Chalcedonian Definition in the context of "Typos of Constans"

The Chalcedonian schism, also known as the Monophysite schism, is the break of communion between the Oriental Orthodox Churches and the Great Church (which later became the Eastern Orthodox Church and Catholic Church) in the aftermath of the Council of Chalcedon. Although the bishops at Chalcedon greatly respected Cyril of Alexandria and used his writings as a benchmark for orthodoxy, opponents of the council believed that the Chalcedonian Definition, which states that Christ is "acknowledged in Two Natures", was too close to Nestorianism and contradicts Cyril's formula "one nature of God the Word incarnate". The Council had also deposed the Pope of Alexandria, Dioscorus, but his supporters continued to consider him their rightful Pope, refusing to recognise the council-appointed Proterius.

The anti-Chalcedonian strongholds were in Egypt, Palestine and later Syria. Over the next century, their communities gradually separated from the official church of the Byzantine Empire, eventually becoming the Oriental Orthodox Churches. The imperial government made many attempts to mend the schism, generally by trying to compromise between the two positions, but these attempts only created further heresies and schisms. The Arab conquests of the Levant and of Egypt in the 7th century fossilised the schism, but ecumenical dialogue between Chalcedonian and non-Chalcedonian Christians has been renewed since the 20th century.

The Council of Chalcedon (/kælˈsiːdən, ˈkælsɪdɒn/; Latin: Concilium Chalcedonense) was the fourth ecumenical council of the Christian Church. It was convoked by the Roman emperor Marcian. The council convened in the city of Chalcedon, Bithynia (modern-day Kadıköy, Istanbul, Turkey) from 8 October to 1 November 451. The council was attended by over 520 bishops or their representatives, making it the largest and best-documented of the first seven ecumenical councils. The principal purpose of the council was to re-assert the teachings of the ecumenical Council of Ephesus against the teachings of Eutyches and Nestorius. Such doctrines viewed Christ's divine and human natures as separate and distinct (Nestorianism), or viewed Christ as solely divine (monophysitism). The Council of Chalcedon issued the Chalcedonian Definition, stating that Jesus is "perfect both in deity and in humanness; this selfsame one is also actually God and actually man." The Council's judgments and definitions regarding the divine marked a significant turning point in the Christological debates.

Dyophysitism (/daɪˈɒfɪsaɪtɪzəm/; from Greek δύο dyo, "two" and φύσις physis, "nature") is the Christological position that Jesus Christ is in two distinct, inseparable natures: divine and human. It is accepted by the majority of Christian denominations, including the Catholic Church, Eastern Orthodox Church, Church of the East, Anglicanism, Methodism, Reformed Christianity and Lutheranism. It is rejected by the Oriental Orthodox churches, who hold to Miaphysitism—that Jesus Christ is of two natures united into one composite nature—while rejecting Monophysitism as heresy along with other extant denominations.

Those who subscribe to the "two natures after the union" formula on either Chalcedonian and Nestorian side were referred to as dyophysites (/daɪˈɒfəsaɪts/). It is related to the doctrine of the hypostatic union and prosopic union.