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  • 8/3/2019 Popper Conjectures&Refutations

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    CONJECTURES.AND REFUTATIONSThe Growth of Scientific Knowledge

    byKARL R. POPPER

    ~ARPER T!RCHBOOKSiHarper &R ow , Publishers .N ew Y ork an d E van sto n

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    Th.ere cou ld be no fairer destiny for any . theory than that it should~o~~ the w ay to a m ore co mp reh en siv e th eo ry in w hich it l iv es o n as aIimiting' case. ;ALBERT EINSTEIN iI!,i

    iI

    1SCIENCE: CONJECTURES AND

    REFUTATIONSMr. Tumbullhad predicted evi lecnsequeacee, andwas now doing the best in his power to br ing abou tt he v e ri fi ca ti on o f h is own p ro p he ci es .

    ANTHONY TROLLOP!!

    IWHEN I r ec ei ve d t he l is t o f p ar tic ip an ts in th is c ou rs e a nd re aliz ed th at I h adbeen asked to speak to philosophical colleagues I thought. after som eh esitatio n a nd co ns ultatio n. th at y ou w ou ld p ro bab ly p refer m e to speaka bo ut th os e p ro ble ms w hic h in te re st m e m os t. a nd a bo ut th os e d ev elo pm en ts. with w hic h I a m m os t in tim ate ly a cq ua in te d. I th er ef ore d ec id ed to do w hat Ihave never done before: to g ive you a report on m y own wor k in th e p hilo -s op hy o f s cie nc e. s in ce th e a utu mn o f 1919 whe n! f irs t b eg an to g ra pp le w itht he p r ob lem . 'W hen sh ou ld a th eo ry b e ra nk ed a s sc ien tific r or 'Is there ac ri te ri on f or t he s ci en ti fi c c ha ra ct er o r s ta tu s o f a th eo ry i"T he p ro blem w hich tro ub led m e at th e tim e w as n eith er. 'W hen is a th eo rytrue?' nor, 'W hen is a the ory accep tab le" M y p ro blem w as d ifi'ere nt:..,I-wi, r uti n is h b et we en s cie nc e a nd s eu do -s cie nf .! knowing very wellt ha t s cie nc e o ft en e rr s. a nd tb at p se ud o- sc ie nc e m a y ppen to s tu mb le o n th e t"truth.I knew , of course, the most w ide! acce t to my problem : that'-scie nc e is < lis t' 's e a r m seudo-science-or from 'meta h sics'-b its

    ~~11Jiirlcalmethod. which is essentially inductlYe. proceed ing {[om,obse !'Va ti o~or ex rim ent. But this d id n ot s at is fy m e . On t he c on tr ar y. I o ft en f ormu la te dm y p ro ble m a s o ne o f d is tin gu is hin g b etw ee n a g en uin ely e mp ir ic al m eth odand a non-em pirical or even a pseudo-em plrieal m ethod-that is to say. ame thod wh ic h . a lt hough itappeals to ob se rv a ti on a nd e xpe rimen t. n e ve rt he le s sA l e cl u re g i ven lit Pe te r h (1USe ,Cambr i dg e . i n Summer 195J. as part of a course ondevelopments an d t r end s i n c cn t empo ra ry B r it is hph i l o sophy . o r gan i ze d by t h eB r i t is h Counci l:omi!!QUv publJs1u:d uutle.r t I u ! tfrlL ' I?ttlhsephn 1 . Science: a Personal Reert' In British' P h i l O s o p h y InMid-Century. ed . C . A. M ace. ~s . I33

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    CONJECTURESd oe s n ot c om e u p to s cie ntif ic s ta nd ard s. T he la tte r m eth od m ay b e e xe mp li-fied b y as tro lo gy , w ith its stu pe nd ou s m ass o f em pirical ev id en ce b ased o no bs er va tio n- on h or os co pe s a nd o n b io gr ap hie s.B ut as it w as n ot th e e xa mp le o f a str olo gy which led m e to m y p ro blem Is ho uld p erh ap s b riefly de scrib e th e atm osp here in w hich m y pro blem a ro se .and the examples by w hich it w as stim ulated. A fter the collapse of theA us tria n Emp ir e th ere h ad b ee n a r ev olu tio n in Aus tr ia : t he air w as fu ll o fr evo lu ti on a ry s lo g an s a nd i de as .J !D . d. p. ~wand o f te n w i ld t he o ri es . Among t het he or ie s wh ic h i nt er es te d m e. a~ J! 1~ t~m 1J l! ~0 }X .2 .f r ela tt ti ty w a s n o d ou bt~Y_f~!he most important. ~ers were~~f history,

    CFreuditP~~~.and ~fre J\~ler.~s.9 .~l~~vidual psy~hology'.~ was a lot of popular nonsense d about these theories, and especi-a ll y a bo ut r el at iv it y ( as s ti ll h ap pe ns e ve n t od ay ), b ut Iwas fort unat e in thosew ho introduced m e to the study of this theory. W e all-the sm all circle ofs tu de nts to w hic h I e lo ng ed -w ere th rille d w ith . t he r es ult o f E dd in gto n'se cl ip se o bs er va ti on s wh ic h in 1 9 19 b ro ug h t t he f ir st i mp or ta nt c on fi rm a ti on o fE in st ei n' s t he or y o f g ra vit at io n. It w as a g reat experience for us, and -onewh ic h h a d a l as ti ng i nf lu e nc e on my In te ll ec tu a ld e ve lc pmen t,T he th ree o th er th eo rie s Ih av e m entio ned w ere a ls o w id ely d iscu ssedamo ng s tu de nt s a t t ha t t im e . rmy se lf h ap pe ne d t o c om e in to p er so na l c on ta ctw ith A lfr ed A dle r, a nd e ve n to c o-o pe ra te w ith him in h is s oc ia l w or k a mo ngth e c hild re n a nd y ou ng p eo ple in th e w ork in g-c la ss d is tr ic ts o f V ie nn a w he reh e h ad e sta bl is he d s oc ia l g u id an ce c li ni cs ,It w as d urin g th e s um mer o f 1 91 9 t hat I b eg an to feel m ore an d m ore d is -satisfied w ith th es e th ree th eo ries -th e M arx ist theo ry o f h isto ry , ps ych o-a na ly si s, a nd i nd iv id ua l p sy ch ol og y ; ; ;_ ndr began to . fe e l dub iQ~l l, ! l2 . 1 !1 !Qe i ! :.cla jm .~.to scienti!i~s~M y problem perhaps first took the sim ple form , _ .'W ha t is w ro ng w ith Marxism, p syc ho- an a ly s is , a n d i nd iv id u al p syc hol ogy?W h y a re th ey s o d iff er en t f ro m p hy sic al th eo rie s, f ro m N ew to n's th eo ry , a nde spe ci al ly f rom t he t he o ry o f r el at iv it y? 'T o m ak e th is co ntras t clear r sh ould ex plain tha t few o f u s _at th e tim e\wo ul d h av e s ai d t ha t w e b el ie ve d in th e truth ofE ins te i ii s t heor . y of g ravi ta -tion. T his show s that it w as not m y doubtm g the. truth o( tbO~MJl the r t h reeth eo rie s w hich bo th ered m e, b ut so meth in g e ls e. Y et n eith er w as itha t I______ .oT_~. c~~.~~, _ _ - , . . ." '1 . .. . . . .. _ . . ~me re ly f elt m a th em at ic al p hy si cs t o b e l ll or ~.! ~a ql ,J ha .p ,J h~ ~9 ~ 01 0 gi ca l o r Jp sy ch olo g ic al t yp eo ftl ie orY. T hu s wh at wo rr ie d m e wa s n eit he r t he p ro bl emo f t ru th . a t th at s ta ge a t le as t, n or th e p ro ble m o f e xa ctn es s o r m ea su ra bility .It w as rath er th at I e lt tha t th ese o the r th re e th eo ries, tho ug h p osin g assc iences . had inf ac t m or e in c omm on w ith p rim itiv e m yth s th an with science;that they resembled astrology rather than astronomy.. .Iound that those of m y friends w ho w ere adm irers of M arx, F reud, andA dler. w ere im pressed by a num ber of points com mon. to these theories,

    ~N l a nd e sp ec ia ll y b y~~~zm...e:planatory pow", ' 1 : ' h es e theoriesappearedr f . l . t o b e a b le t o e xpl am_p ra ct ic ;a .. Jl y. ev e ry th in g t h at h a pp e ne d wi th in t he f ie ld s t o~ w hich th ey referred. T he stu dy o f a ny o f th em s eem ed to h av e the effect of an. 34

    i'(II!

    ,,';

    1 SCIENCE: CONJECTURES AND REFUTATIONSi nt el le ct ua l c on ve rs io n o r r ev el at io n, o pe nin g y ou r e ye s t o a n ew t ru th h id de nf ro n: t h? se n ot y et in it ia te d. Q!~ Io ur ey es w ere th us o pen ed y ou s aw C O D , , -J i r . m i ! l mstances eve here: the world sf 1 of veri cationsof the theo '._ . tSX~- . . .. .22ened a lways co~ .i t&: ..Thus j ts t ru thap~r~(Lm,a "h_~~~;_1tt;d tl!':~ellev_e:rs_:wer~>clearly,peqple_y.:ho:}!ig.~~t ..~~t_.!~~_s_~~_h~ .1Il~nif~t.Ttt~;,~p1?~efu~.e_!l, ,~9.$V!d~l~~..!'~E.~.titIDl.!.~j!linsJ_their c13UJ~r.I?~,._orQ~use.o ft hei r_ repr .e ss ions ..wh ich were s l il l~un-ana ly 'S(l 4 ', ? tl ( :t e ry ing a loudfor treatment. . ,' ' ' T h e m o s i c ha ra ct er is ti c e lem en t in t hi s s it ua ti on s eeme d t o m e t he i nc es sa ntstream of co nfirm atio ns , o f o bserv atio ns w hich 'v erified ' th e theo ries inq uestio n; an d this po in t w as co ns tan tly em ph asized b y th eir ad heren ts. AM arxist could not open a new spaper w ithout finding on every pag e con.firm in g e vid en ce fo r h is in te rp re ta tio n o f h is to ry ; n ot o nly in th e n ew s, b utalso in its p re se nt ati on -wh ic h r ev ea le d th e c la ss b ia s o f th e p ap er -s -e ndesp ecially o f co urs e in w hat th e p ap er d id no t s ay . T he F re ud ia n a na ly stsemphasized that th eir th eo rie s w er e c on sta ntly v er ifie d b y th eir 'c lin ic alo bs er va ti on s' , A s f or A d le r. Iw as m uc h im pr es se d b y a pe rsona l exper ience.O nc e, in 1 91 9.Ie po rte d t o him a c as e wh ic h t o n ie d id n ot s eem p ar tic ul ar lyA dle ria n. b ut w hic h h e f ou nd n o d iff ic ulty in a na ly sin g in te rm s o f'h is th eo ryo f in feriority feelin gs, altho ug h h e h ad n ot ev en seen th e ch ild . S lig htlyshocked, Isked him h ow h e cou ld b e so su re. 'B ecau se o f my thousandfolde xp er ie nc e: h e r ep li ed ; wh er eu po n Ico uld no t h elp sa yin g: 'A nd with thisn ew c as e, Iuppo se, your e xpe ri en c e h a s b e come t hou sa nd- and -on e- fo ld :Wha t I ad in m ind w as th at h is p rev io us o bserv ation s m ay n ot h av e b eenm uc h s ou nd er th an th is n ew o ne ; that e ac h i n i ts turn h ad b ee n i nt er pr et ed i nth e lig ht o f 'p re vio us e xp er ie nc e', a nd a t th e s am e tim e c ou nte d a s a dd itio na l

    . c on fi rm a t~ on .JYha t. ~ a sk ed : uy se lf , d id it co.1 N ,Q more t ha n t ha t a , ca S f[ ue , .. _ __could be .--, e theo ,But this m eant v~ little; I, J. r ef le ct ed ; s ln ce e ve ry c on ce lv at iI e c as e lill be inte reted in the light of. er s ry, o r equ.,tlly:of reu ~. may us e s ytwo very dif-" ie re ni e xa mp le s o fliu ma n b eh llv lo ur: th at o f a m an w ho p us he s a c hild in to 'th e w ate r w Ith th e in te ntio n o f d ro wn in g it; an d th at o f a m an w ho sacrificeshis life in an attem pt to save the child. Each of these tw o cases can be ex-plained w ith equal ease in F reudian and in A dle ria n te rm s. A cc ord in g toF re ud th e fir st m an s uff er ed f ro m r ep re ss io n ( sa y. o f s om e C om po ne nt o f h isO e dip us c om p le x) , w h il e t he s ec on d m a n h ad a ch ie ve d SUbl im a ti on . A cc or d.ing to A dle r th e first m an s uffere d fro m fee lin gs o f in feriority (p rod ucin gp erha ps :h e n eed to p ro ve to h im self th at h e d ared to c om mit so me crim e),an d so did th e sec on d m an (w ho se n eed w as to p ro ve to h im self th at h e d aredt o r es cu e t he c hi ld ). Io uld n ot th in k of an y h um an b eh av io ur w hich co uldno t ~ e i nt er pr et ed m te rm s o f e ith er th eo ry .Itwa s p r ec is el y t hi s f ac t- tr u rt '" 1' ll eY ,a Iw a ysf it t~ d! th at ~ w e re a lw a ys c o: nf um ed -wh ic hi n t he e ye s o f t he iradlDlI'ers constituted the stronges~1 li;ivour of these theories. Ite .._ -6if'illef~-. ... -.em' s th eo ry t e situatio n w as strik in gly d iffere nt. T ak e o ne3S

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    CONJECTUREStypical instance-Efustein's prediction, just then confirmed by the findings ofEddington's expedit ion. Eins tein 's gravi tational theory had led to the resul tthat ~ght m~st be attracted by heavy bodies (such as the sun), precisely asmatenal bodies were attracted. As a consequence i t could be calculated thatl ight from a distant fixed star whose apparent position was c lose to the sunwould reach the earth from such a direction that the star would seem to besl ight ly shif ted away from the sun; or, inother words, that s tars close to thesun would look as ifthey had moved a little away from the sun, and from oneanother. This is a thing which cannot normally be observed since such starsare rendered invisible indaytime by the sun's overwhelming brightness; butduring an eclipse it is poss ible to take photographs of them. Ifthe same con-stel lation isphotographed at night one can measure the dis tances on the twophotographs, and check the predicted effect..Now the imp~sive thins a!?ou!.!..~~_~s~js,,!P'~_~is~_inv91yed in a pre-diction of.!! E?~!Cob~en:ation shows that the predicte~A~~telyabsenf;tIien the theory 1S simply r.efl.lkd. Th~UJ!~,o;ryj_ , com aiik/a with

    .!J!lai]LJ1~M!!flLrf.~lJ_so f obs!r~~-in fact wit res ts which everybodybefore Einstein would have expected.1TIrls is quite different from the situationIave previously described, when it turned out that the tbsories inguestion -~.~~;:.0m.atible wjthJbe-.lllO.!lt 9~tB~1nmlap..behaviQ!Jr& so that it~spractically impossible to describe any human behaviour that might not beclaimed to be a verification of these theor ies.These considerations led me in the winter of 1919-20 to conclusionswhich Imay now reformulate as follows.

    i '--l:.(D It is easy to obtain confirmations. o r verifica tions, fo r nearly every, theory-if we look for confirmations.. . Co~"~?~.n.s_, s~ou1~_o.AAL9n1YjCth~y~.axe_the._tesu1t.of..risk)LJll'.e-~~at IS to say, I f. unenlightened by the theory in quest ion, we shouldhave expected an event which was incompatible with the theory-an eventwhich would have refuted the theory.o Every 'good' scientific theory is a prohibition: it forbids certain thingsto happen. The more a theo!!..fu.~l!U~tter i!is._ , . ~f ! ! J ; > A theory which is not refutable by any conceivable event is non- J ' ' ' ' ; '~~. Irrefutability is not a virtue of a theory (as people often think)but ,:a vice, .',';., . .m . , gy'~ry.g~nuine test of a theory is an a ttempt to falsify it. or to refute it., (. !~stab~~ ~sfalsifiabiJ ltv but there are degrees ' of tesfab1fii j : e s o m e t h e o r i ~ ~are more testable, more exposed to refutation. than others; they take, as itwere, greater risks.~ Confirming evidence should not count e xc ep t w h en it is the result of ag en ui ne t es t o f t he t he or y; and this means that i t can be presented as a ser ious J~

    but unsuccessful attempt to falsify the theory. (Inow speak in such cases of l'corroborating evidence'.)~This is a s~ightoversimplifi.cation. for about half,o~ the Einstein effect may be derivedfrom the classical theory, provided weassume a ballistic theory of light..

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    1 SCIENCE: CONJECTURES AND REFUTATIONS~ ~ome:.gl?_~~c?!~mP1Ul!~~ ..~!~!!oun~ to!le ~~. !eJare st il l up-.!t~~2~~ctJr.J1ogmJrers-for example by introducing' ad hoc some auxiliaryassumption, or by re-interpreting the theory ad hoc in such a way that itescapes refutat ion. Such a procedure is always poss ible, but it r e s c u e s theh~ from refutation onI at e rice of destro' or at l;ist .1 S SCIentific status. (I la ter described such a rescu ing operation as a 'con~'Ve ' if l lonalW twis t ' o r a 'c on ve ntio na li st a tra ta ge m.) .One c an s um up all this by saying that t he c ri te ri on o f t he s ci en ti fi c s ta tu sof a t heor y is i ts fals i f iabil i ty, or r ef u ta b il it y, o r t es ta b il it y.

    nImay perhaps exemplify th is with the he lp of th e var ious theor ies so farmentioned. Einstein's theory of gravi tation clear ly satis fied the cri terion off~b!1!!y.. Even if our measurlngmst.riuUents a t the time did not allow usto pronounce on the resul ts of the tests with complete assurance, there wasclearly a possibility of refuting the theory.Astrology did not pass the te~~strologers were greatly impressed, and 1mtSTed, by wlUlt they beHeved to be confirming evidence-so much so that !

    they were quite unimpressed by any unfavourable evidence. Moreovert by I~g their interpretations.and PIQPhecies sufficiently va8!!e they were a b i c ~ 1to explain aw a an . tt:at mi t have bee~ a rem tion f h had!~ eOI1and the prophemes beenmQre precISe._ !n order to escape falsifica.- ino n Hiey destroyed the testabil ity of their Jheory;l t is a t i c a . l soothsliyers l'lrick to 'ct thin ~o el that the remctions can hardl t1 : t '1..!ybecom~J~~ ,. - .. J)lie M a r x i s i t l L & ; J : Y O f l i j, s t o z y , in spjte of the serious efforts ofso!M..Q{lts_

    ~unders and followers, ultimately adopted this soothsaying practice':, Insome of its earlie r Iol'DIUlations (for example in Marx's analysis of thecharacter of the 'coming' social revolution') t!teir predlctiMS lItre testable,ijd in_f!!~iti~ Yet instead of accepting ~e refutations the followers ofarx re-interpreted both th e theory and the evidence in order to make themagree. Inthis way they rescued the theory from refutat ion; but they did so atthe price of adopting a device which made it i rrefutable. They thus gave a'conventional ist twist ' to the theory; and by tbis stratagem they destroyed itsmuch advertised claim to scientific status;The two psycho-analytic theories Were in a diffe rent c lass. They were

    simply non-testable, irrefutable. There was no conceivable hl.!mIDl-b~...YiQm:..which could cQ!ltrl\jlj~ This does not mean that Freud and Adler werenot seeing certain things correctly: Ipersonally do not doubt that much ofwhat they say is of considerable importance, and may well play its part oneday ina psychological science which is testable. But i t does mean that those'cl inical observat ions' wbich analysts naively bel ieve confirm their theorycannot do this any more than the daily confirmations which astrologers 1ind2 See, fOT e x am p le , m y Open Society and Its Enemies, e h, 1 5 , s ec ti on ill, a n d n o te s13-14.

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    CONJECTURESin th eir p rac tice ) A nd as fo r F reu d's e pic o f th e E go , th e S up er-eg o, an d th eId , no subs ta n ti al ly s tr o ng e r claim to s cie ntif ic s ta tu s c an b e m ad e f or it th anf or Hom er 's collected s to rie s fr om O lym pu s. T he se th eo rie s d es crib e s om ef ac ts . b u t in t he m a nn er o f m y th s. T h ey c on ta in m o st i nt er es ti ng p sy ch o lo g ic als ug g es tio ns . b ut n ot in a te sta ble f or m.A t t he s ame t ime I r ~~, .! :AA t s) l~ .my th s may, _b~_d.~Y~lo'p '~d,nd b~ ~

    t~at histo ricaU l' sPea10ng @ -or very ne ar ly a ll -s c ie n ti fi c t he o ri es ,~~te f rom m ; -a nd t ha t a m y th .. ma y~ nt ai nJm po rt an t_ jl !! ti ci pa ti on so s ci en ti fi c ~ori ple_l!arC~mped_()_c.~esheory of evolutio~ trialand error. or Parmenides' myt~b lock umvers-.fin whichn oth in g e ve r - n a p p e - i i i - a n o - w W c h , - if w e add -iiiioIlierailiieriSion, becomesE in ste in 's b lo ck u niv er se (in w hic h. to o. n oth in g e ve r h ap pe ns . s in ce e ve ry wt hi ng i s, four-dimensionally sp eak in g, d eterm in ed an d la id d ow n fro m th ebegbuUng ) ._ I t hu s f el t that if.hee!>,!, fo u nd '" be ,.,..,cientific, 0 ' ' m e t a " ]h sical' as we mi h t sa 't is not ther found to be unim or t

    1 SCIENCE: CONJECTURES AND REFUTATIONSs ci en ti fi c c ha ra ct er , s om e o f t hem , u n fo rt un at el y, a s i nf lu en ti al a s t he M a rx is ti nt er p re ta ti on o f h is to r y; f o r e x amp l e. t he r ac ia li st i ti te tp r et at io n o f h is to r y-a no th er o f t ho se i mp re ss iv e a nd all-explanatory t he or ie s wh ic h a ct u po n we akm i nd s l ik e r ev e la ti on s .)T hus the problem w hich Iried to solve by proposing the criterion o ff als if ia bility w as n eith er a p ro ble m o f m ea nin gfu ln es s o r s ig nif ic an ce , n or a

    p ro ble m o f tr uth o r a cc ep ta bility . I t wa s th e p ro ble m o f d ra win g a l in e ( as~e11as t~i~an b~ done) b e twe e n t h e s ta tement s. o r s y st ems of sUrtements~Q f:~ ?m pm cal SCIences, an~ aU other s tate n::en ts _ w .h ~th er t~ ey are o f a~ !mQus Of of a m eta pb ys ~l c ha ra cte r, o r s un ply p se ud o- sc ie ntific , Y ea rs]~ter_~928 or 1929-1 called this first p roblemofm ine, ro b/e m o f d e ma rc atio n'. . he c ri te ri on~o (f al si fi ab il lt i s. a s o lu t io n , t o t hi sprOD 'e '" _ _ it says that s ta tem en ts o r ~s o f s ta tem en ts , : :: ;inorder ' 0 b e mp1ma I f s p w i u i " i M f t ia R i i A i W d i t i i ii i if R i i i S J 6 1 i 1~~sg ilab~1 jI ID ''Vsnb- , -,~~I'J~ w..'J,1QUae:Qjilil.!',4 B ut I t can no t c aim to b~~ac yempirical evidence in the scienti f ic sense; :&. t4.Q:ug_1]. jl_~_a.}'_~!!!>i ly_~~~,J1)._some.-genet iY_$w.se.h e 'res ult o f o b~(T here w ere a g rea t m an y o th er th eo rie s o f th is p re -s cie ntific o r p se ud o-3 'C li ni ca l o bs er va ti on s .. l ik e a ll o th er o bs er va ti on s, a re interpretations in the light 0/theories (see b el ow , s ec ti on s i v if.);a nd fo r t hi s re as on a lo ne t he y a re a pt to s ee m to s up po rtth os e th eo ries in th e lig ht o f w hi ch th ey w ere in te rp re te d. B ut r ea l su pp ort ca n be obtainedo nly fro m o bse rv atio ns u nd erta ken as tes ts (b y 'atte mp te d ref utati on s'); a nd f or th is p ur-pose criteria 0/ refutation h av e t o b e l ai d d ow n b ef or eh an d: it must be a g re ed w h ic h o bs er -v a bl e s i tu a ti o ns , if a ct ua ll y o bs er ve d, m ea n t ha t the th eo ry is refuted. But what kind ofc lin ica l r es po nse s w ou ld r ef ute to th e s atisfa ctio n o f th e analyst n ot m er el y a p ar ti cu la ra na ly ti c d ia gn os is b ut p sy ch o- an al ys is i ts el f? A nd h av e s uc h c ri te ri a e ve r b ee n d is cu ss edor ag reed upon by analysts? Is there not, on the contrary, a w hole fam ily of analytic con-c ep ts , s uc h a s ' am b iv al en ce ' (Id o n ot s ug ges t th at t he re is no s uch th in g a s am biv ale nce ),w hic h w ou ld m ak e it difficult, ifn ot i mpo ssib le , to ag ree u po n s uch c rite ri a'l M ore ove r,how m uch headw ay has b e e n m ade in investig ating the question of the extent to w hicht he ( co ns ci ou s o r u nc on sc io us ) e xp ec ta ti on s a nd t he or ie s h el d by t he a na ly st i Df iu en ce t he'c li ni ea lr es po ns es ' o f t h e p at ie nt 1 ( fa s ay n ot hi ng a bo ut t he c on sc io us a tt em pt s t o i Df iu en cet he p at ie nt b y p ro po si ng i nt er pr et at io ns to him, etc.) Y ears ag o I introduced the term

    'Oedipus e jJect ' to d es crib e th e in flu enc e of a th eor y o r e xp ec ta tio n or p red ic tio n u p on t heeve l l1 which it predicts o r d esc rib es: it w ill be re mem be re d th at t he c aus al c ha in le adi ngto Oed ip u s' p a rr ic i de wa s s ta rte d b y th e o ra cle 's p re dic tio n o f this event. This i s a c ha ra c-ter istic a nd r ec urre nt th em e o f su ch m yth s, b ut o ne w hich se em s to h av e fa lle d to a ttr ac tt he i nt er es t o f t he a na ly st s, p er ha ps n ot a cc id en ta ll y. (The p ro bl em o f c on fi rm a to ry d r eamss ug ge st ed b y t he a na ly st is d is cu ss ed b y F re ud , f or e xa mp le in Gesammel te Schr tf t en , m,192 5, wh e re he says on p, 3 14: 'If a ny bo dy as se rts th at m os t o f the d re am s w hic h c an beutilized in a n a naly sis o we th eir o rig in to [th e an aly st's] s ug ge stio n, th en no o bj ec tio nc an b e m ad e fro m th e p oin t of v ie w o f an aly tic t he ory , Y et th ere is nothing inthis f ac t' , h es ur pr is in gl y a dd s. 'w hi ch w ou ld d et ra ct f ro m t he r el ia bi li ty o f o ur r es ul ts . ')" T he c ase of as tro lo gy . n ow ad ay s a ty pic al p seu do -s cien ce , m ay illu stra te this point.I t w as attacked, by Aristotelians and other rationalists, dow n to N ew ton's day, for the)\'rong reason-for its now accepted assertion that the planets had an 'influence' upont er re st ri al \ su bl un ar ') e ve nt s. Inf ac t N ew to n's t he or y o f g ra vi ty , a nd e sp ec ia ll y the lunart he or y o f t he t id es , w as h is to ri ca ll y s pe ak in g a n o ff sp ri ng of a st ro lo gi ca l l or e. N ew to n, i tseem s, was m ost reluctant to adopt a theory w hich cam e from the sam e stable as forexample the theory that ' in fl ue nz a' e pi de mi cs a re d ue t o a n a st ra l 'i nf lu en ce '. A nd O al il eo ,n o d ou bt fo r th e sa me re aso n, a ctu all y re jec te d th e lu na r th eo ry o f th e tid es ; a nd h is m is-g iv in gs a bo ut K ep le r m ay e as il y be explained by his m i sg iv in g s a bo ut a st ro lo g y.38

    mToday In ow . o f c ou rs e, th at th is c r it e rion o f demarca t ion - the c ri te ri on o ft es ta bi li ty . o r f al si fi ab il it y, o r r ef ut ab il it y- is f ar f rom o b vi ou s; f or e ve n n owi ts s ig n if ic an ce i s s e ld om r ea li ze d. A t t ha t t im e . i n 1 9 20 . i t s e eme d t o m e a lm o stt r iv i a l. a l though it s olv ed f or m e a n in te lle ctu al p ro ble m w h ic h h ad w o rr ie dm e deeply. and on e w hich also had ob vious practical con sequences (forex am ple . p olitical o nes ). B ut I d id n ot y et re alize its fu ll im plic atio ns, o rits p hilo so ph ic al s ig nif ic an ce . W h en I e xp la in ed it to a fellow student ofth e M ath em atic s D ep artm en t ( no w a d is tin gu is he d m ath em atic ia n in G re atB ri ta in ). h e s ug g es te d that I s ho uld p ub lis h it. At the tim e I thought th isab su rd ; fo r I w as co nv in ced th at m y p ro blem . s in ce it w as so im po rta nt fo rm e, m us t h av e a gita te d m an y s cie ntis ts a nd p hilo so ph er s w h o w ou ld s ur elyh a ve r ea c he d my r ath er o bv io us s olu tio n. T ha t th is w as n ot th e c as e I le arn tfrom W ittg enstein 's w ork. an d from its reception; and so I published m yr es ul ts t hi rt ee n y ea rs l at er i n t he f orm o f a c ri ti ci sm o f W i tt ge ns te in 's criteriono f mean ing fu lne s s.:V ittg enste~ as y ou all know , tried to show in the. Tractatus ( se e f ore xa mW e ..h i~ po sitio ns 6 .5 3; 6 .5 4; a nd 5 ) th at a ll s o- ca lle d p hilo so ph ic alo ~t.a?hys!~al)proP ositions w ere actually n on- ro osition s or pseud o-r Opo sl tl on s: t h w senseless a m earu ss At genume or

    meaningful) p ro po si ti on s w e re t ru th f un ct io n s 0 m en ta ry o r a to micp ro po si ti on s wh ic h d es cr ib ed ' at om i c f ac ts ', L e.- fa ct s wh ic h c an inprinciple- be a sc er ta in ed b y o bs er va ti on . I n o th er wo rd s, m e an in g fu l p ro po si ti on s w e refu lly re du cib le to e lem en tary o r a to mic p ro po sitio ns w hic h w ere sim ples ta tem en ts d es cr ib in g p os si bl e s ta te s o f a ff ai rs , a nd wh ic h c ou ld i n p ri nc ip leb e e sta blis he d o r re je cte d b y o bs er va tio n, I f w e c all a s ta te me nt a n 'o bs er va -tio n s ta te me nt' n ot o nly if it s ta te s a n a ctu al o bs er va tio n b ut a ls o ifit statesa ny th ir ig th at m a yb e o b se rv ed , w e s h a ll h av e t o s ay ( a cc or di ng to t he Tractatus,S an d 4 .5 2) th at ev ery g en uin e p ro po sitio n m us t b e a. truth-funetlon o t ;. and39

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    CONJECTURESt he re fo re d e d. '! lc i~ ld tmn . ob se rv a ti on s ta temen ts . All o th e r a ppa re n t propo-; i r l o n s - W f u bemeaningless pseudo-proposit ions; in f ac t t he y will be no th in gbu t n ons e ns ic al g ib b er is h .T his ide a w as used b y W ittg en ste in f or a c ha ra cte riz atio n o f s cie nc e, a so pp os ed to p hilo so ph y. W e re ad (f or e xa mp le in 4.11, wh er e n at ur al s ci en ceis tak en to s tan d in opposition'to p hi lo so pb y) : ' Th e t ot al ity o f t ru e p ro po si -t io ns i s t he t ot al n at ur al s ci en ce ( or th e to ta li ty o f t he n a tu r al s c ie n ce s) .' T h ism ean s th at th e p ro pos itio ns w hich b elo ng to s cien ce are th ose de duc ib lefrom true o bs erv atio n s ta te me nts ; th ey a re th os e p ro po sitio ns w hic h c an b everified b y tru e o bs er va tio n s ta te me nts . C ou ld w e k no w a ll tru e o bs er va tio ns ta tem en ts , w e s ho ul d a ls o k now all th at m ay b e a ss er te d b y n atu ra l s cie nc e.This a mo un ts to a c ru de v er ifia bility c rite rio n o f d em ar ca tio n. T o m ak e itslig hU y les s cru de . it c ou ld b e am en ded th us : 'T he statem en ts w hic h m ayp os sib ly fa ll w ith in th e p ro vin ce o f s cie nc e a re th os e w hic h m ay p os sib ly b ev erif ie d b y o bs er va tio n s ta te me nts ; a nd th es e s ta te me nts , a ga in , c oin cid ewith the c la ss o f all g en ui ne o r m ea ni ng fu l statements.' ~l: this approach,~ A ~ _ I ! : ! - . .r . ! r J ! ! . a b il i t' l l f J l l1 i I J K i J J J n e s . s . . ,m u I . . sc i e n t i fi c . c h a r a c t e r . a ll caincitk.Ie rs on ally w as n ev er in te re ste d in th e s o- ca lle d p ro ble m o f m ea nin g; o nth e c on tr ary , it a pp ea re d to m e a v erb al p ro ble m, a ty pic al p se ud o- pro ble m.I w a s in te re st ed o nly i n t he p ro bl em o f d em a rc at io n, i .e . in f in din g a c ri te ri ono f t he s ci en ti fi c c h ar ac te r o f t he o ri es . It w as ju st th is in te re st w hic h m ad e m es ee a t o nc e t ha t W i tt ge ns te in 's v er if ia bi li ty c ri te rio n o f m e an in g wa s i nt en de dto p la y th e p ar t o f a c rite rio n o f d em arc atio n as w ell; an d w hich m ad e m e se ethat, as such, it w as totally i na de qu ate , e ve n if all m is giv in gs a bo ut th ed ub io us co nce pt o f m ean in g w ere se t as id e. F or W ittg en std n's criterio n o fd em ar ca tio n- to u se m y o wn te rm in olo gy in t his c on te xt -i s v er if ia bi li ty , o rdeducibility from o bs erv atio n s ta te me nts . B ut th is c rite rio n is to o n ar ro w(and t oo w id e) : i t e xc lu de s f rom s ci en ce p ra ct ic al ly e ve ry th in g t ha t i s. i n f ac t,

    1cha rac te r is t ic o f it (wh il e f ai li ng i n e ff ec t t o e x cl ud e a s tr olOgy. ). No sci en ti fi c 1 1t he or y c an e ve r be ded ation statement _J?:~,9~criP .ed.a$,try, _ . _ ~ c ~~~_Qf__9b~~n'atj9n._statements;~ A U th is I p oin ted o ut o n v ario us o ccas ion s to W ittg en steinian s a nd m em -b ers o f th e V ie nn a C irc le . I n 1 93 1-2 I s umm ar iz ed m y id ea s in a la rg is h b oo k(r ea d b y s ev er al m em be rs o f the C ir cle b ut n ev er p ub lis he d ; a lth ou gh p art o fit w as in co rp or ate d in m y L o gi c o f S ci en ti fi c D is co ve ry ); and in 1933 I p ub -1 is be d a le tte r to th e E dito r o f Erkenntnls in w hic h I trie d to c om pr es s in to tw op ag es m y id ea s o n th e p ro ble ms o f d em ar ca tio n a nd in du ctio n.s I n t hi s l et te r

    SMy L o gi c o f S ci en ti fi c D i sc ov er y (1959, 1960,1961),here usually referred to as LoSc.D.,is the translation of L oC ik d er F or sc hu ng (1934), with a number of additional notes andappendices, including (on pp. 312-14) the letter to the Editor of Erkenntnis mentioned herein the text which was first published in Erkenntnis, 3. 1933,pp. 426 f.Concerning my never published book mentioned here inthe text, seeR. Catnap's paper'Ueber Pro tokol i s tl i ze ' (On Protocol-Sentences), Erkenntnis, 3, 1932, pp._215-28 where hegives an outline of my theory on pp. 223-8, and accepts it. He calls my theory 'procedureB', and says (p. 224, top): 'Starting from a point of view different from Neurath's' (whodeveloped what Carnap calls on p. 223 'procedure A'), 'Popper-developed procedure B as

    40

    s',

    1 SCIENCE: CONJECTURES AND REFUTATIONSa nd e ls ew he re I d es cr ib ed th e p ro ble m o f m ea nin g as a pseudo-problem, inc on tr as t t o t he p ro bl em o f d em a rc at io n. B u t m y c on tr ib uti on w a s c l as si fie d b y . .. ,m em be rs o f th e C j[ cle .~S.1l-PfQ'p9-~!I,LtQ._g:[email protected] r if i ab i li t: y , c r i te r ion ofmeaning by a f a ls i fi abi li ty , c ri te r ion or .meQlj lng-which effectively m a d e non-

    os en se o f m y V ie ws .(j My p ro te sts th at 1was trying to s olv e. n ot th eir p se ud o-p ro blem o f m ean in g, b ut th e p ro blem o f d em arcatio n, w ere o f n o av ail.M y a tta ck s u po n v er ific atio n h ad s om e e ffe ct. however, T hey soon led toc om ple te c on fu sio n in th e c am p o f th e v erif tc atio nis t p hilo so ph ers o f s en sea nd n on se ns e. T he o rig in al p ro po sa l o fv er ma bU ity a s th e c rite rio n o f m ea n-in g w as at least cle ar. sim ple, an d fo rcefu l. T he m od ifica tio ns an d s hiftswh ic h we re n ow i nt ro du ce d we re t he v er y o pp os it e, " T h is , Ih ou ld s ay , is n ows ee n e ve n b y th e p ar tic ip an ts . B ut s in ce r am u su ally q uo te d a s o ne o f'th ez n Iw is h to r ep ea t t ha t a lt ho ug h r c re at ed t hi s c on fu si on Ie v er p a rt ic ip a te d i n it.Nei th er f al si fi ab il it y n or te st ab ili ty w e re p ro po se d b y m e a s c ri te ria o f m ea n-i ng ; a nd elthough I may plead g uilty to h av in g in tro du ce d b oth te rm s in to th e

    d isc~ s~ ?n . it w as n ot Iw ho in tro du ~d th em in to th e th eo ry o f m ean in g.C ri ti ci sm o f m y a ll eg ed v ie w s wa s W i de sp re ad a nd h ig hl y s uc ce ss fu l. Iav eyet to m eet a critic ism of m y view s.S Me anwhi le , t es ta bil it y i s b ei ng w id el ya cc ep te d a s a c ri te ri on o f d emar ca ti on .part of hi s system.' And after describirig in detail my theorYoftests, Camap sums up hisViewsas follows (p. 228): 'After weighing the various arguments here discussed it appears!o me that the second language form with procedure B-that is intheform here describ

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    CONJECTURES

    Ia ve d is cu ss ed th e p ro ble m o f d en Ia re ;tio n in s om e d et ail b ec au se Ielievethat its solutio nis the k ey to m ost of the fund am en.t~ p ro"!?1 ~th epb ilo~Y_.9 .~~~oing to!~ve you later a list. o f so~e of theseO ftte r p ro ble ms , b ut o nly one6Hl;em.~. ,Prob!em of mductlOn-can bed is cu ss ed h er e a t a ny l en g th .I h ad b ec om e in te re ste d in t he p ro bl em of i nd u ct io n i n 1 9 23 . A lt ho u gh t hi sp ro b lem i s v er y c lo s el y c on n ec te d w i th t he p ro b lem o f d em a rc at io n , I id n otfu lly a pprecia te the connection for abou t five years. .I ap pro ac he d th e p ro blem o f in du ctio n th ro ug h H um e, H u.m e, I relt~ w a sp er fe ct ly r ig ht in p oin ti ng o ut th at ~ nd uc ti on c an no t b e lo gic ally J us tif i~ d.H e h eld th at th ere c an b e n o v alid Ioglcal? a rg um en ts a ll ow i ng u s t o e st ab li sh'th at th ose in sta nc es , o f w hic h w e h av e h ad n o ex pe rie nc e, re se mb le th ose , o fw h ic h w e h a ve h a d e x pe ri en ce ', Consequent ly ' ev en a ft er t he o b se rv at io n o f t hefrequ ent or con sta nt co nju nction o f o bjects, w e h ave n o reaso n to d ra w an yi nf er en ce c on c er ni ng a n y o b je ct b ey o nd t ho se o f w h ic h w e h a ve h a d e x pe ri en c e'.F or 's ho u'd it b e s aid th at w e h av e e xp er ie nc e' lll.- ..e xp er ie nc e te ac hin g u sth at o bj ec ts c on sta ntly c on jo in ed w ith c er ta in o th er o bje ct s c on tin ue to b e s oconjoin ed -then, H um e says, 'I w ou'd renew m y q uestio n, w hy fro m thise xp erie nce w e f orm a ny c on clu sio n b ey on d th ose p a~ t i~ sta nc es, o f ~ hic h ~ eha v e had e xp er ie n ce '. I n o th er w o rd s, a n a tte m pt tO ju stif y th e p ra ctic e o f In-d uc tio n b y a n a pp ea l t o e xp er ie nc e m u st le ad tp a n i n f in i t e r egre s s . As a r e su ltw e c an sa y th at th eo rie s c an n ev er be i nf er re d f rom o b se rv at io n s ta tem en ts ,or ra tionally justified by them . . = J--!ro un d H um e's refu tatio n o f in du ctiv e in fe re? cc clea r an ~ co nc l~ s1 V e.~ utI f eh c om p le te ly d is sa ti sf ie d w it h h is p sy ch o lo g ic al e xp la na ti on o f i nd u ct io n- - - i ! ! . term s of custom or hab it, ..Itha s o ft en b ee n n o ti ce d t ha t t hi s e xp la na ti on o f' H um e 's i s p h i lo so p hi ca ll yno t ve ry sa ti s fa c tory . Itis . h o w ev er . w ith ou t d ou bt in te nd ed a s a psychologicalr ath er th an a p hilo so ph ic al th eo ry ; f or it tr ie s to g iv e a c au sa l e xp la na tio n o f

    a psycho log i cal fa ct- th e fa ct th at w e b elie ve in la ws, in s t a tement s a sse rt ingr eg ul ar iti es o r c on st an tly c on jo in ed k in ds o f e ve nts -b y a ss er tin g th at th isf ac t is d ue to ( i.e . c on sta ntl y c on jo in ed w ith ) c us to m o r h ab it. B ut e ve n th isrefo rm ulatio n o f H um e's th eo ry is s till u ns atis fa cto ry ; fo r w hat I h av e ju stc alled a 'p sy ch olo gic al fa ct' m ay its elf b e d esc rib ed a s a cu sto m o r h ab it-free from the dangers of misinterpretation. (This is one of the reasons why the theory ofinduction does not wo rk .) T h e 'empirical basis' consists largely of a mixture of theories oflower degree of universality (of ' reproducible eff~) . ~ut the fac t r~ins tha t, re la ti veto whatever basis the investigator may accept (at his peril), he can test hiS theory only bytrying to refute it. . . ..!IHume does not say 'logical' but 'demonstrat ive' , a termmology which, I think, IS alittle misleading. The fonowing two quotations ar e from the Treatise 0/ Hum an N a tu re ,Book IPart m sections viand xii, (The italics are allHume's.)10 This and the next quotation arc from I o e. e t t. , section vi. Sec also Hume's EnquiryC o nc er ni rl g H um an U n d er st an d in g , section rv, Part II,and hls AbJt!act. edited 1938 byJ.M. K eyn es a nd P . S ra ff a, p, I S , an d quot ed inL.Sc.D., n ew appendix .vn, t ex t t o n o te 6 .42

    1 SCIENCE: CONJECTURES AND REFUTATIONSth e c us to m o r h ab it o f b eli ev in g i n la ws o r r eg uJ ar itie s; a nd i t is n eith er v er ys urp ris in g n or v ery en lig hte nin g to h ear th at su ch a c us to m o r h ab it m us t b eex plained as du e to, o r co njo in ed w ith , a custo m or h abit (even thou gh ad if fe re nt o n e) . O n ly wh en we re me mb er th at th e w ord s 'c us to m' a nd 'h ab it' 1are used by H um e, as they are in ordinary lang uag e, no t m erely to d esc rib e ~r .e g ul ar b eh av io u r. b u t r at he r t o t h eo r iz e . a bou t i ts o r ig i n ( a sc r ib e d t o f re qu en t )repetition). ca n we r ef orm ul at e h is p sy ch o lo g ic al t he or y i n a m o re s at is fa ct or yw ay , W e ca n th en s ay th at. lik e o th er h ab its , ou r hg h it o [ b el ie 'l in g I 'n l aw s. ifl .~eI!!0duct o. l freqyentreeeti t ion-oft!t~ation t ha t t b ings . .c fac e r~ i ,n ~md .a r e" c on s ta n tl y .s o n io .i ru : d. .w i th Jh in g s o f a no th e r k in d .T h is g e ne ti co -p sy ch o lo g lc al t he or y i s. a s i n di ca te d, i nc or po ra te d i n o rd in ar yla ng ua ge . a nd it is th er ef or e h ar dly a s r ev olu ti on ar y a s H ume t ho ug ht. Itisno d ou bt an ex trem ely po pu lar psycho log ical theory -part o f 'com mo nsense ', one m igh t say . B ut in sp ite o f m y love of both com mon sense andH ume , I fe lt c on vin ce d th at th is p sy ch olo gic al th eo ry w as m is ta ke n; a nd th atit w as in f act refu table on p urely log ical g rounds. .H um e's sycholo whic is t he 0 s cholo ,w as m istaken 1felta bo u t a t l ea st t ee d i tf e r~n t t b i. tJ , gs :,a)t h e t ypi ca l r e su l t Q i re p et it io n ;- (b ) t h egei ieSls"orhi ibt tSfancrespeciany (c) th e ch ara cter o f th os e e xp erien ce s o rm o de s o f b eh av io ur w h ic h m a y b e d es cr ib ed a s 'b el ie Vin g i n a la w' o r ' ex pe ct-i~ law -like succession of even ts ', .---- .T he typ ical resu lt of rep etition -say , o f r epeating a difficu lt p assag e onth e p ia no -is th at m ov em en ts w hic h a t first n ee de d a tte ntio n are in th e e nde xe cu te d w it ho u t a tt en ti on . W e m ig h t s ay t ha t t he p ro ce ss b ec om e s r ad ic al lya bb re via te d, a nd c ea se s to b e c on sc io us : i t b ec om es ' ph ys to lo gl ca l'. S uc h ap ro ce ss , f ar f ro l) !J ~r ea ti t! g~ ~Q .l l~ ~ ec ta ti on o fl aw~ li ke s u cc es si on -; 'o r- ;; ;J : l ~ e f f u . J ! . r a w ~ On th e c on tr ar y b eg in w ith a c on sc io us b elie f a nd d es tr ol (.it b y m ak in g it s up erflu ou s. I n le arn in g to rid e a b ic yc le w e m ay start w ithth e b elie f t ha t w e c an a vo id f allin g if w e s tee r in th e d irec tio n in w hic h W eth re aten to fa ll, an d th is b elie f m ay b e u se fu l fo r g uid in g o ur m ov em en ts .A f te r s uf fi ci en t p ra ct ic e w e m a y f or ge t t he r ul e; in a ny ca se , w e do n ot n eed itany lon ger. O n the o ther h an d, even if it is true that repetitio n m ay createunconscious expectations;. th es e b eco me c on scio us o nly if s om eth in g g oesw rong (w e m ay not have heard the clock tick . bu t w e m ay hear that it hasstopped). .~ Mab its or custo ms d o no t. as a ru le , originate in r ep et itio n. E ve n t heh a'm f o f w alk in g, o r o f s pe ak in g. o r o f f ee din g a t c er ta in h ou rs , begins beforerepetition can play any p art w hatev er. W e m ay say , ifw e lik e, th at th eyd es er ve to b e c alle d 'h ab its ' o r 'c us to m s' o nly a fte r r ep etitio n h as p la ye d it sty pic al p ar t; b ut w e m u st n ot s ay th at th e p ra ctic es in q u es ti on o ri gi na te d a st he r es ul t o f m a ny r ep et it io n s.---- Ud Be li ef i n a l aw i s n o t q u it e t he s am e t hi ng a s b eh av io u r wh ic h b et ra ID .! le ~e 6ia tio n o f a la w- lik e s uc ce ss io n o f e ve nts ; b ut th es e t wo a re s uf fic ie ntly~ d os ef ycO ii ii ec te d t o b e t re at ed 't O ge iI ie r: fh ey m a y; p e rh a ps , i n e xc ep ti on alc as es , re su lt f ro m a m er e r ep etitio n o f s en se im p re ss io ns (a s in th e c as e o f th e43

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    CONJECTURESs to pp in g c lo c k ). Iw a s p re pa re d t o c on ce de th is , b ut I o nte nd ed t ha t n or m-a ll y , a nd inmost cases o f a ny in te re st, th ey c an no t b e s o e xp la in ed . b : s H1Jl! l :ea dm its , e ve n a s in gl e s tr ik in g o bs er va ti on m a b e s uf fic ie nt to c re ate a b elie f~~~Jj91 'L- :~ fact w .c h e tries to exp lain as d ue t.o .an in du ctiv eh ab it, fo rm ed as th e resu lt o f a v ast n um ber of lon g rep etitiv e seq uenceswh ic h h a d b ee n e x pe ri en ce d a t a n e ar li er p er io d o f H f e.llBu t t h is ,Ion tended, .w a s m er ely h is a tte m pt to e xp la in a w ay u nf av ou ra ble f ac ts w h ic h t hr ea te ne dhis theory ; all u nsuccessfu ! attem ptJ~~~~av~!l~~!e!!~~!~~e .'~~~~r.ved~~~.Y2~~g~aI!!ffi~s.!l:~~=aseaity;' lllaeea,a~w ; h k e~ .} -. /lightercig arette w as held near the noses of the young puppies', reports .F. Bdge. ' Th ey s ni ff ed a t it o nc e, tu rn ed ta il, a nd n oth in g w o ul d in du ce th emto c om e b ac k to th e so urc e o f th e s me ll a nd to s nif f a g ain . A f ew d a ys l at er .th ey re acted to th e m ere s ig ht o f a c ig are tte o r ev en o f a ro lle d p ie ce o f w h itep ap er . b y b ou nd in g a w ay , a nd s ne ez in g .' 12 I f W e tr y to e xp la in c as es lik e th isb y p os tu la tin g a v as t n um b er o f lo ng r ep etit iv e s eq ue nc es a t a s till e ar lie r a gew e are n ot o nly ro man cin g, b ut fo rg ettin g th at in th e c le ve r p up pie s' s ho rtliv es there m ust b e roo m no t o nly for rep etition b ut also fo r a g reat d eal ofn ov el ty , a nd c on se qu en t ly o f non -r ep e ti ti on .B ut it is n ot o nly th at c erta in e mp iric al fac ts d o n ot s up po rt H um e; lh er! j."arlUle.cj$jyl!..~rguments ofl \"p. ,~r .~!. r. . .Jg{9L!l . ! l l1 '!]' . ! lm!.MtJ1!us. Icholom~L--b~en tra l id ea o f H um e's theo ry is th at o f repetition, b t r s ed ufon slm i- /'\lagIY ~ or 'r es em b 1a nc e') . T his id ea i s u se d in a v e ry u n cr it Id a r w a y . 'W e a r e . .. .--..1 ed to t t l ' i n k o f t he w a te r- dr op that h ollo ws th e s to ne: o f s eq ue nc es o f u n-q ue st io na bly l ik e e ve nts s lo w ly f or cin g t he m se lv es u po n u s, a s d oe s th e t ic ko f th e c lo ck . B ut w e o ug ht to rea liz e th at in a p sy ch olo gic al th eo ry s uc h a sHume 's , 0~..Ir e eet i~io ! :' !> !: '~ : t~~~p .9 .~~!mi lmi~ ' :. f~~ :1n . .Qa~ .be .~owedto have any e f fec t u . .P2_nus. W e m ust respond to situations as If they w ere~va~ent ; takethem a s similar; interpret them as r ep et it io n s. T h e c le ve rp up pie s, w e m ay a ss um e. s ho wed b y th en : r es po ns e, th eir w ay o f a ctin g o r o fr ea cti ng , t ha t th ey r ec og n iz ed o r i nt er pr ete d th e s ec on d s it ua ti on a s a r ep eti-tio n o f th e f ir st: th at th ey e xp ec te d its m ain e le me nt. th e o bje cti on ab le s m ell,t o b e p r es e nt . ' !' h e s it 1 !a ti o nwa s a repetition-for-the eeeus hey re sponded.!Qj!J~Y..l!1Jtlci;atlng its s i l 1 i U a a i ~ e re e.T h is a pp ar en tl y p s yc ho lo g ic al c ri ti ci sm ha s a p ure ly lo gic al b as is w hic hm ay b e su mm ed u p in th e follo wing sim ple arg um en t. (It hap pen s to be th eo ne f ro m w h ic h Io rig in ally s ta rte d m y c rit ic is m .) ~ e k in d o fr ep eti tio n e !t-v is ag e d bX Hum e c an n e ve r b ~ ~t& 9Wb~ }~~ .. !1 ~ J? :y jp .. .. .m i !! 4" 9 3P .l 1o t b eca~ ~rt "~ fsam~T't "i ley c~ ~lJ, l 'y.Q!L~~~.QUimllari ty_ 'Ihus ,they-arerei!.~!J!iO_1!!..fl!1lJ'f!pl!!...u...f.!l1P..inJ!E~at h as th e e ffe ct u p on m e o f arep etitio n m ay n ot h av e tb is e ffe ct u po n a s pid er.) B ut th is , m e an s th at, fo rlog ical reaso ns. th ere m ust alw ay s b e a p oin t of v iew -such as a system o f

    11 Treatise. s e ct ion x l ii ; s e c ti on xv , r u le 4.11F . B l ig e , ' Zu r E n tw i ck lu n g , e tc .' , ZeftschriJt f. Hundt forschung , 1933 ; cp, D . K a tz ,A nf ma la a nd M en , ch. VI. footnote. 44

    1 SCIENCE: CONJECTURES AND REFUTATIONSe xp ec ta ti o ns , a n ti ci p at io n s . a s sump tl o ns , ~_r_interests:-;-beforetherecan be a ny ~: re p et it io n ; wh ic h pOint o ( - x i M v . CaDsrqueDtli(Cau no t h e m ere ly th e ~ ~ !, o f r e \1St i ti gg" (See n ow a ls o a p pe n di x. x, (1). to m y L.Se.D.} !W e m ust thu s replace, fo r th e p urpo ses o f a p sy ch olog iea1 th eo ry o f theo rig in o f o ur b el ie fs . th e natve id ea o f e ve nt s w h ic h ar e simi lar b y th e idea of:-----:e ve nts t o w h ic h w e r ea ct b y interpreting th em a s b ei ng s im ila r, B ut ifthis ~~.~.~(and I can see no escape from it) t h en _Hu~ .~ s_ .p sy chQJQ~c al t h e or y o f i n -d u c ti o n l ea d s t o a n i n fi n it e r e gr e ss , . p~e~~~~ ! .. ~~ l ~~ ? -u s~ !_~!il_i!lidnn~ft~r eg r es s wh ic h wa s d is co v er ed b y Hume h imse lf . a n d Use d_by .l li p lJ o _ e lt p lo d e'the IogiCal __h eo ry o f h ld u ct io n ." F or w h a t d o w r ; W i sh to e xp la in ? In th ee xa m pl e o f t he p up pi es w e W i s h t o e xp la ii ib e h av l ou r wh i ch tm lY . be .de scn1?edas r e co g n iz in g o r i n te r pr et in g a s itu atio n a s a r ep eti tio n o f a no th er . C le ar ly .\ V e " " c a n n o t hope t o e ip l ai il "t h is bY ' imappea r fo - ea r li er r e Pe ti tl o ns~ on c e Werealize t ha t th e e ar lie r r ep etiti on s m u st a l s o have been repe ti t ions- fo r - them,s o t ha t p re ci se ly the s am e p ro ble m a ri se s a ga in : that of r e co g n iz in g o r i nt er -preting a situation as a repetition of ano ther. .

    t. , T o put it m ore concisely. sim ilarity -fo r-us is th roduc of a response ,:,"f ( , : 1, in vo lv in g in te rp re ta tio ns ( wh ic h m a y b e in ad eq ua te ) _~!!~_~!!!WI1MiQn$.Q t. '":j!; ' J i ! !n ec ta tio ns (w hic h m ay n ev er b e fu lfille d). It is there re im ssible to. \ t . : \ : ex plain an tic ip atio ns. o r ex ectatio ns, as res tin from m an re etition s, as i

    : : ~ . ; \ H , s g g.;:s y um e. o r _eveIl.. e .. ~ s.repe ~ lon-for:~~m ust.~beba$~ .upon . (I, .\ ! ~a~~~ f ?r h~ .u .s , . .,i! ibrref

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    CONJECTURES .c as t o u t t he l og ic al t he or y o f induCtion.b .y r .e .p . e ti ti on .he s t ruc .k . a . ba rgain . W. i .t h \common sense ., , "~~S1~eJ1~_~~ .g ,>~hc :: :r . e : - ~ ! l t r Y .oO~du~ t i~t l _ by repe ti ti on ,. ~ . I l l ,!h e g ui se 0'[ a.p s .g ~lo c al.! .lte o .EE9P' .O~~R-._' i i } _ ~ ~ + ~ b . l c : ~ .po n this .:.- eo~~! ...__.t~...0e xp a in in g o ur p ro pe ns ity to e xp ec t r eg ula riti es ;iiS lh e r es ul t o f r ep eti tio n, Iprop osed to ex plain repetition-for-u s as the \I : su i to f ou . r p~op el ls itY .. t( ).~ xp ec i. re g u la r it ie s a nd t o s e ar c h forthem. .Thus r wa s l ed Drpure ly 10g i ca1cons l aera tlOns to rep l ace1 :he -psycho giealt he o ry o f i nd u ct io n by th e f ollo w in g v ie w . W it ho ut w a it in g, p as si ve ly , f or - -,Jr ep etitio ns to im p re ss o r im p os e r eg u la ritie s u po n u s. ~ cti v~ t; Y to a u ; n - ;p os e r eg ula riti es u po n th e w o rld . W e try t o d i sc ov er s im i la r it ie s InIt, an toin te rp re t it in te rm s o fla w s i nv en te d by u s. W ith ou t w a it in g f or p re m is es w eju mp to c on clu sio ns . T he se m ay h av e to b e d is car de d la te r. s ho uld o bs erv a-tio n s ho w th at th ey a re w ro ng .-: Th is w as a theory of tria l and erro r-o f c onj ec tu re s a nd r ej ut a tl on s .j !_ma de i t p o s si bl e t o u n de rs ta nd ' ih :l .P u r a tt em p ts t o f or ce i nt er pr et at io n s u p ont he wo rl d w e re l og ic al ly p ri or t o t he o b se rv at io n . QL s i. tn ll ar it ie s. S in ce t he rewe r e" lo g l ca l r e ason s b e h in d thlsproeedure, I th ou gh t th at it w ou ld a l'p ly int he f ie ld o f s ci en ce a ls o ; t ha t s ci en ti fi c t he or ie s w e re n o t t he d ig e st o f o b se rv a-t io ns , b ut th at t he y w er e in ve nt io ns -c on je ctu re s b old ly p ut f or wa rd f or tr ia l.to b e e li mi na te d if th ey c la sh ed w ith o bs er va ti on s; w ith o bs er va ti on s w h ic hw er e r ar ely a cc id en ta l b ut a s a r ule u nd er ta ke n w ith t he d ef in it e in te nt io n o ft es ti ng a t he o ry b y o b ta in in g , i f p o ss ib le , a d e ci si ve r ef ut at io n .

    vT he b eli ef th at s cie nc e p ro ce ed s f ro m o bs er va tio n t o t he or y is s ti ll s o w id el yan d so firm ly held that m y den ial o f it i s o ft en m e t w i th i nc re du li ty . Iav ee ve n b ee n s us pe cte d o f b ei ng i ns in ce re -o f d en yi ng w h at n ob od y in h is s en se sc an d o ub t.B u t i n f ac t th e b elie f t h at w e c a n s ta rt w it h p ur e o bs er va tio ns a lo ne . w ith ou ta n y t h i n g i n t h e . r u .l . t \l r eQL a t~o;ry~Jms~a.?f~y-bel11ust i i te(rbythes to ry o f th e m an w h o d ed ic ate d h is li fe t o n at ur al S CI en ce ,w ro te d ow n e ve ry -t hi ng h e c ou ld o b se rv e. a nd b eq u ea th e d h is p ri ce le ss c o ll ec ti on o f o b s er va ti on sto th e R oy al S ociety to be used as in ductive ev id en ce. T his sto ry sh ou lds how u s t ha t t ho u gh b ee tl es m a y p ro fi ta bl y b e c o ll ec te d, o b se rv at io n s m a y n o t.T wen ty -fiv e y ears ag o I tried to bring h om e th e sam e po in tto a g ro up o f 1 1ph ysics stu dents in V ien na b y b eg in nin g a lectu re w ith the fo llo win g in - 1s tr uc tio ns : 'T ak e p en cil a nd p ap er ; c ar ef ull y o bs er ve . a nd w ri te d ow n w h at Jy ou h av e o bs er ve d I'T he y a sk ed , o f c ou rs e. what I w an te d th em to o bs erv e. 1C le ar ly t he i ns tr uc ti on . ' O bs er ve !' i s a b su rd .U ( It i s n o t ' ev e n id iom at ic . u n le ss I Ith e o bj ec t o f t he tr an sit iv e v er b c an b e ta ke n a s u nd er sto od .) g ~~ er va do ll _is i. .m n se 1 ec ti ve . I t n ee ds ~ C h os en. o ? je ct . a. d .e fi ni te t as k. a n. !. nt e.r es .t, a po in t\ \OfVleW, a problem. And I t s de sc ri p ti on pre sup 'p '~ ,~~~_~ , ;, . 4~s~p~~eanguage . iIwith prope rty .:w.Qr li~ ;l t ' :p t~~ppose s , s imi [email protected] . ct a ss i f ic adon , which in it s I ItUrn pre suppose s i t it e re s t~ ' p o i r i t s o f . ' v f e w : ; an(rproble .ms~ 'A h un gry an im al', ~ \. 13 See section 30 of L.sc.D. ~ ,

    4 6 (

    1 SCIENCE: CONJECTURES AND REFUTATIONSwrites Katz,14 'd iv id es th e e nv ir on m en t in to e dib le a nd in ed ib le t hi ng s. Ana nim a l in f lig ht s ee s r oa ds to e sc ap e a nd h id in g p la ce s, . G en er ally s pe ak -in g, ob jects chang e accord in g to the n eed s of th e animal,' W e m ay addth at o bj ec ts c an be c l a ss i fi ed . and ca n b ec om e s im i la r o r d is si m il ar . only inth is w ay -b y b ein g r elated to needs a nd i n te r es ts . Th is ru le a pp lie s n ot o nlyto a nim als b ut a ls o to s cie ntis ts . F or th e a nim al a p oin t o f v ie w is providedb y its n ee ds , th e ta sk o f th e m ome nt, a nd its e xp ec ta tio ns ; f or th e s ci en tis t b yh is t he or et ic al i nt er es ts , t he s pe ci al p ro b lem u n de r i nv e st ig a ti on , h is c o nj ec -tu re s a nd a ntic ip atio ns . a nd th e th eo ries w hich h e a cc ep ts as a k in d o f b ack -ground : h is fram e of reference. his 'horizon of expectations', .. ,..("". ~T1iep ro hle m -'W h ic h c om e s f ir st, t he h yp ot he sis (H) o r t he o bs er va tio n - '- ., .(0); i s s o lu b le ; a s i s theproblem, 'W hich c om es firs t. th e h en (H) o r th eeg g (0)'. The rep ly to the h i it e r- i s~" An-ea r li e r- l d ii d ofegg ; to' t he f orm er . :A ,n . . . \e ar li er k in d of hruothesis ' . Itis qu ite true that any particular hypothesiS \- w e c ho os e w il l h av e- be en pr ec ed ed b y o bs er va ti on s- th e o bs er va tio ns . f ore xam pl e, w h ic h i t i s d e si gn ed t o e xp la in . B u t t he se o b se rv at io n s, i n t he ir turn.p re su pp os ed th e a do pti on o f a f ra m e o f r ef er en ce : a f ra me o f e xp ec ta tio nS : a

    .i ~r~e"of1UeOrIes: IfJJ: iey 'weres~~tlt:in~~Y=-C"fealeajf~ee(rrQixpi iUii -1 t io n a nd t h us g a v e r is e t o t h~j !! .. v~ n ti o _n . .E f JL J1 "y' p J? ! b~~ i$ .~ j !. .~ ! lS~~~ .u~~ JP~Y:

    O . . . -l . ( f ii O L b : e . _ ~ ~ P l a i n e d . w l t . h h . 1 J .' h . . e....o..~J~.~.~....~#. .,.J Jra...p 1. e.w.o rk . t . h ' . 01 . d. ho: Z O . n. ;~~~t~;,;;~.'!~~~~~i=~~s~~~s~f~~~Z!~.nsclo~s " i n lw m ._ l ! X P e c t a t i o n s . , ~ . . . . _ . . . . . . . . ~~el~oiji or i i j 9 h j :isis ~ Ith in k; b ut every organism.has.inborn reac(iQllS...DI..lespons~s; an d am on g th em , res po ns es a dap te d to im-pend ing even ts . These re sp~n. .~~ ! .! ! .~ .~y .de s9! i~~ .~~_~~ llPec ta t iQl l$ .~~~q~timply ing tha t ~~ .~~ere~pect a tiOJ . 1 .I i :~{~~~mQ: t !$.h e n ew - bo rn b a by ' ex p ec ts ',in th is sense. to be fed (and , one cou ld even arg ue, to be pro tected andl ov ed ). I n v ie w o f t he c lo se r el at io n b et we en e xp ec ta tio n a nd k no w le dg e w em ay even sp eak in qu ite a reaso nab le sense o f 'in bo rn kn ow ledg e', This"' 1 m . owledge ' i s .e~aeve r; valid_qJfGri: 'an_:_inb orn~xp~ ~ll!.~~m atterh9 wstr~ !L~!lqJ '._c ,..:.~y W e . . ~ . ~ ~ ( Hie n ew b or n'- ch rr d~ m ay b ea b an d on e d, a nd s ta rv e .)T hu s w e are b orn with e xp e ct at io n s; w i th ' kn ow le dg e ' w h ic h. a lt ho u gh n o tv a li d a p ri or i. i s, es yc 1wl o gi ca ll y o r g e n ! ! ! ~ l I i : ; i . p f i o r i , L e . p rio r to all observa-tio na l e xp er ie nc e. O n e o O lie m o st. im p or ta nt- of th es e e xp ec ta tio ns is th ee xp ec ta tio n o f f in din g a r eg ula rit y. I t is c on ne ct ed w ith a n i nb or n p ro pe ns it yto lo ok o ut fo r re gu la rities . o r w ith a need to find r eg u la ri ti es . a s w e m a y s eef ro m th e p le as ure o f thechild w ho Sii'ilsltesthis~neea:-----~ , , , .-nus i lnsHnct i ;~ ; e x p e c t a t I o i o f fin di ng r eg ula riti es , w h ic h is p sy ch o.logically a prior i. c or re sp o nd s v e ry c lo s el y t o t he ' la w o f c au sa li ty ' w h ic h Ka ntb elieved to be part o f ou r m en tal o utfit an d to be a pr ior i v al id . O n e m ig htt hu s b e in cl in ed to s ay t ha t K a nt f aile d to d is tin gu is h b etw e en p sy ch ol og ic -ally a pr ior i w ay s o f t h in ld ng o r r es po nd in g a nd a pr ior i v alid b elie fs . B u t I d o14 Katz.loc. cit.

    41

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    CONJECTURESno t thin k that his m istak e w ~uite as ero de as that. for the expectation offinding r egu1ar i ti e s i s .ML2.nlY psychological ly a e , rio r i. b ~t a ls o 1 0g ic aU y apriori; it i s l o. g ic a ll t Q r io r t o aUobse ryAf : jona lexpenence . fo r It IS pnor to a nyfe cO iO i~ f s im ilaritie s, as w e h av e s ee n; a nd a ll o bs erv atio n in vo lv es th er ec og n it io n o f s im il ar it ie s ( or d is si mi la ri ti es ). B u t in s pi te o f b ei ng l og ic al lya pr io ri in th is s en se th e e xp ec ta tio n is n ot v alid a priori. F or it m ay fail; weca n e as il y c on st ru ct a n e nv ir onm en t V t wo uld b e a le th al o ne ) .w h ic h, com-p ared w ith o ur o rd in ary en viro nm en t, is s o c hao tic th at w e c om plete ly failt o f i nd regu la r it ie s . (All n at ur al l aw s c ou ld r em a in v al id ; e nv ir onm en ts o f t hi sk in d h av e b e e n used inthe a n ima l e xpe rimen ts men ti o ne d int he n e xt s e et io n .)T hu s K an t's re ply to H um e ca me n ea r to b ein g rig ht; fo r th e d is tin ctio nbetween an a p r io r i v ali d e xp ec ta tio n a nd ' o ne w h ic h is b oth g en etic ally an dl o gi ca ll y p r io r to observation, but no t a p ri or i v alid, is really som ew hat _ .subtle. But K an t proved too much. In trying to show how know ledg e is 'p os sib le, h e p ro po se d a th eo ry w hic h h ad th e u nav oid ab le c on seq uen ce th at ;'. Q ! t t quest fo r k now l~~st ~ ssarilr_!ucceed,_ w hich is clearly m istaken. _~ur hitenect ~dniW its law s from nature butim po se s its law s u po n n atu re', h e w as rig ht. B ut in th in kin g th at th ese la wsa re n ec es sa ri ly t ru e, o r t Ea t , . we n ec c.. !s ar il y s us g ee d i n i mp os ip g t hem .. ..E .o .nna ture .J l e. _was wrong .1s Na tu re v er y o ft en r es is ts q u it e s uc ce ss fu ll y, f or ci ngu sto '- dis ca rd o ui- l aw s a s re fu te d; b ut if w e liv e w e m ay tr y a ga in .T o s um u p t hi s l og ic al c ri ti ci sm o f Hum e' s p sy ch ol og y o f i nd u ct io n we mayc on sid er th e id ea o f b uild in g a n in du ctio n m ac hin e. P la ce d in a simplified' wo rld ' (f or e xa mp le . o ne o f s eq ue nc es o f c olo ure d c ou nte rs ) s uc h a m ac hin em ay th ro ug h r ep etitio n 'le ar n', o r e ve n 'formulate', l aw s o f s uc ce ss io n wh ic hh o ld i n i ts w or ld . Ifs uc h a m ac hin e c an b e c on stru cte d ( an d Ia ve n o d ou btthat it can) then. it m ig ht be arg ued, m y theory m ust be w rong ; for if am ac hin e is c ap ab le o f p er fo rm in g in du ctio ns o n th e b as is o f r ep etitio n, th erec an b e n o lo gica l rea so ns p rev en tin g u s fro m d oin g th e sa me.T he arg um en t s ou nd s co nv in cin g, b ut it is m ista ken . I n c on stru ctin g a nin du ctio n m ach in e w e, th e arc hitec ts o f th e m ac hin e, m ust d ecid e' a p r io r iw ha t co ns titu tes its 'w orld '; w ha t th in gs a re to b e tak en as s im ilar o r eq ua l;a nd w hat kind o f ' la w s' we w ish th e m ach in e to b e ab le to 'd isc ov er' in its'world', In o th er w ord s w e m ust b uild in to th e m ac hin e a fra mew ork d eter-mining wha t is re lev an t o r in tere stin g in its w orld = t he m a ch in e will haveits 'in bo rn ' s el ec tio n p ri nc ip le s. T he p ro ble ms o f s im ila rity will h av e b ee nsolved for it by its m akers w ho thus have in terpreted the 'w orld ' fo r themachine.IS Kant be l i eved tbatNewton's dynamics was a p r io r i valid. (SM his MetaphysicalFoundat ion s o f Na t ura l S c ie n c e, published between the first and the second editions of theCritique of Pure Rea son . ) But if, a s he thought, w e c an explain the validity of Newton'stheory by the fact that our intellect imposes its laws upon nature, it follows, I think. thatou r intellect tmlSl succeed in this; which makes it hard to understand wh y a p r io r i know-ledge such as Newton's should b e $0 hard to come by..A somewhat ful ler s tatement of

    this criticism can be found in ch, 2.especial ly section ix, and cbs.7 and S of the presentvolume. 48ItIIf

    SCIENCE: CONJECTURES AND REFUTATiONSVI

    Ou r p ro pe ns ity " to lo ok o ut f or re gu la ritie s. a nd to im po se la ws u po n n atu re , ileads to the p sy cholog ical phenom eno n of d o gma ti c. t hi n ki n g or, m ore 1 \g e n er al ly , d o gmat ic b e ha v io u r: ~ t~ ! pe ct [email protected] e y er ywhe re a n_~attem~t o f in d t hem e ve n wh er e t he re a r~ nQn ei ~ v el 't !L ~ !L d ,.Q . J! QU i~ ~ .~ eattempts WM~~~ a~ k!q_q!:;.~~_~~~ll~~~~-:an..d,.w,e~~t:.-.exp~ct!l.!!2ns ~ ~ ~ ~ q _ . , , ~ l l . r o ! a re I na de qu ate a ~d . w e o ug ht to ,a cc ep t d ef ea t. T h is dQW .g tt SD ll S t o s om e ~ Itis d em an de d b y-.r:;~"~&r~)Sm " ' _ l i . r ~ _ . .i Si fu at it 5i i'W ff ic K ea n o n ly b e d ea lt W I th b y f or ci ng o u r c on je ct ur es u po n t hew orld . M oreov er, th is dog matism allo ws us to ap proach a g ood theory instag es" b y w ay of app ro xim ations: if w e accept d efeat too easily , w e m ayp re ve nt o ur se lv es f ro m f in di ng th at w e w er e v er y n ea rly r ig ht.Itis c le ar th at th is dogma tic a t ti tude , w hich m ak es u s stic k to o ur firs t im-p re ss io ns . is in dic ativ e o f a s tr on g b elie f; w hile a cr it ical a t ti tude , wh ic h i sr ea dy t o m o di fy i ts t en et s, w h ic h a dm it s d o ub t a nd d em a nd s t es ts , i s i n di ca ti veo f a w e ak er b el ie f. N ow aCQQm jn g t o l !um~U ! L~ ~ l. _l !! !~ _ ~~ ~ 1! la rtheo~.J.~~_.s.lWlgtJLQLa....h~l..ef S 1 1 Q l ) }4 . . .M.. .a_pr.oducLomp-et i !!Qg; th~_s its ho u ld a 1wa ~s$ Q w . _ J l ! J b eX , .R~ ie n~. .J il iv .3 ~ .b .e ._ g re a te .t .i n. ks~ tim# iy e . . ..perSOns. B u i - do gm at ic t hi nk in g , a n u n co nt ro ll ed w is h t o i mp o se r eg u la ri ti es .a -m :a :D l fe s tp l ea sur e i n r it es a nd in r ep etitio n a s s uc h. a re c ha ra cte ris tic o fp rim itiv es a nd c hild re n; a nd in cre as in g e xp er ie nc e a nd m atu rity s om etim esc re ate a n a ttitu de o f c au tio n a nd c riti cis m r ath er th an o f d ogm at is m.I m ay p erhap s m entio n here a po int of ag reem ent w ith psycho-analysis.Psycho-analysts assert that n eurotics and oth ers interp ret the w orld inac co rd an ce w ith a p erso nal s ef p attern w hic~ . i " s. .} ) ,o t .ea s il y g iYe ii J iI , ;andwhich c a n o fte u" he "f ia ce a- -b ac kto ea rI yd riid ho od :'A 'p atte rn o r' s ch em ewhich wasooopte;rvery- 'eai iyUi 'l l fe-is ' D i i i l i l t a i n e d th ro ug ho ut, a nd e ve ry~~ e !p~ri en~~ l ll t. ~ r_p~~ .~~ j .PJ~~ .I . !f_ i . t i . .y~~ij'~gJt? a_s.. t were, an~n:-trlb utin g to its rig id ity . T his is a d es crip tio n o f w ha t I av e can ed th e d og -manca tt it ud e ~- a s 'd .i st 'i nc t f rom t he critical a tt it ud e, wh ic h s ha re s with th ed ogm atic a ttitu de th e q uic k a do ptio n o f a s c hema o f e xpe c ta ti o ns -a myth,p erh ap s, o r a co nje ctu re o r h yp oth esis -b ut w hic h is re ad y to m od ify it. toco rre ct it, an d e ven to g iv e i t u p. Imjp.c).f.,U,e

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    CONJECTURESan d chang ing w orld : w e k no w fro m ex perim ents o n anim als th at varyin gd eg ree s o f n eu ro tic b eh av io ur m ay b e p ro du ce d a t will by cor re spond ing lyvarying difficulties.Io un d m an y o th er lin ks b etw e en th e p sy ch olo gy o f k n o wle dg e a nd p sy ch o-lo gical fie ld s w hich are o ften con sid ered rem ote from it-for exam ple th ep s yc ho lo g y o f art a nd m u sic ; in f ac t, m y i de as a bo ut in du ctio n o ri gin ate d ina con jectu re abo ut th e ev olu tion of W estern po lyp ho ny. B ut yo u w ill b es pa re d t hi s s to ry .

    1 SCIENCE: CONJECTURES AND REFUTATIONSaim o f d is co ve rin g th eir w eak s po ts s o th at th ey m ay be im pro ve d u po n, ist he a tt it ud e o f r ea so na bl en es s, o f r at io n al it y. It makes far-reaching use ofb oth verbal arg um en t and ob serv atio n-o f observation in the interesLQ!'.~~gumP1!Ufm'~~!'h e G ree ks ' d is co ve ry o f th e c ritic al m eth od g av e riseat firs t t o th e m istak en h op e th at it w ou ld lea d to th e s olu tio n o f a ll th e g re ato ld p ro ble ms; th at it w ou ld es ta blish c erta in ty ; th at it w ou ld h elp to proveo ur t he or ie s, t o justify th em . B ut th is h op e w as a r es id ue o f th e d ogm ati c w ayo f th in kin g; in fa ct n oth in can be 'u stifie d o r p ro ve d (o uts id e o f m ath e-m atic s a nd ogicj, T he dem and Jar rationa proo illSCIence ill cates af a il ur e t o k e e p d is tin ct th e b ro ad re alm o f ra tio nality an d th e n arro w re almo f r at io na l c ert ain ty : it is a n u nte na ble , a n u nr ea so na ble d em a nd .N e ve rt he le ss , t he r ol e o f l og ic al a rg um en t, o f d ed u ct iv e l og ic al r ea so n in g ,r em a in s a ll -i m po rt an t f or t he c ri ti ca l a pp ro ac h; n o t b ~ ~_ ~ ~i ta ll ow .. a.J lS .. top r ov e ou r t h eo r ie s , o r t o i n fe r t he ~ !r ~~_pb s~~on: _~~ t emen .~~~~s~( ir uy 1 55 'P 'i fe ly -d et hr Ct iv er ea so ii fu g i s i t p o ss ib le f or u s t o d is co v er wh at o u rtheories i m p l y . ancI ' i j1usto -Cri i iCfie themefleCtrve1Y.~cnt iCism~'1 'sii id~"is 'ana t tempt lo f i il d -i heweak"spo ts ma i f ieo ry7ai ia1 l 'i e s~. as a ru le , c an b e fo un do nly in th e m o re r em o te l og ic al c on se qu en ce s w h ic h ca n b e d er iv ed f ro m it .nis h er e th at p ur ely lo gic al r ea so nin g p la ys an i m po rt an t p ar t in science. l ' . ~H um e w as rig ht in 'stre ss in g th at o ur th eo rie s c an no t b e v alid ly in ferre dfro m w hat w e ca n k no w to b e tru -n eith er'fro m o bs erv atio ns n or fro m a ny -th in g e lse . H e c on clu de d fro m th is th at o ur b elie f in th em w as irra tio nal. I f' be li ef ' m e an s h er e o u r i na bi li ty to d ou bt o ur n atu ra l l aw s , a nd th e c on sta nc yo f n atu ra l reg ula ritie s, th en H um e is a ga in rig ht: th is k in d o f d og matic b elie f \h as , o ne m ig ht s ay , a p hy si olo gic al r at he r than a r a ti on a l b a si s. If,however. Ith e term 'b elie f' is tak en to co ve r o ur c ritic al ac cep tan ce o f sc ie ntific th eo ries \-a entative a cc ep tan ce co mb in ed w ith an e ag ern es s to re vis e th e th eo ry if !w e s uc ce ed in d es ig nin g a te st w h ic h it c an no t p as s-th en H um e w as w ro ng .' !l~~~n .acce..p l~~2.~~ r .~~?ri~ !,~~~~~ in~~!~9!!,!!. There is not I'even an~ ir ra ti onaI Iii. re lymg fo r p r ac tiC if 'i )U r po se supon we ll -t es te dtheories. fer-no m ore ra~onaL~se of a .~ !!o! is~ t~ us..; _jA ss um e th at w e h av e d elib eratelY m ad e I t o u r ta sk to liv e Int hi s u n kn ownw o rld o f o ur s; to a dju st o ur se lv es to it as well a s w e can; to ta ke a dv an ta ge o fth e o pp or tu nitie s w e can find in it; an d to e xp la in i t, if po ss ib le ( we n ee dn ot assum e that it is), an d as far as po ssible , w ithth e h elp o f law s and ex -p l an a to r y t h eo r ie s . Ifw e h av e m a de th is o ur ta sk, th en th ere is n o m o re rationalp ro ce du re th an t he m et ho d o f t ri al a nd e rr or -o / c on je ctu re a nd r efu ta tio m ofb old ly p ro po sin g th eo ries ; o fln j o ur b es t t o s ho w th at th es e a re e rro neo }!_ s;a nd o f a cc ep tin g th em te nta tiv e y if ou r c ri ti ca l e ff o rt s a re un su c ce s sf u l... F ro m th e p oin t o f v ie w h er e d ev elo pe d a ll la w s, all t h eo r ie s , r ema in e s se n ti -ally ten tativ e, o r co nje ctu ra l, o r h yp oth etica l, e ve n w hen w e fe el u na ble tod ou bt th em a ny lo ng er. B efo re a th eo ry h as b ee n refu ted w e c an n ev er k no win w hat w ay it m ay h av e to b e m od ifie d. T hat th e su n will a lw ay s r is e a nd s etw i th in t w en ty -f ou r h o ur s i s s ti ll p ro v er bi al a s a l aw - es ta bl is he d b y i nd u ct io nb ey o nd r ea so n ab le d o ub t' . It is o dd th at t his e xa m ple is s ti ll in u se , th ou gh it. 51'

    vnMy l og ic al c ri ti ci sm o f Hum e' s p sy ch o lo g ic al t he or y, a nd t he c on si de ra ti on sc on nec te d w ith it (m ost o f w hic h I e la bo ra te d in 1 92 6-7 , in a th es is en title d'On H a bit a nd B elie f in Laws ' 16 ) m ay s ee m a little re mo ve d fro m th e fie ld o fth e p hilo so ph y o f s ci en ce . B u t th e d is tin ctio n b etw e en d ogm ati c a nd c rit ic alth in kin g, o r th e d ogm at ic a nd th e c ritic al a ttit ud e, b rin gs u s r ig ht b ac k to o urcentra l pro blem . ~_ ~~ ~tic attitud e is c!~a:.ly r ela ted to the tendency..!2.Y.~.ifi_~l?:!}a.W~al1d_.~~J!eIll~J?'.J~Ys_~~~ jL t? ._~pe lr _ th~Dl. .r :d )o . c o~th em e ve n to th e p oin t o f n eg le ct in g r ef uta tio ns , w h er ea s th e c ritic al a ttitu delsOn~'Qfieadin~ss " t o : C h a n i ( { . 1 l i e . : : n i ' = - J Q ] ~ ~ [ t h e i A ;o_[~~tIj~iri;- to falSifyt h e m , - i f pos~ible . TW s s ug g es ts t ha t w e m a y i de nt if y_~ ~ e .c~ t i. c al at t it ude wi tht he 's c ie n tmc - ai ti tu d e , a n (f i' fl e( fj )gmaUC iiH it ud e 'W i t h t he on e wh i ch we ha vedesC iibed '~aspseu(i< i.sc~eniific. '. ',. " - . . , . .... .. ....~ -t fr ur th er s ug g es ts t ha t g e ne ti ca ll y s pe ak in g t he p s eu d o- sc ie nt if ic a tt it ud e ism ore p rim itive than, an d p rior to , the scien tific attitu de: that it is 'a p re-n , c ie nt if ic a tt it ud e. A n d t hi s p ri m it iv it y o r p ri or it y a ls o h as i ts l og ic al a sp ec t.

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    CONJECTURESm ay h av e s er ve d w en e no ug h in th e d ay s o f A r is to tle a nd P yt he as o f M a ss al ia-th e g rea t tra ve ller w ho fo r c en tu rie s w as c alled a lia r b eca us e o f h is ta le sof T hule. the land of th e frozen sea an d th e m id ni gh t s un .T he m etho d of trial and erro r is n ot. of cou rse , sim ply id en tical w ith th esclentific orcrluciil~iipProach-=-::wit1i th e m eth od 'o f conjeotureandrefutatlon.

    -Tl ie-method' o f trial a nd erro r is a pp lie d n ot o nly b y E in stein b Ut,in a m ore. . d o gm at ic f as h io n ,DY t he am oe fi a a ls o . T h e d if fe re nc e l ie s n o t s o m uch in th e, tria ls as in a critical ' an d c on st ru ct iv e a tt it ud e t ow a rd s e rr or s; " er ro rs wh ic h, . the . sC ien t is t ' consC iously an d C au tio us ly tr ie s to u nc ov er in ' ' ' o r d e r . to re-futehis' th eo rie s 'w ith ' s ea rc hin g a rg um en ts , in clu din g a pp ea ls to th e m o st.s ev er e e xp er im en ta l te sts w h ic h h is th eo rie s a nd h is in ge nu ity p er mi t him to.design.( . ._ ..t he c ri ti ca l a tt it ud e m a y b e -d e sc ri bed a s th e c on sc io us a tte m pt to m ak e o urth eo rie s, o ur c on je ctu re s; s uf fe rin ou ute ad in th e s tr ug g le f or th e s ur vi va l o ft h e f it te s t. It g iv es u s a chance to survivethe e li m in at io n o f an inadequateh yp oth es is -w h en a m o re d ogm atic a tti tu de w o uld e lim in ate it by 'eliminatingu s. (J :J le re is a to uc hin g sto ry o f an In dian c o~ ~..!L !!h ic h d !~ .p .~ ~edb ec au s e' ol lt sb el le fi n d ie "l io ll il es s o f l i f e ; f u C l u d i n g t ha t o f t ig e rs .) W e 't hu so1lmiJltlie f i t i e s t t h e 6 r Y W i ti il ii o u r r e a c n b y - t l ie e ll m ln at io n o f t h o se wh ic h a rel es s f it . (By ' fi tn e ss Io n ot m ea n m er ely ' us ef uln es s' b ut tr uth ; s ee c ha pt er s3 an d 10,below.) I d o n ot th in k th at th is p ro ce du re is irra tio na l o r in n ee d o f

    ~ a n y f ur th er r at io n al j us ti fi ca ti on .vm

    Le t u s n ow tu rn fro m o ur lo gica l c ritic is m o f th e p sy cho lo g y o f e xpe ri en c e too ur real p rob lem -th e pro blem o f t he l og ic o f s ci en ce . A lth ou gh s om e o f th ethings Ih av e said m ay help u s here , in so fa r a s th ey m ay h av e e lim in ate dc er ta in p sy ch olo gic al p re ju dic es in f av ou r o f in du ctio n, m y tr ea tm e nt o f th el og ic al p ro b lem o f i nd u ct io n i s c om p le te ly i nd ep en d en t o f t hi s c ri ti ci sm . a nd o fa ll p sy ch o lo g ic al c on s id er at io n s. P ro v ig ~ y o ~o l ?- ~t do ~ t! ~l ly b e: ij ~y ejn th e. a ll~ J~ ed _p "~ ch olo ! ca lf ac t ~ ~ e m ak e in du ct~ on s. y ~um ay n ow ~ or -g erm y w hole sto ry W Ith t ~ ceP tiC !no f.tw o lO gical pom ts: m ~_ JQ g!W

    .-iemarkso~:!i~r ~~J2!!i!~!-~_c!_i;~~~d>Humes 1 0 W c a C rI tiC is m of ~ u c ~Q.__ ...-. Prom 'W iiat I have said it is o bv io us th at th ere w as a clo se lin k b etw een th et wo p ro ble ms w h ic h in te re ste d m e a t th at ti me : d em ar ca tio n. a nd in du cti ono r s c ie n ti fi c me thod . Itw as easy to see tha~< :.th od of scien ~ is critic ism ,he....~ttemP ted fal~ffia\.tigJ,!S.o... . . .Jt it took me a e w y ea rs to n otic e th at} h~ _!W ?_ . '_J>~le~L~on39 .9 ...9 ~ereJ.n..a ,sense..o~~ . . W h y, I as ked . d o s o m an y s cie ntis ts b eliev e in in du ctio n? I fo un d th ey d ids o b ec au se th ey b elie ve d n at ur al s ci en ce to b e c ha ra cte riz ed b y th e in du cti vem eth od -by a m eth od startin g fro m. and rely ing up on. long sequ en ces ofo bs erv atio ns an d e xp erim en ts . T hey b elie ve d th at th e d iffe re nc e b etw eeng e nu in e s ci en ce a nd m e ta ph y si ca l o r p s eu d o- sc ie nt if ic s p ec ul at io n d ep e nd edsolely upon w hether o r no t the inductive m ethod w as em ployed . T hey52

    1 SCIENCE: CONJECTURES AND REFUTATIONSb el ie ve d ( to p ut it in m y o wn te rm in olo gy ) th at o nly th e in du ctiv e m eth odc ou ld p ro v id e a s at is fa ct or y c ri te ri on o f d ema rc at io n .Ie ce nt ly c am e a cr os s a n i nt er es ti ng f orm ul at io n o f this b el ie f i n a r em a rk -a ble p hilo so ph ic al b oo k b y a g re at p hy sic is t- Ma x B o rn 's Natura l Ph i losophy'o f C au se a nd C ha nc e.1S H e w rite s: 'I nd uc tio n allo ws u s to g en eralize a n um -b er o f o bs er va tio ns in to a g en er al r ule : th at n ig ht f ollo w s d ay a nd d ay f ollo w sn ig ht . . B ut w hile e very da y life has n o d ef in ite c rite rio n f or t he v alid ity o fan induction, . science has w orked out a code. or rule of craft, fo r itsa pp li ca ti on .' B o rn n owhe re r ev ea ls t he c on te nt s o f t hi s i nd u ct iv e c od e (whi ch ,as h is w ord in g s ho ws , co nta in s a 'd efin ite c riterio n fo r th e v alid ity o f an In-d uc ti on ,) ; b u t h e s tr es se s t ha t ' th er e is n o l og ic al a rg um en t' f or i ts a cc ep ta nc e:'it is a q ue stio n o f faith"; a nd b e i s t he re fo re ' wU li ng t o c al l i nd u ct io n a meta-p hy sical p rincip le'. B ut w hy do es b e believe that su ch a cod e of valid in -du ctive rules m ust ex ist? T his becom es clear w hen h e sp eak s o f the 'vastc om m un ities o f p eo ple ig no ra nt o f, o r rejec tin g, th e ru le o f s cien ce, am on gt hem t he m embe rs o f a nt i- va cc in at io n s oc ie ti es and believers in astrology. Itis u seless to arg ue w ith them ; Icanno t com pel them to accept the sam ec rite ria o f v alid in du ctio n in w hich Ib el ie ve : th e c od e o f s cie ntif ic r ule s.'T h is m a ke s it quite c le ar t ha t ' va l id induc tion' wa s h ere m ea nt to serve as ac ri te ri on o f d ema rc at io n b etwe en s ci en c e and p se udo -s ci en e e,B ut it is ob vio us that thi!l rule or craft of 'v alid ind uctio n' is n ot ev enm eta ph ys ic al: it sim ply d oes n ot exist. N o rule c an e ve r g ua ra ntee th at ag en er aliz at io n in fe rr ed f ro m tr ue o bs er va tio ns , h ow e ve r o fte n r ep ea te d, istrue. (B orn him self d oes n ot believe in the tru th of N ew ton ian p hy sics, ins pite o f its s ucc es s, alth ou gh h e b elie ve s th at it is b as ed o n in du ctio n.) A ndt he s uc ce ss o f s ci en ce is n ot b as ed u po n r ule s o f in d~ ctio n~ b ut d ep en ds uPOl!luck t ingen~, a n d th p purely deductive r ule s o f critical atgmnent .- y summarize som e of m y conclusions as fo llow s: -n du etio n, i.e . in fe ren ce b as ed o n m an y o bs erv atio ns. is a m yth . It isa p sy ch olo gic al f ac t. n or a f ac t o f o rd in ar y life, no r o ne of scientific~ure .(2) e a ctu al p ro ce du re o f s cie nc e is to o pe ra te w ith c on je ctu re s: to jumpto n clu sion s-often after o n e s in g le o b se rv at io n { as n o ti ce d f or e xam pl e b yand Born}. .

    ~eated

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    CONJECTURESIX

    If, as I a ve s ug g es te d, t he p ro bl em o f i nd uc ti on is only an i ns ta nc e o r f ac eto f th e p ro ble m o f d em arc atio n. th en th e s olu tio n to th e p ro ble m o f d em arc a-.tion m ust provide us w ith a solution to the problem of induction. T his isi nd ee d t he c as e. I e li ev e, a lt ho ug h i t i s p er ha ps n o t i mm e dia te ly o bv io us .

    F or a b rief fo rm ula tio n o f th e p ro blem o f in du ctio n w e c a n t ur n a ga in toB or n, w ho w rite s: ' . n o o bs er va tio n o r e xp er im en t, h ow ev er' e xte nd ed , c ang iv e m or e th an a f in ite n um be r o f re pe titio ns '; th er ef ore . 'th e s ta te me nt o f ala w-B d ep en ds o n A -alw ay s tran scen ds ex pe rie nce. Y et th is k in d o f state-m en t is m ad e ev ery wh ere an d all the tim e, and som etim es from scantyma ter i al . ' 19In o ther words , t he log ica J .. p r. qbl em.. o fJnduct ioJ l .. .a r ise s .. , a ~~~'sldiSCOverY(s~j~~ll.~~pie.s.s~~t~y.JJom)Jba1ili un ossI1)"le1OUs' ) P i i W b Y _ I" oDs irV it lo n o r C1 tp e rimen tt s i l ! r ; : e it 'transcends e x. penence'; the fact [email protected] ce 'p io po se s _ ~[ _i j.s .~ _ s. )~w .$ )< ev er ywh er ea nd a ll t he t im e . ( Li ke Hume,BOm~isst ruck by th e 's ca nty m ate ria l', i.e . th e le w o bs er ve d in sta nc es u po nw hich the law m ay be based.) To this w e have to add 0he p ri nC ip le O f }empiricism whic h a ss erts th at in s cie nc e, .enly obs~~ ~e arid experim entl. .9ec~d~up~n the accep_tanc,eor r q e . t l o .n ? l ~ g ~ ~ ~ t i f tQ , .$ l ! ! ~ m ! ? J l t s *nclyQingaws an "t eones,~ -- - " " ' T h t s e t h i t ; prfuciples, (a), (b), an d (e), appear a t .f t J:~ t s i gh t to c la sh ; a ndt hi s a pp ar en t c la sh c on st it ut es th e logical p r o b l e m " o j i n d U C i i o n : "

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    CONJECTURESb y r ep ea te dly a pp ly in g t he c ritic al m et ho d, e lim in atin g m a ny b ad th eo rie s,a nd in ve ntin g m an y n ew o ne s. N ot e ve ry bo dy is a ble to d o th is ; b ut th ere isn o o th er w ay .O ther q uestion s hav e som etim es b een asked . T he o rig in al p ro blem o fin du ctio n, it w as s aid , is th e p ro ble m o f justifying i nduc ti on , i .e . o f j us ti fYinginduc ti ve in ference. If y ou an sw er th is p ro ble m b y s ay in g th at w ha t is c alle da n ' in du ct iv e i n fe r en c e' is a lw a ys i nv a li d a n d t he re fo re c le ar ly n o t j us ti fi ab le ,th e fo llo win g n ew p ro blem m us t a ris e:_ ho w d o y ou ju stify y ou r m eth od o f~pJY : the ~!l!.od of trial an d erro r is a method OLeli1!! . i'! f}t- li ng f al se t he o ri es b ob~ .~ !y~ jQ !!"@ ~~ts.~d_~ustification fo r th i_ i~ j" 1 !! {1 )1 ! '. e. o g ic aL r el at io n sh ip ..o f- de du c ib il it y_ 'Y b ic h a ll ow s u s t o a ss e! !l ~~ \f al si ty o f u n iv er s~ l tl !! ~eD .t sJ tw . .U~ l~ lJ b! L tr ut h o fSm g ul ar on e s.- _J-A iio th er" qu es tio n s om etim es a sk ed is th is : w hy is it r ea so n ab le t o p re fe rn on -f als if ie d s ta te m en ts to f al si fie d o ne s? T o this q ue stio n s om e i nv olv eda ns wer s h av e b ee n. p ro du ced , fo r e xam ple p ra gm atic a ns we rs . B ut fro m ap ra gm a ti c p oin t o f v ie w th e q ue st io n d oe s n ot a ri se , since f a ls e t h eo r ie s o f te ns er ve w e ll e no u gh : m o s t f orm ul ae u s ed i n e n g in ee ri ng o r n a vi ga ti on a re k n ownto be f al se , a lt ho u gh t he y m a y b e e xc el le n t a p p ro x im a ti on s a nd e as y t o h an d le ;a nd th ey are u sed w ith c on fid en ce b y p eo ple w ho k no w th em to b e fa ls e.Th e o n ly c o rr ec t a nsw er i s t he s tr ai gh tf or w ar d o n e: l '- ~a Jl ~! Lw .~ S~.9J:t fo rJ ! :! l .!b .: , (even though we ca n n ev er b e s ure w e h av e fo un d it), a nd b eC au se "th ef al sif ie d t he or ie s a re k no w n o r b el ie ve d to b e f al se , w h ile th e n on -f als if ie dth eo ri es m ay s til l b e t ru e. B es id es , w e do no t p r ef e r every non- fal s if i ed theory-on ly one w hich, in the lig ht o f critic ism , appears to be b etter th an itsc om pe tito rs : w hic h s olv es o ur p ro ble ms , w hic h is w ell te ste d, a nd o f w hichw e th in k, o r ra ther co njecture or h op e (co nsiderin g o th er pro visio nallya c ce p te d t h eo r ie s ), t h at it will s ta nd u p to f ur th er te sts .I t h as a ls o b een s aid th at th e p ro blem o f i nd uc tio n is , 'W h y is it reasonablet o b el ie ve t ha t t he f ut ur e will b e lik e th e p as t ? t, a n d t ha t a s a ti s fa c to r y a n swe rto this q ue st io n s ho ul d m a ke it p la in t ha t s uc h a be l ie f i s , in f a c t, r e a sonab l e .M y r ep ly is t ha t i t i s r ea so n ab le t o b el ie v e that t he f ut ur e w i ll b e v er y d if fe re n tf ro m t he p as t i n m a ny v ita lly im p or ta nt r es pe ct s. A dmit te dly it i s pe r fec t lyr e ason ab le t o ac t o n th e a ssu mp tio n th at it will, inm an y r es pe cts , b e like th ep as t, a nd th at w e ll -te ste d la w s will con tinu e to h old (sin ce w e can h ave n ob ette r a ss um ptio n to ac t u po n); b ut it is a ls o r ea so na ble to b elie ve t ha t s uc ha c ou rs e o f a cti on will le ad u s a t tim es in to s ev ere tro ub le , s in ce so me o f th el aw s u p on wh ic h we n ow h e av il y r el y m a y e as il y p r ov e Un re li ab le . ( R em embe rth e m id nig h t s un I) O ne m ig ht e ve n s ay th at to ju dg e fro m p as t ex perie nc e,a nd f rom o u r g e ne ra l s ci en ti fi c k n ow l ed g e, t he f ut ur e will no t b e l ik e t he p as t,in perh aps m ost o f t he w ay s w hich th ose h ave in m ind w ho say th at it will.Wate r will s om et im e s n ot q ue nc h th ir st , a nd a ir will c ho k e t ho s e wh o b re at heit.An ap paren t w ay ou t is to s ay t ha t th e future will b e lik e th e p as t in th es en se th at th e iaw1 of nature w il l n ot c ha ng e, b ut t his is b e gg in g t he q u es ti on .W e speak of a 'law o f natu re ' o nly ifw e th in k th at w e h av e b efo re u s a re gu -la rity w hic h d oe s n o t c han ge; a nd if w e f in d th at ifch an ge s th en w e s ha ll n ot. '--56-"' ~,. ~ , .. , .

    1 SCIENCE: CONJECTURES AND REFUTATIONScont inue to can ~~~ O f c ourse our search for natu ral law si O O i c a te s 'i li ii w e h op e to find th em , a nd th at w e b el ie ve that t h er e a r e n a tu r all aws; but o ur b elie f in an y p artic ula r n atu ra l law c an no th av e a s afer b as isthan otiruns~sfill cn tiC iiI a i$JW ruo .Jiiitti.!!. .. ------.l"tlifDkihit th~ sew ho pu:t~o bleni' o f ind uctio n in terms o f th e reason-ableness o f o u r b el ie fs a re p e rf ec tl y r ig h t i f t he y a re d is sa ti sf ie d w i th a Humean,or post-Humean, s ce pt ic al d e sp ai r o f r ea so n . W e mu st i nd ee d r ej ec t ~ l1 ~ .y ie wt ha t a b el ie fi n s ci en ce i s a s i rr at io n al a s a b e li ef in p ri m it iv e magical . racticej-th at bo t are a m atter of accep tinj a < tota l id eolog y', a c on ve ntio n o r at t a d U W i l 6 i 'S e a O i l fi U t i i :" B ut w e m us t b e c au tio us ifwe f orm ul at e o u r p ro t; :l e i i1 ; w i t h H U i il e ;i S on e o f t he r ea so n ab le n es s o f o u r beliefs. W e sh ould sp lit "(this p roblem in to three-our old prob lem of dem arcation, or o f how todistinguish b et w ee n s ci en c e a nd p ri m it iv e m a g ic ; t he p ro b lem o f t he r at io n al it yo f t he s ci en ti fi c o r critical procedure, a nd o f th e r ole o f o bs er va ti on w ith in it ;and lastly the pro blem o f th e ratio nality o f o ur acceptance o f t he or ie s f ors cie ntif ic a nd f or p ra ctic al p ur po se s. T o al l t he se t hr ee p ro b lem s solutio ns ./have been offered here . ,"O ne s ho uld als o b e c are fu l n ot to c on fu se th e p ro blem o f th e re as on ab le -

    . - poo . ~ ~ _ L .. _ . ._ . T .~ . . C -, .- . , .. . " ~ "" ' - , " . .. . ~ . ,_ . - . ._ . ~ . .. - -

    ~ .: :: ~ ,. ne sso f t he s ci en ti fi c p ro ce d ur e an d t h e ( te n ta tl 'v e ) a c ce p ta n ce o f t h e ! ~ Jm l ts _~ f".'-.ibis p r oc e ame : :t e; ~ if ie s c ie n tf fi c t h eo r ie s -w i th the ' pr O bl em ' of th e r at io n -__ ,. :Y l it y - o i" o th e fw i s e of the belie that this rocJ3ure IfM succee"J. fli p r a c t i c e ., . in practi seien c research, this belief is no ou t unavoidab le andreason able. th ere being no better a ltern ativ e. B ut th~ ~~ f is ~.Y_lffi_;.. j u s~~~ l! t~ Ia v e a r gu~ ( in" " se c tt o nv5 .YOr e ov er ;i f iw e c oU ld S ho w . o n g en er al lo gic al g ro un ds , th at th e. S C ie n.i fi c q u es t i s l ik el Y j.to s uc ce ed . o ne c ou ld n ot u nd ers ta nd w hy a ny th in g lik e s uc ces s h as b ee n s orare inth e l on g h is to ry o f h um an e nd ea vo ur s to k no w more a bo ut o ur w o rld .Y et an other w ay o f pu tting the pro blem o f in du ctio n is in term s of prob- .a b il it y . L e t t b e th e th eo ry a nd e t he e v id en c e: w e ca n a sk f or P(t,e), that is to 's ay , t he p ro b ab il it y o f t,given e. T h e p ro b lem o f i n d uc ti on , i t i s o ft en b el ie ve d.

    ca n th en b e p ut th us : c on stru ct a c a lc u lu s o f p ro bab il it y w hic h allo ws u s tow ork out fo r any theory t w hat its p ro bab ility is. relativ e to an y g iv enemp ir ic a l e v id e n ce e; an d sh ow th at P(t,e) i nc re as es w i th t he a cc umu la ti ono f s up po rt in g e vid en ce , a nd r ea ch es high v alu es -a t a ny r ate v alu es g re at er~ than!.

    ~ InThe_!: ! f!g.!~yf ScJen~iJlc .Qfs'_ !~1J !_L~~ plai~edw~ _!_!'!!E E..~~J_ J_I!!sfl a PE !o ac h to th e p ro ble m is f un da m en ta lly m is ta ke n.23 T o m ake this clear, I~ \ ( i nt ro -d uc ed t he re il ie dI Stii iC 't iO n betWeenprobability an d degree o f corrobora-t io n o r c onf irmat io n . (T he te rm 'c on firm atio n' h as b ite ly b ee n s o m uc h u se da nd m is use d th at I h av e d ec id ed to s urre nd er it to th e v erific atio nis ts a nd tou se f or m y o w n p ur po se s ' co rr ob or ati on ' o nly . T he t er m 'p ro ba bili ty 'is b es t

    .E L.3c.D. ( se e n o t eS a b ov e ). th. x . e s pe c Ia l ly s e ct ion s SO t o 8 3 a ls o s ec ti on 3 4 t r . SecalsO my nQ te :' aSCf of In dep end en t A xio ms fo r P ro 6ab1 li. N .S . 4 7, 1 938 ,p. 275.. ... .. . ('I his note ha s since been reprinted,. with corrections, in t he n ew a p pe n di x - u of L.Sc.D./ , . : . ~ : ; : ~ : >. e e also th O next Dote but ot tO to the prcsen~:aPter.)

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    CONJECTURESused in so me o f the m any sen ses w hich satisfy th e w ell-k no wn calcu lu s o fp ro ba bil ity , a xiom at iz ed , f or e xamp le , b y K ey ne s, J ef fr ey s, a nd m ys el f; b utnothing of course depends on the choice of w ords, as long as w e do no tassume. u nc ri ti ca lly , th at d eg re e o f c or ro bo ra tio n m u st a ls o b e a p ro ba bil ity- th at is to sa y. th at it m ust sa tis fy th e c alcu lu s o f p ro ba bility .)I e xp la in ed in m y b oo k w hy w e ar e in te re ste d in th eo rie s w ith a h igh degreeo f co rrobo ra t ion . A nd I ex plain ed w hy it is a m istak e to co nclu de fro m th isth at w e a re i nte re st ed in highlyprobable theories .!o in te d o ut th at th e p ro b:! _b il it y o f a s ta tem en t ( or s et o f s ta tem en ts ) is a lw a ys t he s :~ ~ 4~ ) es ~~~~ tQ_Q i_~_c()ntento r th e aeaU ctive p ow er o f th e_ j ta t emen t, .a nd ._ . t~~o i ts e xp la na to r y: powe ; . ~~d i tl g 1y eve ry_ i .t !. t~~ .e _~ inga l! ~~ }y ~1 :l! _~ ~t em e nt m u st h av e a 10:pro~bi1ity;"!!!1d vice.versq_:a state-m e nt w it h a h ig h p ro b ab il it y Wil l be s c ie n ti fi ca l ly un in t er e st ing . be cause i t s a yslittle an d h as n o e xp la na to ry p ow er . A lth ou gh w e se ek th eo rie s w ith a h ig hdeg re e o f co rr obor a ti on. gf2cient!st~.!!gLSf!.~lf}JJgbly_p!.q!,!ble .!~e_,,!i(!sb u t e x pl a na t io n s; that ~ . ! E _ ! f ! y " J ' . o . . 1 f ! r f t ! 1 _ . ! ! ! ! f! _ i ' ! ! P . t : 2 . l z g _ l ! J . U l 1 i ! . f !! . f ! _ s . . 2 4 Th eo pp o' sif C v ie w- -t ha t - sc Ie nc e a im s a t h