The Council of Chalcedon (451), which condemned Eutyches (advocated an extreme version of Cyril’s doctrine of the one nature in Christ), tried to steer a middle course between Nestorianism and Monophysitism. Although it uses the term Theotokos, the Persian Church accepted it, while rejecting the decisions of the Council of Ephesus. The Monophysites accepted Ephesus , and rejected Chalcedon. This definition summarizes the orthodox doctrine of Christ.
[The Synod] opposes those who would rend the mystery of the incarnation into a duality of Sons (1); it expels from the priesthood those who dare to say that the Godhead of the Only-begotten is passible/capable of suffering (2); it resists those who imagine a mixture or confusion of the two natures of Christ (3); it drives away those who fancy that the ‘form of a servant’(4) which he took from us was of a heavenly of some other (5) substance (6); and it anathematises those who imagine that the Lord had two natures before their union, but only one afterwards (7).
After the example of the holy Fathers, we all with one voice confess our Lord Jesus Christ one and the same Son, the same perfect in Godhead, the same perfect in manhood, very God and very man, the same consisting of a reasonable soul and a body, of one substance (8) with the Father as touching the Godhead, the same of one substance (9)
with us as touching the manhood, like us in all things, sin excepted; begotten of the Father before the worlds as touching the Godhead, the same in these last days, for us and for our salvation, born of the Virgin Mary, the Mother of God (10), as touching the manhood - one and the same Christ, Son, Lord, Only-begotten, to be acknowledged in two natures, without confusion, without conversion (11), without division, never to be separated (12); the distinction of natures being in no wise done away because of the union, but rather the characteristic property of each nature being preserved, and concurring into one Person (13) and one Subsistence (14), not as if Christ were parted or divided into two Persons, but one and the same Son and Only-begotten God, Word, Lord, Jesus Christ; even as the Prophets from the beginning spoke concerning Him, and our Lord Jesus Christ has instructed us, and the Symbol of the Fathers has handed down to us.