IV. It must, however, be enquired whether purification is the same with a virtue of this kind ? Or does purification indeed precede, but virtue follow ? And whether does virtue consist in purifying, or in the being perfectly purified? For virtue, while in the act of purifying, is more imperfect than that which consists in complete purification, which is now as it were the end. But to be perfectly purified, is an ablation of every thing foreign. Good, however, is something else besides this. Or may we not say, that if the soul was good prior to her impurity, purification is sufficient ? Purification, indeed, is sufficient; but that which remains will be good, and not purification. And what that is which remains, is to be investigated. For perhaps the nature which is left was not good; since otherwise, it would not have been situated in evil. Shall we say, therefore, that it has the form of good ? Or that it is not sufficiently able to abide (perpetually) in good ? For it is naturally adapted to verge both to good and evil. Its good, therefore, consists in associating with its kindred nature ; but its evil in associating with the contraries to this. It is necessary, therefore, that it should associate with this nature, being purified. And this will take place, through being converted to it. Will it therefore be converted after purification ? Or may we not say, that after purification it is converted ? This, therefore, is the virtue of the soul, or rather that which happens to it from conversion. What then is this ? The vision and impression of that which is seen, inserted and energizing in the soul, in the same manner as sight about a visible object. She did not, therefore, possess these, nor recollect them. Or perhaps she possessed them, yet not energizing, but deposited in an unilluminated state. In order, however, that they may be illuminated, and that the soul may know them to be inherent in herself, it is necessary that she should apply herself to that which illuminates. But she will not possess these, but the impressions of them. It is necessary, therefore, to adapt the impression to the true objects from which the impressions are derived. Perhaps, likewise, she may thus be said to possess them, because intellect is not foreign, and especially is not so, when it looks to the illuminating cause. But if it does not, it is foreign even when this cause is present. For sciences also are foreign, if we do not at all energize according to them.