By Charles Freeman, History Today, Volume 58, Issue 2, February 2008.

The doctrine of the Trinity – that God the Father, Jesus the begotten Son of God, and the Holy Spirit are equal but distinct members of a single Godhead – is an article of faith that lies at the core of Christian belief. As the Catechism of the Catholic Church puts it, it is a mystery hidden by God, inaccessible by reason alone, and only known because God has revealed it. So should historians, as well as theologians, be concerned with it? I believe there are good reasons why we should.

The doctrine of the Trinity certainly mystified the doctors of the Church. Before he embarked on a major study of the Trinity, Augustine of Hippo (354.430) confessed, ‘Who understands the omnipotent Trinity? Yet who among us does not speak of it, if indeed it is the Trinity he speaks of?’ Even that most rational of theologians, Thomas Aquinas (c. 1225–74), found himself unable to present a defense. “The truth that God is three and one is altogether a matter of faith; and in no way can it be demonstratively proved,’ was his conclusion.

So the historian has to ask how this particular doctrine ever became embedded at the center of Christian thought. For some there was no problem. Pope Gregory the Great (7.590-604), for instance, claimed that the Trinity had always been known. Although he had to accept that the patriarchs of the Old Testament had rarely preached on the issue. Yet, while it is clear that the scriptures do refer independently to God the Father, his son Jesus, and a Holy Spirit, there is virtually no mention of them as a Trinity, even in the New Testament. The only verses that place the three figures together come in Matthew 28:19 and the conclusion of Paul’s Second Letter to the Corinthians; and neither of them describes any relationship between them. In fact, a straightforward reading of the New Testament suggests that Jesus is almost always presented as subordinate to the Father, and this seems to have been the approach taken by the early Church.

By the early 300s, however, a few theologians were suggesting that Jesus might have existed alongside God from the beginning of time. Among their number was Alexander, bishop of Alexandria. He was confronted by one of his own priests, Arius, who believed Jesus was a distinct creation of his Father, at the beginning of all things, perhaps, but not in existence eternity. Alexander was determined to enforce his authority. Arius to resist him even to the extent of travelling through the eastern empire in find bishops would who support him. The unrest was such that, in 325 the emperor Constantine summoned some two hundred bishops to a council at his palace at Nicaea to settle the matter. The details of the debates are unclear but Alexander’s position was supported by a declaration that Jesus was, in fact, of one substance with the Father (homoousios was the Greek term used) in other words, existing eternally alongside him. The assenbled bishops affirmed their belief in the Spirit, but no mention was made of the Trinity. Almost at once the bishops realized that, in the heat moment, they had accepted a formula that had no scriptural backing. There is virtually no evidence of anyone preaching the homoousios formula in the year following the council of Nicaea, and when Constantine was finally baptized in 337, a bishop took the subordinate line on Jesus’ divinity carried out the ceremony.

Over the next fifty years debate on the relationship between the Father and Son became intense. Many recognized that the problem was, in fact, insoluble. As a group of bishops proclaimed in a creed of 357: “It is beyond man’s knowledge nor can anyone declare the birth of the Son….for it is clear that only the Father knows how he begot his Son and his Son how he was begotten by the Father.” This creed rejected the homoousios formula as being unsupported by scripture and argued instead for a subordinate Jesus in line with earlier tradition. A compromise creed issued by the emperor Constantius in 360 confirmed the unscriptural nature of homoousios and declared instead no more than that the Son was ‘like’ (homoios) the Father, a definition that solved nothing.

As the debate continued, the arguments became impressively sophisticated. Major philosophical issues relating to the nature of ‘substance’, ‘essence’, ‘personality’, ‘creation, ‘likeness and procession’ were thrown about and discussed with vigour. One group, known as the Eunomians after their most gifted exponent, Eunomius, were brilliant in their dissection of each concept in support of their claim that Father and Son were actually ‘unlike’ each other, while on the other side Athanasius, a truculent but determined bishop of Alexandria, not only revived the Nicene formula and but also argued that the Holy Spirit must be placed alongside Father and Son (as had not been done at Nicaea). Athanasius was not a major intellectual but his denunciation of all his subordinationist opponents as heretical Arians impressed many and he was one of the few Greek bishops to attract a following in the Latin West.

Basil of Caesarea, Gregory of Nazianzus and Gregory of Nyssa, three bishops from Cappadocia, developed a more subtle defense of the Nicene position. All three had enjoyed a traditional classical education in Athens and proved adept at using philosophical terms to define a single Godhead, of one substance (the Holy Spirit being added to the other two), within which each had a distinct personality (hypostasis). Yet even their formula still accorded the dominant role to God the Father and it left major questions unresolved. If the Son was defined as begotten of the Father, as the Cappadocians insisted, how could he also have existed alongside him from the beginning of time? By the 370s the debate had reached new levels of complexity and, with no sign of a consensus likely, it would probably have carried on inconclusively until it fizzled out – had it not been for the intervention of an emperor.

When, in 378, Valens, the emperor in the east, was killed at the battle of Adrianopie against the Goths, the western emperor Gratian appointed Theodosius, a tough Spanish soldier, to replace him. The Spanish Christians had supported the Nicene formula and, even though Theodosius did not pretend to be a theologian, this was his own faith. Moreover, he was a stranger to the east (he could not even speak Greek), and he had no idea of the diversity of beliefs that were being expressed, or even of the tradition of freedom of speech that underpinned them. Only a few years before, the court orator Themistius had made a sophisticated defense of freedom of religion. No one, even an emperor, he had argued, could control the soul, and in fact God enjoyed being worshipped in a variety of ways.

Theodosius ignored all this when, in January 380, he issued an edict proclaiming that the only acceptable way of being a Christian was to acknowledge Father, Son and Holy Spirit to be of equal majesty. All other formulas would be considered heretical and their holders subject to punishment both by the state and by God. Presumably he felt that only by imposing doctrinal unity could he strengthen his precarious position. An edict was no more than a declaration of intent but on arriving in his capital of Constantinople for the first time, Theodosius immediately dismissed the Homoian bishop, Demophilus, and appointed the Nicene Gregory of Nazianzus in his place. The emperor then issued the first decree to impose the Nicene formula on the east, in which he ordered all subordinationists to be banned from their churches and expelled from the cities if they caused trouble. They could no longer build their own churches, even outside city walls.

Theodosius felt that he needed some kind of ecclesiastical backing for his policy. He could not call a council representative of the whole church as it would have broken down in conflict so he summoned a group of bishops of his own faith. There were none from the Latin-speaking west and large areas of the eastern empire, including Egypt and Illyricum, were unrepresented. The bishop of Antioch, an impressive figure named Meletius, was to preside. The selected bishops assembled in Constantinople in 381, but almost immediately there was a major setback: Meletius died. In his place, Theodosius appointed the new bishop of Constantinople, the scholarly Gregory of Nazianzus.

Gregory was hopelessly unsuitable. His intransigent management infuriated the bishops and he was forced to resign. He left behind a self-pitying autobiography in which he accused his audience of behaving like adolescents who had no fear of God.

Order was only restored when an elderly pagan senator, Nectarius, was appointed to preside. He was quickly baptized as a Christian and the council continued. Its proceedings remain obscure. Many of its resolutions were political: the activities of each bishopric were confined to its administrative area, and primacy was given to the bishopric of Constaninople, to the fury of the much older Christian cities of Antioch and Alexandria. In this sense, the Council of Constantinople was primarily concerned with consolidating Theodosius control of the Church. However, at some point the bishops did agree on a version of the Nicene Creed that is still used today. While God the Father and Jesus were recognized as ‘of one substance,’ no relationship with the two was prescribed for the Holy Spirit. The nature and status of the Spirit were still hotly disputed. The creed was not published at the time; presumably because it would have been unacceptable to the citizens of Constantinople, who were known for the intensity with which they discussed theological issues, and it was only read out for the first time at a council of 451. The Nicene Creed was not used in the West before the eleventh century.

The Nicenes were now firmly in control in the east. There are reports of widespread rioting as fresh imperial laws against the subordinationists were enforced and they were expelled from their churches. A watershed had been crossed. Once the principle that subjects of the empire could discuss religious issues freely had been breached, there was no turning back. The laws were extended to the west in the late 380s, when Theodosius assumed power of the entire empire, and the crime of heresy was integrated with imperial law. In the 390s, Theodosius went further and issued a series of wide-ranging laws against paganism. His successors, notably his grandson Theodosius II (r. 408-50) elaborated the definition of heresies, ordering the burning of the books of those condemned. By the sixth century, under the emperor Justinian, all imperial subjects had to convert to Christianity.

So why has the story been forgotten? Why is it not common knowledge that the Trinity became part of Christian doctrine only as the result of a series of imperial decrees? One reason was that the rest had already been more responsive to the Nicene formula and so the imposition did not arouse the anger and disruption that it did in the east. There was not the same impulse there towards theological debate. By the time Augustine came to write his thesis on the Trinity in the fifth century, it was established doctrine. Then followed the collapse of the western empire in the late fifth century. Memories of imperial rule faded and when Gregory the Great returned to his native Rome after serving in Constantinople as papal nuncio, he brought with him the tradition that the Council of Constantinople had confirmed what the Church already believed. This is still the official explanation given in both Protestant and Catholic traditions. Nothing is said of the debate that was still lively in 381, other than to deride the subordinationists as heretics threatening what, it is usually claimed, was theologically the only solution. Nor is the broader suppression of freedom of thought ever mentioned.

Theodosius’ role was crucial. Without his political initiative, the Church would never have come to a consensus on such a complex issue. By acquiescing in Theodosius’ policy the bishops were surrendering the opportunity to define the parameters of Christian doctrine through reason and to leave it open to free discussion in areas where reason could not go. After Theodosius decrees, heresies were elaborated and debate constrained. Clever theologians, soon become heretics, as one bishop from Armenia observed in the 450s.

It is possible to argue that the year AD 381 is one of the most important moments in the history of European thought. From then on genuine debate over theological issues was not permitted. The Greek intellectual tradition that had done so much to define the key issues of philosophy withered. Authority replaced reason as the architect truth. Augustine’s massive study on the Trinity gave the overwhelming impression that the doctrine could be theologically justified, and when intellectual life began to revive in the west in the twelfth century, it acted as the gatekeeper to a closed world held within the walls of faith. By now, an ideology of church authority was so firmly in place that the roots of that authority in the decrees of a fourth-century emperor had been totally erased. It was not until the seventeenth century that the concept of religious toleration was revived. The story of its loss in the 380s needs to be retold.