The third reason:
This analogy may apply to something other than what exists necessarily in itself. As for Him—glorified and exalted is He—it is inconceivable that either His essence or His action should depend on anything else, for the receptive subjects are themselves also produced by Him. The same reasoning applies to His producing what they receive as to His producing the receptive subjects themselves. Everything other than Him depends on Him and is produced by Him, whereas He is entirely independent of everything else in every respect. This differs from a created agent whose action depends on a receptive subject, since its action depends on something separate from itself.
However, this may be answered as follows: If an agent’s necessitation of something else depends on another thing, yet this does not preclude its necessitating by virtue of itself—as they maintain concerning the Active Intellect—then, with still greater reason, its necessitation’s dependence on another thing does not preclude its existing necessarily in itself. For an agent that necessitates something else possesses necessary existence and something more: only what exists can bring something into existence, and only what is necessary can necessitate.
Of the Active Intellect, they say:
It exists necessarily through another and necessitates through another; it does not exist necessarily in itself.
What he means is that necessary existence and necessitation by virtue of one’s essence do not preclude dependence on another; they preclude only being produced by another.
The argument may be summarized as follows:
If existence is said to be additional to essence, then essence is the subject in which necessary existence inheres. Thus, what exists necessarily in itself would depend on a receptive subject, not on an agent.
We therefore say:
What exists necessarily is that which does not depend on an agent, not that which does not depend on a receptive subject. For what the argument terminating the infinite regress establishes is that what exists necessarily has neither an agent nor a cause.