Aquinas on the Unity of Definition

Abstract

For Aristotle and his medieval followers, the problem of the unity of definition consists in explaining how the parts of a definition, the genus and the differentia(e), are one thing and not many. The chapter is about Thomas Aquinas’ solution to the problem of the unity of definition. The main claim of the chapter is that the key to Aquinas’ solution is his endorsement of hylomorphism about definition, that is, of Aristotle’s idea in theMetaphysics that a definition displays the same hylomorphic structure as particular sensible substances and that it is the hylomorphic model that enables us to explain how a definition is a unity. It is shown how Aquinas both provides an original interpretation of hylomorphism about definition and creatively adapts it to some of his key metaphysical views.