Commentaria in Summam contra Gentiles, Liber I

Second, he shows that divine truth is the first and highest truth ¹.

I. It is proved first. Divine esse is the first and most perfect. Therefore divine truth is first and most perfect. — The consequence is proved: because, as in Metaphysics II, the order of things in esse is also their order in truth, since being and true follow upon one another. What is therefore first in esse must correspond to the first truth.

It must first be noted, according to the doctrine of Saint Thomas in the First Part ², that the true which is in things is convertible with being according to predication: for every being is true, and every true thing is a being. But the true which is in the intellect is convertible with being according to representation, as the manifesting with the manifested: because to every true intellect there corresponds something in reality; and conversely, to every being there corresponds a true intellect, at least the divine one. It is in this second way that Saint Thomas seems to take the consequence of being and the true in this passage: for he assigns the reason for such a consequence from the fact that the true, when it is said to be that what is, is, and that what is not, is not, pertains to the consequence of the representing and the represented.

It must be noted, second, concerning that proposition taken from Metaphysics II, "As things are disposed in esse, so also in truth," that "disposed" is not taken according as it is in the genus of quality, but according as it imports a certain order. And the sense is that where what is most a being is found to be, there also what is most true is found to be, because the ratio of the true follows upon the ratio of being. Thus Saint Thomas expounds it at Verit., q. 1, a. 1, ad 5.

II. Second. Truth belongs to God essentially, as was said. Therefore most perfectly: for what belongs to something by essence belongs to it most perfectly.

Third. In God, the intellect and that which is understood are entirely the same. Therefore, etc. — The consequence is proved. Because truth consists in adequation. Now the cause of equality is unity, as is said in Metaphysics V, text 20. Therefore, where there is the greatest unity of intellect and of the thing understood, there truth will be greatest and most perfect.

Fourth. Divine truth is the measure of all truth. Therefore it is most perfect. — The consequence is evident, because that which is the measure in any genus is the most perfect thing of that genus. — The antecedent is proved as follows: God is the first intellect and the first intelligible; therefore the truth of every intellect is measured by His truth. The consequence is proved because every truth is either measured by a thing, as the truth of our intellect, or measured by an intellect, as the truth of every thing is measured with respect to the divine intellect, by which it is caused. But whichever way it is measured, it is measured by a first, since each thing is measured by the first of its kind. Therefore it must be that all truth is measured either by the first intelligible or by the first intellect. If, then, God is the first intelligible and the first intellect, He will be the measure of all truth.

It must be noted that in this argument Saint Thomas also implicitly includes the angelic intellect. For since the truth of the angelic intellect has a measure, because it is not the first truth, it must be measured either by some intellect or by some intelligible: for every truth is measured by one or other of these. And so, if we posit that it is measured by a thing, it will have to be measured by the first intelligible. But if by an intellect, it must be measured by the first intellect. And so, since God is the first intellect and the first intelligible, it is necessary that it be measured by the truth of God. For this reason he did not conclude only concerning the human intellect, but universally concerning every intellect, concluding that the truth of any intellect must be measured by His truth.

III. But it seems that something false is assumed in this argument, namely, that the truth of our intellect is measured by a thing existing outside the soul. For a thing is not called true except in relation to an intellect. Therefore it does not measure the truth of the intellect: for a measure does not depend on the thing measured.

It is answered, and it is said first that, although a thing is not called formally true except by comparison to an intellect, nevertheless it is not said to be true first and principally in relation to the human intellect, but in relation to the divine intellect. And therefore the ratio of truth can belong to it prior to belonging to our intellect, although that is not properly truth.

It is said second, that Saint Thomas did not say that the truth of our intellect is measured by the truth of the thing, but by the thing itself. For these differ greatly from one another. For indeed the truth of our intellect is measured by the esse of a thing; but not by the truth of the thing, insofar as it is called true in relation to our intellect.

And when it is said that the measure does not depend on the thing measured, etc.: — it is said that this is true speaking formally: for the measure, according to that ratio by which it is a measure, does not depend on the thing measured insofar as it is of this sort. But it can well depend on it by another ratio. Just as an animal, insofar as it is healthy formally, does not depend on medicine with respect to the ratio of being healthy properly so called — indeed medicine depends on the animal, since it is not called healthy except in relation to the health of the animal — and yet the health of the animal is caused by medicine. So too the truth of the intellect does not depend on the truth of the thing; rather, conversely, the truth of the thing is the truth of the intellect: and yet truth itself depends on the thing, and from the thing itself it is caused in our intellect.