Front Page Titles (by Subject) 2. Karl Popper: The Growth of Knowledge - Literature of Liberty, Winter 1982, vol. 5, No. 4
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2. Karl Popper: The Growth of Knowledge - Leonard P. Liggio, Literature of Liberty, Winter 1982, vol. 5, No. 4 
Literature of Liberty: A Review of Contemporary Liberal Thought was published first by the Cato Institute (1978-1979) and later by the Institute for Humane Studies (1980-1982) under the editorial direction of Leonard P. Liggio.
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2. Karl Popper: The Growth of Knowledge
A second influence on Hayek's general philosophy which gives it a distinctive temper is the thought of his friend, Karl Popper (b. 1902). I mean here, not Popper's hypothetico-deductive account of scientific method, which there is evidence that Hayek held prior to his meeting with Popper,11 nor yet Popper's proposal (which Hayek was soon to accept) that falsifiability rather than verifiability should be adopted as a criterion of demarcation between the scientific and the non-scientific. Again, Hayek has under Popper's influence come to make an important distinction between types of rationalism,12 such that “critical rationalism” is commended and “constructivistic rationalism” condemned. But this is not what I have in mind. I refer rather to certain striking affinities between Hayek's view of the growth of knowledge and that adumbrated in Popper's later writings on “evolutionary epistemology.” As early as the manuscript which later became The Sensory Order (published in 1952, but composed in the twenties), Hayek made it clear that the principles of classification embodied in the nervous system were not for him fixed data; experience constantly forced reclassification on us. In his later writings, Hayek is explicit that the human mind is itself an evolutionary product and that its structure is therefore variable and not constant. The structural principles or fundamental categories which our minds contain ought not, then, to be interpreted in Cartesian fashion as universal and necessary axioms, reflecting the natural necessities of the world, but rather as constituting evolutionary adaptations of the human organism to the world that it inhabits.
The striking similarity between Popper's later views, and those expounded by Hayek in The Sensory Order, is shown by Popper's own application of the evolutionist standpoint in epistemology to the theory of perception:
...if we start from a critical commonsense realism...then we shall take man as one of the animals, and human knowledge as essentially almost as fallible as animal knowledge. We shall suppose the animal senses to have evolved from primitive beginnings; and we shall look therefore on our own sense, essentially, as part of a decoding mechanism—a mechanism which decodes, more or less successfully, the encoded information about the world which manages to reach us by sensory means.13
J.W.N. Watkins’ comment on this view is as apposite in the respect of Hayek as it is of Popper:
Kant saw very clearly that the empiricist account of sense experience creates and cannot solve the problem of how the manifold and very various data which reach a man's mind from his various senses get unified into a coherent experience.
Kant's solution consisted, essentially, in leaving the old quasimechanistic account of sense-organs intact, and endowing the mind with a powerful set of organizing categories—free, universal and necessary—which unify and structure what would otherwise be a mad jumble.
Popper's evolutionist view modifies Kant's view at both ends: interpretative principles lose their fixed and necessary character, and sense organs lose their merely causal and mechanistic character.14
Hayek's account of sense perception anticipates Popper's later views in a most striking fashion, because in both sensation is conceived as a decoding mechanism, which transmits to us in a highly abstract fashion information about our external environment. Again, both Hayek and Popper share the skeptical Kantian view that the order we find in the world is given to it by the creative activity of our own minds: as Hayek himself puts it uncompromisingly in The Sensory Order, “The fact that the world which we know seems wholly an orderly world may thus be merely a result of the method by which we perceive it.”15 One difference between Hayek and Popper is in the fact that, at any rate in his published work to date, Hayek has not followed Popper in his ontological speculations about a world of abstract or virtual entities or intelligibles.16a
[11.] See Hayek's interesting discussion of differences of method as between natural and social sciences in µE-5Õ, the collection which he edited: Collectivist Economic Planning, London: 1956 (originally published 1935), pp. 10-11. Hayek withdraws from the strong methodological dualism about natural and social science adopted here and in many of his earlier writings, explicitly in the Preface to his Studies in Philosophy, Politics and Economics, London: Routledge and Kegan Paul, 1967, p. viii, where he asserts that through Popper's work “the difference between the two groups of disciplines has thereby been greatly narrowed.” For a brilliant discussion of Popper's demarcation criterion for science, see I. Lakatos, “Popper on Demarcation and Induction,” in P. A. Schilpp, ed., The Philosophy of Karl Popper, La Salle, Illinois: 1974, pp. 241-273.
[12.] See F. A. Hayek, “Kinds of Rationalism” in his µB-13Õ, Studies in Philosophy, Politics and Economics, Ch. 5, pp. 82-95, and his Law, Legislation and Liberty, Vol. I, London: Routledge and Kegan Paul, 1973, p. 29.
[13.] Karl R. Popper in P. A. Schilpp, ed., The Philosophy of Karl Popper, pp. 1059-1060.
[14.] J. W. N. Watkins in P. A. Schilpp, ed., The Philosophy of Karl Popper, pp. 401-402.
[15.] Hayek, Sensory Order, µB-10Õ, p. 176, para. 8.39.
[16a.] Hayek does cite Popper's ideas of a third world of abstract entities with apparent endorsement in µB-18Õ, Law, Legislation and Liberty, Vol. III, p. 157.