Existence and Essence in God

To talk about what I am is different than to talk about the fact that I am. In philosophical terms, this is the distinction between essence and existence. But this distinction does not hold when we talk about God, as though they are actually separate things in him the way that they are in us.

God is not only His own essence, as shown in the preceding article, but also His own existence. This may be shown in several ways.

First, whatever a thing has besides its essence must be caused either by the constituent principles of that essence (like a property that necessarily accompanies the species--as the faculty of laughing is proper to a man--and is caused by the constituent principles of the species), or by some exterior agent--as heat is caused in water by fire. Therefore, if the existence of a thing differs from its essence, this existence must be caused either by some exterior agent or by its essential principles. Now it is impossible for a thing's existence to be caused by its essential constituent principles, for nothing can be the sufficient cause of its own existence, if its existence is caused. Therefore that thing, whose existence differs from its essence, must have its existence caused by another. But this cannot be true of God; because we call God the first efficient cause. Therefore it is impossible that in God His existence should differ from His essence.

Secondly, existence is that which makes every form or nature actual; for goodness and humanity are spoken of as actual, only because they are spoken of as existing. Therefore existence must be compared to essence, if the latter is a distinct reality, as actuality to potentiality. Therefore, since in God there is no potentiality, as shown above (Article 1), it follows that in Him essence does not differ from existence. Therefore His essence is His existence.

Thirdly, because, just as that which has fire, but is not itself fire, is on fire by participation; so that which has existence but is not existence, is a being by participation. But God is His own essence, as shown above (Article 3) if, therefore, He is not His own existence He will be not essential, but participated being. He will not therefore be the first being--which is absurd. Therefore God is His own existence, and not merely His own essence (ST I Q3 A4).

We have to be careful about the way that we talk about God. St. Thomas points out (ST I Q3 A3 ad 1) that we the way that we acquire knowledge - from composite beings like ourselves - means that our language lends itself to talking about things as composite beings. But this is not true of God. He is not a composite being. He is absolutely simple. So although we may talk about what God is like in ways that might suggest that he has attributes and accidents after the manner of created things, we must remember that this is not how he is really.