nonexistence, unlike that which has never been nonexistent at any time.

Second:

These things are not necessitated by the Necessary Being alone. If they were, they would be necessary consequences of His essence and would be beginninglessly eternal. Rather, they are necessitated by His essence together with newly arising conditions that complete the necessitating cause. Thus, they are not necessary consequences of what is necessary through itself, but of the complete cause of their existence. This includes the things that come into being and are conditions for their coming into being. When they cease to exist, this is because some of these newly arising conditions are absent, or because an impediment arises that is incompatible with their existence and prevents their cause from being complete. They therefore cease to exist because certain things that come into being are absent, or because others are present, just as they came into existence because certain things came into being.