The knowledge of the soul admittedly contributes greatly to the advance of truth in general, and, above all, to our understanding of Nature, for the soul is in some sense the principle of animal life.

If then nature makes nothing without some end in view, nothing to no purpose, it must be that nature has made all of them for the sake of man.

It is the active exercise of our faculties in conformity with virtue that causes happiness, and the opposite activities its opposite.

We have next to consider the formal definition of virtue.

To run away from trouble is a form of cowardice and, while it is true that the suicide braves death, he does it not for some noble object but to escape some ill.

A body in motion can maintain this motion only if it remains in contact with a mover.

Rhetoric is useful because the true and the just are naturally superior to their opposites, so that, if decisions are improperly made, they must owe their defeat to their own advocates; which is reprehensible. Further, in dealing with certain persons, even if we possessed the most accurate scientific knowledge, we should not find it easy to persuade them by the employment of such knowledge. For scientific discourse is concerned with instruction, but in the case of such persons instruction is impossible.