Ecumenical Councils

Affirmed the full deity of the Son against Arianism. The Son is declared homoousios (of one substance) with the Father — not a created being or lesser deity.

Key Definition We believe in one Lord Jesus Christ, the Son of God, begotten of the Father, Light of Light, very God of very God, begotten not made, being of one substance (homoousios) with the Father.

Key Anathema Those who say 'there was when he was not,' or 'before he was born he was not,' or 'he was made from things that were not,' or assert he is of a different substance or essence from the Father, or that he is created or mutable — these the catholic church anathematizes.

The First Council of Nicaea (325 AD) condemned the Arian teaching that the Son was a created being subordinate to the Father. The council affirmed the Son as homoousios (of the same substance) with the Father, establishing the foundation of Trinitarian orthodoxy and the full deity of Christ. The Nicene Creed (in its original 325 form, expanded at Constantinople 381) flows directly from this council's decision.

Affirmed the full deity of the Holy Spirit against Macedonianism (Pneumatomachi), and expanded the Nicene Creed to include the procession and deity of the Spirit.

Key Definition We believe in the Holy Spirit, the Lord and Giver of life, who proceeds from the Father, who together with the Father and the Son is worshipped and glorified.

Key Anathema Condemned those who denied the full personhood and deity of the Holy Spirit, completing the Trinitarian formulation of Nicaea.

The First Council of Constantinople (381 AD) completed the Nicene formulation by explicitly affirming the deity and personhood of the Holy Spirit against those who accepted the Nicene affirmation of the Son but reduced the Spirit to a subordinate force or creature. The council produced the expanded Niceno-Constantinopolitan Creed — the creed recited in Christian worship to this day. It also affirmed the full humanity of Christ against Apollinarianism.

Affirmed the unity of Christ's person against Nestorianism. Mary is rightly called Theotokos (God-bearer / Mother of God), confirming that the one born of her is truly God incarnate, not merely a human person dwelling with the divine Word.

Key Definition If anyone does not confess that the Emmanuel is in truth God, and that the holy Virgin is therefore Mother of God (Theotokos), since she bore according to the flesh the Word of God who became flesh — let him be anathema.

Key Anathema Condemned Nestorius for effectively dividing Christ into two persons — a human Jesus and the divine Word dwelling in him — rather than one divine person in two natures.

The Council of Ephesus (431 AD) condemned Nestorius, who resisted calling Mary 'Theotokos' on the grounds that she bore the human nature of Christ, not the divine Word. The council, led by Cyril of Alexandria, affirmed that the divine Word and the human Jesus are not two persons loosely united but one undivided person. The Theotokos affirmation is therefore a Christological statement, not a Marian one: it protects the unity of the incarnate Son.

Defined the two natures of Christ — fully divine and fully human — united in one person, without confusion, change, division, or separation. The Chalcedonian Definition is the standard for orthodox Christology in all major Christian traditions.

Key Definition We teach one and the same Christ, Son, Lord, only-begotten, in two natures, without confusion, without change, without division, without separation — the distinction of natures being in no way annulled by the union, but rather the characteristics of each nature preserved and coming together to form one person and subsistence.

Key Anathema Condemned Eutychianism (which confused the two natures, absorbing humanity into divinity) and reaffirmed the rejection of Nestorianism (which divided the person). The four 'withouts' — without confusion, change, division, or separation — are the four boundary markers of orthodox Christology.

The Council of Chalcedon (451 AD) produced the definitive formulation of orthodox Christology. Against Eutyches, who taught that Christ's humanity was absorbed into his divinity after the incarnation (Monophysitism), and against lingering Nestorian tendencies, the council declared Christ to be one person in two natures. The Chalcedonian Definition's four negative adverbs — without confusion, change, division, or separation — mark the boundaries of orthodox speech about the incarnation, ruling out both a blended middle nature and a divided double person.