The 5th cent. witnessed much controversy over how best to describe the relationship between the divinity and humanity in the incarnate Christ while maintaining, on the one hand, the transcendence of the Godhead, and on the other, the full reality of the incarnation.

In the second quarter of the 5th cent. two different approaches to christology emerged, usually referred to as ‘Antiochene’ and ‘Alexandrian’, after the locations of the leading theologians of each. Different concerns and starting points led to differences of emphasis on either side, giving rise to two different conceptions of how salvation for humanity comes about. For the Antiochenes, a concern for the transcendence of the divinity meant that it was important to maintain the distinction between the divinity and the humanity in the incarnate Christ (hence their dislike of ‘theopaschite’ language): for them, salvation for humanity was achieved by means of the humanity of Christ, raised up at the Ascension; as a result, it was important for them to call Mary ‘mother of Christ’ and not ‘mother of God’. By contrast, for the Alexandrians, salvation is brought about by the divine Word ‘becoming’, but without change, fully human at the incarnation. Thus for them it was essential to stress the ‘oneness’ in the incarnate Christ. For each side, the other side’s approach was seen at best as unsatisfactory, and at worst, heretical.

Successive Roman emperors attempted to get the issue resolved by convening a series of Councils, of which those at Ephesus (431) and at Chalcedon (451) proved to be the most important, and as matters turned out, the most divisive. At Ephesus, owing to the delayed arrival of the Antiochene bishops (under John, bp. of Antioch), the Alexandrian bishops (under Cyril, bp. of Alexandria) met by themselves and deposed Nestorius, bp. of Constantinople, a leading proponent of Antiochene christology. When the Antiochene bishops subsequently arrived they held their own council, and condemned Cyril’s. Two years later, in 433, a compromise was reached (the ‘Formulary of Reunion’). Polarization of the different positions, however, continued, and in the course of this three technical terms became prominent in formulations of christology, above all at the Council of Chalcedon: person (parṣopā; Greek prosopon), nature (kyānā; Greek physis), and ‘hypostasis’ (qnomā), the last two of which were understood in different ways by different people. According to the dogmatic Definition of faith laid down at Chalcedon, the incarnate Christ is ‘made known in two natures ... concurring into one person and one hypostasis’. This formulation gave rise to a sharp division between those who spoke of ‘two natures’ in the incarnate Christ (‘dyophysites’) and those who adhered to Cyril’s formula ‘one incarnate nature of God the Word’ (‘miaphysites’).

It was very largely the imposition, by Justin (518–527) and especially Justinian (527–565) of Chalcedon’s Definition of faith as the sole touchstone of orthodoxy that led to the three-way split in Eastern Christianity which is represented today by three separate traditions: 1. the Oriental Orthodox Churches, among which is the Syr. Orthodox; these accept the Council of Ephesus of 431, but not the Council of Chalcedon; 2. the Churches which accept both the Council of Ephesus and that of Chalcedon (the various Eastern Orthodox, Catholic, and Reformed Churches); and 3. the Church of the East, which does not accept either of the two Councils (since its adherents were largely outside the Roman Empire, the imperial councils did not directly concern them).

For both the Oriental Orthodox and the Church of the East the Chalcedonian Definition was seen as illogical, the former objecting to ‘in two natures’ and the latter to ‘one hypostasis’. The basic problem lay in different understandings of two of the terms used, ‘nature’ (physis/kyānā) and ‘hypostasis’ (qnomā): for the miaphysites ‘nature’ implied ‘hypostasis’ (and not ousia), while for the Church of the East qnomā meant ‘set of characteristics’, and not ‘hypostasis’. With these different understandings it can readily be seen that the Chalcedonian Definition was not satisfactory. Thus the miaphysites (Syr. and other Oriental Orthodox) insisted on Cyril’s ‘one incarnate nature’, while the Church of the East spoke of ‘two natures with their qnome’ (where qnome has the sense of ‘characteristics’ and not ‘hypostaseis’). In an attempt to overcome the problem, the ‘Neo-Chalcedonians’ of the early 6th cent. held that either ‘in two natures’ or ‘out of two natures’ was acceptable (the latter, which had been in the draft of the Council’s Definition, was acceptable to the Syr. Orth.), but attempts at bringing about agreement by Justinian and others failed, though this was very nearly achieved under Heraclius in the early 630s with both the Syr. Orth. and the Church of the East. The Arab invasions, which followed shortly after, then fossilized not only the divisions, but also the misleading polemical names given by Chalcedonians to their opponents: ‘Nestorians’ (implying a belief in two sons, the Son of God and the son of Mary), ‘Eutychians’ (implying a belief that the Christ was not ‘consubstantial with us’, as well as ‘with the Father’), and ‘Monophysites’ (implying a Eutychian position) — positions which the Church of the East and Syr. Orth. have always strongly rejected. On every side the polemical literature became increasingly scholastic in character, although a few voices (notably that of Bar ʿEbroyo) were to be heard, pointing out that underlying the conflicting doctrinal formulae there lay a consensus on the essential understanding of the incarnation. The general feeling of antagonism between Churches only became increased as a result of the creation of the Eastern Rite Catholic Churches (Chaldean, 1553; Syrian Catholic, 1782), and of the various Protestant missions of the 19th cent. Though the help in educational matters given by different Western Churches benefited individual Syr. Churches, this never led to any real dialogue, and so matters continued largely unchanged until the late 20th cent. when ecumenical dialogue at last began to remove the fog of misconceptions on all sides.

The aim of modern dialogue is not uniformity, but unity through the acceptance of variety. At the end of the very first meeting of the Oriental and Eastern Orthodox non-official dialogue, in 1964, the communiqué stated ‘on the essence of the Christological dogma we found ourselves in full agreement. Through the different terminologies used by each side, we saw the same truth expressed’. The four non-official dialogues were followed by an Official Dialogue, and at the end of the third meeting (1990) it was recommended that a mutual lifting of anathemas and condemnations should take place (this, however, still remains to be implemented). In 1991 an important agreement on various practical matters was made between the Syr. Orth. and Rum Orth. Patriarchs of Antioch.

Dialogue between the Oriental Orthodox and Catholic Churches began in 1971 with a series of non-official meetings in Vienna initiated by the Pro Oriente Foundation. The very first meeting produced what came to be known as ‘the Vienna Christological formula’, which has played an important part in subsequent Official Dialogue. The 6th meeting of this Dialogue took place in Jan. 2009, with the theme ‘The Nature, Constitution and Mission of the Church’. Meetings also took place between the Syr. Orth. Patr. Ignatius Yaʿqub III and Pope Paul VI in 1971, and between Patr. Ignatius Zakka I and Pope John Paul II in 1984. Each ended with a joint communiqué.

Beginning in 1994, Pro Oriente has arranged a series of non-official meetings entitled ‘Syriac Dialogue’, involving all the different Syr. Churches; these have proved most helpful in clearing away traditional misunderstandings, especially concerning the christology of the Church of the East. In particular it was soon recognized that ‘Nestorius’ (and hence ‘Nestorianism’) means completely different things to different people: to the Church of the East Nestorius is primarily seen as a leading figure, alongside Diodore and Theodore, of the dyophysite cause, but to the Oriental Orthodox he is an arch-heretic who divided Christ into two sons, while to modern scholarship the real character of his christology is disputed and remains unclear. In any case, the theology of the Church of the East is far more under the influence of the writings of Theodore (in a modified form) than of those of Nestorius.

The Church of the East had at first been left out of the wider dialogue in the 1960s and 1970s, but in 1984 Patr. Mar Denḥa IV had an official meeting with Pope John Paul II in Rome, and ten years later, on 11  Nov. 1994, the two heads of Churches issued a historical Common Declaration of Faith. A further important event, in 1997, was the decision of the synods of the Assyrian Church of the East and the Chaldean Catholic Church to inaugurate moves to bring about the full ecclesial union of the two Churches; an important step towards this was the Vatican’s publication (26 Oct. 2001) of ‘Guidelines for admission to the Eucharist between the Chaldean Catholic and the Assyrian Church of the East’, which incorporated recognition of the legitimacy of the Anaphora of Addai and Mari in its original form, without any explicit Institution Narrative. Another momentous decision of the synod of the Assyrian Church of the East in 1997 was to lift unilaterally all anathemas against persons in other Churches whom they had traditionally regarded as heretical, thus setting an example for all other Churches. Unfortunately relations between the Church of the East and the Oriental Orthodox Churches (in particular the Coptic) have remained problematic, at least on the official level, and the Church of the East still has not yet been admitted as a member of the Middle East Council of Churches.