  If matter or evil is ultimately caused by the One, then is not the One, as the Good, the cause of evil?  In one sense, the answer is definitely yes.  As Plotinus reasons, if anything besides the One is going to exist, then there must be a conclusion of the process of production from the One.  The beginning of evil is the act of separation from the One by Intellect, an act which the One itself ultimately causes.  The end of the process of production from the One defines a limit, like the end of a river going out from its sources. Beyond the limit is matter or evil.