The Greek trias, translatable as “triad,” “trinity,” or (I think misleadingly) “Trinity,” had been used a few decades before. But the first known use of the Latin trinitas is by Tertullian, and we assume that he coined this Latin term. Actually, we have to talk of earliest uses, because it appears in two works, Against Praxeas (Adversus Praxean) and On Modesty (De Pudicitia), which are probably late works, and we don’t really know which is earlier. Both are from his Montanist period, and all would agree that they date from between 200 and 225 AD.
Elsewhere, in a talk and a forthcoming paper (and here), I’ve analyzed Tertullian’s talk of “the Trinity” (better: “the trinity“) in his much-read Against Praxeas and other works. Essentially, my point is that trinitas in Tertullian refers not to a tripersonal god, but rather to a triad of divine beings which share portions of a material divine nature, or if you like stuff. One of those beings is God. All of that stuff, in Tertullian’s view, composes the one God, and lesser portions came (a finite time ago) to compose the Son of God and the Spirit of God. Each is “divine” in that they are composed of (various amounts of) that stuff.
Let’s suppose that Tertullian’s On Modesty is earlier than Against Praxeas. If that’s true, then this would be the earliest known use of trinitas. First, some context. The title On Modesty makes it sound like it’s about the length of skirts and such. But Dr. Geoffrey Dunn helpfully explains that pudicitia can mean not only modesty but also “decency, virtue, good character or chastity.” (Tertullian, p. 138, n. 136) I’d suggest calling the work On Decency, as he thinks it is indecent, an outrage against the pure reputation of the church that it should include people who have seriously sinned after conversion.
This pungent little screed is a blast against mainstream Christians he thinks are lax sin-enablers, because they allow penitent adulterers and fornicators back into church membership. Tertullian – and honestly, my impression is that he is a huge, insufferable, self-righteous jerk – thinks that serious sins like this can only be forgiven by God, and never by the church. So he thinks, e.g. even one-time pre-marital sex between betrothed Christians should be punished by permanent exclusion from Christian fellowship. This, he thinks, will set a good example about how serious fornication is, and the (presumably lifetime length) repentance of the offending couple will hopefully reconcile them to God, though the church should never admit them. This is all based, really, on a single verse. But apparently in his day, catholics agreed that some sins permanently put one out of the church; the dispute was just whether or not these sexual sins belonged on the list. The majority thought not, and some bishops ruled this, and Tertullian was outraged by it all.
So this is not a theological discussion. And the passage occurs late in the book, ch. 21. He’s rebutting the idea that Peter getting the Kingdom’s “keys” (Matthew 16) means that the church can forgive adultery etc. by Christians. This is part of a paragraph in which he blasts his opponents as “psychics,” i.e. soulish people, immature Christians, as opposed to “spiritual” ones like Tertullian.
Quid nunc et ad ecclesiam et quidem tuam, psychice? Secundum enim Petri personam spiritalibus potestas ista conueniet, aut apostolo aut prophetae. Nam et ipsa ecclesia proprie et principaliter ipse est spiritus, in quo est trinitas unius diuinitatis, Pater et Filius et Spiritus sanctus. Illam ecclesiam congregat quam Dominus in tribus posuit. (source)
Here’s the translation in the old Ante-Nicene Fathers collection (vol. IV, p. 99):
What, now, (has this to do) with the Church, and) your (church), indeed, Psychic? For, in accordance with the person of Peter, it is to spiritual men that this power will correspondently appertain, either to an apostle or else to a prophet. For the very Church itself is, properly and principally, the Spirit Himself, in whom is the Trinity of the One Divinity – Father, Son, and Holy Spirit. (The Spirit) combines that Church which the Lord has made to consist in “three.”
His argument in this section is obscure; my only interest is: is this, or isn’t it an early use of trinitas to refer to a tri-personal god? This translator’s use of the capital-T “Trinity” suggests this. But I think it is not. But first, here’s another (evidently not quite finished) translation by a later scholar:
But what has that to do with the church and especially yours, psychice? For according to the person of St.Peter this power will be suitable to men of the Holy Ghost either an apostle or a prophet. For the church itself is properly and essentially the Holy Ghost himself, wherein is the trinity of our single God, the Father, the Son and the holy Ghost. He is tying together this church, which Our Lord has stated, can be built on only three souls. (source)
Notice that he’s chosen to render unius divinitatis (of the one divinity / divine nature) as a reference to the one God himself. That is, he reads it as a case of referring to a whole via a part (or here, a metaphysical component or ingredient). Oddly, he doesn’t capitalize “trinity.” This translation is grammatically possible. To say, e.g. “Imitate the divine nature” can be a way of saying “Imitate God himself.”
But I think the first translator is more on track. I suggest that the phrase should be translated “in which is the trinity of the one divinity, the Father and Son and Holy Spirit.” Or for “trinity” we might use “triad“; either way, the point is that trinitas here is a plural referring term, picking out those three named, as three (God, his Son, and his Spirit). Its use doesn’t imply that they are one anything, that they compose one anything, one god, one being, or whatever, though the usage is consistent with this view. What he’s (idiosyncratically and speculatively) assuming is that the three are composed of the same divine stuff.
Why render the phrase as I suggest? Because we know from all his works that Tertullian thinks that the one God is the Father, not the trinity, not the Three together. Nor was he unique in this. Thus, in On the Veiling of Virgins, he seems to quote a then-current (c. 200-210?) “rule of faith,” a simple creed:
The rule of faith, indeed, is altogether one, alone immoveable and irreformable; the rule, to wit, of believing in one only God omnipotent, the Creator of the universe, and His Son Jesus Christ, born of the Virgin Mary, crucified under Pontius Pilate, raised again the third day from the dead, received in the heavens, sitting now at the right (hand) of the Father, destined to come to judge quick and dead through the resurrection of the flesh as well (as of the spirit) his law of faith being constant, the other succeeding points of discipline and conversation admit the “novelty” of correction; the grace of God, to wit, operating and advancing even to the end. (source)
The one God here is obviously the Father, not the trinity.
More tomorrow on “Trinity” vs. “trinity”…