Church Fathers

Theophilus of Antioch (169–181) Ad Autolycum

Theophilus of Antioch's Ad Autolycum is the oldest extant work that uses the actual word "Trinity" to refer to God, his Word and his Wisdom. The context is a discussion of the first three days of creation in Genesis 1–3:

...the three days before the luminaries were created are types of the Trinity, God, his Word, and his Wisdom.

— To Autolycus 2:15[31]

Theophilus of Antioch did not view the Son as an eternally self existing person. Theophilus wrote that God "begat Him, emitting Him along with His own wisdom before all things."[33] Instead of speaking of the Word as the Creator, Theophilus speaks of the "Word as a helper in the things that were created by Him",[33] thus he assigns the role of Creator to God alone, while assigning the lesser position of "helper" to the "begat" Son.

Didache

Scholars such as Clayton N. Jefford have noted that Jesus is not "ever specifically given a designation of divinity within the text. He is simply called "servant, child" (παῖς) in the prayers and referenced as "the Lord" (ὁ κύριος) elsewhere."[23][24] Jefford argues that this may have been for reasons of cultural sensitivity. Specifically towards Jews, as their beliefs on deity (found in the Torah at Deuteronomy 6:4)[25] stand in opposition to belief in a triune God. This allows for a reading of Didache that harmonises fully with the Jewish perspective on God. This allows the reader to come away unoffended, and thus the text can be correctly read without invocation of a triune God.

Polycarp of Smyrna c. 155:

Polycarp was martyred in Smyrna (where he was also Bishop) in the year 155. It is said by Irenaeus of Lyons that he was a pupil of the Apostle John. In his final prayer before his martyrdom, he "praises, glorifies, and blesses" the Father. He does this "through" Jesus.

For this cause, yea and for all things, I praise Thee, I bless Thee, I glorify Thee, through the eternal and heavenly High-priest, Jesus Christ, Thy beloved Son, through whom with Him and the Holy Spirit be glory both now [and ever] and for the ages to come. Amen.

— Martyrdom of Polycarp 14:3[30]

216: Tertullian

Tertullian's treatise against a Patripassian heretic named Praxeas, who claimed that the Father had suffered with the Son on the cross, is arguably the oldest extant treatise with a detailed explicit Trinitarian theology.[39] In his Against Praxeas Tertullian wrote:

And at the same time the mystery of the oikonomia is safeguarded, for the unity is distributed in a Trinity. Placed in order, the three are the Father, Son, and Spirit. They are three, however, not in condition, but in degree; not in being, but in form; not in power, but in kind; of one being, however, and one condition and one power, because he is one God of whom degrees and forms and kinds are taken into account in the name of the Father, and of the Son, and of the Holy Spirit.

— Against Praxeas 2[41]

Others,[who?] however, argue that Tertullian was unitarian,[42] claiming that Tertullian's use of the word "trinity" differs from later Trinitarian use: "For Tertullian, the one God is not the Trinity; rather, the one God is a member of the trinity";[43] "...Tertullian's trinity [was] not a triune God, but rather a triad or group of three, with God as the founding member".[3]