Plotinos: Complete Works, v. 4 In Chronological Order,...

9. How do we get to know vice and virtue? As to virtue, we know it by the very intelligence and by wisdom; for wisdom knows itself. But how can we know vice? Just as we observe that an object is not in itself straight, by applying a rule, so we discern vice by this characteristic, that it does not comport itself with virtue. But do we, or do we not have direct intuition thereof? We do not have the intuition of absolute vice, because it is indeterminate. We know it, therefore, by a kind of abstraction, observing that virtue is entirely lacking. We cognize relative vice by noticing that it lacks some part of virtue. We see a part of virtue, and, by this part, judging what is lacking in order completely to constitute the form (of virtue), we call vice what is lacking to it; defining as the indeterminate (evil) what is deprived of virtue. Similarly with matter. If, for instance, we notice a figure that is ugly because its ("seminal) reason," being unable to dominate matter, has been unable to hide its deformity, we notice ugliness by what is lacking to form.