KARL POPPER AND FALSIFICATIONIST CRITICISM
BOOK V - Page 1
T his book focuses on Karl Popper’s falsificationist thesis of scientific criticism. It also examines his particle-propensity interpretation of the quantum theory, which he advances as an alternative to the Copenhagen interpretation, and discusses the influence of the physicist Alfred Landé.
Karl Popper (1902-1995) was born in Vienna, Austria. He enrolled in the University of Vienna in 1918, where he studied physics, mathematics, and philosophy. In 1928 he received his Ph.D. for a dissertation titled On the Problem of Method in the Psychology of Thinking. He never returned to the subject of psychology again during his professional career, because he became convinced that methodology of science is exclusively a matter of logic and objective knowledge instead of psychology. Popper was personally acquainted with Rudolf Carnap and other members of the Vienna Circle, and although he had been invited to address the group at a meeting in which he set forth his philosophy of science, he was never a member of the Circle. In 1937 he was appointed a senior lecturer to Canterbury University College in Christchurch, New Zealand, and then in 1945 he was appointed to a readership at the London School of Economics, University of London. In 1949 he was made professor of logic and scientific method at the London School. He was knighted in 1964.
Einstein’s Influence and the Falsificationist Thesis of Criticism
In his intellectual autobiography in Schilpp’s The Philosophy of Karl Popper (1974) Popper states that Einstein was the most important influence on his thinking. The influence was not a personal one, since Popper and Einstein did not actually meet until 1950; the influence was through Einstein’s published works. The year 1919 was the fateful year in Popper’s intellectual life. At that time he was interested in the views of several thinkers including Marx’s theory of history, Freud’s theory of psychoanalysis, and Alfred Adler’s theory called “individual psychology.” Popper relates in his “Science: Conjectures and Refutations” (1957) in Conjectures and Refutations (1963), that he had come into personal contact with Alfred Adler and cooperated with Adler in the latter’s social work with children and young people in the working class districts of Vienna during the last years of the Austrian Empire and the subsequent revolution. In the summer of 1919 Popper became dissatisfied with the views of Marx, Freud and Adler, because the persons who accepted and advocated these theories were strongly impressed by the theories’ purported explanatory power, and because study of these theories had the effect of an intellectual conversion or revelation. Most objectionable to Popper was the fact that once the reader’s eyes were opened to the theory, he found that the theory was verified everywhere one might think of applying it. Unbelievers were dismissed as persons who could not see the verifications. In Popper’s view the apparent strength of these theories’ purported “explanatory” power is their principal weakness.
Popper saw in Einstein’s theory a striking contrast to the situation he found in the views of Marx, Freud and Adler. Eddington’s solar eclipse observations in 1919 brought the first important test to bear upon Einstein’s relativity theory of gravitation. This test was distinctive, because in the test there was a risk involved in the theory’s prediction. Had Eddington’s observations showed that the predicted effect is definitely absent, then Einstein’s theory would simply have been refuted. And the risk in Einstein’s case was very great, since the predicted effect was different from what was expected from Newton’s theory, which had long demonstrated great success culminating with the discovery of the planet Neptune. In his autobiography Popper said that what impressed him most was Einstein’s own clear statement that he should regard his theory of relativity as untenable, if it should fail certain tests. This was an attitude that was very different from the dogmatic attitude of the Marxians, Freudians, and Adlerians. Einstein was looking for crucial experiments where agreement with his predictions would by no means establish his theory, but where disagreement with his predictions, as Einstein was the first to say, would show his theory to be untenable. Thus in 1919 Popper concluded that the critical attitude, which does not look for verifications but rather looks for crucial tests that can refute the tested theory, is the correct aim for science, even though the crucial tests can never establish the theory. This is Popper’s falsificationist philosophy of scientific criticism, the central thesis of his philosophy of science.
Explanation, Information, and the Growth of Science
Popper’s philosophy recognizes the dynamic character of science that is not recognized in the philosophy of the positivists, who were interested only in the result, as they understood it. His statements on the dynamics of science are found in appendices to the 1968 edition of his Logic of Scientific Discovery, in his “Truth, Rationality, and the Growth of Scientific Knowledge” in his Conjectures and Refutations, and in “The Rationality of Scientific Revolutions” in Problems of Scientific Revolutions (ed. Harre, 1975) as well as elsewhere in his literary corpus. His falsificationist thesis is not only a philosophy of scientific criticism and scientific explanation, but is also a philosophy of the growth of scientific knowledge. As a philosophy of scientific criticism, it says that the empirical test outcome can never establish or “verify” a scientific theory, but can only refute or “falsify” the theory. And even before a theory’s claims are considered for testing, it is possible to determine whether or not it is a scientific explanation: it is not a scientific explanation if it is not empirically testable.
Another way that Popper describes this condition is that what makes a theory scientific is its power to exclude the occurrence of some possible events, and he calls the singular statements that describe these excluded events “potential falsifiers”. This way of speaking introduces his idea of various degrees of explanatory power: the more that a theory forbids or excludes and therefore the larger the class of potential falsifiers, then the more the theory tells us about the world. Popper calls the variability of degree of explanatory power the “amount of information content” of a theory or explanation. The idea of the amount of information content may be illustrated by reflection on the logical conjunction of two statements a and β. It is intuitively evident that the conjunction a β has no lesser amount of information content than do the component statements taken separately, and it usually has more information content than its components. This is because there are more potential falsifiers for the conjunction than for the component statements taken separately; the conjunction is false if either component is false. In some contexts Popper calls information content “empirical content”, and he calls the falsifiability of the theory its “testability.” All of these terms refer to a logical relation between a theory or a hypothesis and its class of potential falsifiers.
Popper relates the idea of information content to probability theory. He says that the amount of information content is inversely related to the degree of probability that may be associated with a hypothesis. This view can be illustrated also by the logical conjunction: if the probability value P(α) is associated with the statement α and the probability value P(β) is associated with the statement β, then by the probability calculus the probability P(α β) associated with the conjunction α β must be less than the separate probability values P(α) and P(β). Therefore as the information content of a theory increases, the associated probability must decrease. Popper maintains that the whole problem of the probability of hypotheses as viewed by Carnap is misconceived, because on Carnap’s idea of degree of confirmation, scientists should prefer statements having higher associated probabilities, while on Popper’s view scientists should prefer theories with higher information content. Therefore in contrast to Carnap’s idea of degree of confirmation Popper advances the idea of “degree of corroboration”, although in some contexts Popper also uses the phrase “degree of confirmation” in a sense that is synonymous with his idea of degree of corroboration. On the corroboration thesis a scientific theory that has greater information content (because it is more universal, or because it is more accurate than an alternative theory) also has a higher degree of corroboration, if when it is tested it is not falsified. Like the idea of information content, the idea of corroboration is based on the idea of falsifiability, but a theory would not be said to have been corroborated until it had been tested and found to have no falsifying test outcome; the degree of corroboration actually attained does not depend only on the degree of falsifiability. A statement may be falsifiable to a high degree yet it may be only slightly corroborated or it may be falsified.
The measures for corroboration, C(h,e), and probability, P(h,e), for hypothesis h and for basic statement e of evidence describing a test outcome, are related by certain equations. The inverse relation between the measures of corroboration and probability is related as follows:
C(h,e) = 1- P(h,e)
and Popper is willing to admit a proposal by Kemery in the Journal of Symbolic Logic (1954) that the relation may also be expressed in terms of information science concepts as:
C(h,e) = 1- log P(h,e).
Popper states that the measure of the degree of corroboration, C(h,e), may be interpreted as a measure of the rationality of belief in the statistical hypothesis, h, in the light of test outcomes, e, only if e consists of reports of the outcome of sincere attempts to refute the hypothesis by the severest test that can be devised, rather than attempts to verify h. But the degree of corroboration does not measure the degree of rationality in our belief in the truth of h, since C(h,e)=0 whenever h is logically true. Rather, it is the measure of accepting tentatively a problematic guess. On the other hand the measure of explanatory power, E(h,e), may be interpreted as the measure of the explanatory power of h with respect to e, even though e is not a report of any genuine and sincere attempts to refute h. The measure E(h,e) is a purely logical relation to the infinite class of potential falsifiers, and in an appendix to his Logic of Scientific Discovery (1959) Popper relates E(h,e) positively to C(h,e) as follows:
E(h,e) = C(h,e)/[1+ P(h) P(h,e)].
The concepts of relatively greater or lesser degrees of information content and falsifiability provide the basis for Popper’s ideas on scientific progress, the growth of scientific knowledge, and the aim of science. He advances a “metascientific” criterion of progress that enables the scientist and methodologist to know in advance of any empirical test, whether or not a new theory would be an improvement over existing theories, were the new theory able to pass crucial tests, in which its performance is compared to older existing alternatives. He calls this criterion the “potential satisfactoriness” of the theory, and it is measured by the degree or amount of information content. Simply stated, his thesis is that the theory that tells us more is preferable to one that tells us less, and the theory that tells us more is also one which is most falsifiable. From this it follows that the aim of science is high empirical information content as well as successful performance in tests.
It is the criterion of high information content that makes the growth of science rational. The aim of science is not high probability, and the rationality of science does not consist of constructing deductive axiomatic systems, since there is little merit in formalizing a theory beyond the requirements for testing it. Nor does the growth of science consist of the accumulation of observations. Rather the growth of science consists of the repeated overthrow of scientific theories and their replacement by more satisfactory theories. The continued growth and progress of science is essential to the rational and empirical character of scientific knowledge. The growth is continuous, because criticism of theories, which are proposed solutions, in turn generates new problems. Scientific problems occur when expectations are disappointed. Science starts from problems, not from observations, although unexpected observations give rise to new problems. Popper views science as progressing from old problems to new problems having increased depth, when it progresses from old theories to new theories having increased information content. He also views progress in science as approaching more and more closely to the truth understood as a correspondence with the facts and as a regulative idea. Just as there are degrees of information content, so too there are degrees of approach to the truth that he calls “verisimilitude.”
In his “Rationality of Scientific Revolutions” Popper therefore sets forth two criteria for the rationality of scientific revolutions, which are also two logical properties that enable the scientist to evaluate any new theory even before it is tested. The first criterion may be called a criterion of discontinuity: the new theory must conflict with the old one in the sense that it leads to conflicting results. Popper says that in this sense scientific progress is always revolutionary, and that Trotsky’s refrain “revolution in permanence” is applicable to science. The second criterion may be called a criterion of continuity: the new theory must be able to explain fully the success of its predecessor in the sense that either there are applications in which the old theory must appear to be a good approximation to the results of the new theory, or there are cases where the new theory yields different and better results than the old one. Scientific revolutions are rational because unlike ideological revolutions, which are sociological, the former cannot simply break with tradition.
Against Psychologism, Induction, and Naturalistic Semantics
Popper’s philosophy of knowledge is a critique of psychologism and a defense of the objectivity of knowledge. In the opening chapter of Logic of Scientific Discovery, which is titled “A Survey of Some Fundamental Problems”, he devotes a section to the elimination of psychologism. This section follows the opening section on the problem of induction, which he views as a fallacy resulting from the psychologistic philosophy of knowledge. He sets forth his own theory of knowledge in the fifth chapter titled “The Problem of the Empirical Basis”, and the opening section is a critique of the psychologistic view that perceptual experiences are the empirical basis for science. In his “Demarcation Between Science and Metaphysics” (1955) in Conjectures and Refutations he criticizes Carnap’s theory of meaninglessness, which he describes as a “naturalistic theory of meaningfulness” of linguistic expressions. The linguistic expressions of particular relevance are those singular statements that are used for describing observations in science. All of these ideas are interrelated according to Popper: induction as the logic for making generalizations and hypotheses, psychologism which proposes perception as the empirical basis of observation in science, and the naturalistic theory of the semantics of language. Popper rejects all of them together. In his “Epistemology Without a Knowing Subject” (1967) and his “On the Theory of the Objective Mind” (1968) published as chapters three and four in his Objective Knowledge (1972), in Part I of The Self and Its Brain (1977), and also in an appendix to The Open Universe (1982), Popper sets forth his own philosophy of the three “worlds” of reality which locates subjective psychology and objective knowledge in different worlds.
The development of Popper’s own philosophy of science began with the objective of demarcating empirical science and pseudoscience (e.g., astrology, Marxism, Freudianism, and Adlerian psychology). His solution to the problem of demarcation is the criterion of empirical falsifiability, which he also uses to demarcate empirical science from metaphysics, and he contrasts this criterion with the criterion of meaningfulness that Carnap and other logical positivists used for distinguishing science from metaphysics. Carnap’s criterion of meaningfulness is based on the naturalistic philosophy of language. Popper argues that the positivists have never succeeded in distinguishing science from metaphysics or in distinguishing theory from observation, that metaphysics need not be meaningless even though it is not a science, and that positivism excludes scientific theories as meaningless while failing to exclude metaphysics as meaningless.
Popper maintains that there is no observation without theory, and that the observation terms occurring in observation language are “theory impregnated”, such that observation terms are a type of theoretical term that Carnap calls disposition terms, which is in effect just another way of saying that all concepts are universal. The reason that the positivists have not succeeded in distinguishing science from metaphysics, is that they cannot define meaningfulness, and they cannot define meaningfulness because they interpret the problem in a naturalistic way, as though it were a problem in natural science or psychology. Popper maintains that the positivists have confused the psychology of knowledge with the logic of knowledge, which is to say that they have adopted a psychologistic philosophy of knowledge. Popper rejects both behaviorism and psychologism, and maintains that the content of thought, the meanings of words, the semantics of language, are not determined either by the natural laws of the physical world or by the natural laws of psychology. The world of objective knowledge, which is governed by the laws of logic, is a third world that is autonomous from the world of objective physical nature and also from the world of subjective psychology.
In The Self and Its Brain he argues against behaviorism and physicalist reductionism by the display of ambiguous drawings that he emphasizes may be interpreted in different ways by voluntary action, in order to demonstrate the existence of world 2, the world of the mind and of subjective mental experiences. He argues against the psychologistic view by stating that the objects of world 3 are intersubjectively testable. Hence there are the three separate worlds which cannot be reduced to one another: world 1 is the world of objective physical nature, world 2 is the subjective world of psychological experience, and world 3 is the objective world of human artifacts or creations including knowledge. Popper emphasizes that while the three worlds interact through world 2, nevertheless the world of objective knowledge is autonomous of the world of subjective psychological experience including perceptual experiences. Advocates of psychologism and the naturalistic theory of the semantics of language fail to recognize the autonomy of world 3 from the other two worlds.
More recently in his “The Foundations of Information Science: Philosophical Aspects” in The Journal of Information Science (1980) the information scientist Bertram C. Brookes proposed that the task of information science as a discipline can be defined as the exploration of the world of objective knowledge understood as Popper’s world 3, and that this discipline is distinct from documentation and library science, the customary home of information science.
Popper’s rejection of inductive logic is based on his thesis that world 3 is autonomous from worlds 1 and 2. He references Einstein’s stated view that there is no logical path leading to the universal laws that scientists search for, and that these laws can only be reached by intuition. Popper accepts Hume’s thesis that singular statements describing observations cannot justify universal statements, and he rejects the early Wittgenstein’s verifiability criterion of meaningfulness adopted by Carnap and the other logical positivists of the Vienna Circle. He also rejects the probabilistic inductive logic developed by Carnap and set forth in the latter’s The Logical Foundations of Probability, and he expresses dismay that anyone would ever write such a book. In Popper’s view there is no logic of scientific discovery; there is only a psychology of scientific discovery. He explains that the title of his own book, The Logic of Scientific Discovery in not about the psychological processes involved in inventing new scientific theories, but rather is about the growth of scientific knowledge by conjectures and refutations, the proposal and criticism of new theories.
Popper’s philosophy of scientific knowledge is a sustained attack on positivism, but it is not just a critical rejection; he has his own alternative philosophy of observation. The positivists maintained that there is a clear distinction between theory and observation, such that one could separate the language of theory from the language of observation with each containing its own distinctive vocabulary and its own class of universal of statements. The universal statements containing only observation terms are produced by inductive generalization, while those containing theoretical terms are invented by the scientist’s creative imagination. However, with the recognition that theory determines what is observed, the separation between theory language and observation language can no longer be sustained, and the ideas of theory and observation must be reconsidered. And since the existence of an observation language was thought to be the empirical basis for science, the empirical basis for science also must be reconsidered.
The positivists had attempted to base empirical science on “atomic statements”, “protocol statements” and “judgments of perception” stated in the observation language. Popper rejects these ideas with his rejection of the naturalistic philosophy of meaning. Instead he proposes the idea of the “basic statement”, which he defines as a singular statement which together with the universal statements of theory can serve as a premise in an empirical falsification of a theory. The basic statement is fundamentally different in concept from Carnap’s protocol statement. The protocol statement is thought to be justified by perceptual experiences and thereby to constitute a foundation for science. But Popper maintains that this is confusion between the subjective psychological aspect of knowledge and the objective logical aspect. Perceptual experiences are subjective and psychological; they can motivate a decision and hence an acceptance or a rejection of a statement, but a basic statement cannot be justified by them any more than it can be justified by thumping on a table. Basic statements are objective in the sense that they can be intersubjectively tested by repetition of the conditions that occasioned them. And they can be falsified, since they operate as premises from which other statements can be deduced, which in turn can be tested. As a result there can be no ultimate statements in science, as the positivists believed; any statement in empirical science can be refuted by falsifying conclusions that may be deduced from them.
But it is not necessary that a basic statement should be tested in order for it to be accepted; it is only necessary that the basic statement be testable. The function of basic statements is to test theories. Every test of a theory must stop at some basic statement, which the scientists have agreed to accept at least for the present time. To the extent that the basic statements are accepted on the basis of agreement, they are conventional. But the agreement is not arbitrary or capricious; the decision is made by reference to a theory and the problem that the theory is proposed to address. Theory dominates experimental work from its initial planning to its completion in the laboratory. Popper summarizes his views on the empirical basis of science by means of a memorable metaphor: There is nothing absolute about science; it does not rest upon solid bedrock, as it were. The bold structure of its theories rises as it were above a swamp like a building erected on piles, which in turn are driven down to whatever depth is found to be satisfactory to carry the structure for the time being.
Popper’s reconceptualization of the empirical basis of science is also a reconceptualization of the concept of theory in science. Unlike the positivists, Popper does not define the concept of scientific theory in terms of theoretical terms. Instead he views theories as universal statements, and rejects any distinction between empirical laws and theories, since there is no longer any distinction between theory language and observation language based on a distinction between theoretical terms and observation terms. All the universal statements in science are conjectures that are testable and falsifiable. These conjectures are invented by the human mind, and none of them are produced by inductive generalization. To give a causal explanation of an event means to deduce a statement which describes the event using as premises of the deduction one or more universal laws as theories together with singular basic statements that describe the initial conditions. Popper’s ideas for such terms as “theory”, “law”, and “cause” are fundamentally different from the positivists’ ideas for these terms, because Popper’s ideas are separated from the subject matter or ontologies described by the sciences.
Empirical science is not purely formal like mathematics or logic, but neither is it defined in terms of certain substantive concepts about reality as it is described by science today. Future science may revise the substantive content of today’s science, and yet science will still be science as Popper has defined it. As Popper says in reply to Kuhn’s concept of science in “Normal Science and Its Dangers” in Criticism and the Growth of Knowledge (1970), “science is subjectless”. Such could not be said of science by the positivists, for whom the naturalistic philosophy of the semantics of language requires that certain substantive concepts permanently established by observation must always be retained as definitive of the empirical character of science. The rejection of the naturalistic philosophy of the semantics of language implies the reconceptualization of such metascientific terms as “theory”, “law”, “explanation”, and “cause” in a manner that disassociates these ideas from any particular ontology that the semantics of science may describe at any point in history. Empirical science becomes a sequence of alternative ontologies instead of a specific ontology. And with his criterion of increasing information content Popper believes that the sequence of ontologies is not a disconnected random sequence, but rather is one that reveals objective and rational scientific progress. Curiously Popper himself did not follow through on these ideas when he supported Einstein’s criticism of the Copenhagen interpretation of quantum theory, and he advanced his own “commonsense realism” ontology.