Introduction

Determinations about the constitution of human persons are notoriously difficult. Christian theologians and philosophers who investigate this issue are faced with a host of complicated biblical, theological, philosophical, historical, scientific, and practical questions. One of the most pressing of these questions concerns the precise relation between the body and the mind. Are human persons essentially spiritual beings, material beings, or some combination of the two? Contemporary opinions on this question typically fall into one of two broad categories: dualism and physicalism in their various manifestations. ((George Berkeley’s idealistic monism is an important exception, but it does not command a significant following among contemporary philosophers of mind. See George Berkeley, A Treatise Concerning the Principles of Human Knowledge (London: Hackett, 1982).)) Among dualisms, Caretesian dualism seems to enjoy a certain pride of place. Cartesians sometimes consider their view not only the most common position in Christian history but also the most intuitive position across human cultures. ((See, for example, Stewart Goetz, “Substance Dualism,” in In Search of the Soul: Four Views on the Mind-Body Problem (ed., Joel B. Green; Eugene, OR: Wipf & Stock, 2005), 33-60.))  According to Cartesian dualism, a human person “just is” a human soul. The person is identifiable with the immaterial, substantially simple soul. While the soul and body may interact with one another in important and reciprocal ways, the body is not the person, nor even a constitutive part of the person, but merely a contingently possessed tool or instrument of the person. ((Richard Swinburne, a contemporary defender of substance dualism, does speak of the body as a “non-essential part” of a human person.  In this, he differs from Rene Descartes.  See Richard Swinburne, The Evolution of the Soul (rev. ed.; Oxford: Oxford University Press, 1997), 146. Still, Swinburne defines human persons as “pure mental substances” and sometimes uses “person” and “soul” interchangeably. Swinburne’s views will be discussed in more detail below. Richard Swinburne, Mind, Brain, and Free Will (Oxford: Oxford University Press, 2013), 2.)) As some have put it, “You do not have a soul. You are a soul. You have a body.” ((This saying is often, but probably erroneously, attributed to C. S. Lewis. On the origins of the saying, see http://mereorthodoxy.com/you-dont-have-a-soul-cs-lewis-never-said-it/, accessed January 13, 2015.))

Whatever merits or demerits Cartesian dualism possesses as a coherent model of human personhood, this article will suggest that it stands in some tension with the understanding of human personhood implied in the Chalcedonian Definition and the Christological reflections that flowed from it.  The statement produced by the Council of Chalcedon (451) famously defined the “hypostatic union” of two natures in the person of Christ.  According to the Chalcedonian Definition, the incarnate Son of God is “at once complete in Godhead and complete in manhood, truly God and truly man, consisting also of a reasonable soul and body.” ((“The Definition of Chalcedon (451),” in Creeds of the Churches (ed., John Leith; Louisville: Westminster John Knox, 1982), 35-36.)) So the human nature that the Son assumed in his incarnation consists of two parts: a reasonable soul—that is, a soul possessed of mind or reason—and a body. As subsequent Christological reflections made clear, the Son did not assume a distinct human person, but rather he gave personhood to the distinct body and soul that he assumed.  The human soul of Christ must be distinguished from his person in order to avoid the heresy of Apollinarianism. And the Son’s assumption of a distinct human soul cannot imply his assumption of a distinct human person upon pain of Nestorianism. In short, person and soul cannot be equated, at least in the case of the incarnate Christ. This article will seek to tease out the potential problems that this Chalcedonian distinction between person and soul poses for Cartesian dualism and will also suggest some possible ways that Cartesians might resolve these problems.

 

Prolegomena to Theological Anthropology

But first, a brief word on methodology.  I take it that when it comes to developing theological models of human personhood (or any other doctrinal issue, for that matter) Scripture serves as the norma normans: “the ruling rule” to which all other sources of authority must be subordinated.  Scripture, when taken as a whole and read in light of its own categories, must set the parameters for and determine the shape of our theological models.  When it speaks clearly and unambiguously to a particular issue, Scripture must be embraced and affirmed even if its teachings may conflict with theories from other areas of inquiry, such as neurobiology or philosophy of mind.   The relevant question for our purposes is, does Scripture speak clearly and unambiguously to the question of human constitution?  Does the Bible solve the mind-body problem, so to speak? It is my conviction that many of the common proof texts cited in this discussion are underdetermined. In other words, many of the biblical texts cited in favor of this or that anthropological model admit of several possible interpretations.  What is needed, then, is not simple prooftexting (citing, say, 2 Cor 5:8, “we would rather be away from the body and at home with the Lord” as if it provided a “slam dunk” case for substance dualism), but rather attending to patterns of thinking and speaking about human nature that are organically developed across the biblical canon ((One of the best examples of this kind of canonical work is found in John W. Cooper, Body, Soul and Life Everlasting: Biblical Anthropology and the Monism-Dualism Debate (Grand Rapids: Eerdmans, 1989).  For my own part, I think Cooper’s handling of the biblical material is largely sound. The totality of the biblical witness seems to imply something like Cooper’s “holistic dualism,” though perhaps there is a range of philosophical models that can account for it.)) and then seeking to develop patterns of thinking and speaking about human nature in new contexts—patterns which may, in some sense, move beyond the biblical concepts but which nonetheless render the same theological judgments as Scripture. ((This distinction between “concepts” and “judgments” comes from David S. Yeago, “The New Testament and the Nicene Dogma: A Contribution to the Recovery of Theological Exegesis,” in The Theological Interpretation of Scripture: Classic and Contemporary Readings (ed., Stephen E. Fowl; Oxford: Blackwell, 1997), 87-100.  Also important in this regard is avoiding the mistake of thinking that our theological concepts must be used in the exactly the same way as biblical concepts. So, while the Hebrew word for “soul” (nephesh) might mean something like “life” or the “whole person” in a biblical context, this fact does not rule out a different use of the term “soul” in our theological models, namely, as a designator of the immaterial part of human nature.))

I also take it that the Christian tradition, while not to be construed as a second source of revelation alongside Scripture, should nonetheless function as an authoritative (but fallible) guide to interpreting Scripture. ((This view corresponds to what Heiko Oberman calls “Tradition 1,” as opposed to “Tradition 2,” which adopts the two-source theory. Heiko Oberman, The Dawn of the Reformation (Edinburgh: T&T Clark, 1986), 280.)) In this sense, tradition functions as the norma normata: the “ruled rule,” which is subordinated to the ultimate authority of Scripture. Tradition does possess a kind of authority in Christian theology, but it is a derived authority—an authority it possesses by virtue of its fidelity to Holy Scripture.  The ecumenical creeds and councils of the church, developed in the early centuries of Christian history in response to trinitarian and Christological heresies, are especially significant in terms of their authoritative status. While Protestants rightly reject the idea that the creeds and councils are infallible, they would be unwise to dismiss these ecumenical symbols as outdated or optional.  Surely the judgment of Oliver Crisp is correct on this point: “It seems to me that someone dissenting from the findings of an ecumenical council of the Church should have a very good reason—indeed, a very good theological reason—for doing so.” ((Oliver D. Crisp, Divinity and Humanity (Cambridge: Cambridge University Press, 2007), 35 (emphasis original).))  So if it turns out that the ecumenical councils either teach or imply a particular view of human constitution and if that view is integrally related to the Trinitarian and Christological conclusions of those councils, then such a view should be afforded a great deal of deference by contemporary theologians.  And if it turns out that such a view has held sway throughout most of Christian history, then the commitment to the conciliar view is only strengthened.
The place of science in theological anthropology also warrants some comment. Many contemporary theologians and philosophers of mind are especially concerned to develop anthropological models that square with the advances of neuroscience, the study of the brain and nervous system. ((This is true of both physicalist models and some dualist models of human personhood, such as William Hasker’s emergent dualism.  See William Hasker, The Emergent Self (Cornell University Press, 1999).))  For the purposes of this article, it is not necessary to tease out all of the issues involved in the relationship between science and theology.  Still, I take it that the reciprocal relationship between mental states, on the one hand, and activity in the brain, on the other, poses a problem for at least the more radical forms of dualism.  But I also take it that mental events are not equivalent to and do not merely supervene upon physical events, and therefore it is a category mistake to think that scientific study of the brain could ever exhaust the content of mental events. Even if scientists in the future could develop a complete map of my brain and all of the physical events going on in it during every one of my mental states, they still would have no access to the first person experience that is my consciousness. ((So I would not espouse a kind “soul of the gaps” theory in which the soul is posited to fill in the gaps of scientific discovery.  Even if all of the gaps in our knowledge of brain activity were filled, this would have no bearing on the question of consciousness or mental events.  For more along these lines, see David Bentley Hart, The Experience of God: Being, Consciousness, Bliss (New Haven: Yale University Press, 2014). Similarly, Richard Swinburne distinguishes mental events from physical events precisely in terms of “privileged access.” He writes, “A subject’s privileged access to his or her thoughts, desires, beliefs, etc. would remain, even if we were to discover that all such events as had been previously studied had been caused by brain events in accord with an apparent law-like regularity.” Swinburne, Mind, Brain, and Free Will, 86.))  So while science can serve as a kind of “handmaiden” to the task of theological anthropology, I think it is a mistake to believe that it is determinative for that task.
With these preliminary considerations out of the way, we now turn our attention to the main thesis of this article, namely, that the theological anthropology implied in the Chalcedonian Definition poses a potential problem for the Cartesian identification of the person with the soul. The argument proceeds in three steps. First, we will briefly consider in more precise terms what is meant by “Cartesian dualism.”  Second, we will explore the anthropological implications of Chalcedon and its progeny and point up the potential problems that these implications pose to Cartesianism. Finally, we will suggest some ways that Cartesians might solve these problems and weigh the relative merits of these solutions.

 

Cartesian Dualism

By Cartesian dualism, I simply mean any view of human constitution that affirms the following set of propositions:

P1 Human beings are (ordinarily) constituted by two distinct substances: a material body and an immaterial soul.
P2 The soul and the body interact with one another in causally reciprocal ways.
P3 Human persons are to be identified with their souls.
Defining Cartesian dualism in this manner may include some thinkers who predate Réne Descartes, for whom the position is named. (( Eleanore Stump suggests that the Platonic understanding of the soul opposed by Thomas Aquinas was “an account very like that of Cartesian dualism.” Eleanore Stump, “Non-Cartesian Dualism and Materialism without Reductionism,” Faith and Philosophy 12, no. 4 (October 1995): 506.  Further, as John Cooper points out, Descartes “considered himself to be a Christian philosopher in the Augustinian line.” Cooper, Body, Soul, and Life Everlasting, 15.)) Ironically, it may also exclude Descartes himself, if certain revisionist scholars are correct about Descartes’ own position. ((On Descartes’ relation to Cartesian dualism, see Margaret Wilson, Descartes (London: Routledge, 1978), 177-85.)) But it is the position itself, not necessarily its proponents, that is relevant for the purposes of this article.
Quite obviously, Cartesian dualism is form of “dualism,” the belief that humans are made up of both material and immaterial substances (or parts). There are other versions of dualism on offer both in the Christian tradition and in the contemporary philosophical literature, but all forms of dualism would affirm P1 in some sense (though depending on how “substance” is defined, not all dualists would wish to be considered substance dualists).  However, some versions of dualism (such as Spinoza’s non-interactive dualism) would deny P2. But other versions of dualism (such as William Hasker’s “emergent dualism” ((William Hasker, The Emergent Self (Ithaca: Cornell University Press, 2001).)) ) would share P2 in common with Cartesianism.  I take it, then, that P3 is at least one of the distinguishing marks of Cartesian dualism.  A person may possess a body as an instrument or as a non-necessary constituent, but the person is to be identified only with the soul. There are other issues debated among Cartesians, such as the precise point at which the soul interacts with the body or whether instead the soul is be conceived of as filling the space occupied by the body. But these intramural debates need not deter us. The crucial point for our purposes is the Cartesian identification of the person with the soul, the immaterial part of human nature.
Descartes own version of dualism is based upon a certain intuition, an “introspective awareness,” of himself as a simple, psychological substance distinct from his body. ((Goetz, “Substance Dualism,” 39.)) He argues,

[O]n the one hand I have a clear and distinct idea of myself, in so far as I am simply a thinking, non-extended thing [that is, a mind], and on the other hand I have a distinct idea of body, in so far as this is simply an extended, non-thinking thing. And accordingly, it is certain that I am really distinct from my body, and can exist without it. ((René Descartes, Meditations on First Philosophy, 2.54.))

Some may balk at Descartes’ appeal to introspective awareness here, and perhaps there are other ways of arguing for substance dualism that avoid this introspective move. ((Other philosophers claim to have an immediate, intuitive sense that they just are physical substances. See, for example, Peter van Inwagen, “Dualism and Materialism: Athens and Jerusalem?” Faith and Philosophy 12, no. 4 (1995): 476.)) Additionally, as noted above, there may be reason to question whether or not Descartes consistently excluded the body as a constitutive part of human persons. But as he defines it here, Descartes summarizes well the main notion associated with Cartesian dualism: the person, the subjective “I,” is to be identified with the soul or mind, the psychological part of human nature. The body is merely a contingent possession of the person, but it is substantially distinct from the person himself.
Richard Swinburne, one of the most able defenders of substance dualism in the contemporary philosophical literature, understands substance dualism as “the view that those persons which are human beings (or men) living on Earth, have two parts linked together, body and soul.” ((Swinburne, The Evolution of the Soul, 145. Interestingly, in contrast to many other philosophers, Swinburne sees “no real difference” between the Platonic-Cartesian view and the view of Thomas Aquinas. Swinburne, Mind, Brain, and Free Will, 172-73.))  The body is the material, non-essential part of human nature, to which physical properties belong.  The soul in turn is the immaterial, essential part of human nature, to which mental properties belong.  Thus, Swinburne differs from Cartesian dualism in one important respect: he is willing to speak of the body as a part of the human person. ((Swinburne, The Evolution of the Soul, 146.))  Nevertheless, because the body is merely a contingent part, and because the soul is the essential principle of personal identity, Swinburne sometimes uses the term “soul” to describe an individual human person.  He identifies the soul as the “principle of identity of the individual human.” A “personal being” is one in possession of a mental life. ((Richard Swinburne, The Christian God, 194.))  Further, a person is “pure mental substance.”  Having a body might be necessary for a “worthwhile” human existence, but it is not necessary for the existence of human persons. ((Swinburne, Mind, Brain, and Free Will, 2.))  So while Swinburne would disagree that the person “just is” the soul, without remainder, he often uses the two terms interchangeably.

 

Chalcedonian Anthropology

The Council of Chalcedon appears to present a very different understanding of human personhood than the one summarized in this Cartesian scheme. The council convened in 451 to address a series of Christological heresies that had been plaguing the church for over a century. The “Definition” produced by the council affirmed the unity of two natures in the one person or subsistence of Christ.  In this hypostatic union, the Son’s divine and human natures are united “without confusion, without change, without division, without separation.” Against the Arians, Chalcedon affirmed that the person of the Son is “of one substance with the Father.” Against the Nestorians, the council was careful to note that the two natures are “not parted or separated into two persons.” Against the Eutychians, the council claimed that “the distinction of the natures [is] in no way annulled by the union.” And, especially significant for our purposes, against the Apollinarians, Chalcedon affirmed the Son’s assumption of a complete human nature—both a body and “a reasonable soul.”

So what are the anthropological implications of the Chalcedonian Definition? Two points are especially noteworthy. First, the council takes up the key terminological distinctions of Patristic trinitarian thought and applies them to the incarnate Christ.  The person/nature distinction, which was crucial for Nicene trinitarianism, is now applied to the person of the Son in his incarnate state.  Now the person, or subsistence, of the Son is spoken of as having two natures, or substances: the divine nature that he shares eternally with the Father and the human nature that he assumed in the incarnation.  Thus, Chalcedon forges an analogical link between trinitarian personhood and human personhood, and the univocal core of the analogy is the incarnate Son himself. ((Michael Horton similarly suggests that the person of Christ is the “univocal core of God.” Still, Horton argues, our knowledge of Christ remains analogical and ectypical.  Michael S. Horton, Covenant and Eschatology: The Divine Drama (Louisville: Westminster John Knox, 2002), 97-98.))
Second, the council made clear that the human nature that the Son assumed consists in two parts: a physical body and a reasonable, or rational soul.  The context for this affirmation is the Apollinarian heresy, which had denied the Son’s assumption of the higher soul of human nature: the “spirit” (pneuma) or “mind” (nous).  According to Apollinaris and his followers, the Son assumed a human body and an animal soul (psychē), but the person of the Son himself took the place of the spirit or mind of Christ.  Apollinarianism had already been denounced by the Cappadocian Fathers and condemned at the First Council of Constantinople in 381.  The argument of Gregory of Nazianzus had proved decisive: the unassumed is unhealed. ((Gregory of Nazianzus, “To Cledonius Against Apollinaris (Epistle 101),” in Christology of the Later Fathers (ed., Edward R. Hardy; Louisville: Westminster John Knox, 1954), 218-19.))  If there is a component of human nature that is not taken into union with the Logos, then that component would remain corrupted and condemned by sin.  But here again at Chalcedon, the church reaffirmed its insistence that the Son assumed a reasonable soul, that is the higher soul or spirit of human nature possessed of mind or rationality.  This affirmation is significant for our purposes because the council is drawing a distinction between the person of the Son and the soul of Christ, the latter of which inheres in his human nature. To confuse person and nature on this point would be to upend the Definition’s principle terminological clarification, namely, that the singular person and dual natures of Christ must be distinguished conceptually.
This intuition to distinguish the person of Christ from the soul of Christ is also born out in the next two ecumenical councils.  At the Second Council of Constantinople (553), the church reasserted its opposition to Nestorianism—the two-persons heresy rooted in the thought of Nestorius of Constantinople (c. 386-450)—by clarifying that it is the person of the eternal Son of God who is in view in the incarnation.  It is not merely a composite figure, the incarnate Christ, who is the “person” identified in Chalcedonian Christology, but it is none other than the eternal Son, one of the three members of the Godhead.  This assertion is significant for theological anthropology because it once again explicitly applies the person/nature distinction to the man Christ Jesus.  The person of the Son preexists his incarnation, and yet his incarnation involves the assumption of a distinct human soul. So, at least in the case of Christ, the person and the soul must be conceptually distinct.  The Son did not assume a distinct human person in the incarnation; in this sense, his human nature is anhypostatic, i.e., without a person.  At the same time, the human nature of Christ is given personhood by its assumption in the person of the Son; so the Son’s human nature is also enhypostatic, receiving its personhood in the person of the Son.  What is noteworthy is that Constantinople II does not argue similarly with regard to the soul of Christ. There is no apneumatic/empneumatic doctrine affirmed by the council. Instead, the council reaffirms Chalcedon with its insistence that the person of the Son is distinct from the body-soul nature he assumed.
The Third Council of Constantinople (680-81) makes the point even clearer. When the person of the Son assumed a human soul, he also assumed a human will, which inheres in that soul.  The soul that the Son assumed, then, is not merely an abstract universal property, but more fundamentally it is a concrete particular.  The Son assumed a concrete human soul equipped with a concrete human will.  Therefore, the incarnate Christ possesses two wills, one divine and one human, which correspond to his two natures. Yet again the person/nature, person/soul distinction is maintained.
So it seems that by equating person and soul, Cartesians are caught on the horns of a Christological dilemma. Either the person of the Son does not assume a human soul, since he is already a “soul” in the relevant sense, resulting in Apollinarianism.  Or else by assuming a human soul, the person of the Son also assumes a distinct human person, resulting in Nestorianism.  But is there a way for Cartesians to resolve this apparent contradiction? The following section explores two possible avenues for seeking such a resolution.

 

Possible Solutions

Perhaps Cartesians can avoid the heretical implications of this conflation of person and soul by clarifying their terms. In other words, perhaps we are dealing with an equivocation. Perhaps the Cartesian “soul” is not the same as the Chalcedonian “soul.”  In the Cartesian sense, the soul is the person—the individual, immaterial substance capable of bearing properties. Perhaps the “soul” of Chalcedon is not the substance but the properties possessed by that substance.  In this case, the “soul” of the Son (that is, the person of the Son) assumes the “soul” of human nature by taking to himself that set of abstract properties essential to humanity.  He does so without losing his divine properties, that is, the divine nature (what we might call the “divine soul” in the Chalcedonian sense). Let us call this the abstract human soul solution to the Chalcedonian problem posed to Cartesianism. ((The distinction between “abstractist” and “concretist” understandings of the incarnation is fairly common in contemporary literature on the subject.  See Alvin Plantinga, “On Heresy, Mind, and Truth,” Faith and Philosophy 16, no. 2 (April 1999): 182-93.  See also Jonathan Hill’s introduction in Anna Marmadoro and Jonathan Hill, eds., The Metaphysics of the Incarnation (Oxford: Oxford University Press, 2011), 10-19.))

Richard Swinburne opts for this kind of solution.  He argues that the “reasonable soul” of Chalcedon was simply “human soul,” viewed as a universal—a property capable of being instantiated in a number of different things.  In this sense, the Chalcedonian “soul” is closer to Aristotle’s “form,” meaning a “way of thinking and acting.” Swinburne’s sense of “soul,” however, is different.  Indeed, Swinburne recognizes that it must be different upon pain of heresy: “But the Council could not have meant by [reasonable soul] that there were in Christ both a divine and a human soul in my sense of ‘soul.’ For that would have been to say that Christ was two individuals, a doctrine to which Chalcedon was greatly opposed.” ((Swinburne, The Christian God, 196-97.))  So by “soul” Swinburne means the individual, the person capable of bearing mental properties.  In the case of the incarnate Christ, we have a single individual (“soul” in the Swinburnean sense) who possesses both divine and human properties (“soul” in the Chalcedonian sense).  Thus, Swinburne is able to sidestep formally any heretical implications of equating person and soul.
But this abstract human nature view is not without its costs from the perspective of historic Christian orthodoxy. As Oliver Crisp has pointed out, even if abstractists can square their view with Chalcedon, they face greater difficulties with later conciliar developments, specifically with regard to the Sixth Ecumenical Council. ((Crisp, Divinity and Humanity, 34-71.)) At Constantinople III, the church affirmed that Christ has two wills, the one will of the Godhead, and a distinct human will that inheres in his human nature. The Son’s human soul, in this view, is not a universal, but a particular.  It is not merely a set of abstract properties, but a concrete substance. The bishops at Constantinople III apparently believed that this dyothelite, concrete-human-nature understanding of the incarnation was simply the outworking of Chalcedon’s affirmation of Christ’s “reasonable soul.” ((The council reaffirmed the Chalcedonian Definition and applied Chalcedon’s two-natures logic to the two wills of Christ. It even used the four privatives to refer to the union of two wills in the person of Christ “without separation, without change, without partition, without confusion.” See “The Statement of Faith of the Third Council of Constantinople (Sixth Ecumenical),” in Hardy, ed., Christology of the Later Fathers, 383.)) Alvin Plantinga has suggested that the abstractist view was the majority view at Chalcedon, but the bishops of the Sixth Ecumenical Council would demur. ((Plantinga, “On Heresy, Mind, and Truth,” 184. Plantinga’s historical judgment on this point is debatable.  Plantinga cites Philip Schaff in support of his view.  In his discussion of Chalcedon, Schaff argues that “the Logos assumed, not a human person (else we would have two persons, a divine and human) but a human nature which is common to us all.” Philip Schaff, The Creeds of Christendom (New York: Harper & Row, 1877), 1:30. But this is a statement that all orthodox concretists could affirm.  In assuming a concrete human nature, the Son did not assume a distinct human person, as the Nestorians claimed.  Furthermore, the belief that the Son assumed a concrete human nature does not preclude the view that, in another sense, he assumed our common humanity.  The anhypostatic/enhypostatic doctrine seems to affirm both.  In one sense, Christ assumed the human nature common to all: his human nature was anhypostatic, without a separate human person.  But in another sense, Christ assumed a specific human nature: his human nature was enhypostatic, given personhood by the Second Person of the Trinity.  Christ has all of the properties common to humanity but he also possesses a concrete manifestation of these properties.  For an argument along these lines, see Crisp, Divinity and Humanity, 79-89.)) According to the dyothelite tradition, in assuming a human soul, Christ assumed a concrete human will and not merely a set of abstract human properties.
Interestingly, Swinburne tries to make room for the two-wills position in his own Christological proposal, but it is clear that he has adjusted the terms of Constantinople III to fit his abstractist scheme.  Insofar as Christ can be spoken of as possessing two minds or two wills, it is only as two ways of thinking or ways of willing, that is, as two sets of abstract properties possessed by the singular “soul” or person of the Son. ((Swinburne, The Christian God, 208-09.))  It remains an open question as to whether or not this abstract-human-nature understanding of the incarnation can be squared with the Chalcedonian Definition, but it at least stands in tension with the traditional interpretation of Chalcedon’s “reasonable soul” as expressed in subsequent Christological reflections.
Another potential avenue for reconciling Cartesian dualism with Chalcedonian Christology may lie in clarifying the uniqueness of Christ’s participation in the category of human personhood.  Oliver Crisp takes this tack in his attempt to explain how dyothelitism can avoid Nestorianism.  Crisp suggests that ordinarily the coming together of a human body and a concrete human soul would constitute the formation of a distinct human person.  In the case of the incarnate Christ, however, this combination cannot constitute a human person, upon pain of Nestorianism. So perhaps, Crisp suggests (following Brian Leftow), we should state things more precisely.  Perhaps a human zygote “has the property ‘constituting a distinct, individual person when composed of a body + distinct soul, intellect and will, unless assumed by a divine person.’” ((Crisp, Divinity and Humanity, 64.  Crisp is citing Brian Leftow, “A Timeless God Incarnate,” in The Incarnation (ed., Stephen Davis, Daniel Kendall, and Gerald O’Collins; Oxford: Oxford University Press, 2002), 281.))  In other words, the incarnation is a special case; it is in a category by itself.  Ordinarily a human soul (combined with a human body) constitutes a human person; but in the case of the incarnate Christ, the soul is prevented from becoming a human person by virtue of its union with the person of the Son.  Let us call this the sui generis solution to the Chalcedonian problem posed to Cartesianism.
Leaving to one side the ad hoc nature of this proposal, one wonders if perhaps there is simpler solution to the Nestorian objection posed to dyothelitism.  Perhaps we should apply the person/nature distinction to all human persons, and not only the incarnate Christ.  Perhaps the person is distinct from the soul (which is a part of human nature) in all human persons.  If we adopt a more Thomistic understanding of personhood, the human person would be conceived of as the individual subsisting thing (Latin, suppositum) that exists in and through the human nature, conceived of as a body-soul composite. As is well known, Thomas Aquinas identifies the soul as the form of the body; the soul gives to the material body its rational configuration. It is also commonly recognized that this is a rather unique “form” in that it is capable of existing without the material body in the intermediate state. ((Philosophers are divided on the coherency of Thomas’ anthropological model, which seeks to reconcile Aristotle’s hylomorphism with the traditional Christian understanding of the continuing existence of the soul after death.  “And so, Aquinas has to hold, [the soul] is a very unusual form in that, unlike other forms of inanimate things and of animals, it can exist and have a life without being instantiated in matter.” Richard Swinburne, Mind, Brain, and Free Will, 172.  For a defense of the coherency of Thomas’ view, see Stump, “Non-Cartesian Dualism and Materialism without Reductionism.”))  But what is not always appreciated is how Thomas employs the language of person (hypostasis or persona) in this theological anthropology.  Thomas maintains that the person cannot be equated with either the soul or the body.  It is a distinct conceptual category.  He cites Augustine in this regard: “On the contrary, Augustine (De Civ. Dei xix, 3) commends Varro as holding ‘that man is not a mere soul, nor a mere body; but both soul and body.’” ((Thomas Aquinas, Summa Theologica (trans., Fathers of the English Dominican Province; rev., Daniel J. Sullivan; Chicago: Encyclopædia Britannica, 1952), 1.75.4.)) So Thomas argues that the soul cannot be equated with “man,” conceived of either as a species or as an individual. Instead, Thomas maintains that the soul is a part of man along with the body.  He concludes:

Not every particular substance (substantia) is a hypostasis or a person (persona), but that which has the complete nature of its species. Hence a hand, or a foot, is not called a hypostasis, or a person; nor, likewise, is the soul alone so called, since it is a part of the human species. ((Ibid.))

So the soul is in some sense a substance, distinct from and even capable of existing apart from the body, but it is not a hypostasis; it is not a person. ((Though we should be careful to note that for Thomas, the soul is not a substance “in its own right” but merely a subsistent part of the body-soul composite that is a human being. For more on Thomas’ distinction between these two notions, see Stump, “Non-Cartesian Substance Dualism,” 517-18.))  A person has the “complete nature of its species,” which, in the case of a human being, ordinarily includes (bracketing out the question of the intermediate state) a body and a soul.  In sum, Thomas maintains the person-nature distinction even outside of its normal Trinitarian-Christological context and applies it consistently to ordinary human persons as well.
So, to return to the Nestorian objection to dyothelitism, perhaps there is simpler solution than the one Crisp and Leftow prescribe.  Perhaps no human person is identical with his or her soul.  In this case, the person of Christ would not be an exception.  Perhaps the person should always be distinguished from the soul, even in ordinary (that is, non-theanthropic) persons.  Thus, Nestorianism could be avoided by dyothelites without an ad hoc argument.  The Son’s assumption of a concrete human soul/mind/will does not entail his assumption of a distinct human person because no human soul/mind/will constitutes a distinct person. The person is the individual, the suppositum, that exists in and through in the soul (and body).  So perhaps we need a three-part anthropology (person, soul, body) to match Crisp’s three-part Christology (Word, soul, body).

 

Conclusion

Cartesians maintain that the person “just is” the soul.  But as we have seen this equation of the person with the soul poses a potential problem for Chalcedonian Christology.  Chalcedon and its progeny distinguished the person of the Son from his nature, which was composed of a body and a “reasonable soul.” Thomas Aquinas developed an understanding of human personhood consistent with this person/nature distinction, arguing that neither the soul nor the body could be equated with the person.  Cartesians could perhaps avoid the unfortunate Christological consequences of their view by arguing for an abstract-human-nature understanding of the incarnation or by arguing for the sui generis nature of Christ’s personhood.  But as we have seen these solutions are not without their difficulties.  This exercise in Christological anthropology may not prove decisive against Cartesian understandings of human personhood, but perhaps it does point up a potential weakness in developing anthropological models independent of Trinitarian and Christological considerations. ((Marc Cortez’s analysis of Karl Barth’s Christocentric anthropology is a welcome exception to the rule that theological anthropologies are often developed in isolation from Christology. Marc Cortez, Embodied Souls, Ensouled Bodies: An Exercise in Christological Anthropology and Its Significance for the Mind/Body Debate (London: T&T Clark, 2008).))  Perhaps other versions of dualism (hylomorphic, emergent, etc.) may be better equipped to handle the anthropological demands of Chalcedonian Christology.  Some have even considered the Christological implications of a physical account of human personhood. ((Ibid., 110-54.  See also Oliver Crisp, God Incarnate: Explorations in Christology (London: T&T Clark, 2009), 137-54.)) In any event, it is apparent that more work needs to be done in applying the person/nature distinction more consistently to theological anthropology. ((I am grateful to Joshua Farris for reading and commenting on a previous version of this essay. Perhaps it could have been improved had I accepted all of his suggestions, and any weaknesses in the final product are mine alone. Farris’ forthcoming edited volume on theological anthropology looks to be an important contribution to the ongoing conversation over these issues. Joshua R. Farris and Charles Taliaferro, eds., The Ashgate Companion to Theological Anthropology (London: Ashgate, 2015).))