Enneads I.8: Of the Nature and Origin of Evils
Definition of Primary and Secondary Evil
In short, the primary Evil is that which by itself lacks measure. The secondary evil is that which accidentally becomes formless, either by assimilation or participation. In the front rank is the darkness; in the second that which has become obscured. Thus vice, being in the soul the result of ignorance and formlessness, is of secondary rank. It is not absolute Evil, because, on its side, virtue is not absolute Good; it is good only by its assimilation and participation with the Good.
B. BY WHAT PART OF OUR NATURE WE COME TO KNOW EVIL.