We proceed to the seventh article thus:
1. It seems that God is not altogether simple. God's creatures resemble him. Thus all things have being from God the first being, and all things are good since he is the first good. Now nothing that God creates is altogether simple. Therefore God is not altogether simple.
2. Again, whatever is better must be ascribed to God. Now in things around us, what is composite is better than what is simple. Composite bodies, for example, are better than their elements, and animals are better than their parts. Hence we should not say that God is altogether simple.
On the other hand, Augustine says: "God is absolutely and altogether simple" (4 De Trin.6, 7).
I answer: it can be shown in many ways that God is altogether simple. In the first place, this can be proved from what we have already said. There is no combination of quantitative parts in God, since he is not a body. Neither is there in God any composition of form and matter. Neither is there any difference between God's nature and God as subject, nor between his essence and his existence. Neither is there in God any composition of genus and difference. It is thus clear that God is in no way composite, but altogether simple. Secondly, everything that is composite is consequential to its elements, and dependent on them. But God is the first being, as we proved in Q.2, Art.3. Thirdly, everything that is composite has a cause, since elements which are naturally separate cannot be combined into one unless some cause unites them. But we proved in the same article that God has no cause, since he is the first efficient cause. Fourthly, everything that is composite must contain both potentiality and actuality. Either one part is the actuality of another, or at least all parts are as it were the potentiality of the whole. But this is not true of God. Fifthly, everything that is composite is more than any of its parts. This is obvious when the parts are dissimilar. No part of a man is a man, and no part of a foot is a foot. But even when the parts are similar, although something can be affirmed equally of the whole and of every part of it, since a part of air is air, and a part of water is water, we can still say something about the whole which cannot be said of any part. For if the whole water measures two cubits, no part of it does so. In this way, there is something other than itself in everything that is composite. We may also say that there is something other than itself in everything that has a form. A thing that is white, for example, may contain something that is not white. But a form itself cannot contain anything other than itself. Now God is pure form, or rather, pure being. He cannot then be composite in any way. Hilary argues in somewhat the same fashion when he says: "God, who is power, is not compounded from what is weak, nor is he who is light composed of things of darkness" (De Trin.7).
On the first point: God's creatures resemble him as effects resemble their first cause. But an effect is naturally composite in some way, since its existence is at least different from its essence, as we shall show in Q.4, Art.3.
On the second point: composite things around us are better than simple things because the perfection of creaturely good is to be found not in one simple thing, but in many. The perfection of divine goodness, on the other hand, is to be found in what is single and simple, as we shall prove in Q.4, Art.1, and in Q.6, Art.2.