I. 8.7
(Armstrong Selection and Translation from the Enneads)
(A comment on some Platonic texts from the Theaetetus and Timaeus : evil must necessarily exist (i) because matter is necessary to the existence of the visible universe; (ii) because the process of outgoing or down-going from the Good must have a limit, and this limit is Matter, which has no good in it at all.)
But how then is it necessary that if the Good exists, so should the Bad? Is it because there must be matter in the All? This All (the visible universe) must certainly be composed of opposite principles: it would not exist at all if matter did not exist. For the generation of this universe was a mixed result of the combination of intellect and necessity.’ What comes into it from God is good; the evil comes from the ‘ancient nature’ (Plato means the underlying matter not yet set in order). But what does he mean by ‘mortal nature’, granted that ‘this place’ refers to the All? The answer is given where he says, ‘ Since you have come into being, you are not immortal, but you shall by no means be dissolved through me.’ If this is so, the statement is correct that ‘evils will never be done away with’. How then is one to escape? Not by movement in place, Plato says, but by winning virtue and separating oneself from the body: for in this way one separates oneself from matter as well, since the man who lives in close connexion with the body is also closely connected with matter. Plato himself explains somewhere about separating or not separating oneself: but being ‘ among the gods’ means ‘ among the beings of the world of Nous’; for these are the immortals.
One can grasp the necessity of evil in this way too. Since not only the Good exists, there must be an ultimate limit to the process of going out past it, or, if one prefers to put it like this, going down or going away: and this last, after which nothing else can come into being, is the Bad. Now it is necessary that what comes after the First should exist, and therefore that the Last should exist; and this is matter, which possesses nothing at all of the Good. And in this way too the Bad is necessary.