Chapter 2

Models of Human Nature — A Survey from Physicalism to Substance Dualism

Introduction: Knowing What We Are Talking About

Before we can show why physicalism breaks the doctrine of the Incarnation, we have to know what physicalism actually says — and what the other options are. It is no good arguing against a view if we have built it out of straw. So in this chapter I want to take the time to walk through the main models of human nature carefully and fairly. I want each of these views to get a hearing in its strongest form before any criticism comes. Some of them I will end up disagreeing with sharply, but I owe their thoughtful defenders a respectful description first.

The map I will use is borrowed mostly from Joshua Farris, who lays out a clean taxonomy of anthropological positions in his Introduction to Theological Anthropology.¹ Farris helpfully arranges the positions on a spectrum that runs from strict materialism on one end, through several middle positions, to robust substance dualism on the other end. We will travel that same road. As we go, I will pause at each stop to ask four practical questions: What does the view actually claim? Who holds it? What does it say happens when you die? And what early hint does it give us about the Incarnation? That last question is the heartbeat of this whole book — and it is what makes this not just a philosophy chapter but a Christology chapter.

Before we start, I want to flag a methodological idea I will be coming back to. Michael Wilkinson, in Crowned with Glory and Honor, argues that our doctrine of human nature should be shaped by our doctrine of Christ, not the other way around.² Most modern treatments work in reverse: they decide first what a human is, then ask whether Jesus fits the definition. Wilkinson flips that. Christ is the true human, the second Adam, the firstborn among many brothers. Whatever His humanity is, ours is something like that. I find this move enormously freeing. It means that when the church councils tell us that Christ's human nature includes a real human soul, that is not just a statement about Jesus — it is a statement about us.

Reductive Physicalism (Identity Theory)

The strictest form of physicalism is sometimes called identity theory or reductive physicalism. The claim is simple: mental states just are brain states. Your thought "I love my children" is identical to a particular pattern of neurons firing. Pain is C-fibers firing. There is no extra ingredient — no mind hovering above the brain, no soul, no spirit. The person is the body, full stop. Farris describes the view this way: "all of the world can be reduced to its component fundamental physical parts; that is, physics explains everything."³

The classic defenders are mid-twentieth-century philosophers like J. J. C. Smart and U. T. Place. Very few Christian thinkers have ever held this strict version, because it has trouble making sense of even basic things like the qualitative feel of experience or the meaning of our thoughts. Most Christian physicalists today have moved on to softer versions. But reductive physicalism is still important because it sets the floor of the physicalist position — every other physicalist option is trying to recover some of what reductive physicalism gives up.

What about death? The honest answer on identity theory is that death is the end. When the brain stops, you stop. The only hope for any future life is that God somehow reconstitutes you out of nothing later on. As for Christ: if Jesus is just His body, then His death on the cross is the death of His human nature, period. We will see in Chapter 21 how serious that problem is.

Nonreductive Physicalism

The most popular version of physicalism among Christian thinkers today is what is called nonreductive physicalism. The leading Christian advocates are Nancey Murphy in philosophy and theology and Joel Green in biblical studies.⁴ Their view is that yes, human beings are entirely physical — there is no immaterial soul — but mental life is not reducible to physics or chemistry. Thoughts, feelings, prayers, and love are real. They cannot simply be translated into talk about ions and proteins. Nonreductive physicalists want to keep the dignity and depth of mental life while still saying we are made of nothing but stuff.

Murphy is especially clear about her position. For her, the soul is not a thing — it is a "functional capacity of a complex physical organism."⁵ When you say someone has a beautiful soul, you are not pointing to some inner ghost. You are describing what their body, especially their brain, is able to do. Mental properties really do emerge from the physical, and they really do exert what Murphy calls "top-down" causation. But underneath it all, the only ontology — the only stuff there is — is physical stuff. Joel Green presses the same point from the Bible's side, arguing that biblical writers do not think in terms of body plus soul but rather in terms of unified bodily creatures whose inner life is entirely a function of their embodied existence.

I want to be fair here. Murphy and Green are serious Christian scholars who are trying hard to keep the Christian story intact while taking modern brain science seriously. Their motives are good. Their concern that traditional dualism slips into Gnosticism — into a hatred of the body — is a real worry that has come true at moments in Christian history. But however well meant the project is, the bottom line is the same as for reductive physicalism on the question we care most about. When the body stops, the person stops. There is no continuing thing to wait for the resurrection. As Loftin and Farris put it in their critical volume Christian Physicalism?, the so-called nonreductive label hides what is really an ontological reduction: the only thing that ultimately exists, on Murphy's view, is matter.⁶

The Constitution View

A clever third option is the constitution view, defended in different forms by Lynne Rudder Baker and Kevin Corcoran. They want to say something stronger than Murphy: a person is not identical to a body, even though a person is constituted by a body. Farris uses a helpful illustration: a wooden desk is constituted by wood, but the desk is not the same thing as the pile of wood it is made from. The desk has properties (being a desk, being a place to write) that the raw lumber does not have.⁷ So too, on the constitution view, persons are constituted by bodies but are something more than bodies — they have first-person perspectives, moral lives, and relationships that the body alone does not have.

This is an attractive proposal. It tries to keep one foot in physicalism (no immaterial soul) and one foot in something richer than mere matter. But notice the catch: when the constituting body dies and decomposes, the constitution relation dissolves. There is nothing left to constitute the person. The person ceases to exist unless God starts the constitution relation back up later. So even on the most generous reading, the constitution view ends up with the same Christological problem we keep running into. We will look at it in detail in Chapter 35, where I argue that constitution Christology fails to keep Christ united to a human nature during the three days in the tomb.

Emergentism

Closely related but distinct is what we can simply call emergentism, associated with thinkers like Philip Clayton. The idea is that consciousness and mental life are real and irreducible — they emerge from complex physical organization the way wetness emerges from H₂O molecules — but they remain entirely dependent on that physical base. Knock out the substrate and the emergent properties vanish. There is no separate substance that lifts off the brain and persists. So in terms of survival after death, emergentism stands with the other physicalist views: without a divine miracle of reconstitution, death is the end of the person.

Emergentism deserves to be distinguished from the next view, emergent dualism, which sounds similar but says something importantly different.

Emergent Dualism (William Hasker)

William Hasker's emergent dualism is one of the most fascinating proposals in this whole conversation, and it is the one I find most worthy of long, serious engagement among the views I disagree with. Hasker's claim is that the soul is real — it is a genuinely immaterial substance with its own causal powers — but it does not exist before the body. Instead, the soul emerges from the brain once the brain reaches a certain level of complexity. Once it has emerged, though, it is a real soul, and God could in principle preserve it after the brain stops.⁸

So Hasker is trying to give us the best of both worlds. He keeps a real soul (so the Christian intermediate state and the survival of consciousness after death are at least possible) while still tying the soul tightly to the brain (so we take neuroscience seriously). I have a lot of sympathy for what Hasker is doing. He is a friend of dualism, not an enemy of it.

Farris himself notes that Hasker has a hard time accounting for the soul's continued functioning after the body dies, since on Hasker's view the soul depends on the body in such a deep way.⁹ This makes the intermediate state shaky. And for our central question — whether the hypostatic union holds during the three days between Good Friday and Easter Sunday — emergent dualism gives us a soul that came from the brain and may not be able to live without one. That is not the kind of soul we need for the Incarnation to survive death. We need a soul whose existence does not depend on a working body.

Hylomorphism (Thomistic Dualism)

Now we move to a very old and very respectable position: Aristotelian-Thomistic hylomorphism. The word looks intimidating, but the idea is not. Hyle is the Greek word for matter, and morphe means form. On this view, a human being is a single thing made up of two principles: the matter (the body) and the form (the soul). The soul is not a separate ghost stuck inside a body; it is what makes the body a living human body in the first place. Aquinas is the great Christian defender of this view, drawing on Aristotle.

Hylomorphism has a lot going for it. It avoids the cartoon picture of the soul as a tiny pilot inside the skull. It takes the body seriously as part of human nature rather than treating it as a husk. And as Wilkinson notes, even though scholars debate whether hylomorphism is strictly substance dualism, the soul-as-substantial-form is "substance-like enough that the soul exists and operates between death and resurrection."¹⁰ That is the key fact for us. On Aquinas's view, the soul really does survive bodily death, and Aquinas himself wrestled with the triduum mortis problem — the three days when Christ's body lay in the tomb. He concluded that Christ's human soul, separated from the body, kept the hypostatic union going during those three days.

This is striking. It means that even on hylomorphism, an immaterial soul that can outlast the body is essential to keep the Incarnation intact through Good Friday and Holy Saturday. The hylomorphic tradition itself, far from being a rival of substance dualism on the question that matters most, ends up confirming the central claim of this book: physicalism fails the Incarnation, and only an immaterial soul that survives bodily death can hold the hypostatic union together. I will return to Aquinas's specific treatment in Chapter 32.

Substance Dualism — The Author's Position

This brings us to substance dualism, the position I hold and the position this book defends. The basic claim is straightforward: a human being consists of two distinct substances — a material body and an immaterial soul — that are deeply integrated in normal human life but that can come apart at death, with the soul continuing to exist consciously until the body is raised. Farris defines it well: persons are "identical not to the material body but to the immaterial part (e.g., the soul, the spirit, the mind) or some compound configuration of both body and soul."¹¹

Substance dualism is not one view but a family of views. It is important to distinguish my version from the cartoon Cartesian picture that gets so much mockery. I do not think the soul is a tiny invisible person living inside the head and looking out through eyeball windows. The soul and body are not two strangers strapped together. They are profoundly united in life. When you stub your toe, your soul really hurts. When you fall in love, your body really blushes. The integration is so deep that we should call the human a single living being, not a soul wearing a body like a coat.

The terminology I find most helpful is John Cooper's "holistic dualism." Cooper argues that the Bible teaches a functional holism — the body and soul work together as one unified person — that rests on an ontological dualism — the soul is a real substance distinct from the body and able to survive its death.¹² Cooper later admits that "dualistic holism" might be an even better label, because it puts the unity first.¹³ Either way, the point is the same. We are not stitching together two foreign substances; we are describing one integrated human creature whose two genuinely distinct parts can be separated by death and reunited at the resurrection.

The philosophical defense of this position is robust. J. P. Moreland and Scott Rae lay out the case in Body and Soul, drawing on arguments from consciousness, intentionality, personal identity, and the unity of experience. Richard Swinburne in Mind, Brain, and Free Will develops the modal argument: I can coherently conceive of myself existing without my body, which suggests that I am not identical to my body. I will not develop these arguments here; that is the work of Chapter 4. For now, the point is simply that substance dualism is the position that takes the soul seriously as a real, distinct, immaterial substance — directly created by God, the seat of consciousness and personal identity, and capable of surviving the death of the body.

A Summary Comparison

Before moving on, let me lay out a quick comparison of how each view handles the questions that matter most for this book.

Notice the pattern. Every view that denies a real, distinct, immaterial soul fails to keep the hypostatic union together through the cross. The two views that succeed — hylomorphism and substance dualism — both affirm an immaterial soul that can live without the body. The lines of the debate are clearer than they sometimes appear.

Wilkinson's Methodological Reversal

I want to come back to Wilkinson's Chalcedonian methodology before we close, because it bears on how we should weigh everything in the table above. Most modern debates about human nature start with philosophy or science and only later ask whether Christ fits the definition. Wilkinson points out that this is exactly the wrong direction. Scripture presents Jesus as the man, the image of God, the one whose human constitution shows us what human nature really is.¹⁴

This is more than a clever turn. It changes the whole game. If physicalism is right about us, then physicalism must also be right about Christ — and we have already seen the trouble that creates. If, on the other hand, the church's confession that Christ has a real human soul is right, then physicalism cannot be right about us either. Either way, Christology and anthropology stand or fall together. The question of human nature is, in the end, a Christological question.

Conclusion: The Road Ahead

We have walked through the main models of human nature, from the strictest physicalism to robust substance dualism, and we have started to see a pattern. The closer a view sits to pure physicalism, the harder it is for that view to keep the Incarnation intact across death. The closer a view sits to a real, immaterial, body-surviving soul, the better it can hold the hypostatic union together. That is not because I have stacked the deck, but because the metaphysical demands of the Incarnation really are this stiff. The Son had to assume something that could outlast the death of the body, or the cross would have ended the Incarnation.

In the next three chapters I will fill in why I am confident substance dualism is true. Chapter 3 will lay out the biblical case — the persistent body-soul language of Scripture from Genesis to Revelation. Chapter 4 will lay out the philosophical case from consciousness, intentionality, personal identity, and mental causation. Chapter 5 will lay out the empirical case from veridical near-death experiences, where consciousness has been observed to function in conditions where the brain should not allow it. Together, those three chapters give us the foundation we need to turn, in Part II, to Christ Himself — and to begin showing how Scripture presents His humanity as body and soul.

For now, let me leave you with this. The choice between physicalism and dualism is not a dry philosophical sideshow. It is the question of whether the Word who became flesh could remain united to a human nature when that flesh died. As we will see, only one answer keeps the Incarnation intact. The Word made flesh demands the soul.