Feser on Potency and Act

In his reply to Graham Oppy’s criticisms of Thomistic cosmological arguments, Ed Feser denies that creatures exist both actually and potentially at the same time. (“Oppy on Thomistic Cosmological Arguments,” Religious Studies 57 [2021], 503–522, at 509.) He states that the constituents of an object such as a cup of water are potentially a cup of water in the abstract, but in the concrete they are only actually a cup of water. The constituents in question, protons, neutrons, and electrons, are, considered in themselves, potentially a cup of water, but as possessing the form of water they are actually a cup of water and no longer potentially a cup of water.

This doesn’t seem right to me. The real distinction of essence and existence makes Aquinas’ position clear. Without existence an essence is precisely nothing, not any kind of potency at all. But in an actually existing finite being the essence is really distinct from its existence, and is related to its existence as potency to act, as Aquinas argues in De Ente et Essentia. Now the essence is in potency to existence, and not in potency to anything else at all. It is in potency to only one kind of substantial existence, and it is not in potency to non-existence. So either the essence has no potency at all, or it bears the potency to exist when it is actually existing through its composition with the act of existence. In other words, essence is what later scholastics called a subjective potency (the kind of potency that is composed with its act and thus coexists with it) rather than an objective potency (the kind of potency that is opposed to act and ceases to be when its act arrives.) Note that “subjective” does not here mean “relative to someone’s perception” but rather “subject, that is, receiver of act.” “Objective” does not mean “real,” but something like “the objective of a productive activity.”

The same must be true of the relationship between prime matter and substantial form. Certainly the case is less clear here: one could be tempted to think that prime matter, as a principle of potency, was only a potency to receive other substantial forms. But this is not the case. Prime matter’s potency does not undergo any change (see Aristotle, Physics I.9, 192a26–29); it is always a potency for all substantial forms. So when it is actualized by the substantial form of water, it retains the subjective potency to the substantial form of water, as well as potencies for all other substantial forms. Water is a composite of potency and act.