theoriea plays a cen-

tralrole..SUCh a two-stage fOrmulationMsi Ithinlt, the virtue of great

·Verisilli1litude;'and·1tmayalso··ena.1)lllulltO·begin:exp11catingthe role of

.agreement (Or diSagreement )beween fact and theory in. the \rerification

Process. To the histOrian,at least,1t makes l1tt1esense to suggest

that'ver1f:l.cat1on isestabl1.sliing tl1eagreement of fact w:Lth theory. All

histor1cslly<slgnfi'1cant"theories . have agreed withthe .. facts, but. only

more;;.or-less. 'l'!lken i1!d.i'V1duaJ.ly they are on aparw:l.threS,Pectto agree-

ment.ButtheY are not on a par when taken collectively or even in pairs.

Itliiilkesagreata.eal of sense· to ask wbiebot ｾ｡｣ｴｵ｡Ｎｬ＠ and competing

theories f1ts the tactsbetter. Thooghne1ther Priestley' snor lavoisier' e

theory, tor examplei l/.8l"eedprecisely with existing observations, few con-

temporar1eshellitatedmorethan a decade in concluding that lavoisier's

theory provided the better fitotthe two.

As yet; howeVer, this formulation mskesthe task of choosing betvieen

paradigms look both easier and more familiar than it is. If. there t.'ere

but one set of scientific problems, one world within 'llhiChto discover them,

andoIle set of' standards for their solution,. ー｡ｲ｡､ｩｧｭｾｯｭＺｰ･ｴｩｴｩｯｮ＠ might be

settled more or less routinely by some process like counting the number of

prOblems solved by each. BUt, in fact, these conditiODs·are never met

cOIlI.Pletely. ｾｰｲｯｰｯｮ･ｮｴｳｯｦＧ＠ competing paradigms a.,"'"e. alwys at least

slightly at cross-purposes. Neither side will grant all the ｮｯｮ･ｾｩｲｩ｣ｾｬ＠

aSSUl!lPtions that the other needs in order to make it" cone. Like Proust -

and Berthollet arguing about the ｣ｯｾｯｳｩｴｩｯｮ＠ of chemical ｣ｯｾｯｵｮ､ｳＬ＠ they

are bound partly to talk through each other. Though each may hope to con-

vert the other to his way of seeing his science and its problems, neither

may hope to prove his case. The competition between :paradigms is not the

sort of battle that can be resolved by proofs.

We have already seen several reasons why the proponents of competing

paradigms must fail to make complete contact with each other's argu1ll9nts.

ｃｯｬｾ･｣ｴｩｶ･ｬｹ＠ these reasons have been described as the incommensurability

of the pre- and post-revolutionary normal scientific traditions, and we

need only recapitulate them briefly here. In the first place, tha propon-

ents at competing paradigms will often disagree about the list of problems

which ｾ＠ scientific paradigm must resolve. Must a theory of motion ex-

plain the cause of the attractive forces between particles of IlI3.tter or

may it s1mply note the existence of such forces? Nerirl;on's dynamics was

widely rejected because 1 unlike both Aristotle' 8 and Descartes' theories,

it 1mpl1ed the latter anewer 'to the question. When Ii'emon'e theory had

been accepted, a question was therefore banished frOll! science. That ques-

tion, hawev-er, was one that general relativity may proudly claim to have

solved. Or asain. as disseminated in the nineteenth century, Lavoisiez"s

chemical theory forbade chemists to ask why the metals were 00 much alike,

a question which phlogistic chemistry had both asked and answered. The

tranoition to Iavoisier's paradigm had. like the traL,llitio71 to Newtoll's,

meant a loss not only of a permissible question but c-f au aChieved. Eloll.l-

tion. That loss was not, hOll'ever, permanent eithel'. In the twentieth

155

century questions ｡｢ｯｵＮｴｾｴｨ･＠ q1.1alit1es of chemical substances have entered

science again,together 1dthsome anmrers to them.

MClre is:. however ,involved tha:nthe "1ncommensUl'a'bili ty of standards.

Since new paradig!llS 8re born :rran old cries, they ordinarily incorporate

muCh 'Of the· v()cabttJ:tiio.y andapplustus, both' ｣ｯｮｩ･ｰｴｾｵｬ｡ｴＱｶ･ｬｾＭＭＭﾭ

tbatthe traditional. parad.iSm bad previously employed. But they seldan

employ these borrowed elements in qUite thetrad1tionalway. ,Tithin the

ｮ･ｷｾｯｬ､Ｎ＠ terms,concepts, and'expel'1ll1entsfall:into new relat1on-

. ships One with the other. The inevitabJ.eresult:l.s ｾｴ＠ we mUst c:all,

thoUgh the term. is not qUiter1gllt, a misunderstandingbet".reen the tvro

com,pet1tlg schools. The· men who Bcoffedat EinS1:e1n'sgeneraLtheory be-

cause space could not be "curved"-"itwas.not.:thet .. sortof,th1ng,.-were not

s1l!lPly Wl'0llg or mistaken. WJiS;1: theymeant by Bpac:e, i.e., Newtonian space,

Was necessarily flat, homogeneous, 1sotrop1c, and:unai'fected by the pres-

･ｮｾ･＠ ofmtter. If it bad not been, Newton1anphyeic8 would not have

worked. To make the trSnsit10n to Einstein's universe,the wholeconcep-

"'tua1 ｷ｢ｷｨｯｳ･ｯｴｲ｡ｩｩ､ｳｾ｡ｲ･＠ space, ﾷｾｴｩｭ･Ｌｭ｡Ｎｴｴ･ｲｪｦｯｲ｣･Ｌ＠ and so on, .. bad to

be shifted and laid down a,plnoZ!. na.1:urewhole • Only men. who had together

undergone or tailed to undergo that transformation. 'Would' be able to dis-

cover what, 1n phYs1cs, they agreed or disagreed about. ｾ＠ Or l1$':1in, the men

who called copEirnicuBmad:tor proclaiming that. the earth. moved were not

e1therjustwr6I1g orqu1te wrong. Part of what they meant by "earth" was

fixed position. T'ae:Lr earth, at least, could not be moved. CorresPond ..

1ngly: ｣ｯｰ･ｲｮｩｾｵｳｴ＠ innova.tionlmsnot simply to .mqye.,the earth. Ra-!;her

. it vas Il. whole ｮ･ｶｾｩｉｬＮｹ＠ ofreg8.i'd1!lgthepl'oblems of r,hysics and. 8strOnOl!!'J.

one which necessarily cll.anged the mean1.ng of both earth and motion

and Huyghena could 1"e1.11ize tha.t the earth's motion .1813 e questio:f.\ ",.-i-1;h no

content for science.

inCOl!mleDaurability of cOlllJieM.ng Jit'radigmsl. In e. SGllse "nicn I am unable

to explicate further the :proponents of ccmpet:l.ng paradigms pl'<'.ctice their

slowly, the other pcmdultillls that r'epeat -their motions ng!l.in am aga:!n. In

one J ｳＮｯｬｵｴｾ｟ｯｬｬｬＳ＠ S2'S cOOIDotmds. in t!1.e other miXtures. One i3 embedded. in e

,rorlds, the tiro grell, ipS of Bcientir'Gs see different 'thille;1J 'll1el.'l. 'chey look

from the !l8.lOO point in the ｳ｡ＢｾＧＢ＠ direction. Again, tJ:ll.\t 1s not to oe.y, ｴｨｓＧＺｾ＠

they can see I!.nything Ｍｾｨ･ｹ＠ please. Both moe looking at the ,rcrld, and 'the

ｾｾｯｲｬ､＠ has not cb.anged. But they do see 8olOO;;'£la't d:tft'erent ＧｾｨｩｮｚＹＮ＠ and they

see them in differen'c relatiolls one '.;0 'i;he other. 2hat ie"hy a lew -chat

cannot even be demollstrsted to one may ocClteiom'.lly seem :tntu:l.t:!:'!ely ob-vi-

oua to the o·cher. Equally it is ""Illy; before they can hope 'GO cO!i!im:rn.icc;ce

:fully. one or the other must ell:'.Qer:l.ence 'Ghe couvel'sicn tJ:w.t i·ra bo.ve b"en

157

not generally accepted, part:l.Clll.a1'lyon tbecontinent, f'or"morethan bcli'

a century after the Principia &]@eared.Priestleynever accepted.tbe oxy_

gen theory ,nor II:lrd Kelvin the electromagnetic theory I end eo on. The

difficulties Oi' conversion have often been noted. by scientists themselves.

Darwin. in a. particularly ;percept-;ve passage at tbeepd of biS O1'i gill o:t:t-----

Species, wrote: "Although lam fully Convinced of the truth of the ... 'ielTS

S:!.ven in thiS. volume .•.•• , I by no means ex.pect to conv!nceexperienced

naturalists whose minds are stocked with amultituiiB of fa.ctsall viewed,

during a long course of years, from a. point of viewdirect!t opposite to

mine. • • • [B]ut I look with confidence to the future,--to young and ris-

ing' naturalists, who will be able to view both aides of the question with

ｾｴｩ｡ｬｩｴｹＮｮ＠ Ant'l. MIllt. Planck, ｳｵｲｶ･ｹＱｮｧｨｩｳｾ｣｡ｲ･･ｲ＠ in. his Scientific

AutobiographY, sacuy. remarkea.-that: "Anew sC:l.en.t:i.fictrutb. does not tri-

UlII.Ph by convincing its opponents and making them see the liGht, but rather

because its opponents eventually die, and a new generation gl"CWS up that

it is fe.m1liar with it."

These facts and others l1kethem are .too commonly knOlo;ll,tO. need fur-

ther emphasis. But they do need reevaluation. In the past they have Illoet

often been taken to indicate that scientists, be1ngonly hUl!llUl, cannot al-

ways admit their errors, even when confronted with strict proof •. I would

argue, rather, that in these matters neither TJroof nOlO error is at issue.

The transfer of alleg1ance from paradigm to ｾ＠ is a conversion expe-

rience that cannot be forced. Lifelong resistance, lJSl'i;icularly from those

whose productive careers have committed them to an older tradition of nor-

mal SCience, is not a violation of scientific stnndards but en index to the

nature of scientific research itself. The source of resistance is the

158

, assurance that the older paradigm will ultimately solve e.ll its p!'oblems,

that nature can be shoved into the box the psradigJD pl"o1rides. Inevitably,

at times of revolution, that assurance Beems stubborn and piBheaded as in-

deed it is. But it is also something more. That same assuranoe is what

makes normal or puzzle-solving science possible. PJld it 1s only through

normal science that the professional community of scientists succeeds,

first, in exhausting the potential scqpe and precision of the older para_

digm and, then, in isolating the locus of difficulty whose study may ver-

mit a new paradigm.

Still, "to say that resistance is inevitable and legitimate, that

paradigm change cannot be Justified by proof, is not to say that no ｾﾭ

ments are relevant or that scientists cannot be ;persuaded to change their

minds. Though a generation or more is often required to effect the change;

scientific communities have again and again been converted to new ｾｾＭ

digms. Furthermore, these conversions occur not despite the fact that

scientists are human but because ·I;heyare. Though some SCientists, par-

ticularly the older and more experienced ones, may resist indefinitely,

most of them can be reached by one argument or another. CO!l.veraiOllG will

occur a few at a time until, a:1'ter the last hold-outs have died, the whole ,

profession will again be practicing under a Single, but now a different,

Parad18111. We must therefore ask ｾｲＧｄＮ｡ｴ＠ arguments can serve to induce con-

version, and how these are met by those who do not find them compelling.

Before approaching that question directly, however, two caveats nm.st

be introduced. Just because we are asking about persuaSion, or about 11.r-

gument ani counterargument, in a situation in which there can be no proof,

our question is a ne.r one I demanding a Bort of study that has not previcuEl;il

159

beenUlldertaken. In this place we shall have to settle far a very :partial

and impression1sticsurvey. Second, what· has already been said· combines

ｗＱｴｨＺｾＢ･ｲ･ｳｵｬｴｯｦＧｴｨ｡ｴｳｵｲｶ･ｹ＠ to suggest that,'II'hen'saked about persua-

sion. rather .thanproof',the question of the nature·cif sCientific argument

need. have no s1:ngle nOr uniform answex. Scientists e!ubraee a new ｰ｡ｲ｡ｾｬＭＭＭﾭ

for·· all. sorts .of' reasons, 8.Ddusually,fol:\ several. at once. Some of' these

reasons--for example the sumrorship that helped make Kepler a. Copernican--

lie outside' the'e.ppe.rentsphel'e of. science' entirely • Others "must· depend

upon idiosyncrasies of' autobiography and personality • Even the prior rep-

utation ·01'. theiIlnOVator 8.Ddhis teachers often plays an extraol'dinarily

significant role. Ultililately, therefore, w<shEill have to ask this whole

c •• question dii'i'erently. ., OIlrconcernlfillthen be not,what arguments may

serve' to convert the 1nd1V'1dUalbut ratherwhatcircUmatancesmay serve to

convert the· entire group. That problem, however;. I postpone to the IIext

. section, elCalD1n1ng meanwhile.somet;ypical aspects ofthe.argwnentation

. that figures so prominently 1n the battles over paradigm-change.

Mfi.iiY 0: thE!' argl!lllents for and against paradigm" cl:l8nge concern the rel-

at1 ve abilitiesof' the twoparad1gms to solve. problems, . and. overall these

are probably themostefi'ect1ve.Usually the .proponents of the .. new para-

digm u111 emphasize 'particularly their ability.to resolve the problema

that had gerierateda cr1sis·for.theolder .paradilYll' Thus Copernicus ca.tld

claim, erroneouslY as it turned out, that he had. at last solved the vexing

problem of the lellgth of' the calendar year., Iavoisier could clam to have

solved the problems' of ｧ｡ｳｾＱ､･ｮｴｩｴｹ｡ｮ､＠ of. weight-relations. And. Einstein

coiiidcis.:l.fut6 fii!.ve reconeiledelectl'odyna.mics ;n:ths"revised llcience of

motion. TIlis sort of argument proves particularly effective if' the

/

160

differences between the two paradigms suggest (1r permit the design of a.

"crucial" experiment, one whose outcome seems immediately congruent with

one of the paradigms but which proves very difficult to reconcile with

anythiDg but an obviously ad ｾ＠ formulation of the other. French resist-

ance to the wave-theory of light, for example, collapsed quite rapidly af-

ter Fresnel demonstrated the eXistence of a white spot at the center of

the shadow of a circular disc. That was an effect which he had not an-

ticipated but which Poisson, initially one of his ｾｯｮ･ｮｴｳＬ＠ had shown to

be a necessary consequence of his optical equations. Or again,occasion-

ally a particularly effective argument for a new paradigm can be derived

from its ability to resolve problems that neither party could previously

have thought relevant to it. Copernicus, for example, did not knOll the

telescope, and neither did his first opponents. Yet sixty-six years after

his death that instrument began to provide the most ｧ･ｮ･ｲ｡ｬｾｹ＠ effective of

all the arguments f(1r his new astronomy. Similarly, Einstein seems not to

have antiCipated that general relativity would explain the well-known

anomaly in the motion of Mercury's perihelion, and he experienced a par-

ticular triumph when it proved to do so. Just because they CamLot have

been deliberately ''built into" the new paradigm from the start, unantici-

paj;ed successes of this sort are often particularly persuasive. [The

pOints made in this paragraph must be considerably expanded in the final

version. Probably that expansion vill necessitate reorganizati0!l of the

material which follows.]

Yet though arguments like thoce described above are often immensely

persuasive, particularly to those wilom experience (or lack of er.perience)

has prepared for paradigm-change, we must aleo recognize that in principle

161

. ｾｴｨ･ｹ＠ .. =ot. beconclusive.and·that·in ｰｲｅｴＮ｣ｴｩ｣･ﾷｾｴｨ･［ｹｃ＠ <t'arely prove to be so.

Usual.ly one or another. of the'cr1sis-prollferated .... eI's1orlaofthe older

pa.r8lU.8IIIw111 bavepart1allysucceeaedineolv1ng theproblcms which the

Jll:Wparadigm' sproponents declare tba1;.theyalone have resolved.: Defend-

---------<v ...... s'-. oiLtbe·P1'101'-Sc1ent1t1e. vaii1M.CnC8ll thereforelegltl.DfaWl;y !l:t'gue

ｴ｢｡ｴＮｴｨ･ｾ＠ bave.alreadyhad somesuceessand.tbat .. they will ehortly be COlD-

pletelysuccess1'u.l. 'l'he problem at isstie,they.ean properly point out,

w111notbe the first obdurate. puzZle . that re'sea.l"ch Ullder· the old" per.adiglll

bas successfully resolved. That form of counterattack proves parM.culat·ly

effective.becsuse usually, when.the new .. parali1gm 1s 1'irstadvanced, 1t has

nOt 11;gel£ quite 8\1CCeeded in solvins the crisls-maltiilgprobiem, and the

cJa1ms.made in. its .. JIQIIIe:are. characteristically excessive ｾﾷｃｱｰ･ｲｮｩ｣ｵｂＧ＠ sys··

.. tem ｾ､ｮｯｴｰｲｯｶ･Ｌ＠ in tact,·tobee1ther.s1mplerar mo:reaccurate thtl.n

Ptolel/ly's; only I<'epler'ssubsequcn.t t'Ol'tIlUl.ationof the Copernican sjrstem

.. co1lldprqperly ｾｭ｡ｫ･ｴｨ･Ｚ｣ｬ｡Ｑｄｬｳｴ｢｡ｴｃｯｰ･ｲｮＱｃｕＸ＠ had made •.. Or again. when

IavoiBier.sflw. ｾｮ｡ｳ＠ tltheairitsel£. entire, " .. his llew theory oi' combus-

tiont.";:1.ft:not able at an·to:·copevith··theproblems::presented by the prolif-

eration.of ne'li'gases,apo1nt which Priestley made wlthgl..'Ce.t success in

his counterattack.

In ... short. during a parad1gm-debate.boththe old.l:mrad:lgm afJd the new

cand1dnteare.ususlly undergo1I\6e·l;ea4;ydevelopment •. : The. iesue ill the de-

. bate ,therefore, usually does not prove to be which problems .each paradigm

bas solved. Instead. the arg-..uuent is about whieh p&raMgm should be used

1l1 .. atteck1ngproblema.that .. ne1ther .. canyet guite claimj;o have solved.

later,-after the profession has again been un1fiedaudwheuthere ie ｾＱＰ＠

one leftwilliIIg to.·:dei:end. the tre.ditiorw.l .... ｩｾＮ＠ an apparently conclusive

case for the new paradigm can often be constructed. But that te>:tbook

case seldom appears until a time when it is no longer needeo.. A!.1d. ,Then

it does appear, it usually rests on arguments and upon data that became

accessible only after the historic confirmation debate bad ceased.

Foucault's pendulum, which "proves" the earth's rotation, and Fizeau's

experiment on the relative velocity of light in air and ｾｴ･ｲ＠ are only

particularly well-known examples of experiments now used to make pOints

that no longer needed making when the experiments in question were first

performed. Undoubtedly they are e:f'fecti'fe experiments. If they had been

performed sooner, the confirmation-debate to which they seem relevant

would. probably have been shorter. But there is no reason to think that

there would not still have been a debate. Besides, these particularly

convincing demonstrations (and even they could be countered) usually share

one very significant characteristic. Ordinarily they demand eguipment and

concepts that wre not available until after the debaw. USllS.lly, they

are products of a normal scientific tradition that became possible only

when the ーＸＭｾｩｧｭＭ､･｢｡ｴ･＠ had almost ceased.

Even these lines of argument fail to display the heaviest artillery

available to the defenders of the scientific tradition. otten they can

and do admit that, for application to the crisis-making problem, the new

candidate for paradigm has significant advantages. But, simultaneously,

ｴｨｾｰｯｩｮｴ＠ to a host of problems that the old paradigm did ｲ･ｳｯｬｾｾ＠ but that

its cha.llenger cannot. Thus, until the work of Ga.lileo, the Copernicana

could not give nearly so good an account of terrestrial motion as the one

Ptolemy and his succeSBors had given. laVOisier .:as never aDle to el:plain

the common properties of the metals, nor, in the early stage>] of his

theory's development, could he el.'Plain either theproducUon of 1later by

oxygen .. hydrogen. explosion or . the production. of aninf'lamluable . gas from

carl:!on •.. Me.xwell! .. s .. tb,eory,.despite .... its · .. author'.s .. expressed intent, made

.&IW solutioll to the problem of· a mechanical aetherseem :f.mlIossibly dis-

Ｇｴ［ＸｩｩｾＬＸｩｩ､Ｑｴｲ｡Ｑｓ･､ＨＩＤ･ｲｮ･ｷ､ｬＱＧｦｬ｣ｕｉｴｬ･ｳＮ｢･ｓｬ｡･ｓ＠ •. To generiilize, no

new .cendidatef()rparad1gmevel" . solves all the. traditional and .novel prob-

le!Ds that confront. it, and·i.ts apparent failures do provide a basis for

entirely l,egitimate resistan.ee.Some· of' those f'ailures become problems

f.or normal research under the. new paradigm;: others, like the cause of

grIlyity, tb,es1m1larityof.themetals,. or the mechanical aether, are ac-

cOIIIIIIodatedouly by c:ha.tIging1;he standards of the. science itself •

.. . , That IlSedtO:change s1;andards·' opens. up a· whole. new line ofargumen-

tation,and one that is. of a rather d1fferentsort.. Not. all the. argu-

meIl1;s .. l"ele:vant1;()ach()1ce of. pare,41gm .lle.e.d .. ｴＨＩ｣｢ｬｕｾＱｬｏＱｬｴ＠ prc:itllelD .. sol v1ng

at. all. The·opponents"of.;a;new;parad1gm··C8Il··andllometimes.doprocla1m

that. thecballenger, hQ'!leyermany prollle!DB;it can solye,. must be rejected

because it s1m.Ply is not ... seience. Iloris.that.aceusation. entirely un-

tounded •....... The .. meJl •. who. make it .•• areOIlly.de:t:ending. e1;Mdards· .. tll!l.t have been

closely' assoc1ated.w1th the' ーｾｶｩｯｵｳｳｵ｣Ｚ｣･ｳｳｯｦｴｨ･ｩｲｰｲｯｦＧ･ｳｳｩｯｮＮ＠ Or

again;. given anything like a ;. stand-oi'i'on problem .. solVing ability, the

proponents of ･ｩｴｾｲ＠ paradigmmayclaim;tbat .their way of solving prob-

lems is more reasonable, or that. it.iss:iJDpler, or that.it fits better

with the findings of some other science, or of philoscpby, or of religion.

Occasionally the appeal maybe atraigh1;torwardlyto e,uthority, or it may

even be to the personality of' the paradigm's proponents •. When this oc-

curs, paradigm-debates. may. grow. ･ｾＺｴｾｯｲ､ｩｮ｡ｲｩｬｹ＠ bitter. Men hll:\Te lost

\

164

jobs because of them.; promising careers have been abruptly halted.

Obviously reactions like these are excfll3si va and ｲ･ｧｲ｣ｾｴｴ｡｢ｬ･Ｎ＠ In

retrospect, even those scientists who feel their side ｾｬ｡ｓ＠ right are usu-

ally asb.llmed of their participation in them. But that does not mean that

these extreme reactions are irrelevant to the issues of the confirmation-

debate. Just because logic fails, because the issue is conversion, be-

cause men must be made to see a world toot they can now look at w:!.thout

seeing, words ,like ''blind,'' "pigheaded," and "fool" may finally be the

only appropriate terms remaining to the participants in such a debate.

Sometimes, in fact, new converts apply the term "fool" to themselves for

failing sooner to see the light. The men who use these terms do not, by

doing so, cease to behave as scientists. There is a full continuum from

arguments based on data, through those involving standards, to those which

employ vitriol. .And any argument in that entire arsenal can work. Note,

however, a point to be emphasized in the next section: though vitriol is

occasionally a natural and relevant ingredient of SCientific controversy,

there ｾｾ､＠ be no science if it were the only ingredient or even the most

effective one.

Everything said so far should indicate that, insofar as they are

merely logical, debates over paradigm-choice must lead to stalemate. That

they do not do so indicates that SCientists are reasonable human beings,

at least as So group. An argument need not be logically compelling in order

to persuade most of them that they have made a mistake. Only there turns

out to be no single argument that does (or ought to) persuade them all.

InsteaO., what occurs is an increasing shift in the stfJ.tistical distribu-

tion of professional allegiances. At the start a new candidate tor ｰ｡ｲ｡､ｩｾＢ＠

,

may Mve'veryfew sUpporters, and the motives of soine of thel:l are often

suspect. Copernicus wOUld almost certa:l.llly havebeenhorr1.fied by Bruno,

｡ｄＨｦＧＬＺｄ｡ｲｷｩｮＧﾷｷ｡ｳｬ･ｳｳｾＧﾷｴｨｮｮｰｬ･｡ｳ･､ｷｩｴｨｃ｢Ｎ｡ｭ｢･ｲｳＮ＠ But often it makes ,little

. difference wtililt.motivesbriIIg its flrst sJlpp91"ters to alJ3.radigm. If they

are competent they will improve it, explore :l.tspossibilities, and SilOl(

whatitWOUl.dbel:l.keto belong to ascientificcOl!llinmity guided by it •

. '. And as that goes on, if' the parad:l.gmis one destined to. u1n its fight,

thenumbEir and streDgth of the persuaS1vearg\imentstavor:l.ngitw:l.ll :l.n-

crease.' More sc:l.entists will then be converted, 8.ncl. the explora.tion of

the new J?S.rSil.:I.!,!DIw:l.ll ｧｾＨＩｮ＠ •. Graduall;y the number. of' experiments, instru-

ments, articles, and books based upon the paradigm w:l.llmul,tiply; Still

more men, conrlnced ot the new view'sfruitflllhess, will undertake the new

modeforpracticiIIg norlllal science, until at last only a few elder hold-

outs remain. And even they. we cannot .. say, ... were.lIl'.ong •.. Though .the his-

toriancan alwaysf1nd men-.Priestley.for instance-,..who were foolish to

resist for as long 8stheydid,he<w111.not find a point at which resist-

aDCe suddenly becameunscierititico At most he may w:l.sh to saytllat the

man who continues to resist after his whole profession has been converted

｢｡ｬｬＺｬＮｰｳｯｾ＠ ceased tabea scientist. H

XII. Progress through Revolutions

[This section has as yet received much less attention than any of

those which precede. It still seems to me far from rig,.'1t, particularly

in its later pages, and I plan a complete revision for the final version.

But other ｯ｢ｬｩｾｴｩｯｮｳ＠ are now pressing, and I must therefore postpone

further work on the manuscript until the summer. Since I ｨｾｾ＠ at that

time also to complete the other (p?'Ssumably less dras-;;ic) l-evisions that

will ｾ＠ needed before publication, I have decided not to delay further

but to ask for reactions to the draft in its present form. Though they

may be unrecognizable in the final version, the pages which :follow should

at least indicate the main directions in which the conclusion to that ver-

sion will proceed.

I am by no means clear about all the revisions that will be needed.

Many will be stylistic and organizationa.l. In addition, though it will

remain a sketch, the discussion must be expanded at several points. The

"special" cha.ra.cter of the authority exercised by the scientific CO!JllliUO-

ity must be considered in more detail. Also, the parallelism between

progress-through-normal-science and ーｲｯｧｲ･ｳｳＭｴｨｲｯｾｧｨＭｲ･ｶｯｬｵｴｩｯｮｳ＠ must be

made more apparent. (In the eyes of the profession, what else but prog-

ress could the outcome of a successful revolution have been?) Fil":.ally,

the subject of truth-by-ukalle need6 both fu.ller and more t<)1!lp3rate tree.t-

ment. Doub-Uess still other paints \,1.11 emerge wen I face up to this

part of the job.]

l"c.e preced:l.ng pages =y my 8chelretic descriptio;; of.' ｳｴｾＵ｟･ｴＺｴｩｦｩ｣＠ de-

ｶ･ｬｯｰｾｮｴ＠ as far as it here can go. Nevertheless, they cannot quite cou-

clude this monograph. If my c.eilcription seems at all to catch the essentl_a:'

166

structure of· a science's development. it will inevitably also seem to pOOl>

a specialllroblem: .Why ｳｨｯｾ､＠ the. outcome of the process sketched above

ＮＡＩｬｴｳｾｩ･ｮｬＺＡｬｬｳＧｉｉｉｌｬ｡［ｬＱ＿ＡＧ＠ i:t;Y,0:L:. $l"8J1:t;illg thllt ｴｨｾｰ［ｴＧＨＩ｣･ｳｳｩｂ＠ .sCience. how

C&n .. theente;t'prise's apparent cumulativeness. be reconciled with the funda-ｾＬ＠ ｾ｟Ｇ＠ ____ w Ｎ｟Ｌｾ＠ ｟［Ｂｾ＠ ｾ［＠ ＬＬｾ｟ＧＬ＠ ｾ＠ __ , ｾＮＢＬ｟ＢＢＬｾ＠ ＧｾＬ｟ｾＬＬｾ｟＠ ＬＬ｟ｾ｟＠ ＬＧＮｾ＠ v., ｟ＢＮＬｾＮＬＬＬ＠ .,

. mental roleplayed b9l'evoiutloUSiU. its develoPtJH:tltY. IihY. it. there is no

｣ｏｬｬｱｬｾ･ｴ･＠ set of rules for scientific behavior and no fixed .mode for scien-

tific verification. ,should science seem to move ahlllsd as •. say, art. philos- i

ophY,· or theology doellnot'l These questions pose what,! shall call the

problem of progress in the sciences.

. TIro things IllUst at once be said about it •.. First, sCien,ce undoubtedly

dOes progress in ways which. 1f not different in kind, are at least vastly

more apparent than the progress Visible in other creative. pursuits. Sec-

ond,. there ought no longer be. a problem about why this is so. What but .' "--, ".-; "'--- ,- - , '"

ｊｄ｡ｬＧｬＱＬｾｾｳｴ＠ ｾｲｯｻｩＹＺＧ･ｳｳ＠ cQUld ＰｬｬＮ･ｾＷ｣Ｚｴ＠ from ,tile, ｳｯｾＮＨＩｦＬ･ｬＱｴ･ｲｰｲｩｳ･､＼Ｚｬｬ｣ｲｩ｢･､＠ in

.the .preceding· .pages? This is not to say, that the view ... of science here de-

veloped presents no, problem, but only that it presents no, special one. One

may ask,.as ｩｮ､･ｾＬ､Ｎｷ･ｳ｢｡ｬｬＬ＠ questions like Ｌｴｨｾ＠ follcming: Rev can there·

b.E!suClllltllinglls.llcleJlcE!t.What !Jl1l,st nat urE!' including man, be like in

order that Ｌｳ｣ｩ･ｮｾ＠ beposllible at allY Furthermore, though we shall ask

those questions. we shall n()t even begin to BUggest an anmrer. Those

questions will remain as open as they were before. They are not, ho;7ever,

questionsposedl>Y any special features of this monogl"aph. Any other viell

of science necessarily raises them too. Let me, theTefore, try to shmf

that they are .. the only questions. If nature permits the e::istence of the'

sort of enterprise ､･ｳ｣ｲＱ｢ｾ､＠ in these pages, then, wh:i.le it E'.xists and euc-

ceeds, that enterprise cannot help but make prOgreBs. We shall Bee this

168

i1' we learn to accept as cauaea lmat have ordinarily been taken to be ef-

fects. With that inversion the phrases "scientific progl'ess" and even

"scientific obJectivity" may come to seem redundancies.

What aspects of the scientific enterprise make for progress? There

are, I think, several, all rooted in the nature of the particular proi'ea-

sional groups that the evolution of mature science permits. After the

pre-paradigm period and except briefly during revolutioca, a scientific

group yorka at any given time from a single paradigm or front a closely

related set. Very rarelY are two different schools to be found working

on the same problema, and in those few exceptional CBaes the competing

schools always share several major paradigms. Viewed from within any

single school, however, whether scientific or nonscientific. the result

of successful creative work is progress. HO""" could it poss:!.bly be any-

thing else?

The artist, for ｾｬ･Ｌ＠ who extends the technique accessible to his

school or who applies its ex1sting body of technique to a new subject in-

evitably contributes to the progress of his group. In fact, as Gombrich

has brilliantly shown, throughout classical antiquity and again in early

modern t1!lles, painting and sculpture were ｾ＠ cumulative disciplines.

Critics and historians, including both Pliny and Vasa\'1, recorded ;lith

veneration the series of inventions 'from foreshortening thl'ough chiaro-

scuro that had made possible successively more perfect representations of

nature. other creative fields display progress of the sa.me sort. The

theologian ｾｾｯ＠ articulates dogma or the rhiloaqpher who refines the ｋ｡ｮｴｩｾ＠

ｾ･ｲ｡ｴｩｶ･･＠ contributes to progress if only to the progress of those ｾｨｯ＠

share hie premises. No creative school has, I think, ever recognized a

category of workl!h1ch ｷ｡ｳｾ＠ on the one hand,a creat1ve ·succesebut which

was ｮｯｴｾ＠ Oll.theother, a contribution to ,the progrees of' the group. If

we ､ｯｵ｢ｴｾ＠ ＮｬｬｳＧＡＡＮｄＮﾥｾｯＬｾ｟ｾｊ［ｮｯＺＺｷｾｾｾｮｴｩｾＡｾｦＧｾ･ｊＬ｣Ａｬｬ｟ｬｬｊＢｬ＼･Ｎ＠ progJ:'ess, .. that cannot

be because .. individual schools make .. nOml..Ratheritmuat.be., because there

ｾＭＭＭＭＭＭＭＧＭＭｉｉｕＧＡｬｦｴ･ｴＭＭ｡｡ｬ［｢ｷ｡ｾ＠ cempe-'Iling-sehoele each. of-,which constsntlJ .qnestlons I;he liel'Y

foundations .of .the others. The man'llhoSl"gllEls .thatphiloso,phy,for exam-

ple, .hes .. made. no ｰｲｾｳｳ＠ emphasizelilthat there .arestill.4ristotelians,

not that. Ar1stotel1a,n1sm hal! ｾ｡ｩｬ･､＠ ,\;opl·ogress.

But those doubts about progress ariaein the ,sciences too. Through-

out the ーｲ･ＭｰＸＱＧＡＱ､ｩｧｭＮｰ･ｲＱｯ､ＬＮｷｨｾＮｴｨ･ｬＧ･＠ are a multiplicity of· competing

schools. evidence Of prOgress, exCePt ＧｉｉＧＱｴｨＱｮＮｳｾｨｯｯｊＬｳＬ＠ is very bard to find.

This istheperlod, as Isuggestedin.SectionII,:in·vlhich iudividuals

practice science but in 'll'hich the. result of''\'heir ente%'prise does not add

up to sclence as we know 1t. And again, during perlods of revolution when

.. the .. f)'ndameTltal .•. :tenets. of'.lIt •• fleld.are .•... OllCe.more .. '. at .... issue, 40ubts are re-

peatedly.expressed.about the verypossibllit;rof continued. pl"ogreas if' the

p8ra,digmopposed by.the ｭ｡ｮｬｬＱＧ･｡ｫｩｮｧＮｩｳｩ｡､ｯｰｴ･ｾＮｔｨ＿ｾ･＠ who. 0llPosed Newton,

ｦｾ･ｾｊＬ･ＬｰｲＨＩ｣ｊＬ｡Ｑｬｄ･｣ＩＬＮｾｾｾ＠ 1:l:1s ｾＱＺ･ｾｯｲｃＺｅＡＮＱｩＨＩ｜ｬｬｾｬＧ･Ｑ［ｾｳ｣ｩ･ｮＮ｣･＠ to tt.-e

... Dark Ages. Thosel!ho ｣ＺＺｰｰｯｳ･､ｉ｡ｶｏｩｳｩ･ｲＧｳ｣ｨ･ｭｩｾｴｲｹ＠ held that the rejec-

tion of' chemical "princ1ples" .1n favor of' laboratory elemnts '!laS ｴｨｾ＠ re-

jection of achieved chemicalexplanatlon by those wnowould take refuge , . '" . :,'.. .

in a mere name •. A similar, ｴｨｯｾｭｏｬＧ･＠ moderately expressed, feeling that

1tmust end scientific· progress seems to underlie. the c::pposit1Oll of Ein-

stein, .Boehm, and others to .thedominent pr()babitlstic. interpretation of

quantum mechanics. In short, 1t is only during perioos of nomal science

that progress seems.both obvious and assured •. During those periods,

170

however, the scientific cOmmunity could view the fr-l1its of its work in no

-other way.

So far I must seem to be saying that progress is in the eye of the be-

holder and that science seems to progress only because there is ordinarily

no competitor to the scientific community's view of its task. Indeed, ｴｨ｡ｾ＠

must be part of the answer to the problem of progress. Our sense of the

uniqueness of sCientific progress does result from appearance alone. There

is progress in other disciplines though the multiplicity of schools makes

it harder to see. But that is only eo part of the answer and by no means

the most important part. I have, for example, already suggested that, once

the reception of a cammon paradigm frees the scientific community from the

need constantly to reexamine its first principles, the scientific community

can concentrate exclusively upon the subtlest and most esoteric of the phe-

nomena that concern it. Inevitably that does increase ｢ｯｾｾ＠ the effective-

ness and the efficiency with which it solves new problems. O'"...her aspects

of professional scientific life enhance this efficiency still further.

Some of these result fram what I can only call the ul1pl:'ecedenteo. in-

sulation of the scientific community from the demands of the laity and of

everyday life. Obviously that insulation has never been neal'ly complete,

and, even more obviously. it has broken down further since World War II,

possibly with resulting dangers for science. Nevertheless, even today

there is no other community in which individual creative vork is eo exclu-

sively addressed to and ･ｾ｣ｌｌｵ｡ｴ･､＠ by other memoera of the profession. The

most esoteric of poets 01' the most abstract of theologi&ns iu far more

concerned than the scientist mth lay approbation of !lin erective work

though he may be even less concerned with approbation in general. The

171

diffeI'ence proves' conseilucnUal;JUs1fceca.usehe 'is 'Work1ilgonly for an

audience of colleagues, an audience, that is, which shares hlsOW:tJ. st8nd-

, ards,.,the"scientistcan.talte a single' set ofstands.rd.sfor granted.. He

ｮ･ｾＧＬｮｯｴｷｯｲｲｹ＠ 'abou,1:l1hatsClIIIe othersr:OilP'"orschoolwiU .thinltand can

" theretore diepose of' one. problem and' set on. to the next more quickly than

those who workforca 'more ｨ･ｴ･ｲｯ､ｯｸｧｲｏｬｩＺｰｾ＠ , Even mOl'e'1mportant and ho-.r-

'eVer:incomplete ,theinsulation ｾｯＺｦｴｨ･ｳ｣ｩ･ｮｴｩｦｩ｣Ｂ｣ｏＡｬｬｬｬＡｕｉｬｩ＠ ty from society

permits the 1nd.1V1dualbasic scientist to concentrate his attention upon

problems that' he hils go,od reason to be110'1ehe will be able to solve. Un-

like the, engineer, many doctors, and 'most theologians ,the sCientist need

not choose problems because they ursently Ileed solution and inapparent

'disregard' of the' tOQls'ths:t:hehas:at','hand'withwhichto'·'solvethem. In

.. tb1s respect Iblive myself found the contrast between physlcietsand IIl9.!lY

social sc1entists particuJ.arlyinstructive. 'Many of the latter tend, as

the>:f'ormer.almoet'never'dof to' defend their choice ofa research' problem--

e.s., the effects ·()f raciSldiscr1m1nationor the causes of the business

, ,cycle--chiefly'intepms of.the;.s'Ocialimportance of achieving a solution.

Which .group wciuldone.thenex,pectto solve problems at a more rapid rate?

'.rhe effects of insulation from ,the larsersoclety are sr:eatly inten-

sified by another characteristic of the professional scientific community,

the nature 'of:,lts educational ｩｬｬＱｴｩ｡ｴｩｯｮｾ＠ In muSiC, the graphic arts, and

literature the pra.ctitioner; gains his education by exposure to the works

of other artists, principa.llyearlierartists. Textbook!), e:c:ept com-

pendia of orhand.bool\:'sto originalcreatiOlls, have only & secondaloy role.

InhiS'i;ory, philosophY, and. the social sciences tex'cbook litez'a"l:;u-""e has e

greater significance. ',But in these fields even the elementary college

172

course employs parallel readings in original sources, sorne of them the

"classics" of the field, others the contemporary reBearch reports tha.t

practitioners write for each other. As a result the student in any one

of these fields is constantly made aware of the immense var1ety"of prob-

lems which the members of his future group have, in the COurll6 of time,

attempted: to solve. Even more important, he has constantly before him a

number of competing and incommensurable solutions to these problems, so-

lutions which he muet ultimately evaluate for himself.

Contrast this situation '!lith that in at least the contemporary nat-

ural sciences. In these fields the student relies mainly on textbooks

until, in his third or fourth year of graduate work, he begins his cnm

research. Many science curricula do not even ask graduate students to

read in works not written speCially for students. The few that do assign

supplementary reading in research papers and. monographs restr:!.ct such as-

Signments to the most advanced COUl"SeS and to materials that take up more

or less where the available texts leave 01'1'. until the very last stages

in the education of a scientist textbooks are systematically 8ubstit"u:ted

for the creative scientific literature that made them possible. Given

their coxi1'idence in the paradigms vhich make this educational technique

possible, few scientists would w"ish to change it. Why, after all, should

the student of, say, physics read the works of Nel.'ton, Faraday, Einstein,

or Schrtldinger when everything he needs to know about these works is re-

capitulated in a far briefer, more preciee, and more systematiC form in

a number of up-to-date textbooks.

Hithout '!Iishing to defend the excessive lengths to u:J.ich this ｴｾ＠

of education has occasionally been carried, ua cannot help ｢Ｌｾｯ＠ notina in

173

general it has been immensely effective. Of . course it ill a narrow and

rigid education, pr0llably more se ,than ｾ＠ other exceptparbs.ps in Ol"thO-

dox ｴｬｬｅＺｯｬｯｧｹｾＬｂｵｴ＠ fOf ｮ＿ｾｬ＠ ｳｃＱＬｦＳｬｬｴｩＡｴｾ＠ wC)rk •.. for. puz:;;le..;solving ｾＧｩｴｨｩｮ＠

the tradition. that the textb()Okll define, the scientist ia .. a.most. perfectly

ＭＭｾＭＭＭＭＮＭ･＼･ｧｵｩｰｰ･､Ｎ＠ Ji!w.othel'lll9l'e, he 1s well equipl'lld for .anotiteI!;ask as llell, the

generation through normal. science of significant crises. Wnen.a crisis

arises, the scientill1;.is no1;.ofcourse,. so well. equipped. Even though

prolonged crises are probably rei'le.cted .in. ,less rigid e.ducationaJ. practice,

.. scientific ｴｲ｡ｩｾ＠ is n01; well designed. to produce the. man who will easily

､ｾｦｩｬ｣ｯｶ･ｲ＠ afl'l!shapp,;ODach',But so :j.onSa.1I sOlllebody appearawitha new

candidate for ｰ｡ｬＧ｡､ｩｧｭｾＭｵｂｕｉｩｬｬｹＮ＠ a youngman. or one new to the i'ield--the " ' , , ' ',;' ',- -,' '" ,,' -

10Slil due to. rigidity accrues onlyto.theindiv1dual. Given a generation

in which to effect . the change, individual rigidity is . compatible with e. , _',,, .>_ :. ',.' Co .:. -" "

cOllllllUIlity that ,can switch from paradigm to paradigm when the occaSion de-

mands •. PartiC\1la1."ly .i.t 1.s. cCl!Dpa;i;illle.1lP./iln that .. very rigidity provides the

cOllllllUIlity wi.th a sensitive indicator.tha"t; something haagone In-Ollg.

So far we ｾｶ･＠ seemed to,cOlls1der only those.characteristics of the

scientific group which make for rapid and cumulative. progress within a _ ,-," __ "', _ _ __ __ ＬＮｾＧＭ __ ｊｾ＠ "" __ ｾ｟ＢＧＮ｟ＬＬＬ＠ ,._ ._,>."'.',,''', "._,"" __ ,',, _.,_". __ .". ..

nOl'll!f;].. scientific ｴｲ｡､ｩｴｩｯｮｾＬ＠ But ',hese same characteristics make for a

rather different sort of progress across scientific revolutions as well.

In part ase.if"l;he.t progress in only appearance. RevolutiOns are not (In-

tirely cumulative. Like revolutions in. pOlitical life, theology, and ar--- '-'-" -,>' , -- , " .

tistic taste, they involve loss as well as gain, but in the sciences this

loss is largely hidden by the ｴ･ｸｴ｢ｰｯｾ＠ reconstruction 0t hill "cory tbs.t fol-

lows each revolution. But revolutions are never a· total ｢ｾ｡ｫ＠ with ,the

past. In all ｦＱ･ｬ､ｾ＠ some part of past achievemen'c is carried over, and

(

174

the nature of the scientific community ensures that ecieutieta will =y

over more of past achievement ｴｾｾ＠ practitioners of other fields are

l1kely to do. Everything said so far should indicate that the sCientist,

trained to l(Ork within a single normal-scientific tradition, will have a

far clearer and more stubborn conception of the number and nature of his

field's achievements than will his colleague in a nonscientific field.

That being the case, he will be harder to move, less likely to find an al-

ternate paradigm attractive for reasons irrelevant to his field. In par-

ticular, though the individual scientist may, his C=nity is unlikely to

undergo a paradigm shift unless two conditions are met. F:I.rst, the new

paradigm must seem to resolve aome problems that can be resolved in no

other knO".m way. Second, the new paradigm lIr.lst ;prese:rve a releti vely

large amount of the problem-solving ability which had accrued to science

through its predecessor. Though new paradigms seldom or never do every-

thing that their predecessors could do, they usually preserve a good deal

of that paat achievement and permit more besides.

I am not at all sure that there is more to be said about :progress in

the sciences. Given the sort of professional community described in thl<l

earlier sections of this monograph, science could not help but progress.

Yet I am also sure that most readers will find ,one element missing and

another distasteful in this account. let me discuss these tHO in order

and then conclude with a brief ｲ･ｄｙｾｫ＠ on the question that remains for

someone else to ask. The missing element is, I take it, aciEintific truth.

Tae process described as science ｾｬ＠ this monograph is a process of evolu-

tion ｾ＠ primitive beginningS tward an increasingly detailed aIla. re,?illecl

understanding of nature. But nothing that has here been said makes it a

175

- process ｾ＠ of evolution. towards •. -This isalmost-,inevi tablytroubleeome (cer-

tainly it has been so to me) .because weare"iieeply accustomed toseeiDg

ｳｾｩ･ｮ｣･＠ as the ｯｾ＠ ＡＡｮｾ･ＱＱ＾ｾ［ｳ･ＬｷＺｾ＠ ｣［ｨＮｬｩｬＺｬｬｷｾｃ［ＨＩｉｬｉｬＱ［ｳＮｮｴｬｹ＠ neare,r. to 1 ts goal

whether.or n01;that goal is ever to : ｢･ｬｬ｣ｨｩ･ｾ､Ｎ＠ In ,some e.ensewhich we

-------,afalrel'lt-Wwi'iollH1l1ng-te let the ph1lesophel' Ｌ｟ｾ･Ｌ＠ we are sure ｴｨ･Ｎｴｾｵ｣ＢＧＭＭＭＭﾭ

cessive stage of scientif;cknO\lledge.is.more nesrlytrue or more probably

true. or dmply closer. ｴＬｯＬｾｨ･＠ ,truth tbantheonebefore •. Almost every form

of our usual 1magemakestruth the goal toward 'Which science strives and

with respect. towh1ch,its success must be. measured.

:But need there .b.e any suchgoal'l . Will not evolutioD from .do just as ,', ＮｾＢ＠ .C._"" __ ' "",','-, _

Vellas evolution toWards?, ,If it will,:l.tsurelycreates fewer problems.

Thesequestions,it ｳｨｯｵｬ､ｮｯｷ｢･ｮｯｾ､Ｌ＠ a;re,very .lilteones asked just a

century ago in a rather different. connection,and it may be 'Chat we need

to make. the same about-face that ｷ｡ｳｾ､･＠ then. By the. middle of the last

. century many studen,ts Qfbiology andgeo},oSY1fere .collvinced that the spe-, - " " - - , _" _,._ ,,, "',, ,,"" ｾＮ＠ _'" - ._' '" ,'. ,," , " ' - 0",' ,,'_': '. __ " , , ' ,," "

cies of flora and ｦ｡ｾＬ｣ｨ｡ｲ｡｣ｴ･ｲｩｳｴＱ｣＠ of the globe in the nineteenth cen-

tury had evolved from a, smaller Ilumber of more primitive forms most of , ' ＢＧＢＧＧｾＧＧＧ＠ ,".,,, ,', .-'_ c. ,'" "> __ c ' , ".

which bad since ceased .to exist. But they saw nowsy to explaill this evo->' -,' ',' _,-.,_,'" ' ""/. ,'0' .: ＺＺＬＢＬＧＬＺＭｾＧＺＭＬ＠ ,:"'.,-, _ ,;._", , ＺｾＢＢ＠ • _' __ ,.',

. lution.wi thout supposing that ｴｨ･Ｎｲｾ＠ had ｢ｾ･ｮＮ＼ｦｲｑｬｬｬ＠ ｴｨｾ＠ ｢ｾｧｩｮｮｩｮｧ＠ some form ,',,', ,,,' ,; -'.... ,',;' - .

or plan toward. 'Which more primitive species bad striven. as their goal or

end. ｓｩｮ｣ｾ＠ teleological explanations ｯｾ＠ that sort were anathema to most

segments of the nineteenth, century scientific community, the few men ,,:ho

expressed this evolutionary, view usre ,not, taken so seriously as they might

now be. In 1859 that. ｳｩｴｵｾｴｩｯｮ＠ <:han!Z;!!dfor a.n\llliber of reasoDeamong

which the most important was the,simultaneouB announcement by De.l·Hin and

ｾｬｬ｡｣･＠ thatevolut10n to existing forms and on beyond them could be

understood without recourse to a plan or goal laid dew at the start, per-

baps in the mind of God. Natural selection, survival of the fittest, would.

produce the same results including such marvelously adapted organs as the

eye and hand of man, organs which had previously provided immensely powerful

arguments for the existence of a Supreme Artificer.

Only this use of the analogy to natural selection is my own, and even

I do not want to insist upon its applicability in detail. Nevertheless, in

important respects the analogy is extremely close. The process described

in Section XI as the resolution of revolutions is the selection by conflict

within the scientific community of the fittest way to practice future

science. The net result of a sequence of such revolutionary selections,

separated by periods of normal research, is the wonderfully adapted instru-

ment we call modern scientific knowledge. And the entire process may bave

occurred, as ve now suppose biological evolution did, without the benefit

of a set goal, a permanently fixed scientific truth, of which each succes-

sive stage of scientific development was a better exemplar.

Reference to Darwin also serves more effectively to raise the specter

tbat I anticipate many readers of this monograph will find distastefUl.

The animals which survived natural selection were those llhich, partly by

"tooth and claw" and partly by superior fertility crowded cut their neigh-

bors. By the same token, when I say that paradigm selection is settled by

argument among SCientists, I may seem to be eaying that in the SCiences,

too, might makes right. I bave, in fact, been told that on my view of

science Hitler would have been right if only he had succeeded in subjugat-

ing the world.

177

Two things seem Joo· me to. be wrong with that interpretation.. First,

if' we can dispense with. "truth" when describing scientific development, we.

can dispense with "right" as .well .• ' I have surely said. no more than that

the paradigm which wine will be the new :PSI'E1dtgni. '!be obJection must at

ｾＭＭＭＭＭ｟ｬｊＮ･･｡ｳｴＭ｢･＠ rephrased. But it can be,ana then its ＺｦＧｯｾｾ［ｙＧｦＭＧＭＭＭＭﾭ

seem to have ... sa1d:tlJ.at .i.t .. makes no ､ｩＺＱＧｦＧ･ｾｮ｣･＠ .• ｨｯｷ｡ｰｾｧｵｭ･ｮｴ＠ among scien-

tists. is settled, that.H1tler,torexample, could .. have .. beenallowed to

Ｎｳ･ｴｴｬ･ｴｨ･ｭＮｾﾷ＠ '!'hat, 'ot course.would·betotally,absurd',:The.continued ex-

istence of science depends upon the continued existence. of avery special

sort of COmmunity, one. that, among other. things, is committad to solving

problems about nature and knows very .ve:j.l wllatproblems it hass.olved •

. ' When .... ｡ｾｴｨｯＮＬｴＧｩｴｹ［ＮｾｬＬｯｮ･ＮＬﾷ＠ ｡ｮ､ｰ｡ｲｪ［ｩ｣ｵｾｬｹＮｮｯｾＺｴＧｯｦｅｬＮＡＡｳＮＺｌｯＮｮｳｬ｡ｵｴｨｯｲｩｴｹＬ＠ is the

arbiter·of·parad1gm·'·debatestheprocess·Wiii!iBye.ceaaed.·1;obe science ｾ＠Just how special the community has to be··if'· . science is to survive and grow

may be indicated by the very tenuousness ot ｨｾｴｹＧｳ＠ hold on the enter-

prise •. Every civilization of whi.ch we hf\ve any l'ecordsat.sllhas POB-

sesseds technology" an art, arel1gion, a. political .. system, laws, and eo

on. In ｾ＠ case!!. those.:f'acets of Civilization hI!,:ve been. as developed as

our own. But only the Civilizations which.descend from}Iellenic Greece

have possessed more than., the most rudimentary science. ·The overwhelming

majority of sCienti:f'icknowledge is a product of .. Europe and of the last

three centuries. What ｣ｨｾ｣ｴ･ｲｩｳｴｩ｣ｳ＠ ｯｦｭｯ､･ｲｾ＠ Euro.PSan society have

made it uniquely able to support a scientific community is e. problem be-

yond the scope of this monograph. But recognizing that sciencehi<.s been

vastly more localized in space and time than any othel"human creative pur-

suit may help to persuade us of the special nature of the community that

produces it.

178

Is there any other question? Obviously there is--the one from which

this section began. What must nature, including man, be like in order

that science be possible at all? Why should the scientific community be

able to reach a firm consensus unattainable in other fields? '!hy should

consensus endure across paradigm-change after paradigm change? And 'Why

should the result of paradigm-change Within the scientific community be

progress? From one point of View those questions, excepting the first,

have already been answered. But from another they are as open as they

were before. It is not only the scientific community which muet be spe-

Cial. The nature of which that community is a part must also possess

quite special characteristics, and we are no closer to lmowing what they

must be. That, however, is not this monograph's problem. Instead it be-

longs to the sciences themselves or to metaphysics. At this point we re-

quire only one remark about it. Any conception of nature which is com-

patible with the growth of science by proof is compatible with the evolu-

tionary conception of science developed here. The problem of Dature is

made no more difficult by any contention advanced in this mOllogl·aph. On

the contrary, the problem of nature may be made easier. For the looser

conception of science here ､･ｶ･ｬｯｰｾ､＠ may be compatible with a conception

of nature that will not provide a base for science through proof'. That

possibility of greater freedom combined \T.lth its vastly greater verisimil-

itude proVides strong reasone for supposing that science is the cart of

enterprise which this. monograph takes it to be.