Falsification, Revolution, and Continuity in the Development of Science

FALSIFICATION, REVOLUTION, AND CONTINUITY IN THE DEVELOPMENT OF SCIENCE L. KROGER University 0/ GiJttingen, Giittingen, German Federal Republic

Two major conflicting accounts have been given of the nature of scientific development. The older and at first sight more plausible account describes the development of science as a process of accumulation of knowledge piece by piece. It has been severely criticized by its more recent rival, according to which science develops by the replacement of more or less imperfect theories by better theories, in other words by the elimination of error or the abandonment of an insufficient framework of research, i.e., by falsifications or intellectual revolutions rather than by continuous accretion. Referring to this critical development in the philosophy of science I may outline the problem to be discussed in this lecture as follows: I am convinced that the accumulation model of scientific progress is much too simple and untenable. But it had one advantage which the revolutionary model has not: Growth of knowledge is a natural consequence of it, whereas in the revolution model, growth-though one of its central themespresents a problem that has not yet been explored far enough. My general thesis concerning this problem is the following: Although an adequate account of the growth of science as well as of its inherent rationality will contain many or even most of the features of the revolution model, this model will nevertheless remain essentially incomplete, if it is not complemented by additional principles concerning the continuity of scientific investigation; and these principles will be such as cannot legitimately be subsumed under one of the two current heads 'falsification' or 'revolution'. In order to explicate and to substantiate this thesis I shall proceed as follows: (1) I shall examine critically some features of Sir Karl Popper's falsificationism and propose a modified version of it, which is intended

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to preserve the critical spirit and yet to render the monotonous growth of knowledge and the irreversible sequence of successive theories more plausible. (2) I shall try to elucidate the relation of growth and criticism somewhat further by a critical examination of Professor Thomas Kuhn's revolution model of scientific progress, which may be considered as falsificationism transferred into the field of history. (3) Finally, I shall argue that scientific criticism as well as the growth of knowledge depends upon some kind of continuity of successive theories. Turning now to the first of these points, I may begin by recalling some important characteristics that distinguish Popper's falsificationism from earlier inductivist approaches to science. In his philosophy of science the idea of the construction of theories from observed data has been replaced by a radical antiinductivist conception, according to which scientific activity starts from problems and theories rather than from observations. Inductive procedures are declared to be both unnecessary and invalid. The only accepted relation between theory and experiment is provided by the deduction of observationally decidable statements from theories. Thus, since the modus tollens is "the only strictly deductive kind of inference that proceeds, as it were, in the 'inductive direction', that is, from singular to universal statements" (POPPER, 1959, Sec. 6), the conclusion is suggested that only falsifiable statements and theories can be scientific. But more important than this formal argument is the spirit in which it is made: The essential element in scientific activity is considered to be the critical attitude, the readiness to expose every assertion to risk, to possible refutation or rejection. This combination of philosophical criticism and logical analysis of science has been extremely fruitful and important. This paper, though predominantly critical, is strongly influenced by Popper's ideas; and its whole outline, I hope, will show an indebtedness which cannot so easily be made explicit in detail, because it is pervasive. One feature that appears to have confused the discussion of falsificationism and that, at any rate, had confused me for a while is what I am now inclined to call a conflation of two very different ideas: (i) the purely logical idea of the unique importance of the modus tollens for an empirical science as well as of formal falsifiability as a mark of scientific statements; and (ii) the much deeper methodological idea that every scientific theory should be exposed to a maximum of possible risk in order to enhance critisicm and thereby to warrant rationality. The following considerations are an attempt to preserve the second idea

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while criticizing the first. Popper, however, still seems to hold that they are necessarily connected; this is, in any case, how I read his treatment of purely existential statements. To his (1963) he has attached an appendix intended to show that existential statements, even if formulated in observational terms, are nevertheless unscientific. Elsewhere, it is true, POPPER has restricted this assertion to isolated existential statements (1959, Sec. 15). But these are, certainly, neither scientific nor unscientific, because they are not theories. Hence, we should rather ask whether a formal syntactical property of statements belonging to a theory can be used as a simple criterion for the demarcation of science, and more generally, whether the testability and the criticizability of a theory can be equated with its formal falsifiability. The case of existential statements offers a counterexample showing that empirical content or testability are not tantamount to falsifiability. For the sake of argument consider the extreme case of a theory whose only testable statements are all of the purely existential form. A not too unrealistic example would be that of a pure symmetry theory of elementary particles that excludes all dynamics. Such a theory would predict the existence of a set of particles with certain well-defined properties, e.g., values for their charge, spin, isotopic spin; but it could not predict anything about the times and places of the appearance of the particles. They might, for instance, all be observed in random samples, from cosmic rays. If, therefore, the search for some of these particles remained unsuccessful, that would not speak against the theory, whereas the detection of many or most of the predicted particles (and of not too many unpredicted ones) would qualify the theory as a highly interesting empirical theory, though an incomplete and preliminary one, to be sure. What qualifies this theory as scientific although it is formally unfalsifiable? [ think it is the fact that it permits derivation of empirical statements that are highly specific. For, if these are somehow (be that by a happy accident) found to be true, we feel compelled to conclude from the improbability of this experience that there must be at least some truth in theory also. The interesting feature from the point of view of the scientist, then, is that the content of the theory is specified to a considerable degree in terms of experimentally decidable statements, be these falsifiable, verifiable, or both. Thus, the somewhat weaker requirement of empirical specificity takes the place of that of falsifiability. I should like to add two comments. First, the weaker requirement of empirical specificity is not eo ipso at variance with Popper's intention to

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combat dogmatic ideologies and pseudosciences. What is dangerous in these is more often their sweeping vagueness rather than their failure to indicate circumstances under which they would be false. For, on the one hand, they share this feature with many interesting and possibly accepted scientific theories, e.g., in medicine, where it could be unwise, even irresponsible to discard them, although no conditions are specifiable under which they could be called 'false'. On the other hand, the obligation to specify general contentions in experiential terms could become fatal to many ideologies, and that not only because they become refuted, but also because they turn out to be empty. Second, the requirement of empirical specificityis in itself not yet sufficient to characterize an entire methodology. Following Popper, one should quite generally attempt to increase the empirical content of a theory. This means that the requirement of specificity has to be combined with a demand for maximal generality, especially generality in a qualitative sense, i.e., for unified explanations of phenomena that look disconnected to anybody not acquainted with the theory in question (cf. POPPER, 1957). In the rest of this paper I shall assume, as a result of the preceding discussion, that the rationality of science depends upon specification together with generalization rather than upon falsifiability as such, though the former may be connected with falsification in some cases, e.g., in the ideal case of the dynamical theories in physics. Furthermore, from now on I shall take it for granted that the purely logical side of the fundamental falsificationist approach is more or less irrelevant. This conclusion is in accordance with more recent results obtained by several authors. Professor LAKATOS (1970), for instance, has replaced falsification by 'falsification' and has voted for a methodological and liberal modification of falsificationism. The discussion of the D-thesis seems to move in a similar direction; Professor GRUNBAUM (forthcoming)! has made it clear that the notion of falsification can only be maintained if the aims scientists pursue are taken into account. To put it briefly: If there is, in the development of science, any such thing as falsification at all, it will be of a pragmatic rather than logical character. And if we want to keep the idea of criticism alive, we have now to look for its realization in this pragmatic process. This is the reason why I propose, in the second part of this paper, to examine critically Kuhn's notion of scientific revolution, for it is the result 1 I am grateful to Professor Griinbaum for a copy of this paper and comments on it prior to its publication.

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of the presumably most extensive study of the way in which critical revisions have actually taken place in the practice of scientists. And as far as I can see, the recent development of Popper's fundamental ideas by Lakatos comes very close to Kuhn's scheme of an interplay of normal and revolutionary science, thus building a bridge between the two parallel approaches at a nonaccumulative model of science, at least as far as the kind of description of the historical facts is concerned. As to their evaluation in philosophical terms, on the other hand, the disagreement appears to be very deep-rooted indeed (cf. LAKATOS and MUSGRAVE, 1970). In our present context it is possible to ignore most of this controversy by concentrating on a problem that is common to both approaches. To what extent can the conception of wholesale revisions of theories, i.e., of scientific revolutions, serve to determine more closely the critical character of science? And how is it to be reconciled with the growth of scientific knowledge, which takes place throughout the revolutions and even by revolutions? The preceding critique of logical falsificationism shows the problem that is connected with these questions. There can be no purely logical procedure of criticism; one has to resort to history and to observe what scientists really do. But if, on the other hand, the historical process shall be understood as a piece of rational criticism, a purely empirical account of the behavior of groups of scientific experts (proposed by Kuhn? as the basis of a theory of scientific development) will be equally defective. The only way left open to us is the rational evaluation ofhistory. For, if the rationality of science depends upon its objective character, i.e., upon its employing intersubjectively convincing reasonings about some common 'outer' reality, then one should explain the behavior of scientists by their reasons, and not the alleged rationality of the development of science by that behavior. The question of the philosopher of science should be, not what arguments scientists are observed to use, but what arguments of theirs we ourselves can accept as valid. To say this means to propose a metatheoretical paradigm that differs from Kuhn's. Whoever wants to defend it is obliged to unfold its implications and to examine whether these are acceptable or not. Especially far reaching among these is the presupposition that there is a sufficient objective unity in the whole development of a science, so that our present standards of argument are immediately applicable to earlier stages of that science. In 2

This proposed reformulation of his work is discussed in KUHN (1970, pp. 252 ff.),

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other words: we should not be content with the observation and straightforward acceptance of a historical sequence of periods each having its own set of problems, methods, and solutions, even its own language. Instead we are committed to believe that we can learn more and more about the same thing, e.g., the movement of stars or the structure of matter. This implication may look very naive to the historian, but it cannot be avoided, if truth is to be more than an ephemeral conviction of a certain group of competent scientists. For Kuhn, on the other hand, it is consistent to eliminate the concept of truth from his theory." This elimination of truth is connected with another feature of Kuhn's account that will be of interest for our present purpose, namely, his failure to distinguish between two types of scientific revolutions that are significantly different. For the sake of brevity let me use the concept of truth in a very naive way without qualifications. Then I can express the difference in the following way: (i) there are revolutions which lead from a false to a true theory, and (ii) there are revolutions which lead from an incorrect or insufficient theory to a more satisfactory theory, both of them to a certain extent true. Examples of the first kind are the transitions from Ptolemaic to Copernican astronomy or from phlogiston to oxygen chemistry; examples of the second type are the transitions from Newton to Einstein or from classical to quantum mechanics. The first type is compatible with the description that the earlier theory is simply replaced by the new theory, which fits the known (and preferably some additional) facts better than the former. This description in terms of replacement is very crude, indeed; de facto a large number of ideas will be common to both theories, and without some kind of continuity any transition between them would become impossible. Yet, one may still say that this kind of continuity is accidental to the purpose of science, i.e., to the pursuit of truth. For it is no necessary condition of the new theory's being true that the old theory had already some truth in it. In this sense the new theory may start from scratch. The second type of revolution, on the other hand, though it may involve fu"ndamental changes in the outlook of a science, can nevertheless not be described as a replacement. In order to obtain an adequate description we have rather to return to more traditional conceptions: e.g., that the earlier 3 KUHN (1962, Chapter 13; 1970, p, 266). More exactly: Kuhn denies that the concept of truth has any intertheoretic (as opposed to intratheoretic) applications and, thus, deprives it of all importance for the analysis of scientific progress.

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theory is a special or a limiting case ofthe latter, or conversely, that the latter is a generalizing and correcting explanation of the former. The motive for such descriptions is that the former theory is still accepted as far as its successful applications go. Kuhn says that an argument of this type can be used to defend any theory which was not a complete failure (KUHN, 1962, Chapter 9). But this is not true; the phlogiston theory, for instance, is not a limiting case or an approximation of later chemistry in any sense comparable to that in which Newton's theory is related to Einstein's. What is the significance of this difference between the two types of revolutions? I think it is a historical fact about what we consider to be 'science', that we do not expect to some day be forced to give up completely a constitutive piece of it again. Are we really prepared to abandon the idea that the sun, the stars, and the earth are bodies moving through space and attracting each other more or less exactly in accordance with Newton's law of gravitation, or that matter consists of atoms of so many different kinds with such and such an inner structure? I believe the answer will be 'no'. If you object that massive bodies traveling through space may, later on, turn out to be nothing but vortices or singularities in some kind of field, and that their exact motions deviate from Newton's and may, perhaps, deviate from Einstein's predications, etc., I should like to reply by pointing to the difference between this kind of reinterpretation of a theory, possibly including interesting and even practically important corrections, on the one side, and a refutation or rejection of it on the other. Now, if what I here call a 'fact' is accepted as a given explanandum, the task arises to include it in a rational reconstruction of the development of science. And the second type of scientific revolution may teach us how we should complement the historical version of the fundamental falsificationist idea. With this remark I am coming to the third part of my paper. As a first and crude approximation of what I have in mind I shall propose to consider a continuity principle. Before I am able to state it, I have to introduce an assumption that is closely connected with the fact just mentioned. I assume that there is a certain period in the history of some branches of inquiry, when each of them is, as KANT (1889) expressed it, "brought into the assured course of a science"." This will happen, when both the specification and the generalization within a certain field of research have reached a sufficient degree. I must confess that I am unable to determine this degree in general 4

" •.•

in den sicheren Gang einer Wissenschaft gebracht. .." [po 181.

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terms, and I do not know whether this can be done. But this is in itself no argument against the existence and the influence of the continuity principle to be stated below. I believe, furthermore, that at least some necessary conditions for the stage of the 'assured course' could be formulated. But a better way to expound my assumption is to give examples. Physics had entered upon the 'assured course' not later than Newton, chemistry not later than Dalton, and mathematics not later than Euclid. The phrase 'not later than' indicates that statements like these are made only with hindsight and without the help of a general theory. After these preliminary remarks the continuity principle can be stated as follows: Whenever the exploration of a certain field of phenomena has entered upon the stage of development called by Kant "the assured course of a science", every new theory has to be compatible with its predecessors; and if, more specifically, it deals with the same subject matter as one or several of these earlier theories, it has to be connected with that or those theories. After my introductory considerations, the reasons for proposing some such principle are probably obvious: If one is willing to see the development of modern science in light of the outlined anti-Kuhnian paradigm, that is, if one is determined to consider the known highly developed and highly confirmed theories as stepping stones for further research rather than to seek, as it were, completely new ways across a territory supposedly already known, and if, furthermore, the basic requirement of consistency is to be fulfilled by every science, its possible development has to be restricted by some principle of the continuity type. It is certainly true that no interesting new theory can be derived from earlier theories; rather, it will be the solution of new problems. But, if it is to be part of an established science, this solution will have to meet, so to speak, certain theoretical boundary conditions defining the problem situation and qualifying it as that of a developed science. Let me add a few remarks by way of explication. I have to comment on the seemingly too strong requirement of compatibility." Of course, I do not wish to say that two successive theories could not have logically incom5 This paragraph has been inserted after the discussion in Bucharest, when I realized that the few remarks about intertheory relations made below were not suited to prevent misunderstanding. The kind of compatibility I have in mind is explicated in terms of 'connection' between theories, which is a more general relation than just that of an 'approximation' of one theory by another. My thanks for clarification are due to the participants of the discussion, especially to Professor Alan Musgrave.

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patible consequences; the contrary will normally be the case, if the later theory is to be an improvement upon the former. But it must still be consistent to make use of both theories at the same time and even in the same context; and this practice can only be justified if it is possible to qualify one or both of the theories in such a way that they become parts of some unified and consistent expression of our total knowledge of the field in question. Taken in this sense, the requirement of compatibility is, at first sight, trivially fulfilled, whenever two theories are about different phenomena. But as soon as they deal with the same subject matter, e.g., the basic laws of motion, the required compatibility is only obtained if the theories are consistently connected. A standard type of connection will probably be the one mentioned above, which can be described by saying that one or several of the previously established theories are approximations of the new theory, which, in its turn, explains, extends, and corrects the former. Examples are provided by the relation of Newton's mechanics to Kepler's or GaIileo's laws, or of relativity theory to classical mechanics and electrodynamics. But there are other cases in which the connection is more complicated and of a different type. A prominent example is provided by the relation between classical and quantum mechanics. Also in this case there are some quantitative and structural relations, which are expressed in so-called correspondence principles; but, on the whole, the two theories are fundamentally different in structure. They involve different and even incompatible views about causal determination, about the concept of an object, about the role of measurement, etc. And yet they are simultaneously in use; in fact, they are both indispensible in present-day physics. And it is not certain, indeed not even likely, that the conflict between these two coexisting theories can be resolved in favor of quantum mechanics in such a way that the classical theories would turn out as nothing but approximations to be understood entirely in terms of the new theory. For, without committing oneself to any other part of the Copenhagen philosophy of 'The Observer' and of complementarity, one may still accept one of Niels Bohr's fundamental ideas, namely, that we are forced to describe our measurement devices in terms of classical physics. At any rate, that is what physicists really do. They use classical theories for establishing the contact between quantum theories and experiment; and this procedure has been extremely successful. If then for this reason we feel that it is rational to use simultaneously theories that, at first sight, seem to contradict each other, we imply that one con-

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sistent account of this theoretical situation as a whole is possible. To make it explicit is, then, a major scientific task." I lay some stress upon this second type of connection between theories, because it shows how the continuity principle, far from being dogmatic and restrictive, may produce a considerable heuristic force by imposing new problems on us, thereby leading to new theories. The compatibility requirement included in the principle as formulated above need not, and hardly ever will, be satisfied in a trivial way, i.e., by simple logical inclusion or extension, but most likely in a problematic and hence productive way. This is one of the reasons why the integration of different fields of inquiry can become a dominant feature and, perhaps, the strongest progressive force of a science in an advanced stage. This integration is nothing but the invention of a new theory that fulfills a set of several conceptually different theoretical boundary conditions. In order to complete my reflections on the revolution model of scientific development, I return to the question, whether the critical rationality of science can still be preserved although the more rigorous falsificationism, being in need of supplementation by principles alien to it, has to be deprived of its original sharpness. My answer is this: Critical rationality is not only compatible with but even dependent on the continuity of science, at least as far as advanced sciences are concerned. For first, the joint attempt of scientists at developing their theories at once toward finer and finer details (requirement of specificity) and towards more comprehensive integration of qualitatively dissimilar parts (requirement of generality) should be a sufficient basis for the significant discrimination of truth and error, and hence for criticism. But, second, to require more than this, namely, to require replacement or revolutionary overthrow of entrenched theories (as distinct from extensions, reinterpretations, explanations, corrections, and integrations) would mean to require too much. For every criticism will be as strong and as convincing as the positive basis which its arguments are grounded upon. If there were, in modern empirical science, no kernel that could, in spite of critical revisions, be continuously enlarged, we would inevitably relapse into the prescientific stage of competing views that alternate more or less 6 Hence, the interpretation of quantum theory is not an entertaining philosophical enterprise apart from physics, but involves the search for a more comprehensive physical theory that explains the interplay of classical and quantized theories. A good part of the early and by now controversial contributions to this interpretation should be seen in light of the need to justify the simultaneous use of both kinds of theories.

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contingently. There could certainly exist a sharp-witted exchange of arguments, but without progress in a definite direction and without growth of knowledge. Only the formal side of rationality would be represented, as was the case with the sophists of classical Greece. Scientific criticism includes a material side of rationality as well: the continuously increasing positive knowledge of at least some features of the real world. References GRUNBAUM, A., Falsifiability and rationality (forthcoming) KANT, 1., 1889, Kritik der reinen Vernunft, ed. E. Adickes (Mayer and MUlier, Berlin) KUHN, T. S., 1962, The structure of scientific revolutions, International Encyclopedia of Unified Science, vol. 2, no. 2 (University of Chicago Press, Chicago; second edition, 1970) KUHN,T. S., 1970, Reflections on my critics, in: Criticism and the Growth of Knowledge, eds. 1. Lakatos and A. Musgrave (Cambridge University Press, Cambridge), pp. 231-278 LAKATOS, 1., 1970, Falsification and the methodology of scientific research programmes, in: Criticism and the Growth of Knowledge, eds. 1. Lakatos and A. Musgrave (Cambridge University Press, Cambridge), pp. 91-195 LAKATOS, 1. and A. MUSGRAVE (eds.), 1970, Criticism and the growth of knowledge (Cambridge University Press, Cambridge) POPPER, K. R., 1957, The aim ofscience, Ratio, vol. 1, pp. 24--35 POPPER, K. R., 1959, The logic of scientific discovery (Hutchinson, London) POPPER, K. R., 1963, Truth, rationality and the growth of scientific knowledge, in: Conjectures and Refutations, ed. K. R. Popper (Routledge and Kegan Paul, London), pp. 215-250