The Divine Institutes

But who is able to distinguish right from wrong except the wise man? Thus it comes to pass, that he can never be just who is foolish, nor wise who is unjust. And if this is most true, it is plain that he who has not taken away a plank from a shipwrecked man, or a horse from one who is wounded, is not foolish; because it is a sin to do these things, and the wise man abstains from sin. Nevertheless I myself also confess that it has this appearance, through the error of men, who are ignorant of the peculiar character of everything.

And thus the whole of this inquiry is refuted not so much by arguments as by definition. Therefore folly is the erring in deeds and words, through ignorance of what is right and good. Therefore he is not a fool who does not even spare himself to prevent injury to another, which is an evil. And this, indeed, reason and the truth itself dictate. For we see that in all animals, because they are destitute of wisdom, nature is the provider of supplies for itself. Therefore they injure others that they may profit themselves, for they do not understand that the committing an injury is evil.

But man, who has the knowledge of good and evil, abstains from committing an injury even to his own damage, which an animal without reason is unable to do; and on this account innocence is reckoned among the chief virtues of man. Now by these things it appears that he is the wisest man who prefers to perish rather than to commit an injury, that he may preserve that sense of duty by which he is distinguished from the dumb creation. For he who does not point out the error of one who is offering the gold for sale, in order that he may buy it for a small sum, or he who does not avow that he is offering for sale a runaway slave or an infected house, having an eye to his own gain or advantage, is not a wise man, as Carneades wished it to appear, but crafty and cunning.

Now craftiness and cunning exist in the dumb animals also: either when they lie in wait for others, and take them by deceit, that they may devour them; or when they avoid the snares of others in various ways. But wisdom falls to man alone. For wisdom is understanding either with the purpose of doing that which is good and right, or for the abstaining from improper words and deeds. Now a wise man never gives himself to the pursuit of gain, because he despises these earthly advantages: nor does he allow any one to be deceived, because it is the duty of a good man to correct the errors of men, and to bring them back to the right way; since the nature of man is social and beneficent, in which respect alone he bears a relation to God.