Is Christ one nature or two natures in one person?

Tertullian c. 155–c. 220 ADAgainst Praxeas 27.11

We see a twofold state, not confused but joined in one person, God and the man Jesus. ... And so the property of each substance is kept safe, that the Spirit did its own things in him, that is, powers and works and signs, and the flesh underwent its own sufferings: hungry under the devil's temptation, thirsty with the Samaritan woman, weeping for Lazarus, troubled even to death, and at last dead.

Over two centuries before Chalcedon, Tertullian already speaks of two substances, unconfused, in one person.

Gregory of Nazianzus c. 329/330–390 ADLetter 101, to Cledonius 101.19–20

There are two natures, God and man, since there are also soul and body; but not two sons, nor two gods. ... To put it briefly: the elements from which the Savior is made are one thing and another (since the invisible is not the same as the visible, nor the timeless as what is in time), but he is not one person and another. God forbid!

Gregory's "two natures, one Son" became the shared starting point of the later debate. Both Chalcedonians and their opponents quoted him.

Council of ChalcedonDefinition of the Faith Definition

acknowledged in two natures which undergo no confusion, no change, no division, no separation

The council's definition. It was meant to rule out both merging the natures (Eutyches) and dividing Christ into two (as Nestorius was accused of doing).

Sophronius of JerusalemSynodical Letter PG 87.3, cols 3172B-C

Just as, then, we believe in the union of each of the two essences and natures (the essences and natures from which the union in Christ has come to be for us without confusion, and has made him the one Christ and Son, wholly God, and the same one wholly man), so too we confess the natural operation of each, lest we confuse the natures that were united without confusion; since, according to those who are skilled in such matters, natures are known from their operations, and from their operations alone.

Writing to Sergius of Constantinople in 634, Sophronius refuses the compromise of one “composite” operation: because the two natures remain unconfused in the one Christ, each keeps its own natural operation — the argument the Sixth Ecumenical Council (680–681) later vindicated for Christ’s two wills as well. The Greek was transcribed from the page images of Migne PG 87.3 for the Via Patrum library (2026); the scan’s Greek OCR is unreliable and was not used.

Ethiopian Orthodox Tewahedo ChurchThe Faith of the Church On the Incarnation

On this ground the Church of Ethiopia, with the other Oriental Orthodox Churches, affirms that Jesus Christ is not two natures, but one incarnate nature of God the Word.

The Oriental Orthodox churches (Coptic, Ethiopian, Armenian, Syriac, Indian) follow Cyril's phrase "one incarnate nature of God the Word" and reject Chalcedon's "in two natures". They also reject any mixing of the natures.