Abstract

Aquinas considers the questions “Does it exist?” and “What is it?” basic to any science in Aristotle’s sense. In his early works, Aquinas claims that we can answer the second question without answering the first, knowing a thing’s essence without knowing whether it exists. This claim is part of a famous argument for the real distinction between essence and existence in creatures, and for the existence of God. But in his later commentaries on Aristotle, Aquinas appears to abandon the claim, insisting that it is impossible to know what something is without knowing whether it exists. What should we make of this apparent contradiction? It is possible that Aquinas simply changed his mind, or that in his later commentaries he is only explaining Aristotle’s view, with which he disagrees. In this paper, however, I defend a third solution based upon Aquinas’s distinction between two ways of knowing what something is—“by means of a definition” and “by means of a proposition.” For Aquinas explains that in the one way we can know a thing’s essence without knowing its existence, and in the other way we cannot. Thus, the apparent contradiction can be resolved by making just such a distinction. Yet understanding this third solution requires an examination of the semantics of definitions and propositions informing Aquinas’s logical approach to essence. Such an examination not only allows us to resolve the apparent contradiction between his works; it also gives us a better understanding of his logical approach to essence.