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Miaphysitism is Cyril of Alexandria's Christological formula holding that in the person of Jesus Christ, divine nature and human nature are united (μία, mia – "one" or "unity") in a compound nature ("physis"), the two being united without separation, without mixture, without confusion and without alteration.
Historically, Chalcedonian Christians have considered Miaphysitism in general to be amenable to an orthodox interpretation, in contrast to Monophysitism. Since 1142, Oriental Orthodoxy uses the term "Miaphysite" for themselves but prefer to call themselves non-Chalcedonians.
The term "miaphysitism" arose as a response to Dyophysite criticisms of Monophysitism. As Nestorianism had its roots in the Antiochene tradition and was opposed by the Alexandrian tradition, Christians in Syria and Egypt who wanted to distance themselves from the extremes of Nestorianism and wished to uphold the integrity of their theological position adopted this term Miaphysite to express their position.
The theology of miaphysitism is based on an understanding of the nature (Greek φύσις physis) of Christ: divine and human. After steering between the doctrines of docetism (that Christ only appeared to be human) and adoptionism (that Christ was a man chosen by God), the Church began to explore the mystery of Christ's nature further. Two positions in particular caused controversy:
- Nestorianism stressed the distinction between the divine and the human in Christ to such an extent that it appeared that two persons were living in the same body. The view was condemned at the Council of Ephesus.
- Eutychianism stressed the unity of Christ's nature to such an extent that Christ's divinity consumed his humanity as the ocean consumes a drop of vinegar. The view was condemned at the Council of Chalcedon.
In response to Eutychianism, the latter Council adopted dyophysitism, which clearly distinguished between person and nature, stating that Christ is one person in two natures, but emphasizes that the natures are "without confusion, without change, without division, without separation".
The Monophysites rejected this definition as verging on Nestorianism and instead adhered to a wording of Cyril of Alexandria, the chief opponent of Nestorianism, who had spoken of the "one (mia) nature of the Word of God incarnate" (μία φύσις τοῦ θεοῦ λόγου σεσαρκωμένη mía phýsis toû theoû lógou sesarkōménē) but they failed to see the distinction between the emphatic masculine form Mono and the less emphatic feminine form Mia. The distinction of this stance was that the incarnate Christ has one nature, but that nature is still of both a divine character and a human character, and retains all the characteristics of both.
The Council of Chalcedon (451) was often seen as a watershed for Christology among the Chalcedonians as it adopted dyophysitism. However, as Oriental Churches, especially the Copts in Egypt, who held to Miaphysitism, rejected the decision, the controversy became a major socio-political problem for the Eastern Roman Empire. There were numerous attempts at reunion between the two camps (including the Henoticon in 482), and the balance of power shifted several times. However, the decision at Chalcedon remains the official teaching of the Eastern Orthodox Church, the Roman Catholic Church and traditional Protestants. The non-Chalcedonian Orthodox Churches are usually grouped together as Oriental Orthodox. Over recent decades, leaders of the various branches of the Church have spoken about the differences between their respective christologies as not being as extreme as was traditionally held.
John Meyendorff, a historian of this period of Church history, held that the official teaching of the Eastern Orthodox Church is not expressed by Chalcedon alone, but by "Chalcedon plus Cyril" – i.e., the dyophysite position expressed by Chalcedon, plus Cyril's miaphysite expression quoted above in its Orthodox interpretation – with the former attempting to express the inexpressible from one side (the dyophysite side) and the latter doing the same from the miaphysite side, both approaches being necessary and neither sufficient by itself.
Much has been said about the difficulties in understanding the Greek technical terms used in these controversies. The main words are ousia (οὐσία, 'substance'), physis (φύσις, 'nature'), hypostasis (ὑπόστασις, 'being'), and prosopon (πρόσωπον, 'person'). Even in Greek, their meanings can overlap somewhat. These difficulties became even more exaggerated when these technical terms were translated into other languages. In Syriac, physis was translated as kyānâ (ܟܝܢܐ) and hypostasis was qnômâ (ܩܢܘܡܐ). However, in the Church of the East, which followed the East Syriac rite, qnômâ was taken to mean nature, thereby confounding the issue further. The shades of meaning are even more blurred between these words, and they could not be used in such a philosophical way as their Greek counterparts.
The Miaphysite Churches (or "Oriental Orthodox Churches"), all in communion with each other are :
- Armenian Apostolic Church
- Syriac Orthodox Church of Antioch
- Malankara Orthodox Syrian Church
- Coptic Orthodox Church of Alexandria
- Ethiopian Orthodox Tewahedo Church
- Eritrean Orthodox Tewahedo Church
- The Blackwell Companion to Eastern Christianity by Ken Parry 2009 ISBN 1-4443-3361-5 page 88 
- Nine Saints Ethiopian Orthodox Monastery: Monophysitism and Dyophysitism Archived 2011-01-26 at the Wayback Machine
- John McGuckin (2004), Saint Cyril of Alexandria and the Christological Controversy, ISBN 0-88141-259-7 p140 et al
- Meyendorff, John (1989). Imperial unity and Christian divisions: The Church 450–680 A.D. The Church in history. 2. Crestwood, NY: St. Vladimir's Seminary Press. ISBN 978-0-88-141056-3.
- Pope Shenouda III «THE NATURE OF CHRIST»
- MAIN DOCTRINES AND PRACTICE OF THE CHURCH – Ethiopian Orthodox Tewahedo Church
- Severus of Antioch’s Objection To The Council Of Chalcedon:A Re-Assessment
- Coptic interpretations of the Fourth Ecumenical Council
- Joint declarations between the Syriac Orthodox and Roman Catholic Churches
- Common declaration of Pope John Paul II and HH Mar Ignatius Zakka I Iwas
- Syriac Orthodox Resources
- Agreed Statements between representatives of the Oriental and Eastern Orthodox Churches