Hume's arguments in the Treatise require him to employ not only the copy principle, which explains the intrinsic properties of perceptions, but also a thesis that explains the representational content of a perception. I propose that Hume holds the semantic copy principle, which states that a perception represents that of which it is a copy. Hume employs this thesis in a number of his most important arguments, and his doing so enables him to answer an important objection concerning the status of the copy principle. I further argue that the semantic copy principle is necessary, a priori, and discovered through an analysis of our general idea of representational content.