Chapter 11 — From Nicaea to Chalcedon

The early church did not wake up one morning with a fully developed doctrine of the Incarnation in hand. The truth that Jesus is fully God and fully man came into focus the way a photograph develops in a darkroom — slowly, carefully, and under pressure. That pressure came mostly from heresy. Each major Christological heresy forced the church to look harder at Scripture and ask, "What exactly are we confessing about Jesus?" The result was a string of ecumenical councils — gatherings of bishops from across the Christian world — that hammered out the boundaries of orthodox belief. Four of those councils stand out: Nicaea in 325, Constantinople in 381, Ephesus in 431, and Chalcedon in 451.

In this chapter, I want to walk through these four councils together. My thesis is straightforward, and it carries real weight for the rest of this book: the conciliar definitions presuppose and require that Christ has a complete human nature, including a human rational soul. Chalcedon does not just imply this — it says it out loud. Christ is "truly man, of a rational soul and body." That phrase is not a throwaway line. It is a deliberate, hard-won, anti-heretical clause that names exactly what Christ's humanity must include. And once we see this, a serious problem appears for any view of human nature that denies the existence of an immaterial soul. If physicalism is true, the very thing Chalcedon insists Christ possesses does not exist.¹

Nicaea (325): The Son Is Fully God

The story really begins with a quiet, popular, ascetic Alexandrian priest named Arius. Arius was a careful thinker, and his concern was a good one: he wanted to protect monotheism. There is one God, the Father. So how can the Son be God too without making two Gods? Arius's answer was elegant and disastrous. The Son, he said, is the highest and greatest of all creatures — but a creature nonetheless. There was, in his famous slogan, a time "when the Son was not." The Son was made by the Father before time, but He was made.²

Notice what this does. If Arius is right, then the one we worship as Lord is not actually God. He's a super-creature. The Incarnation becomes the story of a created being putting on a body. Salvation becomes the work of a creature, not the Creator. And every prayer addressed to Jesus becomes, technically, idolatry.

The reaction from the wider church was sharp. Bishop Alexander of Alexandria opposed Arius locally. But the controversy spread fast. In 325, the Emperor Constantine called a council at Nicaea (in modern-day Turkey) to settle the matter. Around 300 bishops attended, most of them from the eastern half of the empire. The young deacon Athanasius, who would later become bishop of Alexandria, played a quiet but pivotal role. He spent the rest of his life defending what Nicaea decided.³

The council produced a creed. The crucial line declared that the Son is homoousios (ὁμοούσιος) with the Father — "of the same substance" or "of the same essence." That little word did enormous work. It meant the Son shares the very being of the Father. He is not a similar god, not a lesser god, not a creature. Whatever the Father is, as God, the Son is too. As Athanasius would later put it, the Son is "whole God of whole God" (holos theou).⁴

Now, why does this matter for our book's argument? Because Nicaea sets the table for everything that follows. If the Son is truly God, then when He becomes man, the Incarnation is a real union of the divine nature with a real human nature. Two complete realities have come together in one Person. And once you say that, the next obvious question is: What exactly is this human nature He has assumed? Nicaea did not answer that question. But it made the question unavoidable.

Honesty requires me to admit that Nicaea also left some loose ends. The creed used the words ousia (substance) and hypostasis (subsistence) almost as synonyms. Within a generation, theologians realized this was confusing — and the next round of debates would force the church to distinguish between the two.⁵

Constantinople I (381): Filling Out the Picture

For most of the fifty years between Nicaea and Constantinople, the Arians actually had the upper hand politically. Athanasius was exiled five times. The Cappadocian Fathers — Basil of Caesarea, Gregory of Nazianzus, and Gregory of Nyssa — labored in the East to clarify what Nicaea had taught. They worked out the language we still use: one ousia (essence), three hypostases (persons). One God, three Persons.

The First Council of Constantinople in 381 reaffirmed and expanded the Nicene Creed. It also addressed a related controversy — the so-called Pneumatomachians ("Spirit-fighters") who denied the full deity of the Holy Spirit. Constantinople I rejected that view and confessed the Spirit as "the Lord and giver of life" who "with the Father and the Son together is worshiped and glorified." The doctrine of the Trinity, in something close to its mature form, now stood on the books.

But there is another piece of Constantinople I that matters more for our argument. By this time, a new Christological heresy had emerged — Apollinarianism — and Constantinople I formally condemned it. Apollinarius, bishop of Laodicea, had taught that in Christ, the divine Logos took the place of the human rational soul (nous, νοῦς). Christ had a real body, but His "mind" was the divine Word, not a human mind.⁶

I will save the full treatment of Apollinarianism — and the parallel between it and modern physicalism — for the next chapter. What matters here is that the church at Constantinople I planted a marker. Christ's humanity is not just a body. It must include a real human mind. Anything less is not a complete human nature. That marker would be reaffirmed and sharpened in every council that followed.

Ephesus (431): One Person, Not Two

If Nicaea protected the deity of Christ, and Constantinople I started to protect the completeness of His humanity, then Ephesus protected something different again — the unity of His Person. The pressure this time came from a man named Nestorius, who became patriarch of Constantinople in 428.

Nestorius was, by most accounts, a sincere pastor. He was rightly worried that some popular language about Mary as Theotokos (Θεοτόκος, "God-bearer" or "Mother of God") could mislead people into thinking Mary had given birth to the divine nature itself. So he proposed a different title — Christotokos, "Christ-bearer." But behind that quibble lay something more serious. Nestorius spoke about the human Jesus and the divine Logos in ways that sounded, to his critics, like he was making them two persons loosely joined together — like two roommates in one house.⁷

His main opponent was Cyril of Alexandria, a brilliant and combative theologian. Cyril insisted that there is only one acting subject in Christ — the eternal Son of God. The Son became flesh. The Son was born of Mary. The Son suffered and died — not in His divine nature, of course, but as the one Person who possessed both natures. Mary really is the mother of God, because the one she carried is God. And so the Council of Ephesus in 431 condemned Nestorianism and affirmed Theotokos as orthodox.⁸

Cyril's letters to Nestorius were among the official documents of the council. And in those letters, Cyril repeatedly described Christ's humanity in terms that would prove vital for our argument. He wrote that "the Word in an unspeakable, inconceivable manner united to himself hypostatically flesh enlivened by a rational soul, and so became man."⁹ When Cyril fought for the unity of Christ's Person, he was not denying that the assumed humanity included a soul. He was assuming it. Christ is one Person, with one complete human nature consisting of body and rational soul.

So Ephesus tells us Christ is one. Constantinople I tells us His humanity is complete. Nicaea tells us His deity is real. Now the church needed a single, careful statement that pulled all three threads together without snapping any of them. That statement came twenty years later.

Chalcedon (451): The Definition

The Council of Chalcedon, held in 451 in a town just across the Bosphorus from Constantinople, gathered around 520 bishops — the largest of the early councils. The triggering controversy this time was Eutychianism, a view that swung in the opposite direction from Nestorianism. Eutyches taught that after the union, Christ had only one nature — a divine nature that had absorbed His humanity like a drop of water in the ocean. Chalcedon needed to reject this without falling back into Nestorianism. Walking that line gave us the most important Christological statement ever written.¹⁰

Here is the core of what they wrote. Read it slowly. It is doing more work than it looks like:

I want to walk through this clause by clause, because the whole rest of the book leans on it.

"One and the same Son" — the unity of the Person

The Definition starts and ends with this. Whatever else is true, there is one Jesus Christ. Not two Jesuses. Not a divine Son in partnership with a human son. One Person. This is the answer to Nestorius.

"Truly God and truly man" — two real natures

The natures are full and genuine. He is not partly God and partly man, not a mix or a hybrid. He is fully both. This is the answer to Eutyches and to Arius simultaneously.

"Of a reasonable [rational] soul and body" — what His humanity contains

This is the line I want us to stop on, because it is the line everyone tends to skim past. The Greek phrase is ek psychēs logikēs kai sōmatos (ἐκ ψυχῆς λογικῆς καὶ σώματος) — "from a rational soul and a body." The council is telling us exactly what Christ's human nature is made of. It is not just a body. It is a rational soul and a body. Both, together, in a single human nature.

This is not generic, decorative language. It is a deliberate anti-Apollinarian clause, lifted directly out of Cyril's earlier confessions and the Formula of Union from Ephesus.¹² Timothy Pawl, in his rigorous philosophical defense of the conciliar texts, points out how often this phrase recurs in the official conciliar documents — in Cyril's letter to Nestorius, in Cyril's letter to John of Antioch, in the Formula of Union, in the Chalcedonian Definition itself, and (we'll see in Chapter 13) in the explicit anathemas of Constantinople II. The church kept saying it because it kept needing to be said. A rational soul and a body.¹³

"In two natures" — the four famous adverbs

Now we come to the heart of the Definition. Christ exists "in two natures, inconfusedly, unchangeably, indivisibly, inseparably." In Greek, that is four crisp adverbs: asynchytōs (ἀσυγχύτως), atreptōs (ἀτρέπτως), adiairetōs (ἀδιαιρέτως), achōristōs (ἀχωρίστως). Each one closes a door that some heresy had tried to open.

Without confusion (asynchytōs). The two natures don't blend into a third hybrid thing. Christ's humanity is not divinized humanity. His divinity is not humanized deity. They remain what they are.

Without change (atreptōs). Neither nature is altered by the union. The divine nature does not lose any of its divine attributes. The human nature does not become superhuman. This is one of the reasons I (with the broader tradition) reject kenotic Christology — a topic I'll defend more fully in Chapter 15.

Without division (adiairetōs). The two natures cannot be split into two persons. There is no "human Jesus" to be played off against "the divine Logos." There is one Christ.

Without separation (achōristōs). The two natures are never pulled apart. They are joined permanently. From the moment of the Incarnation onward, the Son is never not united to His human nature. Never.

That last word — "without separation" — is the one I keep circling back to in my own work. It's small, and the Definition almost slips it in as the fourth in a tidy list. But I think it is the linchpin that holds everything together. It is what guarantees that the Son did not stop being incarnate at the cross. It is what guarantees that the hypostatic union endured through the three days between death and resurrection. And — to give you a taste of the argument coming in Chapter 21 — it is exactly the clause that creates a serious problem for any view that says Christ's humanity is nothing but His physical body. Because if the humanity is just the body, and the body died, then in what sense were the natures still united during those three days? The body in the tomb was no longer a living human nature. So either the union was broken (which Chalcedon forbids), or there was something more to Christ's humanity than His body. Achōristōs demands more.

The "Rational Soul" Clause and the Physicalist Problem

Let me put this as plainly as I can. The Chalcedonian Definition does two things at once:

First, it tells us what Christ's humanity is — "a rational soul and a body."

Second, it tells us that this two-natured Person remains undivided and inseparable forever.

Now suppose someone says, "I believe Chalcedon, but I don't believe in immaterial souls. There's no such thing as a soul. Human beings are purely physical organisms, and Christ's humanity was a purely physical organism too." That is the position of Christian physicalism. And here's the problem: the very thing Chalcedon names as one of the two ingredients of Christ's humanity — a rational soul — is precisely what physicalism says does not exist.¹⁴

This is not a hostile reading of physicalism. The physicalists I've read are clear that they intend to deny the existence of any immaterial mental substance. Joel Green, Nancey Murphy, Kevin Corcoran, and others differ on the details, but they agree that there is no soul as the tradition has used that term. So when Chalcedon says Christ has a psychē logikē, the physicalist must either reinterpret that phrase to mean something the council didn't mean (e.g., "the brain" or "the higher cognitive functions of the body") or admit that they are letting their philosophy of mind override the conciliar text.¹⁵

I want to be fair here. Some physicalist Christians will say, "We're not denying anything Chalcedon meant; we're just denying the metaphysical framework the council assumed." That move is more sophisticated, but I don't think it works. Crisp's careful analysis in Divinity and Humanity shows that the council's "rational soul" language was inherited directly from the anti-Apollinarian struggle, and what Apollinarius denied was precisely an immaterial mental substance distinct from the body. To strip that meaning out of psychē logikē is not interpretation — it is replacement.¹⁶

Wilkinson's recent work on what he calls "Chalcedonian anthropology" sharpens the point. If Chalcedon norms our Christology, and Christ's human nature consists of a rational soul and body, then Christ's human nature norms our anthropology. The man par excellence tells us what mere men are. Body and rational soul. To deny that of human nature in general is, in the end, to deny it of Christ in particular.¹⁷

A Counterargument and Response

One thoughtful objection deserves a hearing here. A physicalist might say: "The conciliar fathers spoke from within a Greek philosophical world. They used the categories available to them. We share their conclusion that Christ is fully human, but we describe the human as a unified physical-psychological organism. We're not denying their faith — we're updating their metaphysics."

That is a charitable framing, and I respect the impulse behind it. But I think it asks the councils to bear a meaning their words cannot bear. The fathers were not casual about the term psychē logikē. They chose it specifically to rule out a view (Apollinarianism) that affirmed Christ's body but denied His human mind/soul. To say "we keep the term but redefine it as the body's higher functions" is exactly the move the councils were trying to forbid. Pawl notes that Conciliar Christology requires a fourth necessary condition: whatever plays the role of the human soul in your model cannot be the divine Person, the divine nature, or the body itself. It must be a created, rational, intellectual soul.¹⁸ That condition is hard to satisfy on physicalism.

Conclusion

Here is what we have seen. From 325 to 451, the church gradually built up a coherent confession of who Jesus is. Nicaea: He is fully God, of one substance with the Father. Constantinople I: He is fully human, body and rational mind, against Apollinarius. Ephesus: He is one Person, not two, against Nestorius. Chalcedon: He is one Person in two complete natures, "of a rational soul and a body," and those natures are joined "without confusion, without change, without division, without separation."

That is the Christological framework I will be using throughout the rest of this book. And it is a framework that — at its most explicit, central, defining moment — declares that Christ has a rational soul. Whatever physicalism is, it is not at home in that framework. The next chapter will press this point further by examining the very heresy this clause was written to refuse: Apollinarianism. There we will see, I think, that the structural logic of Christian physicalism leads to the same Christological result the church condemned over sixteen centuries ago — even though no physicalist intends that result. Conscience is not the same as logic, and the logic, as the councils show, has consequences.

Notes

¹ The four councils discussed here — Nicaea (325), Constantinople I (381), Ephesus (431), and Chalcedon (451) — are recognized as ecumenical by all major Christian traditions (Roman Catholic, Eastern Orthodox, Protestant). The Greek phrase rendered "of a rational soul and body" is ek psychēs logikēs kai sōmatos (ἐκ ψυχῆς λογικῆς καὶ σώματος). For the philosophical defense of these definitions, see Timothy Pawl, In Defense of Conciliar Christology, Oxford Studies in Analytic Theology (Oxford: Oxford University Press, 2016), chap. 1, "The Content of Conciliar Christology." ↩

² For a careful and accessible historical-theological treatment of Arius's position and the Nicene response, see Michael A. Wilkinson, Crowned with Glory and Honor: A Chalcedonian Anthropology, Studies in Historical and Systematic Theology (Bellingham, WA: Lexham Academic, 2024), 134–37. ↩

³ Wilkinson, Crowned with Glory and Honor, 142–45. The Cappadocian Fathers — Basil of Caesarea, Gregory of Nazianzus, and Gregory of Nyssa — completed Athanasius's work in the decades between Nicaea and Constantinople I. ↩

⁴ Wilkinson, Crowned with Glory and Honor, 143–44, citing Athanasius's argument that the Son is "whole God of whole God" (holos theou) and that homoousios "necessarily signified that the Father and the Son share an identity of being." ↩

⁵ Wilkinson, Crowned with Glory and Honor, 138–39. The eventual settlement — one ousia in three hypostases — is the classic Cappadocian formulation that became standard at Constantinople I. ↩

⁶ For Apollinarius's anthropology and Christology, see Wilkinson, Crowned with Glory and Honor, 162–63. The full theological case against Apollinarianism is developed in Chapter 12 of the present volume. See also Joshua R. Farris, An Introduction to Theological Anthropology: Humans, Both Creaturely and Divine (Grand Rapids, MI: Baker Academic, 2020), 168–69, on why Apollinarianism leaves Christ saving "only a part of humanity: the bodily part." ↩

⁷ The contested edges of Nestorius's actual position remain debated by historians, but the position condemned at Ephesus and associated with his name is what concerns us here. See Wilkinson, Crowned with Glory and Honor, 173–80, for a full treatment of the Cyril–Nestorius debate. ↩

⁸ Wilkinson, Crowned with Glory and Honor, 175–77. Cyril's mia physis ("one nature") language was later clarified at Chalcedon and should not be read as denying that Christ has two complete natures; it asserts the unity of the incarnate Word as one concrete reality. ↩

⁹ Cited in Pawl, In Defense of Conciliar Christology, chap. 1, "The Content of Conciliar Christology" (under "The claim that Christ had both a body and a soul"). The phrase "flesh enlivened by a rational soul" appears repeatedly in Cyril's correspondence and in the Formula of Union (433). ↩

¹⁰ For a full philosophical analysis of the Chalcedonian Definition's structure and logic, see Pawl, In Defense of Conciliar Christology, chap. 2, "Definitions and Necessary Conditions." ↩

¹¹ The text of the Chalcedonian Definition as quoted (with minor stylistic adjustments) appears in Wilkinson, Crowned with Glory and Honor, 101. ↩

¹² Pawl, In Defense of Conciliar Christology, chap. 1, "The Content of Conciliar Christology," lists the recurrence of the "rational soul and body" formula across multiple official conciliar documents — Cyril's Second and Third Letters to Nestorius, the Formula of Union from Ephesus (431), the Chalcedonian Definition (451), and the fourth anathema of Second Constantinople (553). ↩

¹³ Pawl, In Defense of Conciliar Christology, chap. 1, "The Content of Conciliar Christology" (under "The claim that Christ had both a body and a soul"): "Christ's possession of both a human soul and a human body is taught in accepted letters, in a Formula of Union, in multiple Definitions of Faith, and, negatively, by anathematizing its denial." ↩

¹⁴ See R. Keith Loftin and Joshua R. Farris, eds., Christian Physicalism? Philosophical Theological Criticisms (Lanham, MD: Lexington Books, 2018), introduction, "Christian Physicalism?: An Introduction," for the framing of Christian physicalism as the rejection of any immaterial mental substance. ↩

¹⁵ Farris, Introduction to Theological Anthropology, 169. Farris notes that for Chalcedonian Christology, the framers' "background assumption seems to be a hylomorphic … anthropology," and that this excludes contemporary versions of materialism. ↩

¹⁶ Oliver D. Crisp, Divinity and Humanity: The Incarnation Reconsidered, Current Issues in Theology (Cambridge: Cambridge University Press, 2007), chap. 2, "The 'Fittingness' of the Virgin Birth" and chap. 3, "Anhypostasia and Enhypostasia in Post-Reformation Reformed Theology." Crisp argues that Apollinarianism fails Chalcedonian orthodoxy precisely because it denies that Christ has a human soul, and any view that produces the same result fails the same test. ↩

¹⁷ Wilkinson, Crowned with Glory and Honor, 32–33, on the methodology of "Chalcedonian anthropology." The argument that Christology norms anthropology — and that physicalism therefore fails not only as a Christology but as an anthropology — is developed more fully in Chapter 7 of the present volume. ↩

¹⁸ Pawl, In Defense of Conciliar Christology, chap. 2, "Definitions and Necessary Conditions": "A fourth necessary condition is that whatever it is that plays the role of the human soul in one's model of the incarnation, that thing cannot be the person of Christ, or the divine nature, or something else divine." ↩