Science Refuations

Science Refuations - of KARL POPPER rut Science Conjectures...

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Unformatted text preview: of KARL POPPER rut Science: Conjectures re— tfl’ and Rcfiitatzons ne 2 :se i be ‘3 to ed Mr. 'l‘umbull had predicted evil consequences, . . , and was now doing the best n, in his power to bring about the verification of his own prophecies. try wAnthony Trollope ist 11' rd ci— I l I er .3} When I received the list of participants in this course and realized that I had been asked to speak to philosophical colleagues” I thought, after some 23 hesitation and consultation, that you would probably prefer me to speak 21 about those problems which interest me most, and about those develop- 1:11 ments with which I am most intimately acquainted. I therefore decided 01 to do what I have never done before: to give you a report on my own work m in the philosophy of science, since the autumn of 1919 when I first began W to grapple with the problem, ‘When should a theory be ranked as scientific?’ m __ or ‘Is there a criterion for the scientific character or status of a theory?’ m _ The problem which troubled me at the time was neither, ‘When is a or ,' theory true?’ nor? ‘When is a theory acceptable?” My problem was different. v. I wished to distinguish between science and pseudo-science; knowing very well that science often errs, and that pseudo-science may happen to stum- a ble on the truth. I knew, of course, the most widely accepted answer to my problem: L it 3* FROM Karl Popper, Conjectures and Refutations (London: Rontledge and Kegan Paul, 1963) 33w391 * This essay was originally presented as a lecture at Peterhouse College at Cam— ‘ bridge University in the summer of 1953 as part of a course on developments and : trends in contemporary British philosophy, organized by the British Council. It was originally published as “Philosophy of Science: A Personal Report," in British Philosophy in MidCentury, ed. C. A. Mace, (London: Allen and Unwin, 1957). US 7 He 4 1 CH. 1 SCIENCE AND Psaunoscmnou that science is distinguished from pseudovscience-«or from ‘metaphysics’ ——by its empirical method, which is essentially inductive, proceeding from observation or experiment. But this did not satisfy me. On the contrary, I often formulated my problem as one of distinguishing between a genuinely empirical method and a non—empirical or even a pseudo-empirical inethodwthat is to say, a method which, although it appeals to observation and experiment, nevertheless does not come up to scientific standards. The latter method may be exemplified by astrology, with its stupendous mass of empirical evidence based on observationwon horoscopes and on biographies. But as it was not the example of astrology which led me to my prob— lem I should perhaps briefly describe the atmosphere in which my prob- lem arose and the examples by which it was stimulated. .Mter the collapse of the Austrian Empire there had been a revolution in Austria: the air was full of revolutionary slogans and ideas, and new and often wild theories. Among the theories which interested me Einstein's theory of relativity was no doubt by far the most important. Three others were Marx’s theory of history, Freud’s psycho-analysis, and Alfred Adler’s so—called ‘individual psychology’.* There was a lot of popular nonsense talked about these theories, and especially about relativity (as still happens even today), but I was fortunate in those who introduced me to the study of this theory. We all—~the small circle of students to which I belonged—were thrilled with the result of Eddington’s eclipse observations which in 1919 brought the first important confirmation of Einstein’s theory of gravitation. It was a great experience for us. and one which had a lasting influence on my intellectual devel— opmentl‘ . The three other theories 1 have mentioned were also widely discussed among students at that time. I myself happened to come into personal contact with Alfred Adler, and even to cooperate with him in his social * For a fascinating autobiographical aecount of Popper’s youthful flirtation and painful disenchantment with Marxism, see “A Crucial Year: Marxism; Science and Pseudoscience,” in The Philosophy of Karl Popper, ed. Paul A. Schilpp (La Salle, 111.: Open Court, 1974), 1:23—29. There is also an extended criticism of Freud in Karl R. Popper, Realism and the Aim of Science (New York: Routledge, 1983), 163—74. lEinstein's general theory of relativity entails that light rays must bend in a grav- itational field. Organized by Sir Arthur Eddington, two Royal Astronomical'Society expeditions were dispatched to observe the solar eclipse of 1919, and verified that starlight was indeed deflected by the sun by the amount that Einstein had pre- dicted. The Times of London reported this success as the most remarkable scien— tific event since the discovery of the planet Neptune. The light-bending test of relativity theory is discussed in “Popper’s Demarcation Criterion," in the com« n’ientary on chapter 1, and in “Two Arguments for Explanationism," in the com- mentary on chapter 4. ' __‘ of‘if’ienna where he had established social gu It was during the summer of 1919 that I b _. ', ‘dlnatisfied with these three theories~the Man ihéfielysis, and individual psychology; and l b their claims to scientific status. My problem I "farm. ‘What is wrong with Marxism, psycho: etiology? Why are they so different from phys ' :i' theory, and especially from the theory of rela‘ To make this contrast clear I should exple would have said that we believed in the truth Etation. This shows that it was not my doubt L' _ three theories which bothered me, but somet that I merely felt mathematical physics to be ,- logical or psychological type of theory. Thus \ the problem of truth, at that stage at least, in or measurability. It was rather that I felt tha though posing as sciences, had in fact more myths than with science; that they resembled orny. I found that those of my friends who we and Adler, were impressed by a number of p cries, and especially by their apparent explar appeared to be able to explain practically ever the fields to which they referred. The study have the effect of an intellectual conversion eyes to a new truth hidden from those not y were thus opened you saw confirming instanc full of verifications of the theory. Whatever he Thus its truth appeared manifest; and unbelie did not want to see the manifest truth; who rel it was against their Class interest, or becaus were still ‘un—analysed' and crying aloud for t The most characteristic element in this incessant stream of confirmations, of observat ories in question; and this point was constai herents. A Marxist could not open a newspa] page confirming evidence for his interpretatii news, but also in its presentation—which re paper-and especially of course in what the 1: ian analysts emphasized that their theories we ‘clinical observations’. As for Adler, I was mi experience. Once, in 1919, I reported to hirr seem particularly Adlerian, but which he for; in terms of his theory of inferiority feelings physics’ 1g from itrary, l nuinely npirical :rvation ndards. tendons and on r}? prob- y probe :ollapse air was reories. vity was :eory of lividual £65, and Inmate 6 small esnlt of portant erience l develw scussed scrsonal 5 social ion and Science ilpp {La icism of titledge, r a grow Society lied that rad pre— lc scien« g test of re corn- he com- Poncn a SCIENCE: Coninornnas AND Runorarxons l 5 work among the children and young people in the workingclass districts of Vienna where he had established social guidance clinics. it was during the summer of 1919 that I began to feel more and more dissatisfied with these three theoriesmthe Marxist theory of history, psycho analysis, and individual psychology; and i began to feel dubious about their claims to scientific status. My problem perhaps first took the simple form, ‘What is wrong with Marxism, psycho—analysis, and individual psy— chology? Why are they so different from physical theories, from Newton’s theory, and especially from the theory of relativity?’ To make this contrast clear I should explain that few of us at the time would have said that we believed in the truth of Einstein’s theory of grav- itation This shows that it was not my doubting the truth of those other three theories which bothered me, but something else. Yet neither was it that I merely felt mathematical physics to be more exact than the socio« logical or psychological type of theory. Thus what worried me was neither the problem of truth, at that stage at least, nor the problem of exactness or rneasurability. It was rather that I felt that these other three theories, though posing as sciences, had in fact more in common with primitive ,_ myths than with science; that they resembled astrology rather than astron» '_ only. I found that those of my friends who were admirers of Marx, F reud, I _ and Adler, were impressed by a number of points common to these the- ories, and especially by their apparent explanatory power. These theories appeared to be able to explain practically everything that happened within the fields to which they referred. The study of any of them seemed to have the effect of an intellectual conversion or revelation, opening your eyes to a new tmth hidden from those not yet initiated. Once your eyes were thus opened you, saw confirming instances everywhere: the world was full of verifications of the theory. Whatever happened always confirmed it. il‘hus its truth appeared manifest; and unbelievers were clearly people who did not want to see the manifest truth; who refused to see it, either because it was against their class interest, or because of their repressions which were still ‘un-analysed’ and crying aloud for treatment. The most characteristic element in this situation seemed to me the incessant stream of confirmations, of observations which ‘verified’ the the cries in question; and this point was constantly emphasized by their ad* lrerents. A Marxist could not open a newspaper without finding on every page confirming evidence for his interpretation of history; not only in the news, but also in its presentation—which revealed the class bias of the paper~and especially of course in what the paper did not say. The Freud— ian analysts emphasized that their theories were constantly verified by their ‘clinical observations’. As for Adler, l was much impressed by a personal experience. Once, in 1919, I reported to him a case which to me did not seem particularly Adlerian, but which he found no difficulty in analysing in terms of his theory of inferiority feelings, although he had not even 6 l Cu. 1 Science AND Pscuooscmuce seen the child. Slightly shocked, i asked him how he could be so sure. ‘Because of my thousandfold experience,’ he replied; whereupon i could not help saying: ‘And with this new case, I suppose, your experience has become thousand-andcnedold.’ What I had in mind was that his previous observations may not have been much sounder than this new one; that each in its turn had been interpreted in the light of ‘previous experience’, and at the same time counted as additional confirmation. What, I asked myself, did it confirm? No more than that a case could be interpreted in the light of the theory. But this meant very little, l reflected. since every conceivable case could be interpreted in the light. of Adler’s theory, or equally of Freud’s. l may illustrate this by two very different examples of human behaviour: that of a man who pushes a child into the water with the intention of drowning it; and that of a man who sacrifices his life in an attempt to save the child. Each of these two cases can be explained with equal ease in Freudian and. in Adlerian terms. According to Freud the first man suffered from repres- sion (say, of some component of his Oedipus complex), while the second man had achieved sublimation. According to Adler the first man suffered from feelings of inferiority (producing perhaps the need to prove to himself that he dared to commit some crime), and so did the second man (whose need was to prove to himself that he dared to rescue the child). I could not think of any human behaviour which could not be interpreted in terms of either theory. It was precisely this fact-that they always fitted, that they were always confirmedwwhich in the eyes of their admirers constituted the strongest argument in favour of these theories. it began to dawn on me that this apparent strength was in fact their weakness. With Einstein’s theory the, situation was strikingly different. Take one typical instance—Einstein’s prediction, just then confirmed by the findings of Eddington’s expedition. Einstein’s gravitational theory had led to the result that light must be attracted by heavy bodies (such as the sun), pre« cisely as material bodies were attracted; As a consequence it could be calculated that light from a distant fixed star whose apparent position was close to the sun would reach the earth from such a direction that the star would seem to be slightly shifted away from the sun; or, in other words, that stars close to the sun would look as if they had moved a little away from the sun, and from one another. This is a thing which cannot non mally be observed since such stars are rendered invisible in daytime by the sun’s overwhelming brightness; but during an eclipse it is possible to take photographs of them. If the same constellation is photographed at night one can measure the distances on the two photographs, and check the predicted effect. Now the impressive thing about this case is the risk involved in a prediction of this kind. If observation shows that the predicted effect is definitely absent, then the theory is simply refuted. The theory is incom~ patible with certain possible results of observationwin fact with results ‘Poeruo I Screams: Contacrunas sun Res which everybody before Einstein would have expect lerent from the situation i have previously ClESCIIbet that the theories in question were compatible wit human behaviour, so that it was practically irnpos human behaviour that might not be claimed to be theories. These considerations led me in the winter of l‘ which l may now refornmlate as follows. 1 it is easy to obtain confirmations, or verifies theorvéif we look for confirmations. 2 Confirmations should count only if they are dictions; that is to say, if, unenlightened by we should have expected an event which ‘ the theorywan event which would have refs 3 Every ‘good’ scientific theory is a prohibr things to happen. The more a theory forbic 4 A theory which is not refutable by any our scientific. lrrefutability is not a virtue of a think) but a vice. '5 Every genuine test of a theory is an attempt it. Testability is falsifiability; but there an some theories are more testable, more exp others; they take, as it were, greater risks. 6 Confirming evidence should not count ext of a genuine test of the theory; and this in sented as a serious but unsuccessful attem; now speak in such cases of ‘corroborating 7 Some genuinely testable theories, when fc upheld by their admiremmfor example by auxiliary assumption, or by re-interpretmgl a way that it escapes refutation. Such a pro but it rescues the theory from refutation or ing, or at least lowering, its scientific state a rescuing operation as a ‘conventionalzst 1 stratagem’.) One can sum up all this by saying that ti status ofa theory is its falsifiahility, or refutc in I may perhaps exemplify this vyith the help of mentioned. Einstein’s theory oi gravitation clear falsifiability. Even if our measuring instrument: 'Poeem a Scrunch: Coorncronns AN!) REFUTATIONS 1 7 sure. which everybody before Einstein would have expected.‘ This is quite dif~ :ould terent from the situation I have previously described, when it turned out that the theories in question were compatible with the most divergent c has human behaviour, so that it was practically impossible to describe any have human behaviour that might not be claimed to be a verification of these been theories. time These considerations led me in the winter of 1919—20 to conclusions firm? which I may now reforinulate as follows, reory. 1 It is easy to obtain confirmations, or verifications, for nearly every could theorywif we look for confirmations. I may 2 Confirmations should count only if they are the result of risky pres rat of citations; that is to say, if, unenlightened by the theory in question, vning we should have expected an event which was incompatible with :hild. the theorywan event which would have refuted the theory. 3 Every ‘good’ scientific theory is a prohibition: it forbids certain n and apresi things to happen. The more a theory forbids, the better it is; BCOHd 4 A theory which is not refutable by any conceivable event is non— tfered scientific. lrreiutability is not a virtue of a theory {as people often mseif think} but a vice. vhose 5 Every genuine test of a theory is an attempt to falsify it, or to refute :ould it. "I“estobility is falsifiability; but there are degrees of testability: terms some theories are more testable, more exposed to refutation, than tthey others; they take, as it were. greater risks. tuted 6 Continuing evidence should not count except when it is the result .n on ofa genuine test of the theory; and this means that it can be pre~ sented as a serious but unsuccessful attempt to falsify the theory. (I 3 one now speak in such cases of ‘corroborating evidence.) dings 7 Some genuinely testable theories, when found to be false, are still 3 the upheld by their admirers—afar example by introducing ad hoc some , pre- auxiliary assumption, or by reeinterpreting the theory ad hot: in such id be a way that it escapes refutation. Such a procedure is always possible, but it rescues the theory from refutation only at the price of destroy- i was e star ing, or at least lowering, its scientific status. (l later described such vords, a resetting operation as a ‘conventionolist twist’ or a ‘conventionolist away stra tagem '.) nor— One can sum up all this by saying that the criterion of the scientific ie by status ofa theory is its folsifiability, or refutability, or testability. lie to ed at heck . I I II in 21 act is 1 may perhaps exemplify this with the help of the various theories so for com. mentioned. Einstein’s theory of gravitation Clearly satisfied the criterion of zsults tulsifiability. Even if our measuring instruments at the time did not allow 8 t (Sn. 1 Sumter: AND Pseoooscmwes us to pronounce on the results of the tests with complete assurance. there was clearly 21 possibility of refuting the theory. Astrology did not pass the test. Astrologers were greatly impressed, and misled, by what they believed to be confirming evidencemso much so that they were quite unimpressed by any unfavourable evidence. Moreover, by making their interpretations and prophecies sufficientiy vogue they were able to explain away anything that might have been ii refutation of the theory had the theory and the prophecies been more precise. In order to escape falsification they destroyed the testability of their theory. it is a typical soothsayeris trick to predict things so vaguely that the predictions can hardly tail: that they become irrefutable. The Marxist theory of history, in spite of the serious efforts of some of its founders and Followers, ultimately adopted this soothsaying practice. In some of its earlier formulations (tor example in Marx's analysis of the character of the ‘coming social revolution’) their predictions were testable, and in tact falsified} Yet instead of accepting the rehttutions the followers of Marx res—interpreted both the theory and the evidence in order to make them agree, In this way they rescued the theory from refutation; but they did so at the price of adopting a device which made it irrefutable. 'l‘liey thus gave a ‘conventionalist twist" to the theory; and by this strutagem they destroyed its much advertised claim to scientific status. The two psycho—analytic theories were in a different class. ’l‘hcy w...
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