Aquinas on essence and existence

Turner C Nevitt, Fordham University


In this dissertation I develop versions of Aquinas’s “logical” approach to essence and existence and consider whether and in what ways they can be defended in the context of contemporary analytic philosophy. In the course of the dissertation I also raise a number of new and old problems with Aquinas’s theories of essence and existence and defend novel solutions to them. After motivating a consideration of it, in chapter one I start to develop Aquinas’s “logical” approach to essences by means of real definitions. I clarify the explanatory role of definitions and distinguish various types of definitions. I begin chapter two by explaining six formal requirements real definitions must meet in order to play their explanatory role. I also explain how the sixth requirement—that definitions be composed of a genus and specific difference—is not the uncritical assumption of natural-kind essentialism, but the solution to a problem posed by complex real definitions. I then consider what ways Aquinas’s “logical” approach to essences can be defended. In chapter three I explain the limits Aquinas places on the range of real definitions—what can and cannot be defined—and then consider how he thinks we discover the real definitions of things. I begin chapter four by motivating a consideration of Aquinas’s theory of existence. I then start to develop his “logical” approach to existence by means of the verb “is” or “exists,” which I complete in the first half of chapter five. In the second half of chapter five I consider what ways Aquinas’s “logical” approach to existence can be defended.

Subject Area

Medieval literature|Metaphysics|Philosophy

Recommended Citation

Nevitt, Turner C, "Aquinas on essence and existence" (2015). ETD Collection for Fordham University. AAI10013387.