Journal of Analytic Theology, Vol. 6, August 2018
© 2018 Christopher M. P. Tomaszewski  •  © 2018 Journal of Analytic Theology

Michael Gorman. Aquinas on the Metaphysics of the Hypostatic Union. Cambridge: Cambridge University Press, 2017. xi+177 pp. $99.99 (hbk).

Christopher M. P. Tomaszewski
Baylor University

The metaphysics of human nature is notoriously difficult and fraught with controversies in both the philosophical and theological literature. The metaphysics of God and His nature is even more difficult and even more beset with disputes in this literature. The work of Saint Thomas Aquinas on both topics is as voluminous as it is intricate. Michael Gorman’s undertaking in Aquinas on the Metaphysics of the Hypostatic Union, then, is unenviably exacting. But it is also thoroughly rewarding, for in Jesus Christ our humanity meets His transcendent Divinity, and study of this unique union provides more than ample opportunity for philosophy and theology to enrich one another. Fortunately, Gorman’s efforts to guide us through the wisdom offered by Aquinas on this subject are up to this task. He draws fluently and impressively on both the primary and vast secondary sources in Latin, English, French and German to illuminate Aquinas where he has been unclear, charitably but rigorously corrects other commentators where Gorman sees they have misread Aquinas, and interpolates Aquinas’ full account of the Hypostatic Union in those places where Aquinas fails to give a complete explanation. It hardly bears saying that Gorman’s analysis of Aquinas’ treatment of this central theological doctrine of Christianity touches on numerous topics of intense interest to both philosophers and theologians: human nature, the Divine attributes, the metaphysics of persons and existence, and questions about Christological consistency.

The book, noticeably concise for its recondite subject matter, is divided into six chapters. The first chapter introduces some of the central concepts and Thomistic philosophical terminology that is crucial to explaining and probing the metaphysical worries presented by the fact that God became man. This may seem like a tedious exercise to theologians (at least for those not already inclined toward Scholastic theology), but for Aquinas and those in his tradition, a full understanding of what supposits, natures, essences, and accidents are is crucial to threading the needle between Nestorianism, the heresy according to which Christ is really two persons, and Monophysitism, the heresy according to which Christ is not really human after all. Without Aquinas’ elaborate philosophical scaffolding in place, it is harder than one might imagine to avoid both of these errors simultaneously. Gorman does an admirable job of introducing these concepts without leading his readers to lose the forest for the trees.

The second chapter lays out Aquinas’ basic view of the Incarnation. Much of this material will be very familiar to philosophers and theologians who are already acquainted with Scholastic analyses of the Hypostatic Union, or even to those well-versed in conciliar Christology. But Gorman includes in this chapter two discussions of distinctions that are important to Aquinas’ theory of the Hypostatic Union, but are sometimes overlooked. The first is the distinction between human nature and human reality. Although “human reality” is coined by Gorman, the distinction drawn is clearly in Aquinas, as Gorman shows. Human nature is just what is essential to every human person, namely a composite of body and soul. Human reality, on the other hand, is the human nature together with all the accidents and individuating principles which are not essential to men as such. The distinction is worth noting because Aquinas sometimes uses “human nature” to refer to both human nature proper and human reality, and this can cause confusion as to what Christ assumed in the Incarnation. The second distinction is between union in nature and union in person. Union in nature is a union between two natures in such a way as to produce a third nature distinct from both of them, whereas union in person is a union between two natures in such a way that one person results without any conflation of natures. This distinction is important to the doctrinal claim that Christ is fully Divine and fully human, as well as to seeing that no new nature or essence comes into existence at the Incarnation.

In the third chapter, Gorman analyzes Aquinas’ approach to the difficulties that arise from the Hypostatic Union on the part of Christ’s Divinity, and in particular to those difficulties that stem from His absolute simplicity and immutability. This chapter should be especially fascinating to those philosophers and theologians who are interested in how Aquinas reconciles his view of the Incarnation with his classical theism. One might be tempted to think, for example, that Divine simplicity (and the doctrine of immutability which follows from it) is clearly inconsistent with the claim that God the Son became a man.1  As Gorman puts it, “[I]f Aquinas thinks that simplicity is a divine attribute, how can he think that the divine Christ is composite” (53)? With respect to Divine simplicity, Gorman shows that this puzzle is the result of a straightforward misunderstanding of Aquinas’ theory of Divine simplicity. Nowhere in his explanation of God’s simplicity does Aquinas ever claim that a Divine person could not be composed of more than one substantial nature. That is, a composition of natures is not one of the kinds of composition that Aquinas takes to be ruled out by the simplicity of God. With respect to Divine immutability, the solution is more complicated: Gorman takes us on a satisfying tour of Aquinas’ theory of mixed relations (relations such that A is really related to B but B is not really related to A) is in search for the solution to this difficulty. But as I discuss below, the troubles arising for the Hypostatic Union from Aquinas’ theory of Divine simplicity, and in particular for his identification of each of the Divine Persons with the Divine Essence, run significantly deeper than Gorman lets on here.

Gorman treats in the fourth chapter the Christological difficulties that take their origin in Christ’s human nature. Specifically, the chapter focuses on the question of why Christ’s human nature does not ground a human person. After all, every human nature other than Christ’s grounds a human person, and so one might wonder whether we can count Christ’s human nature as a genuine instance of human nature if His human nature doesn’t ground a human person.2 Gorman does a worthy job here of explaining how Aquinas re-evaluates what a human nature is in light of this difficulty. As Gorman discusses in the conclusion of his book, this case illustrates Aquinas at his best as a philosopher and theologian. Aquinas takes a concept that comes to us from the use of natural reason in investigating the world around us, such as that of human nature, and sees that the concept must be revised in light of revelation (in this case, the revelation of the Incarnation). But he does so in a minimalist way that preserves most or all of our intuitions about the original concept derived from reason alone. Both the achievements of reason and the demands of faith are respected.

Chapter five consists in Gorman’s examination of a Christological issue that doesn’t attract much, if any, attention among non-Thomists: the question of how many existences Christ has. Obviously, such a question sounds bewildering to most contemporary analytic philosophers, for whom existence is both univocal and absolute. This makes the chapter perhaps the most arduous and obscure in the book, but Gorman spends a significant portion of the chapter helpfully distinguishing and clarifying the questions that Aquinas is asking before diving into his answers.

Finally, the sixth chapter explores some of the traditionally thorny questions about the consistency of Christology. For example, how can Christ be both passible, as his human nature requires, and impassible, as Aquinas holds that His Divine nature requires? In the first part of the chapter, Gorman explains and criticizes one strategy pursued by contemporary commentators on Aquinas, the so-called “mereological replacement strategy.” According to this interpretation of Aquinas, reduplicative sentences such as “Christ is passible qua human” should be read as “Christ has a human nature as a part, and this nature is passible” (129). Gorman rejects this on both substantive and interpretive grounds, and in the second part of the chapter advances his own extensive reconstruction of what he thinks Aquinas ought to have said about the proper interpretation of reduplicative sentences and the role they play in preserving the consistency of his theory of the Incarnation.

Having examined the general outline of Gorman’s book, I want to offer three criticisms. The first concerns a claim about natures that Gorman makes at the end of chapter one: he claims that reifying natures leads to “theological difficulties” and is a “philosophical mistake” (33-34). Now, if all that Gorman means by this is that it would lead to theological difficulties and would be a philosophical mistake to treat a nature as a res, in the technical, Thomistic sense of that word, then he is clearly right. But Gorman says that natures are not even “quasi-thing-like,” and that reifying them is even “worse than reifying accidents” (34). So I take it that he means by “reify” here what contemporary analytic philosophers mean by it and not what Aquinas would mean by it. And if that’s the case, then as a matter of interpreting Aquinas and as a matter of what Gorman’s own interpretation of Aquinas commits him to saying about natures, I don’t think that such a claim can stand. Aquinas himself says, “But nothing prevents saying that the human nature in Christ is a certain individual or singular or particular; and similarly any part of the human nature, as hands and feet and bones, each of which is a certain individual, yet it is not what is predicated of the whole, since none of them is an individual subsisting per se.”3 If Christ’s human nature can be called a certain individual, singular, or particular just like hands, feet, and bones, this would seem to be more than enough to reify Christ’s human nature, at least as contemporary analytic philosophers understand reification. It would certainly be erroneous, at least, to say that Christ’s human nature is abstract, or universal, or not real. So it’s hard to see why we can’t or shouldn’t reify it.

More importantly, though, Gorman’s treatment of how Aquinas avoids difficulties elsewhere in his Christology would seem to commit him to a reification of Christ’s human nature. In chapter 3, Gorman reads Aquinas (rightly) as arguing for the compatibility of the Incarnation with Divine immutability by appealing, in part, to the ability of Christ’s human nature to bear accidents. And in chapter 4, Gorman reads Aquinas (again, rightly) as arguing for the possibility that Christ’s human nature could have grounded a supposit (even though it doesn’t, never has, and never will) by appealing, in part, to the individuation of such a nature ontologically prior to its belonging to a supposit. But if Christ’s human nature can bear accidents and be individuated in a way that is ontological prior to its belonging to a supposit, then it would seem to be clearly a thing. So even Gorman’s own reading of Aquinas commits Aquinas to treating Christ’s human nature as a thing in the contemporary analytic sense of “thing”.

My second point of concern about Gorman’s book lies in his rather quick treatment of the compatibility of Divine simplicity with Christ’s Incarnation. Gorman is quite right to point out, as I note above, that Divine simplicity is not immediately a difficulty for the Incarnation, because subsistence in more than one nature is not any one of the kinds of composition that Aquinas takes to be ruled out by Divine simplicity. But when we add that Aquinas believes that the Word is identical with the Divine nature (something to which Aquinas is committed partly in virtue of his commitment to Divine simplicity), additional worries surface. For Aquinas, “… Christ is composed of humanity and divinity,” as Gorman notes (43). But the Divine nature is not composed of humanity and Divinity. Indeed, it is absurd to believe that the Divine nature is in any sense composed of humanity whether one accepts Divine simplicity or not. Neither is the Divine nature composed of Divinity: it just is Divinity. So more has to be said about how one reconciles the identity of the Word with the Divine nature with Aquinas’ belief that Christ is a composite Person after the Incarnation.

My final objection is to Gorman’s account in chapter six of how to dispose of worries about consistency in Aquinas’ Christology. Gorman does this in a rather theoretically expensive way, introducing a very extended theory of predication which licenses locutions such as “Christ is impassible qua God” despite the fact that, strictly speaking, Christ isn’t impassible. Gorman acknowledges that this account of predication is “strange,” given that it doesn’t obey what is ordinarily understood to be an essential mark of predication, namely that if “F” is predicable of X, then X is F. Gorman accepts this high cost to avoid the specter of contradiction in the claims “Christ is passible” and “Christ is impassible.” In his analysis of Aquinas’ treatment of this worry, Gorman pleads ignorance of how it is that Aquinas can avoid contradiction just by his claim that although it would contradictory to predicate opposites of Christ “according to the same” (144), no contradiction results from predicating opposites of Christ “according to diverse things” (144). Gorman doesn’t think that the relevant texts “really address the consistency problem at all.”

But it’s wrong to think that because Aquinas does not have a long metaphysical yarn to spin in ST III about how predicates like “passible” and “impassible” are predicated of Christ in virtue of his diverse natures, Aquinas has not addressed the consistency problem at all. This is because, for Aquinas, all it takes to avoid contradiction in his Christology is to point out the different respects in which opposed predicates such as “passible” and “impassible” are predicated of Christ. And this is because for Aquinas, like any good Aristotelian, there is no contradiction in asserting and denying F of X, even at the same time, so long as it is not done in the same respect. So when Aquinas says that it would be contradictory to predicate opposites of Christ “according to the same” but not contradictory to predicate opposites of Him “according to diverse things,” Aquinas is simply reminding us of what a contradiction is. He is not alluding to some longer metaphysical theory he has thought out about how to avoid having to assert what would otherwise be a contradiction, but which he has neglected or refused to share with his readers. For Aristotle and Aquinas, there just is no contradiction between “Christ is passible” and “Christ is impassible” unless these predications are made in the same respect. The requirement that an affirmation and denial of the same predicate be in the same respect in order for there to be any contradiction is simply a fundamental and irreducible element of what “contradiction” means. So no analysis of what reduplicative phrases mean is necessary to take advantage of Aquinas’ account of Christology consistency in ST III other than simply noting that such reduplicative phrases signify a difference in the respect in which a predicate is predicated of its subject. Gorman is tilting at logical windmills.

In summary, Gorman offers an excellent introduction to Aquinas’ metaphysics of the Hypostatic Union. His treatment is as erudite as it is accessible, and at least in my estimation, his interpretation of Aquinas is nearly irreproachable. I pointed out some small quibbles where I’ve found that interpretation somewhat faulty and omissive, and a more substantial objection where I believe that Gorman is spinning his theoretical wheels in vain. But on the whole, the book is an invaluable contribution to the literature on what Aquinas likely would have said is the most important subject on which he wrote.

We often think of theological mysteries in terms of their depth. But while the Incarnation is certainly among the deepest of all mysteries, it is perhaps better in some respects to think of it as a mountain from which we can gain a better perspective on several other mysteries that mesmerize philosophers and theologians alike: human nature, Divine nature, and personality. Aquinas has blazed a painstaking but rewarding trail up that mountain, and Gorman proves himself in this volume to be an exemplary guide to those willing to make the climb.

1 See Christopher Hughes, On a Complex Theory of a Simple God: An Investigation in Aquinas’ Philosophical Theology (Ithaca, NY: Cornell University Press, 1989), ch. 7, for a critical discussion.

2 Of course, it is critical that Christ’s human nature be the same as ours, for as Saint Gregory Nazianzus reminds us, “What has not been assumed has not been healed.”

3 “Sed ipsam humanam naturam in Christo nihil prohibet dicere esse quoddam individuum, aut singulare, aut particulare; et similiter quaslibet partes humanae naturae, ut manus et pedes et ossa, quorum quodlibet est quoddam individuum: non tamen quod de toto praedicetur, quia nullum eorum est individuum per se subsistens.” [Thomas Aquinas, Quodlibetales 9.2.1, trans. Jason West ( [accessed 16 January 2018]).


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The Journal of Analytic Theology is a publication of the Center for Philosophy of Religion at the University of Notre Dame.

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