existent. Both propositions are self-evident, but the agent that brings something else into being has an even stronger claim to existence. And just as existence is from the locus of an attribute, that locus may be an inanimate thing or a living being, capable or incapable. Although an attribute depends upon an existing locus, this is dependence upon a receptive subject, whereas an effect’s dependence upon its agent is dependence upon an agent.

It is well known that something that has an agent depends more strongly upon its agent than something that has a receptive subject depends upon that subject.

Moreover, the receptive subject is a condition for what it receives; it need not precede it, since the two may be concurrent. An agent, by contrast, cannot be concurrent with its effect; rather, it must precede it.

For this reason, rational people agree that two things cannot each be the agent of the other, whether in the sense of being an efficient cause or in any other sense. However, each of two things may be a condition for the other. This is a cycle of concurrent dependence, whereas the former is a cycle of prior dependence. This has been explained at length in another