Phaedo and Polemo

It is likely that he means something like this: that no one could completely change, not even by punishing them, those who are not only naturally inclined but also accustomed to sins of this kind, the sort committed by the most abandoned. This too is shown to be false from the history of certain men who became philosophers. For who would not rank among the most abandoned the man who somehow brought himself to submit to a master who put him in a brothel, so that he would receive anyone who wished to shame him? Such things are told of Phaedo. And who will not say that the vilest of all men was the one who burst into the school of the most venerable Xenocrates with a flute-girl and a band of revellers who shared his debauchery, to insult a man whom even his companions admired?

Yet teaching had the power to turn even these men and to make them advance so far in philosophy that the one was judged by Plato worthy to recount Socrates' discourse on immortality and to portray his steadfastness in prison: how he paid no heed to the hemlock, but fearlessly, with complete calm of soul, discussed matters so many and so great that even those who are thoroughly composed and troubled by no circumstance can hardly follow them; and the other, Polemo, turning from a profligate into a man of the greatest self-control, succeeded to the school of Xenocrates, a man renowned for his dignity. So Celsus does not speak the truth when he says that no one could completely change those who are naturally inclined to sin and accustomed to it, not even by punishing them.