Category: .Popper, Karl

The asymmetry between verifiability and falsifiability

Again, the attempt might be made to turn against me my own criticism of the inductivist criterion of demarcation; for it might seem that objections can be raised against falsifiability as a criterion of demarcation similar to those which I my­self raised against verifiability.

This attack would not disturb me. My proposal is based upon an asymmetry between verifiability and falsifiability; an asymmetry which results from the logical form of universal statements. For these are never derivable from singular statements, but can be contradicted by singular statements. Consequently it is possible by means of purely deductive inferences (with the help of the modus tollens of classical logic) to argue from the truth of singular statements to the falsity of universal statements. Such an argument to the falsity of universal statements is the only strictly deductive kind of inference that proceeds, as it were, in the ‘inductive direction’; that is, from singular to univeral statements. [19]

Knowledge without dogma

I have tried to show that the most important of the traditional problems of epistemology — those connected with the growth of knowledge — transcend the two standard methods of linguistic analysis and require the analysis of scientific knowledge. But the last thing I wish to do, however, is to advocate another dogma. Even the analysis of science — the ‘philosophy of science’ — is threatening to become a fashion, a specialism. Yet philosophers should not be specialists. For myself, I am interested in science and in philosophy only because I want to learn something about the riddle of the world in which we live, and the riddle of man’s knowledge of that world. And I believe that only a revival of interest in these riddles can save the sciences and philosophy from narrow specialization and from an obscurantist faith in the expert’s special skill, and in his personal knowledge and authority; a faith that so well fits our ‘post-rationalist’ and ‘post-critical’ age, proudly dedicated to the destruction of the tradition of rational philosophy, and of rational thought itself. [xxvi]

Discussion and the growth of ideas

The Western rationalist tradition, which derives from the Greeks, is the tradition of critical discussion–of examining and testing propositions or theories by attempting to refute them. This critical rational method must not be mistaken for a method of proof, that is to say, for a method of finally establishing truth; nor is it a method which always secures agree­ment. Its value lies, rather, in the fact that participants in a discussion will, to some extent, change their minds, and part as wiser men.

It is often asserted that discussion is only possible between people who have a common language and accept common basic assumptions. I think that this is a mistake. All that is needed is a readiness to learn from one’s partner in the dis­cussion, which includes a genuine wish to understand what he intends to say. If this readiness is there, the discussion will be the more fruitful the more the partners’ backgrounds differ. Thus the value of a discussion depends largely upon the variety of the competing views. Had there been no Tower of Babel, we should invent it. The liberal does not dream of a perfect consensus of opinion; he hopes only for the mutual fertilisation of opinions and the consequent growth of ideas. [474]

Science: Conjectures and Refutations

Now the impressive thing about this case [Eddington’s expedition] 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 observation — in fact with results which everybody before Einstein would have expected. 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.

(1) It is easy to obtain confirmations, or verifications, for nearly every theory — if we look for confirmations.

(2) 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 — an event which would have refuted the theory.

(3) Every ‘good’ scientific theory is a prohibition: it forbids certain things to happen. The more a theory forbids, the better it is.

(4) 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.

(5) 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.

(6) 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’.)

(7) Some genuinely testable theories, when found to be false, are still upheld by their admirers—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. [47-8]

Our devastating system of education

Institutions for the selection of the outstanding can hardly be devised. Institutional selection may work quite well for such purposes as Plato had in mind, namely for arresting change. But it will never work well if we demand more than that, for it will always tend to eliminate initiative and originality, and, more generally, qualities which are unusual and unexpected. This is not a criticism of political institutionalism. It only re-affirms what has been said before, that we should always prepare for the worst leaders, although we should try, of course, to get the best. But it is a criticism of the tendency to burden institutions, especially educational institutions, with the impossible task of selecting the best. This should never be made their task. This tendency transforms our educational system into a race-course, and turns a course of studies into a hurdle-race. Instead of encouraging the student to devote himself to his studies for the sake of studying, instead of encouraging in him a real love for his subject and for inquiry, he is encouraged to study for the sake of his personal career; he is led to acquire only such knowledge as is serviceable in getting him over the hurdles which he must clear for the sake of his advancement. In other words, even in the field of science, our methods of selection are based upon an appeal to personal ambition of a somewhat crude form. (It is a natural reaction to this appeal if the eager student is looked upon with suspicion by his colleagues.) The impossible demand for an institutional selection of intellectual leaders endangers the very life not only of science, but of intelligence.

It has been said, only too truly, that Plato was the inventor of both our secondary schools and our universities. I do not know a better argument for an optimistic view of mankind, no better proof of their indestructible love for truth and decency, of their originality and stubbornness and health, than the fact that this devastating system of education has not utterly ruined them. [ch. 7, 147-8]

What it means to be a liberal

To avoid misunderstandings I wish to make it quite clear that I use the terms ‘liberal’, ‘liberalism’, etc., always in a sense in which they are still generally used in England (though perhaps not in America): by a liberal I do not mean a sympa­thizer with any one political party but simply a man who values individual freedom and who is alive to the dangers inherent in all forms of power and authority. [xiii]

The need for precision as relative to a problem

When I wrote my Logik der Forschung I thought that the quest for the meanings of words was about to end. I was an optimist: it was gaining momentum. The task of philosophy was more and more widely described as concerned with meaning, and this meant, mainly, the meanings of words. And nobody seriously questioned the implicitly accepted dogma that the meaning of a statement, at least in its most explicit and unambiguous formulation, depends on (or is a function of) that of its words. This is true equally of the British language analysts and of those who follow Carnap in upholding the view that the task of philosophy is the “explication of concepts”, that is, making concepts precise. Yet there simply is no such thing as an “explication”, or an “explicated” or “precise” concept.

However, the problem still remains: what should we do in order to make our meaning clearer, if greater clarity is needed, or to make it more precise, if greater precision is needed? In the light of my exhortation the main answer to this question is: any move to increase clarity or precision must be ad hoc or “piecemeal”. If because of lack of clarity a misunderstanding arises, do not try to lay new and more solid foundations on which to build a more precise “conceptual framework”, but reformulate your formulations ad hoc, with a view to avoiding those misunderstandings which have arisen or which you can foresee. And always remember that it is impossible to speak in such a way that you cannot be misunderstood: there will always be some who misunderstand you. If greater precision is needed, it is needed because the problem to be solved demands it. Simply try your best to solve your problems and do not try in advance to make your concepts or formulations more precise in the fond hope that this will provide you with an arsenal for future use in tackling problems which have not yet arisen. [30]

Why there can be no precise concepts

[T]he quest for precision, in words or concepts or meanings, is a wild-goose chase. There simply is no such thing as a precise concept (say, in Frege’s sense), though concepts like “price of this kettle” and “thirty pence” are usually precise enough for the problem context in which they are used. (But note the fact that “thirty pence” is, as a social or economic concept, highly variable: it had a different significance a few years ago from what it has today.)

Frege’s opinion is different; for he writes: “A definition of a concept … must determine unambiguously of any object whether or not it falls under the concept … Using a metaphor, we may say: the concept must have a sharp boundary.” But it is clear that for this kind of absolute precision to be demanded of a defined concept, it must be demanded of the defining concepts, and ultimately of our undefined, or primitive, terms. Yet this is impossible. For either our undefined or primitive terms have a traditional meaning (which is never very precise) or they are introduced by so­-called “implicit definitions”—that is, through the way they are used in the context of a theory. This last way of introducing them—if they have to be “introduced”—seems to be the best. But it makes the meaning of the concepts depend on that of the theory, and most theories can be interpreted in more than one way. As a result. implicitly defined concepts, and thus all concepts which are defined explicitly with their help, become not merely “vague” but systematically ambiguous. And the various systematically ambiguous interpretations (such as the points and straight lines of projective geometry) may be completely distinct.

This should be sufficient to establish the fact that “unambiguous” concepts, or concepts with “sharp boundary lines”, do not exist. [28-9]

Precision for its own sake

[B]oth precision and certainty are false ideals. They are impossible to attain, and therefore dangerously misleading if they are uncritically accepted as guides. The quest for precision is analogous to the quest for certainty, and both should be abandoned.

I do not suggest, of course, that an increase in the precision of, say, a prediction, or even a formulation, may not some­times be highly desirable. What I do suggest is that it is always undesirable to make an effort to increase precision for its own sake—especially linguistic precision—since this usually leads lo loss of clarity, and to a waste of time and effort on preliminaries which often turn out to be useless, because they are bypassed by the real advance of the subject: one should never try to be more precise than the problem situation demands.

I might perhaps state my position as follows. Every increase in clarity is of intellectual value in itself; an increase in pre­cision or exactness has only a pragmatic value as a means to some definite end—where the end is usually an increase in testability or criticizability demanded by the problem situation (which for example may demand that we distinguish between two competing theories which lead to predictions that can be distinguished only if we increase the precision of our measurements). [24-5]

The social character of scientific method

The sociology of knowledge is not only self-destructive, not only a rather gratifying object of socio-analysis, it also shows an astounding failure to understand precisely its main subject, the social aspects of knowledge, or rather, of scientific method. It looks upon science or knowledge as a process in the mind or ‘consciousness’ of the individual scientist, or perhaps as the product of such a process If considered in this way, what we call scientific objectivity must indeed become completely ununderstandable, or even impossible; and not only in the social or political sciences, where class interests and similar hidden motives may play a part, but just as much in the natural sciences. Everyone who has an inkling of the history of the natural sciences is aware of the passionate tenacity which characterizes many of its quarrels. No amount of political partiality can influence political theories more strongly than the partiality shown by some natural scientists in favour of their intellectual offspring. If scientific objectivity were founded, as the sociologistic theory of knowledge naively assumes, upon the individual scientist’s impartiality or objectivity, then we should have to say good-bye to it. Indeed, we must be in a way more radically sceptical than the sociology of knowledge; for there is no doubt that we are all suffering under our own system of prejudices (or ‘total ideologies’, if this term is preferred); that we all take many things as self-evident, that we accept them uncritically and even with the naive and cocksure belief that criticism is quite unnecessary; and scientists are no exception to this rule, even though they may have superficially purged themselves from some of their prejudices in their particular field. But they have not purged themselves by socio-analysis or any similar method; they have not attempted to climb to a higher plane from which they can understand, socio-analyse, and expurgate their ideological follies. For by making their minds more ‘objective’ they could not possibly attain to what we call ‘scientific objectivity’. No, what we usually mean by this term rests on different grounds. It is a matter of scientific method. And, ironically enough, objectivity is closely bound up with the social aspect of scientific method, with the fact that science and scientific objectivity do not (and cannot) result from the attempts of an individual scientist to be ‘objective’, but from the friendly-hostile co-operation of many scientists. Scientific objectivity can be described as the inter-subjectivity of scientific method. But this social aspect of science is almost entirely neglected by those who call themselves sociologists of knowledge.

Two aspects of the method of the natural sciences are of importance in this connection. Together they constitute what I may term the ‘public character of scientific method’. First, there is something approaching free criticism. A scientist may offer his theory with the full conviction that it is unassailable. But this will not impress his fellow-scientists and com­petitors; rather it challenges them: they know that the scientific attitude means criticizing everything, and they are little deterred even by authorities. Secondly, scientists try to avoid talking at cross-purposes. (I may remind the reader that I am speaking of the natural sciences, but a part of modern economics may be included.) They try very seriously to speak one and the same language, even if they use different mother tongues. In the natural sciences this is achieved by recognizing experience as the impartial arbiter of their controversies. When speaking of ‘experience’ I have in mind experience of a ‘public’ character, like observations, and experiments, as opposed to experience in the sense of more ‘private’ aesthetic or religious experience; and an experience is‘public’ if everybody who takes the trouble can repeat it. In order to avoid speaking at cross-purposes, scientists try to express their theories in such a form that they can be tested, i.e. refuted (or else corroborated) by such experience.

This is what constitutes scientific objectivity. Everyone who has learned the technique of understanding and testing scientific theories can repeat the experiment and judge for himself. In spite of this, there will always be some who come to judgements which are partial, or even cranky. This cannot be helped, and it does not seriously disturb the working of the various social institutions which have been designed to further scientific objectivity and criticism; for instance the laboratories, the scientific periodicals, the congresses. This aspect of scientific method shows what can be achieved by institutions designed to make public control possible, and by the open expression of public opinion, even if this is limited to a circle of specialists. Only political power, when it is used to suppress free criticism, or when it fails to protect it, can impair the functioning of these institutions, on which all progress, scientific, technological, and political, ultimately depends.

In order to elucidate further still this sadly neglected aspect of scientific method, we may consider the idea that it is advisable to characterize science by its methods rather than by its results.

Let us first assume that a clairvoyant produces a book by dreaming it, or perhaps by automatic writing. Let us assume, further, that years later as a result of recent and revolutionary scientific discoveries, a great scientist (who has never seen that book) produces one precisely the same. Or to put it differently, we assume that the clairvoyant ‘saw’ a scien­tific book which could not then have been produced by a scientist owing to the fact that many relevant discoveries were still unknown at that date. We now ask: is it advisable to say that the clairvoyant produced a scientific book? We may assume that, if submitted at the time to the judgement of competent scientists, it would have been described as partly ununderstandable, and partly fantastic; thus we shall have to say that the clairvoyant’s book was not when written a scientific work, since it was not the result of scientific method. I shall call such a result, which, though in agreement with some scientific results, is not the product of scientific method, a piece of ‘revealed sicence’.

In order to apply these considerations to the problem of the publicity of scientific method, let us assume that Robinson Crusoe succeeded in building on his island physical and chemical laboratories, astronomical observatories, etc., and in writing a great number of papers, based throughout on observation and experiment. Let us even assume that he had unlimited time at his disposal, and that he succeeded in constructing and in describing scientific systems which actually coincide with the results accepted at present by our own scientists. Considering the character of this Crusonian science, some people will be inclined, at first sight, to assert that it is real science and not ‘revealed science’. And, no doubt, it is very much more like science than the scientific book which was revealed to the clairvoyant, for Robinson Crusoe applied a good deal of scientific method. And yet, I assert that this Crusonian science is still of the ‘revealed’ kind; that there is an element of scientific method missing, and consequently, that the fact that Crusoe arrived at our results is nearly as accidental and miraculous as it was in the case of the clairvoyant. For there is nobody but himself to check his results; nobody but himself to correct those prejudices which are the unavoidable consequence of his pecu­liar mental history; nobody to help him to get rid of that strange blindness concerning the inherent possibilities of our own results which is a consequence of the fact that most of them are reached through comparatively irrelevant approaches. And concerning his scientific papers it is only in attempts to explain one’s work to somebody who has not done it that we can acquire those standards of clear and reasoned communication which too are part of scientific method. In one point—a comparatively unimportant one—is the ‘revealed’ character of the Crusonian science particu­larly obvious; I mean Crusoe’s discovery of his ‘personal equation’ (for we must assume that he made this discovery), of the characteristic personal reaction-time affecting his astronomical observations. Of course it is conceivable that he discovered, say, changes in his reaction-time, and that he was led, in this way, to make allowances for it. But if we com­pare this way of finding out about reaction-times, and the way in which it was discovered in ‘public’ science—through the contradiction between the results of various observers—then the ‘revealed’ character of Robinson Crusoe’s science becomes manifest.

To sum up these considerations, it may be said that what we call ‘scientific objectivity’ is not a product of the individual scientist’s impartiality, but a product of the social or public character of scientific method; and the individual scientist’s impartiality is, so far as it exists, not the source but rather the result of this socially or institutionally organized objectivity of science. [ch. 23, 488-92]