Hayek's theory of knowledge is his most distinctive contribution both to economics and to social science. Its foundation is “our irremediable ignorance” (Hayek 1982a, p. 13), both as social actors and as social theorists. “The dispersion and imperfection of all knowledge are two of the basic facts from which the social sciences have to start” (Hayek 1952a, p. 50). The knowledge which members of modern societies possess is necessarily imperfect and incomplete, and can never be perfected. This is so for several reasons which are all interlinked; first, because in any modern society knowledge is fragmented and dispersed among millions of individuals; second, because the limits of human reason mean that many things remain unknown and unknowable to individual members of society whether in their roles as social actors or social theorists; and third, because the unintended consequences of human action and the tacit nature of so much of the knowledge that individuals do possess means that modern societies have to be understood as organisms evolving through time, representing extremely complex phenomena which defy the normal methods of science either to explain or to control.