The goal of this essay is to explore various ambiguities and tensions that (it will be argued) characterize Hayek’s social theory from the 1940s to the 1970s. As used in this essay, the term social theory denotes a set of abstract claims about the nature of the social world and the methods appropriate for studying it. The claims about the nature of the social reality, or the social ontology, made by Hayek during that period concern in particular the relationship between individual people and two other domains or facets of reality: first, the physical matter out of which they are composed; and, second, the social structures or wholes in which they are, on Hayek’s ‘true’ individualistic account, embedded ( 2010). The first of those relations becomes significant for Hayek because, as we shall see, it is central to his efforts in the 1940s to mount a defense of his preferred subjectivist methodology of economics against a set of critics who wished to replace all references to ‘mental’ states—such as ‘purposes’ and ‘intentions’—by concepts defined solely in physical terms. The second relationship, between individual people and social wholes, is of course central to Hayek’s efforts to explain how market economies work and also how they come to be established in the first place.