There are many ways we might try to make sense of how it can be the case that Jesus Christ is one Person with two distinct natures. In my view, philosophy can certainly help the theologian find the best overall understanding here. An excellent example that demonstrates this is Marmodoro and Hill’s edited volume The Metaphysics of the Incarnation.
In this post I’m going to explain two models of the Incarnation that Thomas Flint discusses in his essay in the Marmodoro and Hill volume. I plan to make use of his distinction as I write on the Incarnation in the future, so I’d like to provide some context for those discussions.
It’s important to note that both of the models Flint discusses work within the concrete nature view of the Incarnation. I have explained that view in another post. This post won’t make much sense unless you read that prior one. In any case, let’s say that if one holds to the concrete nature view, one is a “concretist” (as opposed to an “abstractist”).
Locating Concrete-Compositional Christology
Irrespective of whether you are a concretist or an abstractist, there are at least three ways that you can understand how the Incarnation “works.” As Jonathan Hill explains in his chapter to The Metaphysics of the Incarnation, these ways are that the Incarnation involves the Word either (1) transforming, (2) entering into a relation, or (3) both.
On a transformation view, the Word becomes an X such that the Word, as X, is a truly human person. Here’s one way to see how this works. Suppose that you think substance dualism is true, where a human person just is a rational soul (or “mind”). On this sort of view, one might say that the Word becomes a human mind, and thereby becomes a truly human person. It seems to me that the view William Lane Craig defends in Philosophical Foundations for a Christian Worldview says this. (I say this is Craig’s view specifically because he explains it in his Defenders class.) There’s some terminology I’ll have to leave out, but Craig’s basic view seems to go like this: The Word, if he were to become incarnate, would actually be a truly human mind. Another way to put this (since Craig is an abstractist) is that the Word has the rich property of being-a-truly-human-mind-when-incarnate. When the Word is incarnate, he then exemplifies the property being-a-truly-human-mind. When the Incarnation obtains, the Word becomes a human mind, and therefore a human person, in addition to being a divine Person.
On a relational view, the Word becomes related to an X (or X’s) such that the relation to X (or X’s) allows the Word to be truly human. Once again we can use Craig’s view to help us, since it seems to involve both transformation and a particular relation. Craig says that by uniting to a human body in the right way, it’s the case that the Word is a truly human mind. This “uniting,” Craig says, involves the Word coming to relate to a human (he says “hominid”) body. When the Word becomes related to a human body, the Word (1) is a truly human mind (as I explained above) and (2) brings to the union all the right properties necessary and sufficient for human personhood.
By the way, I’m not endorsing Craig’s view. I’m only using it for illustration purposes. Even though Craig tries to address shortcomings of Apollinaris’ Christology, Craig’s view can still seem Apollinarian.
In any case, we can say that Craig’s model is, in part, an abstract-relational one. But as I said, concretists can also accept relational models. This is where the Word enters into a relation with (at least) a human body and (perhaps) also a human soul. We can call these “concrete-relational” models.
One way to achieve a concrete-relational Christology is to accept compositionalism, and therefore to accept a concrete-compositional Christology. As Hill explains, this means that “the incarnate Christ is a genuine unity, but a composite one, just as the human body itself is genuinely a single thing, but with parts.” As he explains in footnote 29 of that same page, the term “parts” here isn’t taken literally by everyone who accepts concrete-compositional Christology. Those that do take it literally espouse mereological models, and those who don’t espouse what we can (unimaginatively) call non-mereological models. The term “mereology” refers to that branch of philosophy that studies the relations between parts and wholes.
Flint’s Car Collection
The prior distinctions allow us to move on to Flint’s chapter. Strictly speaking, Flint addresses (and objects to) concrete-compositional models that are mereological. But the twofold distinction he makes in his paper can apply to non-mereological models as well, making each of the views he discusses a family (or genus) of views.
The first concrete-compositional view that Flint discusses is what he calls, with a nod to the classic car, the “Model T” view. (The T is supposed to refer to St. Thomas Aquinas.) On this view, the Word assumes a concrete human nature (which Flint calls “CHN”) as a part of himself. Hill offers an (albeit rough) analogy:
On Monday I consist of a certain quantity of matter [and therefore a certain weight]. By Friday, having enjoyed a number of generous dinners in the intervening time, I consist of that same quantity, plus some additional matter. But the person who exists on Friday is not some new composite person, made of me plus some fat. He is identical to me, the same person who existed on Monday; all that has happened is that that same person has now acquired some parts that he did not have before.
The second concrete-compositional view is what Flint calls the “Model A” view. This view says that the Word unites himself to CHN, but the resulting composite is not the Son. Rather, the “Son remains simply one part of the composite entity that results from his assuming a human nature.” In other words, the Word (or God the Son) plus CHN forms a composite whole that includes a divine Person as a “part,” and that whole itself is not itself the Person of the Word (or God the Son).
With that said, here’s a way to put the difference between the Model T and Model A views. On the first, the Word is a composite Person. But on the latter, he is not; instead, he’s a Person in a composite. Still another way to understand the difference here is to ask this question: Does “Jesus” refer to a Person, or not? If it does, then we are working with a Model T view, where the Word plus CHN refers to a Person who has a concrete human nature as a “part.” If it does not, we have a Model A view, where “Jesus” refers to that whole that is formed when the Word unites to CHN. The Word—a divine Person—is one “part” of Jesus.
Here’s one more way to put the distinction, which is really a corollary of what I just explained. Consider the phrase “the Word is Jesus.” As anybody with a modicum of philosophical knowledge (or historical knowledge of ‘90s) knows, the truth of this statement depends on what the meaning of “is” is. Let’s call the first meaning the “is of identity.” This amounts to the phrase “the Word is Jesus” saying that “the Word is numerically identical to Jesus” or simply “the Word = Jesus.” (Often the phrase “just is” stands in for “is numerically identical to.”) If this is how we understand the phrase, we are working with a Model T view. On the other hand, we can take “is” as the “is of predication.” This means that the term “Jesus” in “the Word is Jesus” is a predicate that is apt (or true) of the Word. This is what’s going on with the Model A view; it isn’t that the Word just is Jesus, but that the Word is (in a predicative sense) Jesus.
I have attempted to explain what Thomas Flint means by the “Model T” and “Model A” views of the Incarnation. Both assume a concrete nature view of Christ’s human nature (or CHN), and can serve as genera of concrete-compositional views. There are a number of ways in the literature that one might explain how the Word and CHN are related, and you can find some of them proposed by the other contributors to The Metaphysics of the Incarnation.
In any case, I am going to refer to Model T and Model A views in (perhaps many) later posts for at least two reasons. One reason is because I’m going to be investigating Christology as one of my main research areas for quite some time. The other reason is because I refer to these concrete-compositional models in some forthcoming papers that I plan to explore in more detail on this website. Stay tuned for those explorations!
 Thomas P. Flint, “Should Concretists Part with Mereological Models of the Incarnation?” in The Metaphysics of the Incarnation, eds. Anna Marmodoro and Jonathan Hill (Oxford: Oxford University Press, 2011), 67-87.
 Jonathan Hill, “Introduction,” in The Metaphysics of the Incarnation, eds. Anna Marmodoro and Jonathan Hill (Oxford: Oxford University Press, 2011), 1-19.
 J. P. Moreland and William Lane Craig, Philosophical Foundations for a Christian Worldview (Downers Grove: InterVarsity Press, 2017), 595-611.
 Moreland and Craig, 606.
 See Oliver Crisp, Divinity and Humanity (Cambridge: Cambridge University Press, 2007), 45n18.
 Hill, 12 (emphasis added).
 Flint, 71.
 Hill, 13.
 Flint, 79.