Jack Birner

F. A. Hayek’s The Sensory Order (1952) is often considered to be a theory of cognitive psychology. While it contains a theory on the psychology of perception, it has the function of illustrating Hayek’s solution to the mind–body problem. The solution, which has been strongly influenced by Moritz Schlick’s epistemology, takes the form of a physicalist identity theory. An attempt is made to trace Schlick’s influence on Hayek to the latter’s stay in Zürich, which resulted in a manuscript (1920) that contains the main features of the 1952 book. One of the consequences of Hayek’s theory is that we cannot describe the functioning of our mind completely without using expressions that refer to subjective experiences. For Hayek this is not a fundamental problem but a practical one that does not jeopardize his physicalist identity theory. Unlike the manuscript, The Sensory Order contains a rudimentary sketch of an evolutionary research program. When Hayek elaborated that program later, though, he focused on cultural evolution rather than on the evolution of the mind.

Karl Popper and Friedrich von Hayek became close friends soon after they first met in the early 1930s. Ever since, they discussed their ideas intensively on many occasions. But even though an analysis of the origins and contents of their ideas and correspondence reveals a number of important and fundamental differences, they rarely criticize each other in their published work. The article analyzes in particular the different ideas they have on the role of reason in society and on rationalism and the roots of these differences. Popper’s “Towards a Rational Theory of Tradition” of 1948 contains a criticism of Hayek’s idea—published, for instance, in “Individualism: True and False” of 1945—that we must accept tradition without trying to change it. An analysis of the differences between the two authors touches on topics such as the possibility of public intervention in society, the role of social science in this, the methodology of social science, and the differences between liberalism and social democracy. The article concludes with some possible explanations for Popper and Hayek downplaying their differences in public. The fact remains that they never resolved the tension between Popper’s critical rationalism and Hayek’s conservative rationalism.

Karl Popper’s Objective Knowledge stands at the threshold of his last major philosophical phase, the period from his retirement from the London School of Economics in 1969 until his death in 1994. The two great books that he wrote before he came to London, Logik der Forschung and The Open Society and Its Enemies, contain much more than the innovations in the theory of scientific method and the theory of democracy for which they are famous. Logik der Forschung, translated into English as The Logic of Scientific Discovery, is by no means just a tract, even a revolutionary one, on the methods of science, since about one third of the text is devoted to searchingly original treatments of the frequency theory of probability and of the interpretation of quantum mechanics, whilst the unpublished manuscript on which the book was based, Die beiden Grundprobleme der Erkenntnistheorie, at whose content it often hints, presents a wealth of significant material on the psychology of human learning and its biological context. Popper had, after all, been a student of Karl B¨uhler, and had absorbed the theories of problem solving developed within the W¨urzburg School. The Open Society and Its Enemies, for its part, is not so much a book defending democratic liberalism as a defence of democratic liberalism nestling within a book that discusses every other topic under the sun. It offers profound and provocative studies of the thought of Plato and Marx, an abundance of scholarly, if often controversial, historical interpretations of the work of Heraclitus, Aristotle, Hegel, J. S. Mill, Wittgenstein, Mannheim, and others, the elements of a new theory of rationality, and many elucidations of the workings of science that go beyond what is explicit in Logik der Forschung. One insight worth mentioning, since it is little known, is the clear recognition in section II of Chapter 11 that most important advances in science are revolutionary, not cumulative; a commonplace today perhaps, but one that many philosophers attribute to Kuhn. Another insight, also often forgotten, is the emphasis in Chapter 23 on the social character of science, which acts as the main custodian of its claim to objectivity.