Gilbert Ryle is most famous for accusing the Cartesian dualist of committing a category mistake. Yet the nature of this accusation and the idea of a category mistake more generally remains woefully misunderstood. The aim of this paper is to rectify this misunderstanding. I show that Ryle does not conceive of category mistakes as mistakes of predication, as is widely believed. Instead, I show that category mistakes are mistakes of conjunction and quantification. This thesis uniquely unifies and explains the wide variety of Ryle’s remarks, judgments, and arguments.