Aquinas on the Metaphysics of the Hypostatic Union

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My Aquinas group has been diving into the third part of the Summa Theologica for the last several months, after spending over a decade on getting to that point by reading the Summa chapter by chapter. The third part involves St. Thomas Aquinas's analysis of the Incarnation.

I have been enlightened by nuance and depth of the Incarnation. I have come to appreciate its centrality to Christianity. This may seem obvious, and I would not have denied knowing it on an intellectual level, but learning about the balance of doctrines designed to preserve both the Logos's role as divine and true humanity of the Incarnation. What I think I came to appreciate was the way in which the Incarnation represents respect for human dignity. Human nature plays a role in salvation; salvation is not effected separate, apart or on humanity, but through and with human nature.

This book unpacks the issues that arise from the effort to find a balance. The author, Michael Gorman, takes the reader methodically through the pertinent concepts. Since the doctrine is that the Incarnation consists of two natures in a single person, this means tackling the concepts of “person” and “nature,” which leads to dealing with the arcana of “supposits” and “substances.” These are tricky concepts that have a tendency to slide around in my mind and require my constant attention to pin down.

I want to say that persons, supposits and substances are those things that “subsist,” that endure to provide continuity throughout and despite changes in the matter of a thing. Your cells are constantly splitting and dying; you may lose an arm or have a heart transplant. What continues to exist during and despite these changes? You do, i.,e the person “you.” A nature is the thing that defines one kind of thing from a different kind of thing.

In the Incarnation, the “thing” that existed at all times was a divine person, namely the Logos. The Logos assumed a human nature in addition to His divine nature without changing the Logos into something different. The joining of divine and human natures was at the level of the peson, not at the level of the nature, which is why there was a “hypostatic union,” since “hypostasis” means “person.”

So far, so easy, but things get difficult when we start asking questions like “if God is simple, then how can He be a compound of human and divine natures?”, what does it mean to say that God does not suffer, how can Christ not be a human person, etc.

Gorman offers explanations for these questions, but some are not particularly satisfying, though no fault of Gorman, since he is simply giving his best take on the positions of the Angelic Doctor. For example, my personal bete noir has been “simplicity,” namely, how can God in his divine nature be such that His essence is his powers and He is pure act, and still have one person of the Trinity be a composite being of human nature and divine nature.

The answer, according to Gorman, involves some fine hair splitting about what it means to be “simple.” Gorman is very useful in warning that one should never “over-read” Aquinas:

“The text to focus on is ST I, q. 3. Aquinas does not ask, in a generic and undifferentiated way, “Is God simple?” and then answer “Yes.” Instead, he develops a specific notion of divine simplicity that consists in the negation of certain specific kinds of composition. This is important, because if we assume that Aquinas holds that God is simple in just any sense we ourselves can imagine, then we will be likely to jump too quickly to the conclusion that he is contradicting himself when he says that Christ is composite.”

From there we pay attention to what Aquinas says:

“Of course, Aquinas's claim that Christ is composite might contravene his understanding of divine simplicity, but that would have to be demonstrated in light of what Aquinas actually means by divine simplicity, which is, to repeat, not just anything we might imagine to be implied by the word “simplicity,” but the specific negations that Aquinas argues for.2
In article 1, Aquinas says that God lacks corporeal parts, in article 2 that he lacks composition of ​form and matter, in article 3 that he lacks composition of nature and supposit, in article 4 that he lacks composition of essence and existence, in article 5 that he lacks composition of genus and difference, and in article 6 that he has no accidents. Article 7 provides additional reasons for thinking that God is simple without adding anything to the notion of simplicity embedded in the denials contained in the preceding six articles (unless perhaps the mention there of ​act-potency ​composition gives us something that is not implicit in the previous articles, in which case we should add it to the list). Article 8, finally, says that God does not enter into composition with anything, but that is not relevant to the present inquiry: Asking whether God is a component of anything is different from what we are asking about here, namely, whether God has any components.
Divine simplicity, understood in this way, does not exclude substantial composition. The point is fairly easy to see with regard to articles 1–2 and 4–6, because Christ's being composed of two natures is not an instance of any of the modes of composition that those articles rule out. The union of divinity and humanity in Christ is not a union of corporeal parts, of form and matter, of essence and existence, of genus and species, or of anything with an accident (or of ​act and potency).

And:

“To make that denial is not to take any stand at all on whether a divine person can have a second substantial nature – an issue that is far from Aquinas's mind at this point. As long as Christ's human nature does not arise from his divinity – which, of course, it does not – that human nature's being united in person to the Word is not excluded by the denial that article 3 is making. ​
So in ST I, q. 3, while Aquinas does indicate a number of ways in which a divine person cannot be composite, he does not deny substantial composition. Based on his way of understanding divine simplicity, therefore, there is no opposition between divine simplicity and having substantial composition. If this sounds odd to us, that will be because we are unwittingly imposing our own understanding of simplicity on Aquinas. If we keep our eye on precisely what he means by divine simplicity, we will see that for him, divine simplicity is consistent with a divine person's having two natures.”

That was a surprisingly underwhelming answer to a conundrum I've been pondering since I first started reading Aquinas 20 years ago.

Actually, it's not bad to get that answer because it does free up the mind to consider what it means for something to be simple but have two natures.

Another one involves the question of Christ's human personhood, which Christ does not have. The history of Christianity has been tortured by the “One or Two” question, namely, how many natures does Christ have, how many wills, how many energies, how many of anything, for which the answer is always “two.” This rule ends at the level of “person” as in how many “persons” in Jesus? Then the answer is “one.”

But how can this be? Natures are sorted out to things - one to a customer - and “rational natures” are awarded to “persons.” Natures don't just float free unattached to persons. If Jesus had a true human nature, what did he lack to make that nature a human person?

Gorman's answer is that the question is not what was lacking, but what was extra, in the case of the Incarnation, the extra thing being a “divine person,” which, so to speak, took up the slot for “human person.”

Obviously, I found this to be a useful, engaging book. However, I have to recognize that I've been reading Aquinas for a few decades and had recently gone over the Incarnation. From that perspective, this book was right on the money, but I would have to wonder how lost I would be without that background. I think Gorman is about as accessible to a beginning Thomist as you might find, but be prepared for a lot of concepts to come your way.