Jowett: delusion

Pro. Yes, that is by far the commonest delusion. PHILEBUS  

Ath. What, then, leads us astray ? Are beautiful things not the same to us all, or are they the same in themselves, but not in our opinion of them ? For no one will admit that forms of vice in the dance are more beautiful than forms of virtue, or that he himself delights in the forms of vice, and others in a muse of another character. And yet most persons say, that the excellence of music is to give pleasure to our souls. But this is intolerable and blasphemous ; there is, however, a much more plausible account of the delusion. LAWS BOOK II

Must not injustice be a strife which arises among the three principles — a meddlesomeness, and interference, and rising up of a part of the soul against the whole, an assertion of unlawful authority, which is made by a rebellious subject against a true prince, of whom he is the natural vassal — what is all this confusion and delusion but injustice, and intemperance, and cowardice, and ignorance, and every form of vice ? THE REPUBLIC   BOOK IV

But I, who am the speaker, felt that I was. And now let me remind you that, although in our former selection we chose old men, we must not do so in this. Solon was under a delusion when he said that a man when he grows old may learn many things — for he can no more learn much than he can run much ; youth is the time for any extraordinary toil. THE REPUBLIC BOOK VII