Hypostatic union

“And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth.”

— John 1:14 (ESV)

The hypostatic union is the doctrine that the one person of Jesus Christ subsists in two complete natures, divine and human, without either nature being changed, mixed, divided, or separated. The name comes from hypostasis, the Greek term the church settled on for an individual, personal subsistence: the “union” is a union of two natures in one hypostasis, not a blending of the natures into a third thing.¹ Communicatio idiomatum and extra calvinisticum describe consequences of this union — how the properties of each nature relate to the one person who bears them both.

Confessional Definition

The 1689 Second London Baptist Confession states that Christ’s two natures “were inseparably joined together in one person, without conversion, composition, or confusion; which person is very God and very man, yet one Christ, the only mediator between God and man.”² Each of those four negatives rules out a historic error: “conversion” would turn one nature into the other; “composition” would blend them into a third; dividing the person produces two Christs instead of one; confusing the natures erases the real distinction between them. The sections below trace how the church arrived at exactly these four guardrails.

Biblical Basis

John opens his Gospel by identifying Jesus as the eternal Word who “was with God, and the Word was God” (John 1:1), then states plainly that “the Word became flesh” (John 1:14): the same subject who is God takes on flesh, rather than a second being appearing alongside him. Luke records that the child Jesus “increased in wisdom and in stature and in favor with God and man” (Luke 2:52), a genuinely human development Scripture never treats as compromising his deity elsewhere affirmed.

Historical Development

The doctrine took shape through a sequence of councils, each ruling out an inadequate way of stating how Christ’s two natures relate in his one person. Apollinarianism was condemned at the Council of Constantinople in AD 381. Nestorianism arose next, from Nestorius’s objection to calling Mary “Mother of God.” A synod at Ephesus in AD 449, remembered in history as “the robber council,” then sanctioned the opposite error, Eutychianism.³

A second council met at Chalcedon in AD 451, deposed the bishops responsible, and adopted Pope Leo’s letter to Flavian of Constantinople as “a true exposition of the faith of the Church.” Working from that letter, the council produced the Chalcedonian Definition: Christ is “perfect as respects Godhead, and perfect as respects manhood… consubstantial with the Father as to his divinity, and consubstantial with us as to his humanity… one and the same Christ… existing in two natures without mixture, without change, without division, without separation; the diversity of the two natures not being at all destroyed by their union in the one person, but rather the peculiar property of each nature being preserved, and concurring to one person, and one subsistence.”⁴ This was one of six general councils whose doctrinal decisions “all Protestants, at the time of the Reformation, professed their agreement” with.⁴

Chalcedon did not end the conflict. Roughly two centuries later, Emperor Heraclius tried to reconcile the remaining parties by proposing two natures but only one will and operation, a position called Monothelitism; the orthodox majority rejected it, holding that two natures implies two wills.

Opposing Views

Apollinarianism. The divine Logos itself took the place of Christ’s rational soul, rather than the Son assuming a complete human nature that included a genuinely human mind.³

Nestorianism. Either affirms, or was understood to imply, a twofold personality in Christ: the divine Logos “dwelling in” the man Jesus much as the Spirit indwells believers, rather than being personally united to a human nature so as to constitute a single person.³

Eutychianism. Christ’s two natures existed only before the union and fused into one afterward, so that after the incarnation he has a single, blended nature rather than two distinct ones.³

Kenotic “single rational element” Christology. A 19th-century theory held that the divine Logos itself became, or directly served as, Christ’s human soul during the incarnation, so that no separately created human soul was needed. Its proponents denied being either Apollinarian or Eutychian.

Objections and Responses

Denying Christ a human mind still leaves him fully divine and fully capable of saving us. The church’s answer, against Apollinarianism, was that a Redeemer who lacked a genuinely human mind wasn’t a genuinely human Redeemer: it was convinced Christ had to be “a perfect man, possessing within Himself all the elements of our nature.”³

Calling Mary “Mother of God” makes a creature the source of deity. This was the charge against Nestorius, and Hodge notes it turns entirely on what the title is taken to mean: there is a sense in which it is true (she is the mother of the one person who is God, in his human nature) and a sense in which it would be blasphemous (that she is the source of his deity, which no one actually taught). Nestorius’s own objection to the title was to the second sense; the church’s insistence on keeping it was to protect the first, since denying Mary that title on Nestorius’s terms risked implying Christ’s humanity belonged to a separate person from his deity.³

Fusing the two natures into one still leaves Christ a single, unified Redeemer, which is what a real union should look like. Hodge answers that fusing the natures produces a third thing that is neither God nor man, “as in chemical combinations an acid and an alkali when united, produce a substance which is no longer either acid or alkaline”: a Christ who is genuinely both God and man requires two distinct natures preserved in union, not one blended nature that is strictly speaking neither.⁴

The kenotic theory avoids Apollinarianism and Eutychianism; it isn’t either of those condemned views. Hodge’s answer is that it revives both under a new label: “it agrees… with the Apollinarians in saying that the Logos was the rational element in Christ; and it agrees with the Eutychians in saying that Christ had but one nature.” It also denies Christ had two wills, which the Council of Constantinople’s decision against Monothelitism had already settled follows necessarily from having two natures.⁵

Related Doctrines

References

Herman Bavinck, Reformed Dogmatics: Abridged in One Volume, ed. John Bolt (Grand Rapids: Baker Academic, 2011), chap. 14, “The Only Begotten Son of the Father.” ↩
The Second London Baptist Confession of Faith (1689), chap. 8, “Of Christ the Mediator,” para. 2. ↩
Charles Hodge, “Chapter III. Person of Christ,” in Systematic Theology, Volume II (New York: Charles Scribner and Company, 1872), 399-401. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶
Hodge, 401-402. ↩ ↩² ↩³
Hodge, 436-437. ↩