If St. Thomas Aquinas calls your idea stupid, you must really be doing something wrong. Aquinas is famous for his charity in argumentation.

Aquinas customarily presents a stronger case for his opponent’s views than the opponent himself offers. It’s a classy thing to do, especially if you need to demolish those views.

But in a rare moment of unrestrained candor, Aquinas calls out David of Dinant for having “most stupidly postulated” God to be prime matter. (Aquinas’s exact words are “stultissime posuit,” in Summa Theologiae I, 3, 8.)

“Prime matter” is a technical term for the abstract state of pure potentiality. David of Dinant’s mistaken idea seems to have been that, because God is capable of doing anything he wants, his nature must be nothing but an infinite soup of pure possibilities.

Unlike finite creatures (rocks, trees, fish, et cetera), it seems God must not be constrained by any actual finite nature.

So does that mean God is nothing but pure potency? Not at all, says Aquinas. In fact, Aquinas’s position is that God is pure actuality, with no admixture of potency at all.

In other words, Aquinas’s explanation of God’s nature is the exact opposite of David of Dinant’s explanation. God is pure actuality, not pure potency.

Even a saint like Aquinas, it seems, loses patience with an answer that couldn’t possibly be any more wrong.

Even a saint like Aquinas, it seems, loses patience with an answer that couldn’t possibly be any more wrong, and so he can’t help but call a spade a spade right at the outset.

I confess, I have the same immediate reaction when I hear David of Dinant’s dopey theory still being bandied about. The ridiculous idea of a “God who may be” is today not only still entertained, but also positively feted, generating absurd tomes calling us to be “reimagining the sacred.”

I’m sure there must be some good thoughts buried somewhere in those boring books, but whatever they are, they are eclipsed for me by a fundamental act of philosophical malpractice: namely, the failure to understand the nature of God as pure actuality.

What is God like? Aquinas answers this question by affirming the position of “classical theism,” which is the philosophical view that, because God is pure actuality, he must be understood to possess divine attributes like immutability, eternity, and simplicity.

“The doctrine of simplicity is the most fundamental and therefore also the most difficult of the standard divine attributes,” writes philosophy professor Eleonore Stump in her excellent little book The God of the Bible and the God of the Philosophers.

Stump shows how not just the opponents of classical theism, but even also sometimes its proponents, fail to understand these classic divine attributes. With patient scholarship, she shows how Aquinas is able to offer an incomparably exemplary philosophical account of these divine attributes that coheres perfectly with the Bible’s narrative accounts of divine action.

“Another way to think about the doctrine of simplicity as Aquinas understands it is as the expression of a kind of quantum metaphysics,” writes Stump in The Oxford Handbook of Aquinas.

Just as she does in The God of the Bible and the God of the Philosophers, she’s making an analogy with the limits that human knowledge encounters in quantum physics. Just as physicists must characterize light, to be true to its nature, as both a wave and as a particle, so too philosophers and theologians must characterize God, to be true to his nature, in two complementary ways.

As Aquinas realizes, we must philosophically describe God abstractly and existentially as pure actuality with no potency, and concretely and essentially as someone with whom we enter into personal relation.

There is no contradiction with this Thomistic “quantum metaphysics,” observes Stump.

There is no contradiction with this Thomistic “quantum metaphysics,” observes Stump, just as quantum physics itself is not a series of incoherent contradictions, but rather a rigorously rational delineation of what we can and cannot say about light.

Quantum physics developed in order to be true to the reality of the fundamental nature of things like light, however mysterious and elusive it may be to fully grasp those natures.

The only qualification I myself would make to Stump’s brilliant analogy is to point out how the God of Aquinas’s “quantum metaphysics” is the exact opposite of the subatomic realities of quantum physics.

Resembling the “God” of David of Dinant, the subatomic realm is composed mostly of potentiality, with only very faint traces of actuality. Those traces only firm up when we interact with them, injecting more actuality via observation.

But God in himself is pure actuality, with no admixture of potency. We ourselves only firm up, and fully actualize our own potential, when he personally interacts with us.

And no one but Aquinas has yet offered a better philosophical theory for describing this metaphysical reality.