The Trinity

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In an English manuscript made in the years around 1210, a teacher of theology sketched four small circles to help students hold a hard idea in the mind at once. Three circles ran along the edges, lettered for the Father, the Son, and the Holy Spirit; a fourth at the center read simply Deus, God. Lines linked the center to each outer node and were lettered est — “is” — while the lines among the three outer nodes read non est, “is not.” The Father is God; the Son is God; the Spirit is God; yet the Father is not the Son, the Son is not the Spirit, the Spirit is not the Father. The diagram, later called the Scutum Fidei, the Shield of Faith, compressed into a single figure a claim that had cost the church four centuries of argument to state: that God is one, and that God is three, and that neither admission may be allowed to swallow the other.

Standard form of the Scutum Fidei or Shield of the Trinity, summarizing the opening of the Athanasian Creed. — AnonMoos, via Wikimedia Commons (public domain)

Seeds and the long argument

The doctrine is not stated as a doctrine anywhere in the documents it claims as its root. What the New Testament offers, on the reading the tradition gives them, are triads — places where Father, Son, and Spirit stand together in a single grammatical breath, named as though they belonged to one order of reality. The commission at the close of Matthew sends the disciples to baptize “in the name of the Father, and of the Son, and of the Holy Spirit,” a single name governing three. Paul closes a letter to Corinth with a benediction in three movements — the grace of Christ, the love of God, the fellowship of the Spirit. The prologue of John opens before creation with the Word that was with God and was God, the Logos through whom all things were made. These are seeds, not a system; the system is what the church grew from them, under the pressure of having to say in what sense the man it worshipped was God without thereby confessing two gods, or three.

The first thinker to give the structure a Latin name was Tertullian of Carthage, the formidable, acid-tongued jurist-theologian who died around 225. Writing against a teacher named Praxeas, who had collapsed the three into one figure under different masks — the Father himself suffering on the cross — Tertullian reached for vocabulary the West would never relinquish. He coined the term trinitas, and he set down the formula that became the Latin charter of the doctrine: one substance, three persons, una substantia, tres personae. The three, he wrote in a sentence the tradition has carried ever since, are “all of one, by unity of substance,” distinct not in their being but in their order, their aspect, their manifestation — the unity distributed into a trinity without being divided. The treatise survives in both its Latin original and modern translation, and its vocabulary became the West’s permanent inheritance. He was reaching, with the borrowed tools of Roman law and Stoic physics, for a way to hold difference and identity in the same hand. In the East, Origen of Alexandria worked the same problem from the other side, teaching the eternal generation of the Son — that the Father had never been without his Word, that the begetting was not an event but a relation outside time — even as he left the Son in some subordinate rank that later generations would find too low.

Nicaea and a single letter

The argument that forced the question to a council began in Alexandria in the early fourth century, with a presbyter named Arius. His logic was clean and hard to refute on its own terms. If the Son is begotten, then there was a moment — or a condition prior to all moments — when the Son was not; what is begotten has a beginning, and what has a beginning is not eternal as the Father is eternal. The Son, on this account, is the first and highest of all creatures, the agent through whom God made the world, exalted above everything else that exists and yet, finally, made: not God in the full and unqualified sense, but the supreme creature. The slogan that traveled with the teaching was blunt — “there was when he was not.”

The emperor Constantine, newly the patron of a faith he found splitting in his hands, summoned the bishops to Nicaea in 325. What they produced was a creed built to exclude Arius by a word he could not sign. The Son is homoousios with the Father — of one substance, consubstantial, the very same being. The choice was deliberate and risky; homoousios was not a biblical word, and it had a checkered past in earlier controversies. But it drew a line no careful Arian could cross. The contrast that haunted the next half-century lay in a single Greek letter: homoousios, of the same substance, against homoiousios, of like substance — the position of a large middling party who wanted the Son genuinely divine and genuinely like the Father without conceding the full identity of being. One iota separated them, and on that iota the church spent sixty years. To confuse the two words is to lose the whole quarrel; the entire point was that likeness, however exalted, was not sameness, and that anything short of sameness left the Son on the creature’s side of the one line that mattered.

Vasily Surikov’s rendering of an ecumenical council, the kind of gathering at which the fourth-century creeds were framed. — Vasily Surikov, via Wikimedia Commons (public domain)

Nicaea settled a word and unsettled everything else. The decades after the council were a confusion of synods, rival creeds, exiles, and reversals, with the term homoousios itself suspected by many of the orthodox because it could be heard in a modalist sense — as if it erased the distinctions of the persons into one undifferentiated being. The cause was carried, against the court and often from exile, by Athanasius of Alexandria, who staked his life on the conviction that only a Son who is fully God could make humans divine — that the whole logic of salvation depended on the bridge between God and the world being God’s own being and not a creature’s. If the Son were less than God, then what he joined to himself in the incarnation could not be lifted into the divine life.

One ousia, three hypostases

The grammar that finally held was the work of three closely linked theologians of fourth-century Asia Minor — Basil of Caesarea and the two Gregorys, of Nazianzus and of Nyssa — the Cappadocian Fathers. Their contribution was less a new doctrine than a fixed vocabulary that let the doctrine be stated without collapsing into one of its two opposite errors. The trouble had been that two Greek words — ousia, substance or essence, and hypostasis, concrete subsistence — had long been used almost interchangeably. The Cappadocians drove a permanent wedge between them. There is one ousia: a single divine nature, undivided and entire, in which Father, Son, and Spirit each wholly share. There are three hypostaseis: three real and distinct modes of existing that possess that one essence without partitioning it into thirds. The persons are distinguished not by the essence, which is wholly common, but by their relations of origin — the Father unbegotten, the Son begotten, the Spirit proceeding.

Basil of Caesarea pressed a further point the council of 325 had left thin: the full deity of the Holy Spirit, against those who would honor the Spirit while leaving its rank undefined. The work was ratified at the Council of Constantinople in 381, which expanded the Nicene confession and gave it the strengthened clause on the Spirit — worshipped and glorified together with the Father and the Son — that the churches have recited ever since. The settlement became, in the East, less a conclusion than a permanent structure: one ousia in three hypostaseis, the fixed grammar within which everything afterward about God would be said. Gregory of Nyssa answered the obvious objection — three persons sharing one nature, are these not three gods, as three men share humanity yet are three? — by arguing that the divine three never act separately. Every divine work begins from the Father, moves through the Son, and is completed in the Spirit; the unity of the operation witnesses to the unity of the nature.

What the doctrine says

Stated from within, the doctrine is not arithmetic and does not pretend to dissolve its own paradox. It denies, on one side, that the three are three gods, and denies, on the other, that they are one person wearing three masks — the error called modalism, which Tertullian had fought in Praxeas. Between these it holds a third thing: one God who is, in the very ground of the divine being, a communion of three.

The persons are distinguished by what the tradition calls the processions. The Son is begotten of the Father — not made, not created, but eternally generated, as light from light, with no interval in which the Father was Father without the Son. The Spirit proceeds — a different word for a different relation, traditionally called spiration, the breathing-forth — neither begotten nor unoriginate. These are not events in God’s biography; they are eternal relations that constitute the persons as the persons they are. To be the Son simply is to be eternally from the Father; to be the Father is to be the unoriginate source. The relations are the distinctions, and the distinctions are nothing added to the one essence.

The persons are not partitioned off from one another into separate compartments of the Godhead. Each is wholly in each, interpenetrating without confusion and without division — a mutual indwelling the Greek tradition named perichoresis and the Latin rendered circumincessio. Where one person is, there the others are; the Son is in the Father and the Father in the Son, not as parts in a whole but as the whole divine life present entire in each. The doctrine also learned to mark a distinction between the Trinity as it acts toward the world in creation and salvation — the economic Trinity, from oikonomia, the ordering of the household of redemption — and the Trinity as it eternally is in itself, the immanent Trinity. The first is the Trinity revealed; the second is the Trinity that the first reveals. The two are not two Trinities, and the relation between them would become the pivot of modern reflection.

In the Latin West the architecture took a distinctive turn in Augustine of Hippo, whose great work On the Trinity (De Trinitate), composed across nearly three decades from around 400, shifted the center of gravity from the relations among the persons to the one divine essence, and then sought the imprint of the triune God in the structure of the human mind. If the human person is made in God’s image, Augustine reasoned, then the image of the Trinity should be legible within the soul. He found it in a series of mental triads, most famously memory, understanding, and will — three faculties that are not three minds but one mind, distinct yet co-extensive, each containing and implying the others. The mind remembering, knowing, and loving itself became the West’s enduring analogy for the God who is one substance in three persons: not a proof, but a trace, the creature carrying the watermark of its maker.

Filioque, schism, and the diagram

The Augustinian emphasis bore a consequence that would help split Christendom. If the persons are constituted by relations of origin, and the Son shares fully in the Father’s essence, then it seemed natural to Latin theologians to say that the Spirit proceeds from the Father and the Son — in Latin, Filioque. The phrase was inserted into the creed in the West as an anti-Arian safeguard, emphasizing the Son’s full equality with the Father; it appears at the Third Council of Toledo in 589 and spread through the Latin-speaking churches over the following centuries, though Rome itself long resisted adding it to the creed’s text. The East objected on two grounds at once. Procedurally, an ecumenical creed had been altered by the West alone, against an explicit canon forbidding any change to its wording. Theologically, the Greeks held that the Spirit proceeds from the Father alone — the Father being the single source within the Godhead — and that the added clause confused the persons’ relations of origin. The dispute, sharpened in the ninth century in the conflict surrounding the patriarch Photius, hardened over five hundred years into one of the principal grievances dividing the churches; the mutual excommunications of 1054 are conventionally taken as the formal rupture of East and West, with the Filioque among the wounds that would not close.

Rublev’s icon (c. 1411) reads the three visitors of Genesis 18 as an image of the Trinity, the three equal in dignity around a single cup. — Andrei Rublev, via Wikimedia Commons (public domain)

The Western synthesis reached its scholastic summit in Thomas Aquinas, who treated the persons as subsistent relations — the relation of paternity, of filiation, of procession, each so fully identical with the divine essence that it does not add a fourth thing to God but simply is God under the aspect of that relation. Alongside the high theology ran the popular pedagogy of the Shield of Faith. First attested in a manuscript of Peter of Poitiers’ genealogical Compendium from around 1208, and used heraldically by the mid-thirteenth century in the chronicle of Matthew Paris, the diagram distilled the opening of the so-called Athanasian Creed into a figure a layperson could read at a glance. That creed itself — the Quicumque vult, “Whoever wishes to be saved” — bears Athanasius’s name by long tradition but is not his work; it is a Latin composition of the fifth or sixth century, probably from southern Gaul, unknown to the Greek church for centuries. Its relentless cadences — “neither confounding the persons nor dividing the substance” — set the doctrine to a kind of liturgical drumbeat.

Dissent and renewal

The doctrine never lacked for those who found it an arithmetic that would not balance. The shade of Arius returned in new dress. The Spanish physician and theologian Michael Servetus published On the Errors of the Trinity (De Trinitatis erroribus) in 1531, attacking the Nicene settlement as an unscriptural intrusion of philosophy into the gospel; he was burned at Geneva in 1553 at the urging of the Reformed authorities, a death that made him a byword and helped provoke early pleas for religious toleration. Out of the ferment came the Polish Brethren and, through the Italian exile Faustus Socinus, the rationalizing anti-Trinitarian movement called Socinianism, which insisted that Father, Son, and Spirit could be honored without the metaphysics of one substance in three persons. From these currents the later Unitarian churches descended, holding the oneness of God and the humanity, however exalted, of Christ — the persistent counter-tradition for which the doctrine of three was a corruption of the doctrine of one.

The mainstream of the doctrine, far from withering, was renewed in the twentieth century. The Protestant theologian Karl Barth made the Trinity the opening move of his dogmatics rather than a late appendix to it, grounding the whole in God’s self-revelation, though he preferred to speak of three “modes of being” — Seinsweisen — rather than persons, wary that the modern word “person” smuggled in three separate centers of consciousness. The Catholic theologian Karl Rahner pressed an axiom that reshaped the field: the economic Trinity is the immanent Trinity, and the immanent Trinity is the economic Trinity. The God who gives himself in history, Rahner argued, is none other than the God who eternally is; there is no hidden fourth God behind the revealed three. Against the long Augustinian habit of beginning from the one essence, a movement sometimes called social trinitarianism — associated with Jürgen Moltmann and others — pressed back toward the Cappadocian starting point of the three-in-communion, reading the perichoretic life of the persons as a model of relation, freedom, and shared life. The argument that began over a single letter at Nicaea had become, sixteen centuries on, an argument about what it means for the ground of all being to be, in itself, a society of love.

What the Shield of Faith drew in four circles, then, was never a solved equation. It was a refusal — of two simplifications, each easier than the truth it guarded — held in place by a grammar that took the church four hundred years to forge and has never set down since.

→ Related: Cappadocian Patristics · Arius · Athanasius · Origen · Tertullian · Augustine Of Hippo · Basil Of Caesarea · Logos · Apophatic Theology · Holy Spirit · Thomas Aquinas · Neochalcedonian Christology · Pseudo Dionysius The Areopagite · Gnosticism · Neoplatonism · Platonism · Plotinus · Gnosis · Christian Mysticism · John Of Damascus · Corpus Hermeticum