We’re blogging through St. Thomas Aquinas’ Compendium Theologiae, sometimes called his Shorter Summa. Find the previous posts here.
In the previous chapter, Thomas shows that God’s essence is simply existence itself, ipsum esse, a point he’d been working up to for some chapters. In this chapter and several that follow, he’s concerned to prove some corollaries, and to situate God within certain traditional metaphysical categories—or, more accurately, to show that He is a special case, and the standard categories don’t really apply.
In our look at Chapter 10, on the identity of God with His essence, we necessarily spent time looking at the notions of genus and species as metaphysically understood. You might wish to go back and review.
We infer from the above that God is not contained as a species within any genus. Species is constituted by specific difference added to genus. Hence the essence of any species possesses something over and above its genus. But existence itself, ipsum esse, which is God’s essence, does not comprise within itself any factor that is added to some other factor. Accordingly God is not a species of any genus.
As Thomas says, a species is distinguished from the genus that contains it by a specific difference. An apple tree and a cherry tree are both fruit trees, but an apple tree bears apples and a cherry tree does not. That specific difference is added to the basic notion of fruit tree. But mere existence, mere being, is ultimately the root of all categories: it is undifferentiated being. And so, since God is existence Himself, there is no specific difference in Him, and so He isn’t a species.You might say, wait: a species is a set of individuals. How could one being be a species to begin with? It’s a good question, and one which puzzled me mightily; and the answer will come rather later on in this series. For now, the necessary point is that Thomas is ruling out a whole host of possible ways of misunderstanding God, and this is one of them.
Furthermore, since genus potentially contains specific differences, in every being composed of genus and differences, act is commingled with potency. But we have shown that God is pure act without any commingling of potency. (Cf. chap. 9.) Therefore His essence is not composed of genus and differences; and so He is not in any genus.
We’ve see this argument before, and will see it again. Species is a composition of genus and specific difference; and every true composition ultimately is a composition of act and potency. We’ve already established that God is pure unchanging actuality; and hence, by reduction ad absurdum we see that He cannot be a species within a genus.
Next time, we’ll see that not only is He not a species, He’s not a genus either.