Letters from a Stoic 88 : 28
Now philosophy asks no favours from any other source; it builds everything on its own soil; but the science of numbers is, so to speak, a structure built on another man's land – it builds on everything on alien soil; It accepts first principles, and by their favour arrives at further conclusions. If it could march unassisted to the truth, if it were able to understand the nature of the universe, I should say that it would offer much assistance to our minds; for the mind grows by contact with things heavenly and draws into itself something from on high. There is but one thing that brings the soul to perfection – the unalterable knowledge of good and evil. But there is no other art which investigates good and evil. I should like to pass in review the several virtues.