In the care of the sick we demand the physician be free from error, but in the conduct of life it is not only the philosopher whom we expect to be free from error, but all men alike, including those who give little attention to virtue. Clearly there is no explanation for this other than that the human being is born with an inclination toward virtue; all men speak of themselves as having virtue and being good.
There is no sense in seeking many proofs for each point, but rather cogent and lucid ones. The teacher should rather touch upon each point just enough to penetrate the intellect of his listener with persuasive arguments that cannot easily be refuted. Most important of all is for him to show himself to act consistently with the wise words he speaks.