Against Celsus 3.67

It is likely that he means something like this: that no one could wholly change, not even by punishing them, those who are not only by nature inclined but also accustomed to sins such as the most abandoned commit. But 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 a man who somehow endured to yield to a master who set him in a brothel, so that he should receive anyone who wished to abuse him? Such things are related about Phaedo. And who will not say that the man who burst into the school of the most venerable Xenocrates with a flute-girl and a band of fellow revelers, to insult a man whom even his companions admired, was the most defiled of all men? Yet the word was strong enough to convert even these and make them advance so far in philosophy that the one was judged by Plato worthy to narrate Socrates' discourse on immortality and to portray his steadfastness in prison, as he paid no heed to the hemlock but fearlessly and with all calm of soul went through so many and such great arguments, which even the most settled people, troubled by no circumstance, can scarcely follow; and the other, Polemo, having become from a profligate a man of the greatest self-control, succeeded to the school of Xenocrates, famous for his dignity. So Celsus does not speak truly when he says that no one could wholly change those by nature inclined and accustomed to sin, not even by punishing them.