Discourses, "On Friendship" (§1)

“What a man applies himself to earnestly, that he naturally loves. Do men then apply themselves earnestly to the things which are bad? By no means. Well, do they apply themselves to things which in no way concern themselves? Not to these either. It remains then that they employ themselves earnestly only about things which are good; and if they are earnestly employed about things, they love such things also. Whoever then understands what is good can also know how to love; but he who cannot distinguish good from bad, and things which are neither good nor bad from both, how can he possess the power of loving? To love, then, is only in the power of the wise.”