28. If however, they do not yet know this, they must of course be instructed before they can be moved. And perhaps the mere knowledge of their duty will have such an effect that there will be no need to move them with greater strength of eloquence. Yet when this is needful, it ought to be done. And it is needful when people, knowing what they ought to do, do it not. Therefore, to teach is a necessity. For what men know, it is in their own hands either to do or not to do. But who would say that it is their duty to do what they do not know? On the same principle, to persuade is not a necessity: for it is not always called for; as, for example, when the hearer yields his assent to one who simply teaches or gives pleasure. For this reason also to persuade is a triumph, because it is possible that a man may be taught and delighted, and yet not give his consent. And what will be the use of gaining the first two ends if we fail in the third? Neither is it a necessity to give pleasure; for when, in the course of an address, the truth is clearly pointed out (and this is the true function of teaching), it is not the fact, nor is it the intention, that the style of speech should make the truth pleasing, or that the style should of itself give pleasure; but the truth itself, when exhibited in its naked simplicity, gives pleasure, because it is the truth. And hence even falsities are frequently a source of pleasure when they are brought to light and exposed. It is not, of course, their falsity that gives pleasure; but as it is true that they are false, the speech which shows this to be true gives pleasure.