If it is said, “The nonexistence of the cause is contingent,” then, if it is nonexistent by virtue of itself, a contingent thing can be nonexistent by virtue of itself rather than through a cause—which is precisely what is to be established.

If, however, it is nonexistent through a cause, the same argument applies to that cause as to the other. This entails that the nonexistence of every contingent thing is explained by the nonexistence of another contingent thing.

This is invalid for several reasons.

First, there is no more reason to explain the nonexistence of this by the nonexistence of that than the reverse. Every contingent thing depends on a determining, efficient cause, whether termed an agent, a cause, a necessitating cause, a causal factor, or anything else.

Thus, if it is said, “This contingent thing is nonexistent because its efficient cause is nonexistent, and that efficient cause is nonexistent because its own efficient cause is nonexistent,” both are equally dependent on an efficient cause. There is therefore no more reason for the nonexistence of one to be due to the nonexistence of the other—which itself depends, in its nonexistence, on an efficient cause—than for the nonexistence of the latter to be due to the nonexistence of the former, whose nonexistence depends on an efficient cause, since both are alike in this respect.

Another reason is that, if the nonexistence of this is due to the nonexistence of that, and the nonexistence of that is due to the nonexistence of yet another, then, if the third nonexistence is the first, circularity in causal priority necessarily follows. If it is different, an infinite regress of causes and effects necessarily follows. Both are impossible.

All of this shows that the nonexistence of a contingent thing does not depend on an efficient cause in the same way that