That the natural man can confirm whatever he will is manifest from the numerous heresies in the Christian world, each of which is confirmed by its adherents. Who does not know that evils and falsities of every kind may be confirmed? It is possible to confirm, and the wicked actually do confirm, that there is no God, and that nature is everything, and is self-created; that religion is only a means whereby simple minds may be held under restraint; that human prudence does everything, and Divine Providence nothing, except that it maintains the universe in the order in which it was created; also that murder, adultery, theft, fraud, and revenge are allowable, according to Machiavelli and his followers. The natural man can confirm these and such like things, yea can fill books with the confirmations; and when these falsities are confirmed they appear in an infatuating light, and truths in such obscurity that they cannot be seen but as spectres at night. In a word, take the falsest thing and form it into a proposition, and tell an ingenious person to confirm it, and he will confirm it, to the complete extinction of the light of truth. But put aside his confirmations, return, and look at the proposition itself from your own rationality, and you will see its falsity in all its deformity. (DLW n. 267)
They who by various considerations can confirm a dogma once received whatever its quality, and by various reasonings make it appear like the truth, believe themselves wiser than others. But this is very far from the part of a wise man; any one can do this who is distinguished by some ingenuity, and the wicked more skilfully than the well-disposed. For it is not of the rational man to do this, inasmuch as the rational man can see as from a superior [light] whether what is confirmed be true or false. And seeing this, he makes no account of things confirmative of falsity, and in his own mind regards such things but as ridiculous and vain, however another may believe them chosen from the school of wisdom itself. In a word, nothing is less the part of a wise man, yea nothing is less rational, than to be able to confirm falsities; for it is the part of a wise man and is rational first to see that a thing is true, and next to confirm it; inasmuch as to see what is true is to see from the light of heaven, which is from the Lord, whereas to see the false as true is to see from a delusive light which is from hell. (AC n. 4741).