Hayek's work crosses several disciplines. Originating in economic debates about the appropriateness of controlling market forces, it contains a distinctive philosophical theory. Hayek is sceptical about constructivist rationalism, the idea that human institutions can and should be deliberately designed to meet human purposes. Instead, he argues that a spontaneous order evolves out of particular actions and decisions which could not have any such order as their objective. Hayek acknowledges a debt to thinkers such as Adam Smith, Hume and Ferguson in formulating these ideas. They lead to a specific scepticism about socialism, construed as a system of centralized economic planning which displaces the operation of the market. In his The Road to Serfdom (1944) he claims that such comprehensive planning erodes individual liberty and cannot succeed because it would not be possible to centralize all the knowledge required for its operation. In his own favoured system, general welfare flows from individuals acting as they choose, against the background of a system of laws and traditions which embody the wisdom of proven fitness. Hayek's work shows interesting affinities with that of other twentieth-century philosophers. His opposition to comprehensive social reconstruction is close to Popper's. He acknowledges similarities with Ryle's distinction between knowing how and knowing that in his The Constitution of Liberty (1960). Evident throughout his work is a negative conception of liberty of the kind sponsored by Isaiah Berlin, according to which liberty consists in the absence of coercive interference by other human agents. Like Berlin, he urges the distinctness of democratic practice and liberty as so defined, and the possibility of conflict between them.
Hayek's ideas received wider attention in the 1980s as one of the acknowledged influences on the British prime minister Margaret Thatcher. They also provided a sharp contrast to theories of social justice of the kind espoused by philosophers such as Rawls and Dworkin. For Hayek, it is misconceived to adopt a moralizing attitude towards the result of a market system of distribution which is not the intended consequence of any individuals' actions. More strongly, he argues in his Law, Legislation and Liberty (1976) that such redistributive aspirations are actually incompatible with the rule of law, which involves treating individuals impartially. Attempts to rectify material inequalities are held to rest on incoherent notions of desert and need, to threaten liberty through coercive reallocation and to undermine the efficiency of the economic system which provides resources for distribution in the first place.
In specifically philosophical, rather than political, critical reaction there has been interesting discussion of the extent to which Hayek's work does or could improve on the justifications of classical liberalism. Questions have been raised about the extent to which he can consistently argue for his favoured system, given the very limited role he assigns to reason in human affairs; about the coherence of the evolutionist grounds for the superiority of surviving institutions; and, more generally, about the extent to which he