[18] And dialectic science, which is the sister, the twin sister of rhetoric, as some persons have called it, separating true from false arguments, and refuting the plausibilities of sophistical arguments, will cure the great disease of the soul, deceit. It is profitable, therefore, to abide among these and other sciences resembling them, and to devote one’s especial attention to them. For perhaps, I say, as has happened to many, we shall become known to the queenly virtues by means of their subjects and handmaidens.