Last time we met, one month ago, we learned God is Truth. Go back and review. This week we’ll ease back into things with a short chapter, but one which contains some important points vis-à-vis realist vs. idealist or skeptical philosophy.
 THE foregoing being established it is evident that in God there is pure truth, in which there can be no alloy of falsehood or deception. For falsehood is incompatible with truth, even as black with white. Now God is not merely true, but is truth itself. Therefore there can be no falsehood in Him.
 Moreover. The intellect is not deceived in knowing what a thing is, as neither is the sense about its proper sensible. Now all knowledge of the divine intellect is as the knowledge of one who knows what a thing is, as was proved above. Therefore it is impossible that there be error, deception or falsehood in the divine knowledge.
 Further. The intellect does not err about first principles, whereas it does sometimes about conclusions, to which it proceeds by arguing from first principles. Now the divine intellect is not argumentative or discursive, as we proved above. Therefore there can be no falsehood or deception therein…
Notes Your senses do not err, you see what you see, or rather, your optical bits present, in whatever form they are currently capable, of information to your intellect, which sorts them out. Now you might hallucinate and, say, think that man ahead is Bob, and your intellect knows Bob. But that is not because your senses falsely reported Bob, but because you reasoned improperly from the sense impressions you had and possibly because of other false premises or thoughts you entertained (“Bob is supposed to meet me” but it turns out he was delayed).
Also, we would not know there were such things as hallucinations if we also didn’t know there were real perceptions. And while all of are are supplied, via induction, fundamental truths, i.e. first principles, which we know indubitably, each of us occasionally reasons incorrectly. Example: God is love, therefore love is God, therefore love is all you need.
Lastly, don’t forget that God does not need to reason, to move from premises to conclusion, because God knows all at once.
 Moreover. An intellectual virtue is a perfection of the intellect in knowing things. Now the intellect cannot, according to an intellectual virtue, speak false, but always speaks true: because to speak true is the good act of the intellect, and it belongs to virtue to perform a good act. Now the divine intellect is more perfect by its nature than the human intellect is by a habit of virtue, for it is in the summit of perfection. It remains, therefore, that falsehood cannot be in the divine intellect.
Notes The intellect cannot speak falsely, but our will can make us lie. We know we lie, and we know because of our intellects. A lie is an imperfection. Now lying is a huge subject, one which St Thomas considered fully. See this.
 Further. The knowledge of the human intellect is somewhat caused by things; the result being that man’s knowledge is measured by its objects: since the judgment of the intellect is true through being in accordance with things, and not vice versa. Now the divine intellect is the cause of things by its knowledge. Wherefore His knowledge must needs be the measure of things: even as art is the measure of the products of art, each of which is so far perfect as it accords with art. Hence the divine intellect is compared to things as things to the human intellect.
Now falsehood resulting from inequality between man’s mind and things is not in things but in the mind. Wherefore if there were not perfect equality between the divine mind and things, falsehood would be in things but not in the divine mind. And yet there is no falsehood in things, because as much as a thing has of being, so much has it of truth. Therefore there is no inequality between the divine intellect and things: nor is any falsehood possible in the divine mind.
 Again. As the true is the good of the intellect, so is falsehood its evil: for we naturally desire to know the true and shun to be deceived by the false. Now evil cannot be in God, as was proved above. Therefore falsehood cannot be in Him.
Notes Notice that all knowledge of the human intellect is caused by things, only that some is. Some knowledge, that which we receive by induction or revelation, is caused divinely. But what is true is still that which accords with what is. And, as our good saint says, a falsehood is not in things but in us, in our intellects.
Plus, I’m sure the indirect point that falsity is evil did not escape your notice.
 Ch. lx.
 Cf. ch. lix.
 Ch. lviii.
 Ch. lvii.
 2 Ethic. vi. 2.
 Ch. xxviii.
 Ch. 1.: In evidence…p. 109; Sum. Th. P. I., Q. xiii., A. 8.
 6 Ethic. ii. 3.
 Ch. xxxix.