What the statesman is most anxious to produce is a certain moral character in his fellow citizens, namely a disposition to virtue and the performance of virtuous actions.
If a man of good natural disposition acquires Intelligence [as a whole], then he excels in conduct, and the disposition which previously only resembled Virtue, will now be Virtue in the true sense. Hence just as with the faculty of forming opinions [the calculative faculty] there are two qualities, Cleverness and Prudence, so also in the moral part of the soul there are two qualities, natural virtue and true Virtue; and true Virtue cannot exist without Prudence.
The physician himself, if sick, actually calls in another physician, knowing that he cannot reason correctly if required to judge his own condition while suffering.
... the good for man is an activity of the soul in accordance with virtue, or if there are more kinds of virtue than one, in accordance with the best and most perfect kind.
If purpose, then, is inherent in art, so is it in Nature also. The best illustration is the case of a man being his own physician, for Nature is like that - agent and patient at once.
Whatever we learn to do, we learn by actually doing it; men come to be builders, for instance, by building, and harp players by playing the harp. In the same way, by doing just acts we come to be just; by doing self-controlled acts, we come to be self-controlled ; and by doing brave acts, we become brave.
In the case of some people, not even if we had the most accurate scientific knowledge, would it be easy to persuade them were we to address them through the medium of that knowledge; for a scientific discourse, it is the privilege of education to appreciate, and it is impossible that this should extend to the multitude.