"If you will think, Socrates, of the nature of punishment, you will see at once that in the opinion of mankind virtue may be acquired; no one punishes the evil-doer under the notion, or for the reason, that he has done wrong,—only the unreasonable fury of a beast acts in that manner. But he who desires to inflict rational punishment does not retaliate for a past wrong which cannot be undone; he has regard to the future, and is desirous that the man who is punished, and he who sees him punished, may be deterred from doing wrong again. He punishes for the sake of prevention, thereby clearly implying that virtue is capable of being taught."