Hence, neither of them would possess power. It follows that each of them having power while acting alone is impossible. And if neither were capable except when the two are together, then each would be instrumental in making the other capable: this one would only be capable through the other’s empowering him, and that one would only be capable through this one’s empowering him. Thus each would be acting upon the other, which amounts to circular causality among agents and causes—something necessarily impossible and unanimously rejected by rational minds on many grounds, for a thing cannot be the agent of itself; how then could it be the agent of its own agent?

Moreover, the agent is, by its very nature, prior to its effect. Consequently, this one would have to be essentially prior to that one, and that one essentially prior to this, which would make a thing prior to itself by two degrees—an absurdity. Just as circularity is impossible with respect to the cause, it is likewise impossible with respect to the full exercise of causation; and just as an infinite regress is impossible in the cause, it is impossible in the complete reality of its causal action.

This differs from simultaneous circularity within effects, which all rational people deem permissible. As for an infinite regress within effects, that is a well-known point of dispute. All these issues have been treated at length elsewhere.

The point intended here is that every perfection free of deficiency that is possible for any existent is necessary for the Necessary Existent and inseparable from Him. It cannot be absent from Him while remaining possible for others. Therefore, it cannot be merely possible—i.e., both existent and nonexistent—for in that case His possessing it would depend on something outside Himself. Either each of the two would have to bestow that perfection upon the other, or the second alone would be the bestower; and if the latter were the case, then that other—endowed with the attributes