Every error comprehends contradiction: for since he who errs does not wish to err, but to be 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 not do that which he wishes and does that which he does not wish. For if anyone shall show this, a man will himself withdraw from that which he does; but so long as you do not show this, do not be surprised if a man persists in his practice; for having the appearance of doing right, he does what he does. For this reason Socrates also trusting to this power used to say, I am used to call no other witness of what I say, but I am always satisfied with him with whom I am discussing, and I ask him to give his opinion and call him as a witness, and though he is only one, he is sufficient in the place of all. For Socrates knew by what the rational soul is moved, just like a pair of scales, and then it must incline, whether it chooses or not. Show the rational governing faculty a contradiction, and it will withdraw from it; but if you do not show it, rather blame yourself than him who is not persuaded.