What the expression is intended to mean, I think, is that there is a better and a worse element in the character of each individual, and that when the naturally better element controls the worse then the man is said to be "master of himself", as a term of praise. But when - as a result of bad upbringing or bad company one s better element is overpowered by the numerical superiority of one s worse impulses, then one is criticized for not being master of oneself and for lack of self control.
PlatoI can show you that the art of calculation has to do with odd and even numbers in their numerical relations to themselves and to each other.
PlatoAnd first he will see the shadows best, next the reflections of men and other objects in the water, and then the objects themselves, then he will gaze upon the light of the moon and the stars and the spangled heaven...Last of all he will be able to see the sun.
PlatoWhen a person meets the half that is his very own, whatever his orientation, whether it's to young men or not, then something wonderful happens: the two are struck from their senses by love, by a sense of belonging to one another, and by desire, and they don't want to be separated from one another, not even for a moment.
PlatoBut he who has been earnest in the love of knowledge and of true wisdom, and has exercised his intellect more than any other part of him, must have thoughts immortal and divine. If he attain truth, and in so far as human nature is capable of sharing in immortality, he must altogether be immortal.
Plato