Summa contra Gentiles1.59 Chapter LIX. That God is not ignorant of the truth of enunciations

It follows from the foregoing that, although the knowledge of the divine intellect is not like that of a composing and dividing intellect, it is not ignorant of the truth which, according to the Philosopher, is solely about composition and division of the intellect.

For since the truth of the intellect is the equation of thought and thing, in so far as the intellect asserts that to be which is, and that not to be which is not, truth in the intellect belongs to that which the intellect asserts, not to the operation whereby it asserts. Because the truth of the intellect does not require that the act itself of understanding be equated to the thing, since sometimes the thing is material, whereas the act of understanding is immaterial. But that which the intellect in understanding asserts and knows, needs to be equated to the thing, namely to be in reality as the intellect asserts it to be. Now God, by His simple act of intelligence wherein is neither composition nor division, knows not only the essence of things, but also that which is enunciated about them, as proved above. Wherefore that which the divine intellect asserts in understanding is composition or division. Therefore truth is not excluded from the divine intellect by reason of the latter's simplicity.

Moreover. When something non-complex is said or understood, the non-complex in itself is neither equal nor unequal to the reality, since equality and inequality imply a comparison, and the non-complex in itself contains no comparison or application to a reality. Wherefore in itself it cannot be said to be either true or false: but only the complex which contains a comparison between the non-complex and the reality, expressed by composition or division. But the non-complex intellect by understanding what a thing is, apprehends the quiddity of a thing in a kind of comparison with the thing, since it apprehends it as the quiddity of this particular thing. Hence, although the non-complex itself, or even a definition, is not in itself true or false, nevertheless the intellect that apprehends what a thing is is said to be always true in itself, as stated in 3 De Anima, although it may be accidentally false, in so far as the definition includes complexion either of the parts of the definition with one another, or of the whole definition with the thing defined. Wherefore a definition, according as it is taken to be the definition of this or that thing, as understood by the intellect, will be said to be false either simply, if the parts of the definition do not hold together, as if we were to say an insensible animal, or false in its application to this particular thing, as if one were to apply the definition of a circle to a triangle. Hence, though it be granted, by an impossibility, that the divine intellect knows only non-complex things, it would still be true in knowing its quiddity as its own.

Again. The divine simplicity does not exclude perfection: because in its simple essence it has all the perfections to be found in other things by the aggregation of perfections or forms; as was proved above. Now, our intellect, by apprehending the incomplex, does not as yet reach to its ultimate perfection, since it is still in potentiality as regards composition and division: even as in natural things simple things are in potentiality in respect of mixed things, and parts in respect of the whole. Accordingly God, in respect of His simple act of intelligence, has that perfection of knowledge which our intellect has by both kinds of knowledge, whether of the complex or of the non-complex. Now truth is acquired by our intellect in its perfect knowledge thereof, when it arrives at composition. Therefore there is truth in God's mere act of simple intelligence.

Again. Since God is the good of every good, through having in Himself all manner of goodness, as we have shown above, the goodness of the intellect cannot be lacking to Him. Now truth is the good of the intellect, as the Philosopher declares (6 Ethic.). Therefore truth is in God.

And this is what is stated in the psalm: But God is true.