Aristotle, Nicomachean Ethics
H. Rackham, Ed.

Again, things that come under a single Idea must be objects of a single science; hence there ought to be a single science dealing with all good things. But as a matter of fact there are a number of sciences even for the goods in one Category: for example, opportunity, for opportunity in war comes under the science of strategy, in disease under that of medicine; and the due amount in diet comes under medicine, in bodily exercise under gymnastics.