Concepts help economize on information. Conventional wisdom correctly associates conceptualism with formalism but misunderstands the role concepts play in law. Commentators from the Legal Realists onward have paid insufficient attention to the distinction between concepts and the categories they pick out (or, to borrow from philosophical semantics, the intension and extension of legal relations). Even though two concepts may identify the same category, they can differ greatly in terms of information costs. This Article applies tools of cognitive science to explore the economics of legal concepts. Both the mind and the law are information-processing devices that manage complexity and economize on information by employing concepts and rules, the specific-over-general principle, modularity, and recursion. These devices work in tandem to produce the economizing architecture of property. As in cognitive science, we expect simplicity of description and generality of explanation to coincide. This Article then applies the cognitive theory of property to longstanding puzzles like the role of baselines—such as nemo dat (“one cannot give that which one does not have”) and ad coelum (“one who owns the soil owns to the heavens above and the depths below”)—the notion of title, and the function of equity as a safety valve for the law. The theory developed here provides a more elegant description of the law, better generalizes to new situations, and therefore helps to explain and justify the robustness of traditional baselines in property law. The cognitive theory also allows one to reconcile reductionism and holism in property theory, as well as static and process descriptions of the contours of property.