Plato's own theory was that punishment had a twofold purpose, to reform and to deter. "No one punishes an offender on account of the past offence, and simply because he has done wrong, but for the sake of the future, that the offence may not be again committed, either by the same person or by any one who has seen him punished."—See the Protagoras, 324, b, and Grote's Plato, ii. 41.