29. Just as evil is a privation of good, and ignorance a privation of knowledge, so non-being is a privation of being — not of being in a substantive sense, for that does not have any opposite, but of being that exists by participation in substantive being. The first two privations mentioned depend on the will of creatures; the third lies in the will of the Maker, who in His goodness wills beings always to exist and always to receive His blessings.
Our being exists by participation in God’s substantive being — the only true substantive being. As such it lies in his will and must always exist. However, good and knowledge depend on our will. As such, by denying them, we create the shadows of evil and ignorance.