Communicatio idiomatum

“They crucified the Lord of glory.”

— 1 Corinthians 2:8

The communicatio idiomatum (“communication of properties”) is the principle that what belongs to either of Christ’s two natures may rightly be said of his one person: the Son of God, as a single subject, can truly be said to have suffered and died (a property of his human nature) and to be eternal and almighty (a property of his divine nature). Reformed theology holds that this communication happens at the level of the person, not between the natures themselves: nothing that is true of Christ’s humanity becomes true of his deity, or the reverse.¹ Girolamo Zanchi’s formula, as Duby summarizes it: the communication is “real” with respect to the person, though “verbal” with respect to the other nature as such.²

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.”³ Because the union is “without… confusion,” the properties of each nature stay that nature’s own; the confession locates the union in the one person, not in a merger of the natures’ properties. Herman Bavinck states the same point of Reformed Christology generally: “it was the person of the Son who became flesh… It was not the substance… but the subsistence… of the Son that assumed our nature. The unity of the two natures is unalterably anchored in the person.”⁴

Biblical Basis

Scripture routinely predicates one nature’s properties of Christ under a title drawn from the other nature, which is exactly the pattern the communicatio idiomatum names. Paul tells the Ephesian elders to shepherd “the church of God, which he obtained with his own blood” (Acts 20:28): blood belongs to Christ’s human nature, but it is said of “God.” Paul likewise says the rulers of this age “crucified the Lord of glory” (1 Cor. 2:8): crucifixion belongs to the human nature, while “Lord of glory” names the person by his deity.² In neither case does the text say that God’s nature bled or that a human being is intrinsically glorious; it predicates a property of one nature to the single person under a title supplied by the other nature.

Historical Development

The Council of Chalcedon (AD 451) settled that Christ is “one person in two natures, without confusion, without change, without division, without separation,” but later theology split over what that formula permits.⁴ Roman and Scholastic theology held that properties are really communicated from the divine nature to the human nature itself, commonly illustrated by heat permeating iron until it glows: on this view Christ’s humanity was “divinized” from the moment of conception, sharing directly in divine glory, wisdom, and power.⁴

Lutheran theology placed the communication at the level of the person rather than the human nature as such, but still held that the two natures were “united and commingled” with each other’s properties, which in practice meant Christ’s humanity received attributes like omnipresence.⁴ Extra calvinisticum covers this Lutheran “ubiquity” dispute and Charles Hodge’s Reformed response to it at greater length. A later, internal Lutheran dispute (the Giessen and Tübingen schools, 1607-1624) split further over whether Christ merely concealed the communicated divine attributes during his earthly humiliation or ceased, in some sense, to use them at all until his exaltation.⁴

Reformed theology applied the maxim finitum non capax infiniti (the finite cannot contain the infinite) to Christ’s exaltation as well as his humiliation, denying that his human nature ever acquires divine properties at any stage. This secured room for a genuinely human development in Christ’s life while anchoring the union in his person rather than in the natures’ substance.⁴

Opposing Views

Roman Catholic / Scholastic. Properties are really communicated from the divine nature to the human nature itself. Christ’s humanity is divinized from conception onward, sharing directly in divine glory, wisdom, and power, and so is held to be worthy of worship in its own right.⁴

Lutheran. The communication is to the person, but the two natures are still held to be “united and commingled” with each other’s properties, so that Christ’s human nature comes to share attributes like omnipresence. See Extra calvinisticum for the fuller history of this dispute and the Reformed response to it.⁴

Objections and Responses

If properties aren’t really shared between the natures, verses like Acts 20:28 and 1 Corinthians 2:8 must be loose or merely figurative language. The Reformed answer is that the communication is real, but real of the person: Christ truly shed his own blood, and the one who was crucified truly is the Lord of glory, because the single person who did these things is truly both God and man. What is denied is only that either property crosses over to the other nature itself, not that its predication to the person is real and true.²

Denying a real communication between the natures makes the union too loose, verging on Nestorianism. Bavinck’s answer is that the opposite follows in practice: consistently applying finitum non capax infiniti to Christ’s exaltation as well as his humiliation is precisely what lets Reformed theology hold a genuinely human, developing Christ alongside a truly divine one. Treating his humanity as already glorified or omnipresent from birth, as the Roman and Lutheran views do, is what turns his human development into “mere appearance.”⁴

Related Doctrines

References

Matthew Barrett, None Greater: The Undomesticated Attributes of God (Grand Rapids: Baker Books, 2019), s.v. “communicatio idiomatum.” ↩
Steven J. Duby, God in Himself: Scripture, Metaphysics, and the Task of Christian Theology, Studies in Christian Doctrine and Scripture (Downers Grove, IL: IVP Academic, 2019), chap. 4, “Theology and Metaphysics Revisited,” 227-228. ↩ ↩² ↩³
The Second London Baptist Confession of Faith (1689), chap. 8, “Of Christ the Mediator,” para. 2. ↩
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.” ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹