We suppose first, then, that the wise man knows all things, as far as possible, although he has not knowledge of each of them individually; secondly, that he who can learn things that are difficult, and not easy for man to know, is wise (sense perception is common to all, and therefore easy and no mark of wisdom); again, he who is more exact and more capable of teaching the causes is wiser, in every branch of knowledge; and of the sciences, also, that which is desirable on its own account and for the sake of knowing it is more of the nature of wisdom than that which is desirable on account of its results, and the superior science is more of the nature of wisdom than the ancillary; for the wise man must not be ordered but must order, and he must not obey another, but the less wise must obey him.