Popper and Non-Justificationism

Inductive inferences have observations as premises and theories as conclusions. They are notoriously invalid but often are deemed unavoidable. Critical rationalism views them as unnecessary. This point of view grew gradually out of Karl Popper’s attempt to describe science without their use in Die beiden Grundprobleme der Erkenntnistheorie (1932-33), where he still operated within the framework of justificationism, that is, while viewing the aim of scientific method as the proper (justified) assessment of the truth value of certain sentences. He hoped to build a theory of the proper assessment of sentences, that is, of the possibility of proving the truth or falsity of some sentences. He began with the fact that a theory is false if it contradicts a singular sentence describing some observation reports. Popper then said that such singular sentences were veridical, that is, truthful as opposed to illusory, so they may be used to produce final proofs of the falsity of some universal sentences. For example, the singular sentence, “That swan is black,” if it is a true report of some observation, can be used to produce a final proof of the falsity of the universal sentence, “All swans are white.” But, he argued, proof of universal sentences or the demonstration that they are probable requires inductive inferences. As a consequence no such putative proof can be valid.

Popper himself found the theory he presented in Die beiden Grundprobleme der Erkenntnistheorie without chapter 5 inadequate for three reasons. The first reason is that singular statements are not veridical. He began work on this problem in chapter 5 of Die beiden Grundprobleme. This chapter contains a theory of science which differs on important points from the theory found in the rest of that volume. The second reason that Popper’s first attempt broke down is that one can circumvent refutations by ad hoc stratagems, as Hans Reichenbach quickly pointed out in a note which responded to Popper’s first publication of his view in Erkenntnis. The third reason was Popper’s inability to handle the problem of the demarcation of science from non-science with his idea that we show how science properly assigns truth values to sentences with no inductive inference. On a justificationist theory of the task of the philosophy of science such as Reichenbach’s, which was identical to Popper’s theory as he wrote Die beiden Grundproblemewithout chapter 5, science should be demarcated by the proper assignment of truth values: science is the set of sentences with justifiably assigned truth values. The task of the philosophy of science is to explain how these assignments are properly made. (Reichenbach said the calculus of probabilities serves that purpose.) Popper argued that it is not possible to properly assign either the truth value True or some degree of probability to universal sentences. He called such sentences “fictions”, which is a term he had earlier taken over from Hans Vaihinger. On the theory presented in Die beiden Grundprobleme without chapter 5, after science had done its job, there were still, on the one hand, some fictions which ought to be deemed scientific such as the theories of the Würzburg school in psychology and, perhaps, as he said later, Einstein’s physics, and, on the other hand, other fictions which should be deemed unscientific, such as the psychologies of Freud and Adler. He could not distinguish between these two sets of theories within his justificationist framework, since, on this view, only proofs or refutations of these theories could do that. He asserted, however, that no proof was possible and refutations could establish only the falsity of universal propositions.

As a consequence of these three difficulties Popper developed an entirely different theory of science in chapter 5, then in Logik der Forschung. In order to overcome the problems his first view faced, he adopted two central strategies. First, he reformulated the task of the philosophy of science. Rather than presenting scientific method as a tool for properly assigning truth values to sentences, he presented rules of scientific method as conducive to the growth of knowledge. Apparently he still held that only proven or refuted sentences could take truth values. But this view is incompatible with his new philosophy of science as it appears in his Logik der Forschung: there he had to presume that some non-refuted theories took truth values, that is, that they are true or false as the case may be, even though they have been neither proved nor refuted. It is the job of scientists to discover their falsity when they can. So, he worked around the difficulty posed by the fact that, on the one hand, he had to assume that theories were refutable and thus had truth values, whereas, on the other hand, he thought that only proven or refuted theories had truth values at all. He argued that his view could be interpreted as realist or as antirealist. He hedged his bets as best he could and appealed to Mach, who had stipulated that one should avoid participation in any metaphysical dispute.

In Logik der Forschung Popper solved his three initial difficulties in the following ways. First, instead of claiming that singular sentences were veridical, he said that basic statements are only provisionally accepted, provided that they were repeatable and so testable. He thereby introduced the following rule: consider only repeatable basic statements. He claimed that the provisional acceptance of basic statements does not disqualify them as refutations of theories—no longer simply universal sentences—because for the most part we can agree on which basic sentences we provisionally assume to be true. Second, he proposed the rule that one should always replace some theory which is contradicted by a basic statement by whichever new alternative has the highest degree of falsifiability. This rule should guarantee that refutations lead to progress. Reichenbach had declared that there was no logic of scientific method, that is, no proof or refutation. The basis for his claim that there could be no refutation was that any theory could be protected from a putative refutation with some ad hoc maneuver. Popper responded to Reichenbach with his Logik der Forschung (Logic of Research) and by introducing methodology into his deliberations. The methodological rule enabled him to avoid ad hoc protection of theories and thus enabled him to show how theories could be refuted. Third, he introduced the rule: only refutable theories—the term “fiction” no longer appears in his work—are scientific and may be deemed scientific.

This view was no longer justificationist, that is, it no longer claimed properly to assign truth values to sentences. All “assignments” are conjectural. But Popper had at that point no non-justificationist theory of rationality in general; his theory applied to science alone. He did not at that point notice problems which his theory raised for the broader framework of rationality which all philosophers of science had used since antiquity, the framework that identified the rational with the proven.

The conflict between Popper’s new theory of science and his older theory that only proven or refuted sentences can take truth values was removed by Tarski. Tarski’s definition of truth, as Tarski explained to Popper, allows for non-proven but still true sentences. Tarski thereby did away with the theory of truth that had given Popper so much trouble. Tarski did not necessarily offer Popper an adequate theory of truth for his philosophy of science. But Tarski did free him from a false theory which was a great impediment to the construction of a truly fallibilist, realist theory of science. Popper never clearly explained the importance that Tarski had for him at the time. This failure to explain how the logic of his problem changed as a result of Tarski’s theory was part of his repression of the fact that he had held a justificationist theory of truth for a long time, even after he began writing a fallibilist book. After his meeting with Tarski, he was free to develop his fallibilist theory of science in new ways, because he could claim that theories could be true even though there was no proof of them. During his earlier years in London, during 1946-1965 or so, he returned to the possibilities this fact opened up.

In Logik der Forschung Popper developed a theory of the growth of scientific knowledge without justification. But he had no general theory of rationality without justification. Indeed, he still limited rationality to science and methodology. However, at least three problems arose for this limited view of rationality.

Popper maintained at that point that scientists gain knowledge not by proofs but by refutations of good conjectures and by replacing them with new and better ones. These new conjectures avoid earlier mistakes, explain more, and invite new tests. He originally thought of this theory as eo ipsoa theory of rationality: outside of science and methodology he made no allowance for rationality. He identified research, science and methodology, as the title of his book indicates.

Difficulties piled up fast. First, if rationality is limited to science, how is methodology rational? Methodology can only be rational if methodology is the empirical study of science—as Whewell said—or if non-empirical research can be rational. Popper could not view methodology as a science of science because he held that it is not merely descriptive but also prescriptive. Yet it should be rational.

The second problem arose as Popper tried to apply his methodology of the physical sciences to the social sciences. The Poverty of Historicism and The Open Society and Its Enemies defend the open society on the grounds that only open societies preserve reason, that is, criticism, and as a consequence only open societies can be civilized. But why is a choice for the open society rational? He had no answer. He merely said that the acceptance of reason was a consequence of sympathy for others. Nothing can be said to convince those to change their minds who accept the barbaric consequences of fascism or communism.

The third problem concerns metaphysics. Before he had ever developed his own philosophy of science, he had defended in his doctoral dissertation the view that metaphysical hypotheses can serve as working hypotheses in the construction of scientific theories. His discussion there merely concerned the use of physicalist metaphysics as a guide for psychological research. He said that this was fine, but one should not decide a priori that a view of psychological processes as physical is needed or even possible. Scientific research—he was not clear then what that meant—should decide this. He was later pressed, however, to decide between competing metaphysical theories with which to interpret science, even in the absence of a scientific answer. Was the world determined or not? Questions such as this raised the question as to whether one metaphysical theory can be better or worse than another and whether one could find out which one is better. He gave up his earlier view of rationality as limited to scientific research and methodology, but he still insisted that for science some metaphysical theories are merely heuristic, and no more than that.

To extend his theory that rationality consisted of scientific research and methodology alone, Popper loosened his standard of rationality. Rejecting the older standard of rationality -- proof - - as too high, he began to view the standard for science, refutability, as too high for the rationality that obtains outside science. Whereas earlier he had replaced justification with refutation, he now replaced refutation with criticism. Popper thereby created a new philosophical perspective by generalizing his theory of scientific research. The name he gave to this extension is “critical rationalism.” Popper introduced it in the introduction to his Conjectures and Refutations, where he characterized it briefly as the critical attitude. He used it also to describe views he developed earlier, in The Open Society and Its Enemies.

Could his critical rationalism apply to other fields? Could various fields also not only do without (epistemological) justification but also raise their levels of rationality with the use of critical methods? Critical rationalism became a project to employ critical methods as a substitute for epistemological justification in all areas of life.