Why are there so many kinds of Christianity?

The Council of Chalcedon defined that Christ exists in two natures, "unconfusedly, immutably, indivisibly, inseparably" united in one person. A substantial part of the church, above all in Egypt, Syria and Armenia, did not accept that definition.

Those churches still exist. The Oriental Orthodox churches, self-governing in Egypt, Syria, Armenia, Ethiopia, Eritrea and India, are the churches that separated over Chalcedon, and their separation is about fifteen hundred years old. The Church of the East, in the Persian empire, went its own way in the same century: by the 480s it governed itself and had affirmed a Christology of its own.

In 1054 legates from Rome and the Patriarch of Constantinople exchanged sentences of excommunication. The sentences named persons, not churches, and the declaration that later lifted them says they were not meant to break communion. Behind them lay centuries of divergence over the authority of the bishop of Rome, over a Western addition to the creed, and over language, liturgy and empire.

In December 1965, Pope Paul VI and Patriarch Athenagoras I issued a joint declaration removing those sentences "both from memory and from the midst of the Church", and regretting "the offensive words, the reproaches without foundation, and the reprehensible gestures" that had accompanied them. The churches remain separate. The specific excommunications of 1054 do not.

The document conventionally treated as the start of it is Luther’s Disputation on the Power and Efficacy of Indulgences, ninety-five propositions written in 1517 and aimed at a particular practice: payment in exchange for the remission of penalty.

It is worth reading for what it is not. It is a request for an academic disputation, it is not a proposal to found a new church, and the questions it opens about authority and repentance turned out to be much larger than the practice it began with.

Pew’s study of global Christianity put the number of Christians in 2010 at about 2.18 billion, close to a third of the world’s population, with roughly half Catholic, about 37 per cent Protestant in the broad sense, and about 12 per cent Orthodox.

The broad Protestant share is where the count of denominations becomes unhelpful. Pew notes that many of the churches in it are independent, non-denominational, or part of a family that is very small or otherwise difficult to classify. The figures of tens of thousands that get quoted come from the Center for the Study of Global Christianity, which reported 45,000 denominations in 2019 and says what it counts: an organised church "usually within a specific country", so that the Catholic Church, present in 234 countries, counts as 234. Individual congregations are not counted as denominations.

Chalcedon had a doctrinal statement at its centre and a dispute about power running alongside it, and the acts show the second on their face: the first session opens with Rome’s legates demanding that Dioscorus of Alexandria be refused a seat, and the twenty-eighth canon gives Constantinople "equal privileges" with old Rome, ranked next after her. The Eastern and Western churches had been drifting linguistically and politically for centuries before 1054. The Reformation had German princes behind Luther and, in England, a king’s marriage.

The weighting is argued, and the churches’ own accounts differ. The Catholic Encyclopedia of 1912 put "the real source of all the trouble" in the ambition of Constantinople’s patriarchs; the joint declaration of 1965 names, among other factors, "lack of understanding and mutual trust".

Modern dialogues between the Eastern Orthodox and Oriental Orthodox churches have produced joint statements suggesting that the two sides held substantially the same faith in different technical vocabularies, and that the fifth-century split turned partly on the meaning of the Greek words involved. The joint commission said in 1990 that both families "have always loyally maintained the same authentic Orthodox Christological faith", "though they have used Christological terms in different ways", and recommended that each side lift the anathemas it had pronounced.

The statement was the commission’s recommendation to the churches, not a decision of them, and it looks forward to removing "the last obstacle to the full unity and communion of our two families". But it raises a real question about how many of these divisions are about what they appear to be about.

Counting Christian bodies depends entirely on what counts as one, and there is no neutral rule. Independent and non-denominational congregations, the ones Pew finds hard to classify, are exactly the ones the counting methods handle worst: the Center for the Study of Global Christianity counts one only once it forms a network with a name.

So the familiar claim that Christianity is fragmenting into ever more pieces is hard to test in the form it is usually stated. A rising count of organisations, each counted once per country, is not the same thing as a rising number of traditions.

The Nicene Creed calls the church one, and every church that confesses it has to account for the visible fact that it is not. The Catholic Church teaches that the one Church of Christ "subsists in the Catholic Church", while "many elements of sanctification and of truth are found outside of its visible structure". The Orthodox council held in Crete in 2016 spoke of the Orthodox Church "as the One, Holy, Catholic, and Apostolic Church". The Westminster Confession, a Reformed confession, places the universal church first in one "which is invisible" and "consists of the whole number of the elect", and then in a visible church throughout the world.

These are not merely different descriptions of the same situation. They imply different answers to who is separated from whom, which is why the question of reunion is harder than the goodwill on all sides would suggest.

Across the oldest divisions the documents claim the same inheritance. The Catholic Church and the Church of the East confess together the faith "formulated by our common Fathers in the Nicene Creed". The two families divided at Chalcedon record it themselves: both accept the first three councils, "which form our common heritage". The disagreements are severe and they sit on top of a shared inheritance that the disagreements themselves assume.

Saying that is not ecumenical politeness. It is what the documents show: churches out of communion with each other for fifteen centuries still opening the same books.