Commentaria in Summam contra Gentiles, Liber I

Having excluded the first cause for which some thought it vain to inquire whether God is, Saint Thomas now excludes the second ¹, which seems to stand opposed to the first.

I. For there were some, as Rabbi Moses relates ², who said that God's existence is neither known in itself nor can be demonstrated, but is held only by faith; they were moved to this by the weakness of the arguments which some brought forward to prove that God exists.

There are, however, three (1). The first. In God, esse is the same as essence. But by the way of reason one cannot arrive at knowledge of what God is. Therefore neither can one arrive at knowledge of whether He is.

Second. The principle for demonstrating whether a thing is, is the account of the name. This, however, is the definition, according to Aristotle, Metaphysics IV. And this cannot be had of God. Therefore, and so on.

The third is this. Those things which exceed sense and sensible things are indemonstrable, because the principles of demonstration take their origin from sense. Now that God exists is of this kind. Therefore, etc.

II. But Saint Thomas refutes this opinion in four ways. First, from the art of demonstration, by which we are taught to conclude causes from effects. For from the fact that we see something to have been effected in things, we can demonstrate and conclude, as Aristotle argues, that there must be a first cause, which we call God ³.

2. Second, from the order of the sciences. For if there were no knowable substance above sensible substance, there would be no science above natural science. But it is evident that divine science is above natural science. Therefore there must be some knowable substance above sensible substance.

But this argument seems to fail, for two reasons. First, because, even given that there were a knowable substance above sensible things, it does not nevertheless follow that its esse could be demonstrated. For it could be supposed that it exists, and other predicates about it be known through demonstration.

Second, because for some science to be above the natural, it suffices that there be some immaterial substance about which there can be science; it is not necessary that God exist and that what is of God be known through demonstration.

To the first of these it is said that, since the existence of the subject of any naturally discovered science is presupposed, that existence must either be known through the senses, or be self-evident from the terms, or be demonstrated in that science itself or in another. Since therefore the existence of God, of whom metaphysics treats, is not known through the senses, nor from the terms, as the aforementioned opinion ⁴ holds, it must necessarily be demonstrated. The metaphysician therefore cannot demonstrate anything about God from the supposition that He exists, unless it be demonstrated either through Him or through another.

To the second, one may reply in two ways. First, that if there were no other knowable substance besides those immaterial ones which the philosophers investigated by natural reason to be the movers of the heavenly bodies, there would be no divine science: because the consideration of those would belong to natural philosophy, to which it pertains to consider both things that move themselves and their parts.

Second, that which St. Thomas intends, in order to preserve the claim that an intelligible substance must be posited above sensible substances—that is, that there be a genus of separate substances, under which God is also contained, using the term "genus" in a broad signification. Since this is demonstrated to exist, it follows that God's existence is demonstrated, at least under the common aspect of immaterial substance.

3. Third, the aforementioned opinion is refuted by the zeal of the philosophers, who have attempted to demonstrate that God exists.

Fourth, by the authority of the Apostle, in Romans 1, who says: The invisible things of God are clearly seen, being understood through the things that have been made.

III. But to the first argument on the opposite side ⁵ Saint Thomas replies that esse can be taken in two ways: in one way, as signifying the actual existence by which a thing exists; in the other way, as signifying the composition of the intellect. If it is taken in the first way, then it is true that God is His own esse; but what this is like is unknown to us, just as His essence is. If, however, it is taken in the second way, then God's being falls under demonstration. — But supply: In this way esse is not understood when it is said, In God essence and esse are the same.

To make this answer evident, it must be noted that, since in every proposition "est" signifies the composition of the proposition, inasmuch as it is a kind of copula and conjunction of the predicate with the subject, sometimes in a proposition, beyond the composition of the proposition, it also signifies actual existence, as when it is said, "Socrates is"; but sometimes it signifies only the truth of the proposition, that is, the composition which the intellect forms concerning the thing, that is, that the intellect, in forming such a composition, is adequate to the thing, and on this account is true; as, when we say that man is an animal, it is signified that the intellect, understanding animal of man, apprehends it as it is in the thing. Similarly, when we say "blindness is," because blindness is not a being in the nature of things but only a negation, it is signified that the intellect, apprehending something as lacking the power of sight, is adequate to the thing: for "est" does not signify actual existence, even in a proposition of second apposition, unless it is attributed to a real being; but it signifies only the composition of the proposition.

(1) There are, however, three. — Has something fallen out of the text of the Ferrariensis? Cf. below n. III, To the first argument on the opposite side. Certainly the arguments that follow are not among those "which some used to bring forward to prove that God exists": rather they pertain to the support of the error of those who say that God's existence cannot be demonstrated.

It must also be known that we are in one state when we know that God is, and in another when we know that Socrates is. For since esse in Socrates is really distinct from his essence, it is nothing other than the actuality by which Socrates exists. Therefore the esse of Socrates is then known completely when it is known that through it Socrates exists in reality. And this indeed must be known when it is known that Socrates is, since Socrates is a true real being. — But the divine esse does not differ really from the divine essence, but only by reason, on the part of our intellect, when we apprehend the divine essence under the aspect of an actuality of being proportioned to created esse. Therefore the divine esse is not apprehended perfectly and completely when it is known to be that actuality of being by which God exists in reality, but only when it is known that it is the divine essence, which is ipsum esse subsistens. Rightly therefore Saint Thomas says that through the demonstration by which we know that God is, we do not know the esse by which God subsists in himself, that is, with perfect and complete quidditative knowledge, just as we do not know the divine essence as it is in itself; but we know the esse that signifies the composition of the intellect — that is, we know that esse belongs to God as an actuality of being, but because we know only the composition which the intellect makes of a thing with its adequate esse, and that the intellect thus composing is true, and thus that it is so in reality as the intellect understands it. This, however, presupposes knowledge of the divine esse as it is an actuality of being, and grounds the truth of the proposition, but not as regards its very quiddity as it is in itself.

By this the objection of Scotus is removed, I Sent., d. III, q. 1, who says that "si est" need not be distinguished as it is a question about the truth of a proposition, or as it is a question about the esse of God: because, as he says, if there can be a question about the truth of a proposition in which esse is sought of a subject as a predicate, then in order to conceive the truth of that question one must first conceive its terms. — For it is said that indeed in such a question the esse of God is first conceived: yet not by a perfect and quidditative concept, but only as it is the actuality of essendi.

IV. To the second argument ⁶ Saint Thomas replies by denying that in the arguments by which it is demonstrated that God exists, the divine essence and quiddity must be assumed, that is, the very definition, of which it is said in Metaphysics IV that the ratio signified by a name is its definition. But in place of the quiddity an effect is taken, from which the ratio of this name "God" is drawn: as happens in demonstrations quia.

For the understanding of this response, note that the reason assumed to demonstrate whether it is of something is the definition of what the name means, quid nominis, and not the quidditative definition, which is called the definition of what the thing is, as Saint Thomas says in Prima, q. II, a. 2 ⁷; and it is stated in II Poster. ⁸: for the question of what the thing is follows the question of whether it is, as is clear from II Poster. Now this sort of "what" of the name God is taken from the divine effects. Hence the demonstrations by which that God exists is shown are a posteriori on the part of the thing, but a priori on our part: because the effects of God are more known to us than God himself. Therefore Saint Thomas says that one need not use the quiddity of God as the middle term for proving that God exists, but only his effect: this is to say that one need not use as the middle term what the thing God is, but what the name means, taken from the effect.

V. To the third argument ⁹ Saint Thomas replies that the origin of this knowledge is indeed in the senses: because the effects of God, from which the demonstration is taken to prove His esse, are sensible; although God exceeds all sensible things and sense itself.

It must be noted that from this response Saint Thomas gives us to understand that the cognition of a thing can be understood as originating from sense in two ways. In one way, because the thing itself must first be known in itself through sense before anything about it is known through the intellect. And in this sense the proposition is false: for we know many things about God and the intelligences, and yet neither God nor the intelligences fall under sense in themselves. — In another way, because either the thing itself must fall under sense, or the intellect must be led by the hand to its cognition through something that falls under sense. And then the proposition is true, as experience also teaches: for we find that concerning immaterial substances we have no cognition except insofar as we arrive at knowledge of them from sensible things.