The Communicatio Idiomatum

The communicatio idiomatum, or communication of idioms¹, is the Church’s disciplined rule for speaking truly of the one Lord Jesus Christ. It states that there is a single personal subject, the eternal Son, to whom all predicates are rightly attributed, some according to the divine nature and some according to the human nature. The predicates are not swapped between natures, nor are the natures blended, but every statement that Christians make about Jesus has the same referent. The one who is eternally begotten of the Father is numerically the same person who was born of Mary, suffered under Pontius Pilate, died, rose, and reigns. Because the subject is one and the natures are two, the Church attaches predicates with the reduplicative instrument according to, so that birth, growth, suffering, death, and finite knowing are said of the Son according to the assumed humanity, while creating, sustaining, judging, and infinite knowing are said of the same Son according to the uncreated divinity. The rule does not create a verbal trick. It expresses the ontological fact of the hypostatic union: one person in two natures without confusion, change, division, or separation. Hence Mary is Theotokos because she bore, according to the flesh, the very Word made flesh, and hence the Church dares to say that one of the Trinity suffered in the flesh, while insisting that the divine nature as such remains impassible.

This rule presupposes and safeguards divine simplicity and triune life. God is not a solitary monad. The one essence subsists as Father, Son, and Holy Spirit in relations of origin, and this perichoretic simplicity means that there is no second act in God when the Son assumes our nature. The Incarnation is not a new event in God but a new created terminus of the one necessary and simple act in creatures. Aspect grammar gives this precision: viewed in itself, the divine act is necessary and eternal; viewed with respect to creatures, the same act freely specifies contingent effects in time and place. Cambridge change locates the newness in the world, not in the divine essence. When we confess that God became man we mean that the same hypostasis who is eternally God now also subsists in a created human nature; the novelty lies entirely in the humanity that begins to exist, while God remains who God is. This asymmetry lets the Church speak with daring confidence across the union without turning God into a temporal process or dissolving history into an illusion.

Because identity in God is by provenance, and because the person is the seat of identity, the communicatio idiomatum begins by fixing the subject of every sentence. Jesus, the Christ, the Son, the Word pick out the same who in every true predication. That univocity of reference at the level of the person anchors language and devotion. Once the subject is fixed, the predicates are distributed according to the two natures, which preserves the analogical interval between Creator and creature. The divine is uncreated, simple, and impassible; the human is created, finite, and passible. The interval is not erased in Christ; it is personally bridged. The rule therefore never migrates properties from one nature into the other. It attaches them to the person with the right mode. God suffered, according to the flesh. This man upholds all things, according to the divine power. Such sentences name the same who and honor the distinct what in which the who subsists.

Dionysian apophasis supplies a perpetual guardrail for this bold speech. We affirm from effects, we negate every limit that our affirmations smuggle in, and we consent to silence where words fail. This discipline keeps us from importing passibility into the divinity or evaporating the concreteness of the humanity. It also emboldens the strong names the councils require. The Good remains itself, proceeds through all, and returns all to itself. In Christ that rhythm is enacted historically. The Son remains what he is. He proceeds into history by assuming a mortal life. He returns all to the Father by perfect filial obedience. The communicatio idiomatum is nothing other than the grammar that allows the Church to say this truth without shrinking from transcendence or from the scandal of the cross.

Przywara’s rhythm essence in and beyond existence explains why Christ’s humanity is neither crushed nor sidelined in this union. The assumed nature retains its proper form and operations. It acts, suffers, learns, and wills in a truly human way, now sustained and elevated by grace of union. The grace of union crowns nature without abolishing it. The communicatio idiomatum names how this crowned nature functions as the instrument and locus of the one subject’s saving work. Because the person is one, what the humanity does is the work of the Son. Because the natures remain distinct, the human action is not converted into a divine operation nor the divine into a human one. The same Son operates divinely with the divine will and operation, and humanly with the human will and operation, and the unity of agent secures the unity of the saving history.

Doctrinally the rule gathers the great Christological settlements into one coherent speech. Ephesus secures the single subject in the confession of Theotokos. Chalcedon secures the distinction of natures and their integrity. Constantinople II sharpens the classic formula one of the Trinity suffered in the flesh. The later councils on wills and operations in Christ guard the truth that the human will and operation are real and active. The communicatio idiomatum is the living logic that lets these judgments govern preaching, catechesis, prayer, and sacrament. Preaching fixes the subject and then distributes predicates according to nature. Catechesis trains the ear to hear the according to that protects truth. Prayer addresses one Lord and confesses both his humility and his majesty. Icons show one face and teach by line and color what the councils teach by words. The sacraments enact the same grammar at the altar and the font.

In the Eucharist the rule is tested and perfected. The one who is seated at the right hand of the Father is truly present per substantiam under consecrated signs. The presence is personal according to the humanity, for the body and blood of Christ are present by the power of his word and Spirit; the adoration is directed to the same person who is God. There is no split subject that would reduce the sacrament to a distant symbol, and there is no confusion that would treat the divine essence as locally contained. By Cambridge change the presence here and now is a new relation in us and in the consecrated elements, not a change in God. The analogical interval keeps the mode of presence human and sacramental. The identity of the person guarantees that the Church truly adores the Lord.

The rule also answers the old heresies inside a single grammar. Nestorian anxiety vanishes because there is no duplication of subjects; the one who is born of Mary is the very Son. Monophysite blur is excluded because the properties of each nature remain and operate. Patripassian confusion is averted by reduplication; the Father does not suffer, yet one of the Trinity suffered in the flesh because the Son is the suffering subject according to the assumed humanity. Arian lowering is blocked because the one we name is consubstantial with the Father, so the human predicates magnify his humility without diminishing his divinity. The same rule that disciplines predication guards worship, since the name we adore names one Lord.

Finally, the communicatio idiomatum is a pastoral grammar of salvation. As God the Son gives. As man he receives and returns. He learns obedience in a human will and offers perfect filial love in a human heart. He dies a human death and rises with a glorified human body. Baptism incorporates us into this one person’s death and rising. The Eucharist feeds us with this one person’s self-gift and makes the many one body in him. Moral and contemplative life become right reception of the Gift, since the Church learns to speak and to live according to the same rule. The definition therefore is not a scholastic curiosity. It is the nerve of Christian confession and the pattern of Christian worship. One subject carries every saving predicate. Two natures determine the mode of each. All novelty is in creaturely termini. All glory is of the one Lord Jesus Christ, true God and true man, to whom be praise with the Father and the Holy Spirit, now and forever.

1. This link is the full treatment of the doctrine. Enjoy the fuller treatment here if you need another 7000 words on the subject 😉 The Communication of Idioms – RobertDryer ↩︎