Aristotle, Nicomachean Ethics
H. Rackham, Ed.

[4] First then let us assert that Wisdom and Prudence, being as they are the virtues of the two parts of the intellect respectively, are necessarily desirable in themselves, even if neither produces any effect. [5]

Secondly, they do in fact produce an effect: Wisdom produces Happiness, not in the sense in which medicine produces health, but in the sense in which healthiness is the cause of health. For Wisdom is a part of Virtue as a whole, and therefore by its possession, or rather by its exercise, renders a man happy. [6]

Also Prudence as well as Moral Virtue determines the complete performance of man's proper function: Virtue ensures the rightness of the end we aim at, Prudence ensures the rightness of the means we adopt to gain that end.

（The fourth part¹ of the soul on the other hand, the nutritive faculty, has no virtue contributing to the proper function of man, since it has no power to act or not to act.²） [7]

But we must go a little deeper into the objection that Prudence does not render men more capable of performing noble and just actions. Let us start with the following consideration. As some people, we maintain, perform just acts and yet are not just men （for instance, those who do what the law enjoins but do it unwillingly, or in ignorance, or for some ulterior object, and not for the sake of the actions themselves, although they are as a matter of fact doing what they ought to do and all that a good man should）, on the other hand it appears, there is a state of mind in which a man may do these various acts with the result that he really is a good man: I mean when he does them from choice, and for the sake of the acts themselves. [8] Now rightness in our choice of an end is secured by Virtue³; but to do the actions that must in the nature of things be done in order to attain the end we have chosen, is not a matter for Virtue but for a different faculty.

We must dwell on this point to make it more clear. [9] There is a certain faculty called Cleverness, which is the capacity for doing the things aforesaid that conduce to the aim we propose, and so attaining that aim. If the aim is noble, this is a praiseworthy faculty: if base, it is mere knavery; this is how we come to speak of both prudent men and knaves as clever. [10] Now this faculty is not identical with Prudence, but Prudence implies it. But that eye of the soul of which we spoke⁴ cannot acquire the quality of Prudence without possessing Virtue. This we have said before, and it is manifestly true. For deductive inferences about matters of conduct always have a major premise of the form ‘Since the End or Supreme Good is so and so’ （whatever it may be, since we may take it as anything we like for the sake of the argument）; but the Supreme Good only appears good to the good man: vice perverts the mind and causes it to hold false views about the first principles of conduct. Hence it is clear that we cannot be prudent without being good.