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  • 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 hesitation and consolation, that

  • you would probably prefer me to speak about those problems which interests me most, and

  • about those developments with which I am most intimately acquainted. I therefore decided

  • to do what I have never done before: to give you a report on my own work in the philosophy

  • of science, since the autumn 1919 when I first begin to grapple with the problem, "When should

  • a theory be ranked as scientific?" or "Is there a criterion for the scientific character

  • or status of a theory?"

  • The problem which troubled me at the time was neither, "When is a theory true?" nor

  • "When is a theory acceptable?" my problem was different. I wished to distinguish between

  • science and pseudo-science; knowing very well that science often errs, and that pseudoscience

  • may happen to stumble on the truth.

  • I knew, of course, the most widely accepted answer to my problem: that science is distinguished

  • from pseudoscienceóor from "metaphysicsby 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 pseudo-empirical method ó that 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 observation ó on horoscopes and on biographies.

  • But as it was not the example of astrology which lead me to my problem, I should perhaps

  • briefly describe the atmosphere in which my problem arose and the examples by which it

  • was stimulated. After 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. The 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 allóthe small circle of students to which I belongówere

  • 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 development.

  • The three other theories I have mentioned were also widely discussed among students

  • at the time. I myself happened to come into personal contact with Alfred Adler, and even

  • to cooperate with him in his social work among the children and young people in the working-class

  • districts of Vienna where he had established social guidance clinics.

  • It was the summer of 1919 that I began to feel more and more dissatisfied with these

  • three theoriesóthe 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 psychology?

  • 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 gravitation. This shows that it

  • was not my doubting the truth of those three other theories which bothered me, but something

  • else. Yet neither was it that I nearly felt mathematical physics to be more exact than

  • sociological 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 measurability. It

  • was rather that I felt that these other three theories, though posing as science, had in

  • fact more in common with primitive myths than with science; that they resembled astrology

  • rather than astronomy.

  • I found that those of my friends who were admirers of Marx, Freud, and Adler, were impressed

  • by a number of points common to these theories, and especially by their apparent explanatory

  • power. These theories appear 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, open your eyes to a new truth hidden from

  • those not yet initiated. Once your eyes were thus opened you saw confirmed instances everywhere:

  • the world was full of verifications of the theory. Whatever happened always confirmed

  • it. Thus its truth appeared manifest; and unbelievers were clearly people who did not

  • want to see the manifest truth; who refuse to see it, either because it was against their

  • class interest, or because of their repressions which were still "un-analyzed" 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 theories in question; and this point was constantly

  • emphasize by their adherents. 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 ó which revealed the class bias of the paper ó and especially

  • of course what the paper did not say. The Freudian analysts emphasized that their theories

  • were constantly verified by their "clinical observations." As for Adler, I 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 analyzing in terms of his

  • theory of inferiority feelings, Although he had not even 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-and-one-fold."

  • 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 a theory. But this meant very little,

  • I reflected, since every conceivable case could be interpreted in the light Adler's

  • theory, or equally of Freud's. I may illustrate this by two very different examples of human

  • behavior: 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 Adlerian terms. According

  • to Freud the first man suffered from repression (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 behavior which could not

  • be interpreted in terms of either theory. It was precisely this factóthat they always

  • fitted, that they were always confirmedówhich in the eyes of their admirers constituted

  • the strongest argument in favor 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 ó Einstein's

  • prediction, just then confirmed by the finding 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), precisely 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 normally 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 distance 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 incompatible with certain possible results of observationóin

  • fact with results which everybody before Einstein would have expected.[1] This is quite different

  • from the situation I have previously described, when it turned out that the theories in question

  • were compatible with the most divergent human behavior, so that it was practically impossible

  • to describe any human behavior that might not be claimed to be a verification of these

  • theories.

  • These considerations led me in the winter of 1919-20 to conclusions which I may now

  • reformulate as follows.

  • It is easy to obtain confirmations, or verifications, for nearly every theory ó if we look for

  • confirmations.

  • Confirmations should count only if they are the result of risky predictions; that is to

  • say, if, unenlightened by the theory in question, we should have expected an event which was

  • incompatible with the theory ó an event which would have refuted the theory.

  • Every "good" scientific theory is a prohibition: it forbids certain things to happen. The more

  • a theory forbids, the better it is.

  • A theory which is not refutable by any conceivable event is non-scientific. Irrefutability is

  • not a virtue of a theory (as people often think) but a vice.

  • Every genuine test of a theory is an attempt to falsify it, or to refute it. Testability

  • is falsifiability; but there are degrees of testability: some theories are more testable,

  • more exposed to refutation, than others; they take, as it were, greater risks.

  • Confirming evidence should not count except when it is the result of a genuine test of

  • the theory; and this means that it can be presented as a serious but unsuccessful attempt

  • to falsify the theory. (I now speak in such cases of "corroborating evidence.")

  • Some genuinely testable theories, when found to be false, are still upheld by their admirers

  • ó for example by introducing ad hoc some auxiliary assumption, or by reinterpreting

  • the theory ad hoc in such a way that it escapes refutation. Such a procedure is always possible,

  • but it rescues the theory from refutation only at the price of destroying, or at least

  • lowering, its scientific status. (I later described such a rescuing operation as a "conventionalist

  • twist" or a "conventionalist stratagem.")

  • One can sum up all this by saying that the criterion of the scientific status of a theory

  • is its falsifiability, or refutability, or testability.

  • II

  • I may perhaps exemplify this with the help of the various theories so far mentioned.

  • Einstein's theory of gravitation clearly satisfied the criterion of falsifiability. Even if our

  • measuring instruments at the time did not allow us to pronounce on the results of the

  • tests with complete assurance, there was clearly a possibility of refuting the theory.

  • Astrology did not pass the test. Astrologers were greatly impressed, and misled, by what

  • they believed to be confirming evidence ó so much so that they were quite unimpressed

  • by any unfavorable evidence. Moreover, by making their interpretations and prophesies

  • sufficiently vague they were able to explain away anything that might have been a refutation

  • of the theory had the theory and the prophesies been more precise. In order to escape falsification

  • they destroyed the testability of their theory. It is a typical soothsayer's trick to predict

  • things so vaguely that the predictions can hardly fail: 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

  • (for example in Marx's analysis of the character of the "coming social revolution") their predictions

  • were testable, and in fact falsified.[2] Yet instead of accepting the refutations the followers

  • of Marx re-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. They thus gave a "conventionalist twist" to the theory;

  • and by this stratagem they destroyed its much advertised claim to scientific status.

  • The two psycho-analytic theories were in a different class. They were simply non-testable,

  • irrefutable. There was no conceivable human behavior which could contradict them. This

  • does not mean that Freud and Adler were not seeing certain things correctly; I personally

  • do not doubt that much of what they say is of considerable importance, and may well play

  • its part one day in a psychological science which is testable. But it does mean that those

  • "clinical observations" which analysts naÔvely believe confirm their theory cannot do this

  • any more than the daily confirmations which astrologers find in their practice.[3] And

  • as for Freud's epic of the Ego, the Super-ego, and the Id, no substantially stronger claim

  • to scientific status can be made for it than for Homer's collected stories from Olympus.

  • These theories describe some facts, but in the manner of myths. They contain most interesting

  • psychological suggestions, but not in a testable form.

  • At the same time I realized that such myths may be developed, and become testable; that

  • historically speaking all ó or very nearly all ó scientific theories originate from

  • myths, and that a myth may contain important anticipations of scientific theories. Examples

  • are Empedocles' theory of evolution by trial and error, or Parmenides' myth of the unchanging

  • block universe in which nothing ever happens and which, if we add another dimension, becomes

  • Einstein's block universe (in which, too, nothing ever happens, since everything is,

  • four-dimensionally speaking, determined and laid down from the beginning). I thus felt

  • that if a theory is found to be non-scientific, or "metaphysical" (as we might say), it is

  • not thereby found to be unimportant, or insignificant, or "meaningless," or "nonsensical." But it

  • cannot claim to be backed by empirical evidence in the scientific sense ó although it may

  • easily be, in some genetic sense, the "result of observation."

  • (There were a great many other theories of this pre-scientific or pseudo-scientific character,

  • some of them, unfortunately, as influential as the Marxist interpretation of history;

  • for example, the racialist interpretation of history ó another of those impressive

  • and all-explanatory theories which act upon weak minds like revelations.)

  • Thus the problem which I tried to solve by proposing the criterion of falsifiability

  • was neither a problem of meaningfulness or significance, nor a problem of truth or acceptability.

  • It was the problem of drawing a line (as well as this can be done) between the statements,

  • or systems of statements, of the empirical sciences, and all other statements ó whether

  • they are of a religious or of a metaphysical character, or simply pseudo-scientific. Years

  • later ó it must have been in 1928 or 1929 ó I called this first problem of mine the

  • "problem of demarcation." The criterion of falsifiability is a solution to this problem

  • of demarcation, for it says that statements or systems of statements, in order to be ranked

  • as scientific, must be capable of conflicting with possible, or conceivable, observations.

  • Thanks for watching.

When I received the list of participants in this course and realized that I had been asked

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カール・ポッパー卿の「改ざんとしての科学 (Sir Karl Popper's "Science as Falsification")

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    姚姚   に公開 2021 年 01 月 14 日
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