they cannot conceive of an essence that entails existence yet admits of either existence or nonexistence.
As for the later philosophers, who regard the existence of contingent beings as something additional to their essences, those essences are actualized only when they exist and cannot be separated from existence. Nor, on their view, can one conceive of an essence that itself admits of either existence or nonexistence. Thus, affirming an essence that admits of either existence or nonexistence while nevertheless entailing existence is not a position held by any school.
[The third aspect]
This is invalid, for if it entails existence, it cannot admit of nonexistence. Conversely, if its nonexistence is possible, it cannot entail existence. To claim that its existence and nonexistence are both possible, yet that it entails existence and cannot be nonexistent, is to combine two contradictory propositions.
If it is said:
“Considered in itself, its existence and nonexistence are both possible; considered in relation to its cause, however, its existence is necessary.”
The answer is:
To say, “Considered in itself, its existence and nonexistence are both possible,” does not mean that either its existence or its nonexistence is necessary. Rather, it means that its essence, considered in itself, calls for neither existence nor nonexistence, but must have one or the other by virtue of something else.
The supposition is that it exists, so its existence is necessary through another. Necessary existence, even through another, precludes nonexistence. Thus, this essence, whose existence is necessary through another, cannot be nonexistent in any way whatsoever.