Well, said Epictetus, if we were inquiring about white and black, what criterion should we employ for distinguishing between them? "The sight," he said. And if about hot and cold, and hard and soft, what criterion? "The touch." Well then, since we are inquiring about things which are according to nature, and those which are done rightly or not rightly, what kind of criterion do you think that we should employ? "I do not know," he said. And yet not to know the criterion of colors and smells, and also of tastes, is perhaps no great harm; but if a man do not know the criterion of good and bad, and of things according to nature and contrary to nature, does this seem to you a small harm?