The readiness acquired by previous training conduces much to the perception of such things as are requisite; but those things which can be perceived only by mind are the special exercise for the mind. And their nature is triple according as we consider their quantity, their magnitude, and what can be predicated of them. For the discourse which consists of demonstrations, implants in the spirit of him who follows it, clear faith; so that he cannot conceive of that which is demonstrated being different; and so it does not allow us to succumb to those who assail us by fraud. In such studies, therefore, the soul is purged from sensible things, and is excited, so as to be able to see truth distinctly. For nutriment, and the training which is maintained gentle, make noble natures; and noble natures, when they have received such training, become still better than before both in other respects, but especially in productiveness, as is the case with the other creatures. Wherefore it is said, “Go to the ant, thou sluggard, and become wiser than it, which provideth much and, varied food in the harvest against the inclemency of winter.” Or go to the bee, and learn how laborious she is; for she, feeding on the whole meadow, produces one honey-comb. And if “thou prayest in the closet,” as the Lord taught, “to worship in spirit,” thy management will no longer be solely occupied about the house, but also about the soul, what must be bestowed on it, and how, and how much; and what must be laid aside and treasured up in it; and when it ought to be produced, and to whom. For it is not by nature, but by learning, that people become noble and good, as people also become physicians and pilots. We all in common, for example, see the vine and the horse. But the husbandman will know if the vine be good or bad at fruit-bearing; and the horseman will easily distinguish between the spiritless and the swift animal. But that some are naturally predisposed to virtue above others, certain pursuits of those, who are so naturally predisposed above others, show. But that perfection in virtue is not the exclusive property of those, whose natures are better, is proved, since also those who by nature are ill-disposed towards virtue, in obtaining suitable training, for the most part attain to excellence; and, on the other hand, those whose natural dispositions are apt, become evil through neglect.