Against the academics
If a man, said Epictetus, opposes evident truths, it is not easy to find arguments by which we shall make him change his opinion. But this does not arise either from the man's strength or the teacher's weakness; for when the man, though he has been confuted, is hardened like a stone, how shall we then be able to deal with him by argument?
Now there are two kinds of hardening, one of the understanding, the other of the sense of shame, when a man is resolved not to assent to what is manifest nor to desist from contradictions. Most of us are afraid of mortification of the body, and would contrive all means to avoid such a thing, but we care not about the soul's mortification. And indeed with regard to the soul, if a man be in such a state as not to apprehend anything, or understand at all, we think that he is in a bad condition: but if the sense of shame and modesty are deadened, this we call even power.