2. The ideas of contraries, as ideas in the mind, are not contrary to one another: otherwise they could not be together in the mind, or be known together: the idea therefore whereby evil is known is not inconsistent with good, but rather belongs to the idea of good (ratio qua cognoscitur malum ad rationem boni pertinet).* If then in God, on account of His absolute perfection, there are found all ideas of goodness (rationes bonitatis, as has been proved (Chap. XL), It follows that there is in Him the idea (ratio) whereby evil is known.
3. Truth is the good of the understanding: for an understanding is called good inasmuch as it knows the truth. But truth is not only to the effect that good is good, but also that evil is evil: for as it is true that what is, is, so it is true that what is not, is not. The good of the understanding therefore consists even in the knowledge of evil. But since the divine understanding is perfect in goodness, there cannot be wanting to it any of the perfections of understanding; and therefore there is present to it the knowledge of things evil.
4. God knows the distinction of things (Chap. L). But in the notion of distinction there is negation: for those things are distinct, of which one is not another: hence the first things that are of themselves distinct, mutually involve the exclusion of one another, by reason of which fast negative propositions are immediately verified of them, e.g., 'No quantity is a substance.' God then knows negation. But privation is a sort of negation: He therefore knows privation, and consequently evil, which is nothing else than a privation of due perfection.
8. In us the knowledge of evil things is never blameworthy in mere point of knowledge, that is in the judgement that is passed about evil things, but accidentally, inasmuch as by the observation of evil things one is sometimes inclined to evil. But that cannot be in God; and therefore there is nothing to prevent His knowing evil.
With this agrees what is said, that Evil surpasseth not [God's] wisdom (Wisd. vii 30) and, Hell and perdition are before the Lord (Prov. xv, 11) and, My offences are not hidden from thee (Ps. lxviii, 6); and, He knoweth the vanity of men, and seeing doth he not consider iniquity? (Job xi, 11.)
It is to be observed however that if God's knowledge were so limited as that His knowledge of Himself did not involve His knowing other beings of finite and partial goodness, at that rate He would nowise know privation or evil: because to the good which is God Himself there is no privation opposed, since privation and its opposite are naturally about the same object; and so to that which is pure actuality no privation is opposed, and consequently no evil either. Hence on the supposition that God knows Himself alone, by knowing the excellences of His own being, He will not know evil.* But because in knowing Himself He knows beings in which privations naturally occur, He must know the opposite privations, and the evils opposite to particular goods.
It must be further observed that as God, without any argumentative process, knows other beings by knowing Himself, so there is no need of His knowledge being argumentative in coming to the knowledge of evil things through good things: for good is as it were the ground of the knowledge of evil, evil being nothing else than privation of good: hence what is evil is known through what is good as things are known through their definitions, not as conclusions through their premises.
1.70 : That God knows Base and Mean Things
1.72 : That God has a Will