The Chalcedonian Definition (Dyophysitism)

The Story

For most of Western and Eastern Orthodox Christianity, the Definition issued by the Council of Chalcedon in 451 is not a heresy at all — it is the very benchmark by which heresies are measured. It declares that Jesus Christ is “one and the same Son,” acknowledged “in two natures” (divine and human), and that these natures are joined in a single person and hypostasis “without confusion, without change, without division, without separation.” This is the formula Catholics, the bulk of the Eastern Orthodox, and the mainstream of Protestantism still recite as the boundary of right belief.

And yet, from the moment the bishops rose from the fifth session at Chalcedon, a very large portion of the Christian world refused to sign. To them, the Definition was not the solution to the Christological crisis but a betrayal of it — a smuggling of Nestorius’s two-Christs back in through the side door. Within a generation, churches across Egypt, Syria, Armenia, and beyond had broken communion over it. That breach has never fully healed.

The Definition was assembled under pressure. Two years earlier, the so-called “Robber Synod” of Ephesus (449) had rehabilitated the monk Eutyches and deposed his opponents; the Tome of Pope Leo I, a letter insisting that Christ’s two natures each retained their own properties, was never read into the record there. Chalcedon reversed all of it. Leo’s Tome was read into the record and acclaimed, Eutyches’s teaching of a single blended nature was condemned, and the commission — papal legates alongside Anatolius of Constantinople, Maximus of Antioch, Juvenal of Jerusalem, and others — hammered out a text meant to satisfy both the Alexandrian instinct for unity and the Antiochene instinct for distinction.

It satisfied neither party fully. The Alexandrian tradition, following Cyril, had spoken of “one incarnate nature of God the Word,” and to hear Chalcedon say “in two natures” sounded like dividing Christ. The churches that kept Cyril’s language — the Coptic, Armenian, Ethiopian, Syriac, and related communions, numbering perhaps sixty million faithful today and usually called the Oriental Orthodox — held instead to miaphysitism: one united nature, divine and human, combined “without separation, without confusion, and without alteration.” Crucially this is not Eutyches’s idea of humanity swallowed up by divinity; the miaphysite confesses Christ fully human and fully divine in one composite nature. The disagreement with Chalcedon was over how to count, and what “nature” meant.

In the modern period the picture has grown stranger still. Beginning in the 1970s and accelerating through the 1980s and 1990s, formal dialogues between the Catholic Church and the Oriental Orthodox produced signed christological agreements — the 1973 Paul VI–Shenouda III declaration, the 1988 common formula, and parallel statements with the Syriac and Armenian churches — concluding that both sides had, in fact, confessed the same Christ in different vocabularies. The ancient anathemas, they judged, rested largely on a verbal misunderstanding. If they are right, then Chalcedon condemned a heresy that, on inspection, was never there.

Who Draws the Line

There was no single council that “condemned” the Chalcedonian Definition; it was itself the act of a council. But three large families of churches have, at various times, treated it as the error rather than the cure.

The Oriental Orthodox rejected it at once and have never received it as ecumenical. Their objection was that Chalcedon’s “in two natures” (en duo physesin) implicitly divided the one Christ and so amounted to crypto-Nestorianism — the very thing Cyril of Alexandria had fought. They confess only the first three councils (Nicaea, Constantinople, Ephesus) and stop there.

The Assyrian Church of the East stands at the opposite pole and is equally outside the Chalcedonian settlement. It never accepted the Council of Ephesus (431) that condemned Nestorius, and it preserves an Antiochene “two-natures” Christology that Chalcedonians historically branded Nestorian — though the Assyrian Church rejects that label and has never anathematized the man Nestorius. To Chalcedon’s heirs it was too divided; to the Oriental Orthodox, Chalcedon itself leaned in the Assyrian direction.

Even where Chalcedon reigns, its authority rests on contested grounds: which body of bishops counts as binding, and whether an emperor’s enforcement (Marcian convened and pressed the council) confers truth. The line between orthodox and heretic here was drawn by the churches that won imperial backing — and the churches that lost it have spent fifteen centuries insisting the line was drawn in the wrong place.

Why You Might Accidentally Believe This

If you have ever said that Jesus “got tired and hungry as a man but could forgive sins as God,” you have reasoned your way toward Chalcedon. The Gospels show a figure who sleeps in a boat and stills the storm, who weeps at a grave and raises the dead. The plainest way to hold both is to say there are two registers in him — a genuine humanity and a genuine divinity — neither absorbing the other. That is the Chalcedonian instinct before it becomes a formula.

The four negative adverbs feel like simple honesty rather than dogma. You do not want to say the divine melted into the human (that loses God), nor the human into the divine (that loses a real man), nor that there are two separate sons walking around. “Without confusion, without division” is what you reach for when you refuse to round Jesus off in either direction and would rather leave the mystery standing than resolve it falsely.

The Strongest Case For This View

The scriptural backbone is the insistence that the same one who is divine is also fully, ordinarily human. John 1:14 says “the Word became flesh and dwelt among us” — became flesh, not merely seemed to, and the Word remains the Word. Hebrews makes the humanity load-bearing: Christ was made “like his brothers in every respect” (Hebrews 2:17) and “in every respect has been tempted as we are, yet without sin” (Hebrews 4:15). A savior who only appeared human, or whose humanity was swallowed by deity, could not stand in for human beings. On this reading, two intact natures are required for the logic of salvation to work.

At the same time, Chalcedonians insist, the unity is non-negotiable: it is one person who is at once Lord and tired traveler. They point to texts where divine and human are said of the same single subject — the Lord of glory is crucified (1 Corinthians 2:8), the church of God is “obtained with his own blood” (Acts 20:28). To preserve both the unity and the two-sidedness, the defenders argue, you need a vocabulary that says one who (person) and two whats (natures). That is exactly the distinction Chalcedon codified.

The four adverbs do precise defensive work. Without confusion (Greek asynchytōs) and without change (atreptōs) guard against Eutyches and the idea that the natures blend into a third thing or that God mutates. Without division (adiairetōs) and without separation (achōristōs) guard against splitting Christ into two acting subjects. Each adverb fences off a real error people actually taught. Far from being abstract, the formula is a map of the wrong turns, marking each one as out of bounds.

The Strongest Case Against

The miaphysite objection is that you cannot speak of “two natures” after the union without quietly implying two subjects, two acting agents — and that is Nestorius in disguise. Cyril of Alexandria, whom both sides claim, taught “one incarnate nature of God the Word.” To his heirs, abandoning that for Chalcedon’s “in two natures” was not refinement but capitulation to Antioch. They argue that a nature in a living being is never abstract; it always belongs to a someone, so two natures threaten two someones. One Christ, they insist, means one concrete reality, not a pair held together by a label.

The Antiochene and Assyrian objection runs the other way: that Chalcedon, by binding the natures so tightly in one hypostasis, risks letting the divine swallow the human and risks ascribing suffering and death directly to the impassible God. They preferred to safeguard the full integrity of the manhood, even at the cost of language Chalcedonians found too loose. From this angle Chalcedon is not too Nestorian but not careful enough about what may and may not be said of God.

There is also a sharper, more modern complaint shared by Biblical Unitarian and other critics: that the whole apparatus of “one hypostasis in two natures” is a fourth- and fifth-century philosophical construction that the New Testament writers would not have recognized. The words physis and hypostasis do appear in scripture, but never in the technical senses Chalcedon assigns them. To these critics, the Definition does not so much report what the apostles believed as build a metaphysical scaffolding around it — and a scaffolding that, by its own framers’ admission, could be read as heresy from either side. The very fact that sixty million Christians have rejected it as Nestorian, while others reject it as monophysite-adjacent, suggests the formula does not so much resolve the tension as relocate it.

What the New Testament Actually Says

The New Testament gives Chalcedon its raw materials but not its terminology. It plainly presents a Jesus who hungers, sleeps, grieves, dies — and one to whom worship, divine titles, and a share in creation are attributed in texts such as John 1:1-3, Colossians 1:15-20, and Philippians 2:6-11. What it does not do is supply the metaphysical apparatus of “one person in two natures,” nor does it ever state the later Trinitarian formula in so many words. That distinction between person and nature, the term homoousios, and the four adverbs that police it are all post-biblical interpretive tools — worked out across the second to fourth centuries and fixed at Nicaea (325) and Constantinople (381) — however well-motivated their framers believed them to be.

Several key texts cut more than one way. Philippians 2 describes Christ as being “in the form of God” yet taking “the form of a servant.” Chalcedonians and other Trinitarians read this as a divine person assuming a second, human nature; miaphysites read it as one self-emptying subject; and Biblical Unitarian readers take the same passage as the exaltation of a genuinely human Messiah — the unique Son whom God “highly exalted” and gave “the name that is above every name” (Philippians 2:9-11) — not a statement about a second co-equal deity. Colossians 1:15 calls him “the firstborn of all creation”; the same words have anchored opposite christologies for sixteen centuries, read by some as the eternal Word through whom all things were made and by others as the supreme place given to the risen man over a renewed creation. The grammar does not decide between them.

The “deity of Christ” argument and the “only God can save” argument belong to the Trinitarian side of this dispute, not to the narrator. Trinitarians point out that the New Testament applies to Jesus titles, worship, and works the Old Testament reserves for the one God, and reason that a savior who reconciles the world to God must himself share the divine identity — “in him the whole fullness of deity dwells bodily” (Colossians 2:9), the Word who “was God” (John 1:1), confessed by Thomas as “my Lord and my God” (John 20:28). Biblical Unitarians answer that throughout the New Testament it is God the Father who saves, and that he does so through his exalted human Son — “there is salvation in no one else” said of the man God raised from the dead (Acts 4:10-12), “one mediator between God and men, the man Christ Jesus” (1 Timothy 2:5), who “offered for all time a single sacrifice for sins” (Hebrews 10:12). Both sides read the very same passages; the texts constrain the options without settling them.

This is the honest core of the matter. The NT rules out some readings — a Jesus who is merely a phantom, or a Christ with no real exaltation at all, or a man elevated only by accident, will struggle with the data — but it underdetermines the precise solution. Chalcedon, miaphysitism, the Antiochene scheme, and modern Unitarian readings are all attempts to systematize the same scattered evidence. The Definition is one answer to a question the apostolic writers left open, and the existence of ancient, learned, devout churches on every side is the best proof that the text alone did not force the conclusion.

Further Reading

• John Anthony McGuckin, Saint Cyril of Alexandria and the Christological Controversy (1994)
• Aloys Grillmeier, Christ in Christian Tradition, Volume 2 (1987, with later parts)
• Richard Price and Michael Gaddis, The Acts of the Council of Chalcedon (3 vols., 2005)
• Frances M. Young, From Nicaea to Chalcedon: A Guide to the Literature and Its Background (2nd ed., 2010)
• V. C. Samuel, The Council of Chalcedon Re-Examined (1977) — a sympathetic Oriental Orthodox account
• Sebastian Brock, “The ‘Nestorian’ Church: A Lamentable Misnomer,” Bulletin of the John Rylands Library (1996)