Sayings of Socrates 9

If the entire soul, then, follows without rebellion the part that loves wisdom, the result is that in general each part can carry out its own function—can be just, in other words—and in particular each is able to enjoy pleasures which are its own, the best, and, as far as possible, the truest. . . . 

When one of the other parts takes control, there are two results: it fails to discover its own proper pleasure, and it compels the other parts to pursue a pleasure which is not their own, and not true. 

—Plato, Republic , 587a