When did the Trinity become doctrine?

The short version: the belief that Father, Son and Holy Spirit are each God is older than the word for it, and the word is older than the definition. Christians baptised “in the name of the Father and of the Son and of the Holy Spirit” in the first century; they began calling God a “triad” around 180; and they agreed, at least on paper and for most churches, on how to state the doctrine only in 381. Historians can trace those stages. Whether the later definitions faithfully express what the New Testament implies is a theological question, and the main positions are set out below.^[1]​^[2] Consensus

What the New Testament says, and does not say

The New Testament speaks of Father, Son and Spirit together. The clearest instance is the command to baptise “in the name of the Father and of the Son and of the Holy Spirit” (Matthew 28:19), and Paul closes a letter with a blessing in three parts: “the grace of the Lord Jesus Christ, the love of God, and the communion of the Holy Spirit be with all of you” (2 Corinthians 13:13).^[3]​^[4] Consensus What it does not contain is the word “Trinity”, or any statement of how three can be one. Apart from Matthew 28:19, no saying of Jesus in the first three Gospels uses the language of the later creeds.^[1] Consensus

The verse often quoted as the plainest statement of the doctrine, 1 John 5:7–8 in the King James Version (“there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one”), is not part of the original text. This “Johannine comma” began as a Latin addition, appears in only a handful of late Greek manuscripts, was printed in Greek in the Complutensian Polyglot and entered Erasmus’ widely used Greek text in his third edition of 1522. Most modern translations omit it or relegate it to a footnote.^[5] Consensus

The first words: trias and trinitas

The vocabulary came in the late second and early third centuries.

• Theophilus of Antioch, c. 180, explaining the days of creation, says that “the three days which were before the luminaries are types of the Trinity (trias), of God, and his Word, and his Wisdom” (To Autolycus 2.15, ANF translation). It is the first use of trias for God, and his triad is God, Word and Wisdom, not Father, Son and Spirit.^[6] Consensus
• Tertullian of Carthage, c. 213, writing Against Praxeas, used trinitas and described three persons (personae) of one substance (substantia). Much of the Western church’s later vocabulary for the doctrine starts with him.^[7] Majority

Both were arguing against rival answers. Monarchians such as Noetus of Smyrna, Praxeas and Sabellius taught that Father, Son and Spirit were names or modes of one God, so that the Father himself suffered on the cross. Adoptionists, such as Theodotus the leather-worker, excommunicated in Rome around 190, held that Jesus was a man whom God adopted at his baptism.^[8]​^[9] Majority The doctrine of the Trinity took shape as the way between these two.

Nicaea, 325: the Son

The fourth-century argument began with the Son. Around 318 Arius, a priest of Alexandria, taught that the Son had a beginning and was created. The Council of Nicaea in 325 answered that the Son is “begotten not made, of one substance with the Father” (trans. J. N. D. Kelly), using a word, homoousios, that is not in the Bible.^[10]​^[11] Consensus Of the Holy Spirit the creed said only “and in the Holy Spirit”. It took sixty more years of argument, including a period when imperial councils banned the word ousia altogether, before the matter was settled.^[12] Consensus

The Cappadocians and Constantinople, 381: the Spirit

The settlement came from three theologians from Cappadocia in central Asia Minor: Basil of Caesarea, his brother Gregory of Nyssa, and their friend Gregory of Nazianzus. Earlier writers had used ousia (being, substance) and hypostasis (reality) almost interchangeably; the creed of 325 itself condemned anyone who said the Son was “of a different hypostasis or substance”. The Cappadocians gave the words different jobs: God is one ousia in three hypostaseis. That let them affirm the full equality of Father and Son without merging them, and extend the same equality to the Spirit.^[2]​^[1] Consensus

In 381 the emperor Theodosius I called a council to Constantinople, which declared the Spirit fully divine. The creed associated with it adds that the Spirit is “the Lord and giver of life, who proceeds from the Father, who with the Father and the Son is worshipped and glorified”. Its text is first recorded at Chalcedon in 451, and most scholars accept its link to 381.^[13]​^[1] Majority This is the creed most churches today recite as “the Nicene Creed”.

After 381: the filioque

The doctrine was not quite finished. Latin theologians, following Augustine, taught that the Spirit proceeds from the Father and the Son, in Latin filioque. The word entered the creed in Spain at the Third Council of Toledo in 589, spread through the Frankish church, and was sung in the creed at Rome around 1014. Eastern theologians rejected both the doctrine and the change to a creed agreed by a council, and the filioque became one of the issues in the split between the Catholic and Orthodox churches.^[14] Majority

The case on each side

Contested Historians agree on the dates. They disagree on whether the dates mark a discovery, a change, or both.

Some modern movements reject the doctrine altogether. Most other Christians do not regard the Latter-day Saints or Jehovah’s Witnesses as Christian in the sense of the creeds of 325 and 381, while those movements claim to restore the original faith; this series describes them without ruling (§11).^[15] Contested

Common misconceptions

• “Constantine invented the Trinity at Nicaea.” The creed of 325 defined the Son’s relation to the Father and gave the Spirit one line. The full doctrine came after Constantine’s death, at Constantinople in 381. Consensus
• “The word Trinity is in the Bible.” It is not. It first appears around 180, in Greek, and around 213, in Latin.^[6]​^[7] Consensus on the Greek; Majority on the Latin date
• “1 John 5:7 proves the Trinity was in the original text.” That verse is a later addition, absent from all early Greek manuscripts.^[5] Consensus
• “Early Christians did not think Jesus was divine.” They worshipped him from the first generation; the argument was over how to state that without saying there are two gods.^[16] Consensus

Why it matters

The Trinity is the clearest example of a belief that is old in substance and later in its formulation. Most of the vocabulary that defines Christian orthodoxy, from trinitas to homoousios and hypostasis, was coined or given its technical meaning between 180 and 381, and the Bible’s own text was once expanded to say more plainly what the doctrine had come to say.

For the second-century vocabulary and the Monarchians, see Chapter 5: Many Christianities. For Nicaea, the Cappadocians and 381, see Chapter 6: Constantine, the Creeds and the Councils. For the filioque, see Chapter 8: The Medieval West. For the Johannine comma and the manuscripts, see Chapter 0: How We Know.