If one were to maintain that the agent who causes the mixing is other than the agent who turns the two elements into clay, this would be to claim that an actor can bring about the necessary pre-condition without its inseparable consequent—something that cannot exist without that consequent—and such a claim is impossible.

The point becomes clearer when we posit two agents that are not inseparable. In that case the existence or act of either could occur without the existence or act of the other, which would entail mixing without clay or clay without mixing—both absurd. If, on the other hand, the two agents are declared mutually inseparable, then neither of them can be necessary-in-itself and self-sufficient; each would be dependent on the other and could exist only through the existence of that other. Hence they must both have a cause distinct from themselves; otherwise a vicious circle would ensue—a circularity in efficient causes, the “prior circularity,” for it would require that this one bring that one into being so that it cannot exist without it, while that one brings this one into being so that it cannot exist without it.

As for the simultaneous, correlative circularity, that occurs only in effects—such as fatherhood and sonship, both of which arise from procreation. With respect to efficient causes and the conditions of their efficacy, it is impossible for two things to be each the cause of the other or the condition for the other’s action. Thus, if two entities were supposed to be necessary-in-themselves and each exerted influence over the existence of the other so that it was a condition for it, neither of them could exist until the condition for its existence had already been realized. Yet, by hypothesis, nothing exists besides the two of them to bring about that condition: this one is the condition for that one, and that one is the condition for this one, so neither of them ever comes into being. This shows that within the cosmos there is nothing necessary-in-itself; the Necessary Being is one, transcendent beyond the world.

This is further underscored by the fact that the existence of each depends on the other’s act of bringing it into existence—an instance of prior circularity, since the cause must precede its effect. It is not the simultaneous circularity, which occurs only in two effects or in mutually concomitant attributes that do not require an agent, such as the eternal attributes of the Exalted Creator.