(CG 1/060). That God is Truth (Book 1: Of God As He Is In Himself) (Summa Contra Gentiles) (Aquinas, Thomas, St.)

THE understanding is not liable to error in its knowledge of abstract being, as neither is sense in dealing with the proper object of each sense. But all the knowledge of the divine mind is after the manner of a mind knowing abstract being (Chap. LVIII): it is impossible therefore for error or deception or falsehood to creep into the cognitive act of God.

3. The intellect does not err over first principles, but over reasoned conclusions from first principles. But the divine intellect is not reasoning or argumentative (Chap. LVII), and is therefore not liable to deception.

4. The higher any cognitive faculty is, the more universal and far-reaching is its proper object: hence what sight is cognisant of accidentally, general sensibility or imagination seizes upon as a content of its proper object. But the power of the divine mind is the acme of cognitive power: therefore all things knowable stand to it as proper and ordinary objects of knowledge, not as accidental objects. But over proper and ordinary objects of knowledge a cognitive faculty never makes a mistake.

5. An intellectual virtue is a perfection of the understanding in knowing. It never happens that the understanding utters anything false, but its utterance is always true, when prompted by any intellectual virtue; for it is the part of virtue to render an act good, and to utter truth is the good act of the understanding. But the divine mind, being the acme of perfection, is more perfect by its nature than the human mind by any habit of virtue.

6. The knowledge of the human mind is in a manner caused by things: hence it comes to be that things knowable are the measure of human knowledge: for the judgement of the mind is true, because the thing is so. But the divine mind by its knowledge is the cause of things. Hence God's knowledge must be the measure of things, as art is the measure of products of art, whereof the perfection of each varies according to its agreement with art. Thus the divine mind stands to things as things stand to the human mind. But any error that arises out of any inequality between the human mind and the thing is not in things, but in the mind. If therefore there were not an absolutely perfect correspondence of the divine mind with things, the error would be in the things, not in the divine mind. There is however no error in the things that be: because each has so much of truth as it has of being. There is then no failure of correspondence between the divine mind and the things that be.

Hence it is said: God is truthful (Rom. iii, 4): God is not like man, that he should lie (Num. xxiii, 19): God is light, and there is no darkness in him (1 John i, 5).