1. The fourth article of this question concerns the identity of essence and esse (“to be”, the act of being) in God. This article is magnificent.
2. Against the identity of essence and existence in God, Thomas offers two objections. The first is that if God were merely the act of existing, then in God there would be nothing super-added to the act of being. But in creatures, the mere act of being without any added characteristics is referred to as “esse commune”, or “the common act of being”, which is predicated of everything that exists. In this case, God would simply be “existence” in general, and everything could be said to be God, inasmuch as everything exists. But scripture manifestly contradicts such a notion, as for example, when it says that the name of God cannot be rightly applied to stones and wood.
3. The second objection is from the possibility of different kinds of knowledge of God. If essence and existence were the same in God, then to know the one would be to know the other. But while we can prove that God exists, we cannot know the divine essence in this life, so the two must be distinct.
4. For the Sed Contra, he cites St. Hilary.
5. In the Corpus, he offers three arguments for the identity of essence and existence in God. Each of these arguments is profoundly illuminating. The first is from the relationship between a thing’s qualities and its essence. Whatever qualities are in a thing must either be a part of its essence, must flow from its essence, or must arise accidentally from some other external cause. He uses the example of laughter in man. A man incapable of laughter would not be inhuman by that fact, as for example a man without a rational soul would be, but ordinarily the ability to laugh flows from the essential characteristics of humanity. But if a man goes outside in midwinter and stands still for an hour, you may find that his hands are cold. This coldness of the hands is neither essential to his humanity, nor an accidental manifestation of his humanity, but an accident brought about by the influence of his cold surroundings.
6. Thomas points out that if the existence of a thing is distinct from its essence, then it must be either in the second or third category. I.e., existence must either flow from the essence of a thing, or be brought about in it by some exterior agent. But the former possibility is absurd, since an essence without existence cannot bring about that existence—what does not have the act of being cannot supply it of itself. Therefore, if a thing’s existence is distinct from its essence, then its existence must be caused by another agent. But as was shown above (cf. the second way), God is the first efficient cause. Therefore it is impossible that his existence is caused by another. So it must be identical with his essence.
7. Second, he argues that the act of being is what makes any form or essence actual, since if a thing’s essence and its existence are distinct, the essence, without the act of being, is merely a possibility. Thus, among things in which essence and existence are distinct, the essence is a kind of potency brought into act by the act of being. But in God there is no potency, as has been mentioned elsewhere, so this cannot be true of him. Therefore essence and existence must be the same in him.
8. Third, he says that what has being but is not itself being, exists by participation. But since God does not participate in or receive his form from any higher being, he must not simply “have” existence from another (cf. the fourth way), but be his own existence.
9. In Thomas’s reply to the first objection, he distinguishes two ways in which a thing can have nothing added to it: first, inasmuch as its essence by definition excludes any addition (as “irrational animal” excludes the addition of rationality); second, inasmuch as its essence is left indeterminate (as “animal” is left unspecified as to its rationality). God’s existence, he says, has nothing added to it in the former way: it is already fully determined. Common existence has nothing added to it in the latter way: as totally undetermined.
10. To the second objection, he replies that “to be” may be said in either of two ways: in one way it is the determinate act of a particular essence, in another way it reflects the intellectual conjunction of subject and predicate. We know that God exists only in the second way.
11. This reply is rather odd, because it seems to leave open the question, “What ‘being’ is being predicated of God in the statement ‘God is’?” It cannot be esse commune, because God’s act of being is distinct from universal being, as has already been discussed. But neither can it be God’s own proper act of being, which we are incapable of knowing. The solution, it seems, is to add another distinction: between primitive conception of being in the intellect, and the actual being of things. That “God exists” may at first seem to place God in the class of beings that are, i.e. ens commune, is not problem once we realize the distinction between ipsum esse and esse commune. However, our affirmation of God’s existence can still be held true, even if he is only said to “exist” through analogy. A full discussion of this problem will be reserved to qq.12-13.
Outline of Article
—Mere “being” with nothing added to it is common to all things, so that if God were mere “being”, God would be everything.
—If God’s being and essence were identical, to know one would be to know the other. But the latter can be known, while the former cannot.
—Features distinct from a thing’s essence are either caused by the essence or caused by some other agent. God’s existence cannot be caused by another agent. But existence cannot be supplied by a non-existing essence. Therefore in God, existence and essence are one.
—Essence is to potency as Esse is to act. But God is pure act, and therefore is his own Esse.
—Whatever does not have existence in itself exists by participation. God does not participate in any higher forms, so he must exist of himself.
—Esse commune is mere being, without any determinations of quality or form. But God’s esse is being, determined to the utmost extent.
—In the judgment “God exists”, we do not claim to know God’s act of being, but merely to grasp that there is such an act of being, by its reflection in created things.