Every error comprehends contradiction: for since he who errs does not wish to err, but to he right, it is plain that he does not do what he wishes. For what does the thief wish to do? That which is for his own interest. If, then, the theft is not for his interest, he does not do that which he wishes. But every rational: soul is by nature offended at contradiction, and so long as it does not understand this contradiction, it is not hindered from doing contradictory things: but when it does understand the contradiction, it must of necessity avoid the contradiction and avoid it as much as a man must dissent from the false when he sees that a thing is false; but so long as this falsehood does not appear to him, he assents to it as to truth.

He, then, is strong in argument and has the faculty of exhorting and confuting, who is able to show to each man the contradiction through which he errs and clearly to prove how he does............