Aristotle, Nicomachean Ethics
H. Rackham, Ed.

But the further question may be raised, What is the use of these intellectual virtues? Wisdom does not consider the means to human happiness at all, for it does not ask how anything comes into existence. Prudence, it must be granted, does do this; but what do we need it for? seeing that it studies that which is just and noble and good for man, but these are the things that a good man does by nature. Knowing about them does not make us any more capable of doing them, since the virtues are qualities of character; just as is the case with the knowledge of what is healthy and vigorous—using these words to mean not productive of health and vigor but resulting from them: we are not rendered any more capable of healthy and vigorous action by knowing the science of medicine or of physical training.