The Esse/Essentia Argument in
Aquinas's De ente et essentia
Despite all of the attention which has been paid to the issues which Aquinas raises in an important argument in Chapter 4 of De ente et essentia 1 (I shall call it the Esse/Essentia [E/E] Argument), no one has offered a detailed account of exactly what the argument is. 2 There have been discussions of its general character, of the interpretation of certain of its segments and conclusions, and of the argument's place in the broad context of Aquinas's thought. It seems to me, however, that one must be clear about the precise structure of the argument before one can address these more general questions. In Section 1, therefore, I shall set out the E/E Argument in detail and discuss some misconstruals of the argument's structure. On the basis of the exegetical work done in Section 1, I shall sketch in Section 2 an interpretation of the E/E Argument paying special attention to its status as an argument for the real distinction between esse and essence. I shall then consider briefly in Section 3 one interpretation of the argument which differs from mine.
At the beginning of Chapter 4 Aquinas rejects the view that separate substances are composed of matter and form. 3 Insofar as they do not exhibit the composition of matter and form, separate substances are simple. The view that separate substances are in some sense simple, however, is open to two possible objections. First, it might be objected that if separate substances are simple, they are like God, which is impossible. Second, it might be pointed out that Aquinas himself has claimed that individuation is dependent on matter. 4 If separate substances do not have matter, then it will be impossible to individuate them. Aquinas devotes the remainder of the chapter