Nicomachean Ethics

Every art and every kind of inquiry, and likewise every act and purpose, seems to aim at some good: and so it has been well said that the good is that at which everything aims.

But a difference is observable among these aims or ends. What is aimed at is sometimes the exercise of a faculty, sometimes a certain result beyond that exercise. And where there is an end beyond the act, there the result is better than the exercise of the faculty.

Now since there are many kinds of actions and many arts and sciences, it follows that there are many ends also; e.g. health is the end of medicine, ships of shipbuilding, victory of the art of war, and wealth of economy.

But when several of these are subordinated to some one art or science⁠—as the making of bridles and other trappings to the art of horsemanship, and this in turn, along with all else that the soldier does, to the art of war, and so on,⁠—then the end of the master-art is always more desired than the ends of the subordinate arts, since these are pursued for its sake. And this is equally true whether the end in view be the mere exercise of a faculty or something beyond that, as in the above instances.