If it is asked, “Why may the completion of the cause for the second contingent event not simply be the non-existence of the first—since that non-existence coincides with the second?” we answer:

Non-existence, unless it entails some positive reality, cannot be a constituent of the cause of an existent, for non-existence has no effect whatsoever in bringing something into being. Consider instead a man walking on the ground: each time he crosses one stretch, a new power and intent arise in him to traverse the next. As for the First—if one claims that He brings things into existence, one after another, by His very Essence—this necessitates that His agency be perfect for every effect at the moment it appears. His Essence’s producing the first effect is a positive reality, and for the second to exist simultaneously with the first, which is its contrary, is impossible. The disappearance of what is impossible thus points to a perfect power accompanying the act. This differs from the view that the state of the Essence with respect to both the first and the second contingent is identical, with nothing new arising in Him or elsewhere that would display the perfection of His agency for the second when it occurs.

The matter is clarified by the fourth proof: when the second event is conditioned by the first event that precedes it, while the Necessary Being also precedes it as an eternal sufficient cause, a contradiction follows. On that assumption, everything by which events come into existence would already be present before them, and none of the agents producing them would arise together with them. This eliminates the possibility of any event having a cause at all, for a cause must accompany its effect—let alone be an eternal cause. Hence, the assertion of a sufficient cause conflicts with the claim that happenings occur through conditions antecedent to them, and it equally conflicts with the claim that the completion of causes arises together with the effects.