....... CONJECTURES sense similar to that in which processes or things may be said to be parts of the world; that the world consists of facts in a sense in which it may be said to consist of (four dimensional) processes or of (three dimensional) things. They believe that, just as certain nouns are names of things, sentences are names of facts. And they sometimes even believe that sentences are some- thing like pictures of facts, or that they are projections of facts.7 But all this is mistaken. The fact that there is no elephant in this room is not one of the processes or parts ofthe world; nor is the fact that a hailstorm in Newfound- 10 land occurred exactIy I I I years after a tree collapsed in the New Zealand bush. Facts are something like a common product oflanguage and reality; they are reality pinned down by descriptive statements. They are like abstracts from TRUTH, RATIONALITY, AND THE a book, made in a language which is different from that of the original, and determined not only by the original book but nearly as much by the principles GROWTH OF SCIENTIFIC KNOWLEDGE of selection and by other methods of abstracting, and by the means of which the new language disposes. New linguistic means not only help us to describe 1. THE GROWTH OF KNOWLEDGE: THEORIES AND PROBLEMS new kinds of facts; in a way, they even create new kinds of facts. In a certain sense, these facts obviously existed before the new means were created which I were indispensable for their description; I say, 'obviously' because a calcula- tion, for example, ofthe movements of the planet Mercury of 100 years ago, MY aim in this lecture is to stress the significance of one particular aspect of carried out today with the help of the calculus of the theory of relativity, may science-its need to grow, or, if you like, its need to progress. I do not have certainly be a true description of the facts concerned, even though the theory in mind here the practical or social significance of this need. What I wish to was not yet invented when these facts occurred. But in another sense we might discuss is rather its intellectual significance. I assert that continued growth is say that these facts do not exist asfacts before they are singled out from the essential to the rational and empirical character of scientific knowledge; that continuum of events and pinned down by statements-the theories which if science ceases to grow it must lose that character. It is the way of its growth describe them. These questions, however, although closely connected with our which makes science rational and empirical; the way, that is, in which scientists discriminate between available theories and choose the better one problem, must be left for another discussion. I have mentioned them only in order to make clear that even should the solutions I have proposed be more or or (in the absence of a satisfactory theory) the way they give reasons for less correct, there would still be open problems left in this field. rejecting all the available theories, thereby suggesting some of the conditions with which a satisfactory theory should comply. 7I had in mindWittgensteininthe Tractatus.Note that thispaperwaswrittenin 1946. You will have noticed from this formulation that it is not the accumulation of observations which I have in mind when I speak of the growth of scientific knowledge, but the repeated overthrow of scientific theories and their replace- ment by better or more satisfactory ones. This, incidentally, is a procedure which might be found worthy of attention even by those who see the most important aspect of the growth of scientific knowledge in new experiments and in new observations. For our critical examination of our theories leads us to attempts to test and to overthrow them; and these lead us further to experiments and observations of a kind which nobody would ever have dreamt of without the stimulus and guidance both of our theories and of our This lecture was never delivered, or published before. It was prepared for the International Congress for the Philosophy of Science in Stanford, August 1960, but because of its length only a small part of it could be presented there. Another part formed my Presidential Address to the British Society for the Philosophy of Science, delivered in January 1961. I believe that the lecture contains (especially in parts 3 to 5) some essential further developments of the ideas of my Logic of Scientific Discovery. 214 215 """'-- - CONJECTURES 10 TRUTH, RATIONALITY, AND THE GROWTH OF KNOWLEDGE criticism of them. For indeed, the most interesting experiments and observa- tions were carefully designed by us in order to test our theories, especially progress (unless we adopt a very narrow view of our possible aims in life); our new theories. for almost every gain is balanced, or more than balanced, by some loss. And In this paper, then, I wish to stress the significance of this aspect of science in most fields we do not even know how to evaluate change. and to solve some of the problems, old as well as new, which are connected Within the field of science we have, however, a criterion of progress: even with the notions of scientific progress and of discrimination among com- before a theory has ever undergone an empirical test we may be able to peting theories. The new problems I wish to discuss are mainly those con- say whether, provided it passes certain specified tests, it would be an im- provement on other theories with which we are acquainted. This is my first nected with the notions of objective truth, and of getting nearer to the thesis. truth-notions which seem to me of great help in analysing the growth of knowledge. To put it a little differently, I assert that we know what a good scientific theory should be like, and-even before it has been tested-what kind of Although I shall confine my discussion to the growth of knowledge in theory would be better still, provided it passes certain crucial tests. And it is science, my remarks are applicable without much change, I believe, to the this (meta-scientific) knowledge which makes it possible to speak of progress growth of pre-scientific knowledge also-that is to say, to the general way in in science, and of a rational choice between theories. which men, and even animals, acquire new factual knowledge about the world. The method of learning by trial and error-of learning from our II mistakes-seems to be fundamentally the same whether it is practised by Thus it is my first thesis that we can know of a theory, even before it has been lower or by higher animals, by chimpanzees or by men of science. My interest tested, that ifit passes certain tests it will be better than some other theory. is not merely in the theory of scientific knowledge, but rather in the theory of My first thesis implies that we have a criterion of relative potential satis- knowledge in general. Yet the study of the growth of scientific knowledge is, factoriness, or of potential progressiveness, which can be applied to a theory I believe, the most fruitful way of studying the growth of knowledge in general. even before we know whether or not it will turn out, by the passing of some For the growth of scientific knowledge may be said to be the growth of crucial tests, to be satisfactory infact. ordinary human knowledge writ large (as I have pointed out in the 1958 This criterion of relative potential satisfactoriness (which I formulated Preface to my Logic of Scientific Discovery). some time ago,2 and which, incidentally, allows us to grade theories accord- But is there any danger that our need to progress will go unsatisfied, ing to their degree of relative potential satisfactoriness) is extremely simple and that the growth of scientific knowledge will come to an end? In par- and intuitive. It characterizes as preferable the theory which tells us more; ticular, is there any danger that the advance of science will come to an end because science has completed its task? I hardly think so, thanks to the in- that is to say, the theory which contains the greater amount of empirical information or content; which is logically stronger; which has the greater finity of our ignorance. Among the real dangers to the progress of science is explanatory and predictive power; and which can therefore be more severely not the likelihood of its being completed, but such things as lack of imagina- tested by comparing predicted facts with observations. In short, we prefer an tion (sometimes a consequence oflack of real interest); or a misplaced faith interesting, daring, and highly informative theory to a trivial one. in formalization and precision (which will be discussed below in section v); All these properties which, it thus appears, we desire in a theory can be or authoritarianism in one or another of its many forms. shown to amount to one and the same thing: to a higher degree of empirical Since I have used the word 'progress' several times, I had better make quite content or of testability. sure, at this point, that I am not mistaken for a believer in a historical law of progress. Indeed I have before now struck various blows against the belief in ill a law of progress, 1and I hold that even science is not subject to the operation My study of the content of a theory (or of any statement whatsoever) was of anything resembling such a law.