Commentaria in Summam contra Gentiles, Liber I

Having set forth the prologue, Saint Thomas proceeds to the manifestation of divine things, which he intends to treat in this work ¹. This book, moreover, is divided into two principal parts, inasmuch as there are two things that are known about God: first, he treats of those things that can be investigated by human reason; second, of those things that have been revealed and exceed human understanding, and this in the fourth book.

As to the first, he makes three points, as he himself shows in the preceding chapter. For in the first book he determines those things that befit God in himself; in the second, the procession of creatures from him; in the third, the order of creatures toward him as toward their end.

Concerning the first, he does three things. For since, in order to consider those things that befit God in himself, it is necessary to know that he is, as it were a necessary foundation, he therefore first sets before that consideration the one by which it is demonstrated that God is. Second, he treats of the divine simplicity, by which we can in some way know what God is, chapter XIV. Third, he shows what sort of being God is, chapter XXVIII.

Concerning the first point: because some judge, for two reasons, that the inquiry into whether God exists is vain, he does two things: first, he removes the said reasons; second, he demonstrates his intended point, in chapter XIII. — Concerning the first, he does two things: first, he inquires into the first cause; second, into the second, in chapter XII. — Concerning the first, he does two things: first, he sets out the arguments of the opponents; second, he resolves them, in the following chapter.

II. As to the first point, then: there were some, says Saint Thomas, who judged the aforesaid consideration superfluous, on the ground that that God exists is self-evident, such that its contrary cannot be thought; and for this reason they said no demonstration is needed for this matter. And this seems to have been the opinion of Anselm, as Saint Thomas reports in Verit. q. X, a. 12. Some confirm this position with several arguments.

The first of these is as follows. That God exists is known as soon as the terms are understood. Therefore it is known per se. — The antecedent is proved: because by the name "God" we understand that than which a greater cannot be thought. But this cannot exist in the intellect alone: for what exists both in the intellect and in reality is greater than that which exists in the intellect alone.

The second is that something greater than God could then be thought, if he himself could be thought not to exist: namely, that which cannot be thought not to exist.

The third is because in God esse and essence are the same. Now those propositions in which a thing is predicated of itself must be most evident.

The fourth is this: that God's existence is naturally known, since man's desire naturally tends toward Him. But those things that are naturally known are known through themselves.

The fifth is, because God is that by which all other things are known, since the divine light is the principle of all intelligible cognition.