Adolf Reinach belongs to the Brentanian lineage of Austrian Aristotelianism. His theory of social acts is well known, but his account of ownership has been mostly overlooked. This paper introduces and defends Reinach's account of ownership. Ownership, for Reinach, is not a bundle of property rights. On the contrary, he argues that ownership is a primitive and indivisible relation between a person and a thing that grounds property rights. Most importantly, Reinach asserts that the nature ownership is not determined by positive law but presupposed by it. Some have objected that such realism raises insuperable difficulties as to the origin of ownership, difficulties that could only be dealt with under a more conventionalist approach. I argue that the independence of the nature ownership from positive law is, in fact, compatible with the claim that its existence is dependent on human conventions.