One substance, three Persons: is the Trinity of Against Praxeas a Latin logic of degrees, and does it make the Son a lesser God?

Tertullian, answered from the texts and cited to the page.

Tertullian answers

Degrees, yes; lesser, no. Hear what I wrote. The three are three not in condition, but in degree; not in substance, but in form; not in power, but in aspect, and yet of one substance, one condition, one power, inasmuch as He is one God, from whom these degrees and forms and aspects are reckoned.¹ Weigh each pair. In every one of them the first term is what Praxeas wishes to erase, and the second is what I will not surrender.

Condition, substance and power are the things that make a God a God, and I say plainly they are one. Degree, form and aspect belong to the arrangement, the economy, in which the one Unity is distributed into a Trinity and the Persons are set in their order.¹ A man who hears "degree" and cries "lesser" has taken a word of order for a word of worth.

Consider how the Son is known. Scripture does not hide the order; it shows it. In creation God says, Let there be light, and the Word appears, and from that moment God willed creation to be effected in the Word, Christ present and ministering to Him.² Two are there: one who commands that the thing be made, another who executes the order and creates.

But in what sense another? I have explained it on the ground of Personality, not of Substance, in the way of distinction, not of division.² Observe what I do not say. I do not say the one commanding is God and the one executing is a creature. If John is right that the Word was God, then the executor is God, and the commander would not command at all were he only one, for he would have waited to command himself.²

A servant of the work is not thereby a lesser divinity. An emperor's son who administers the empire does not make two empires or half an emperor. The same economy sets the Son on earth and the Father in heaven, and I answered Praxeas on exactly this ground: this is not a separation, it is nothing but the divine dispensation.³ God exists everywhere by power and authority, and the Son, being indivisible from Him, is everywhere with Him; yet in the economy the Father willed the Son to be regarded as on earth and Himself in heaven.³

The Son prays from below and the Father answers from above, and that is the Gospel's own account, the voice of the Son and the voice of the Father, as many Persons as voices.³ Is the one who answers greater in office? So the Scripture arranges it. Is He of another substance? Not once do I say so, and I say the opposite on every page. Hence the charge that I have made a Son who is less belongs to the very man I wrote against.

Praxeas, to save a monarchy, would have the Father and the Son the selfsame Person, and so he abolishes the Son. He cannot even keep his own number: when he distinguishes Jesus as flesh from Christ as spirit he divides the very thing he swore was one, and I told him he had learned his monarchy in the school of Valentinus.⁴ I hold to a distinction without destroying the inseparable union, as the sun and the ray, the fountain and the river are one thing in two aspects.⁴

And what of the Spirit? The Third Name in the Godhead and the Third Degree of the Divine Majesty, the Declarer of the One Monarchy and at once the Interpreter of the Economy.⁵ A third degree of majesty is still majesty. So I ask you the question I put to the Jews in my own day. What difference would there be between us and them, if there were not this distinction you are for breaking down?⁵

God chose to renew His covenant so that His Unity might be believed after a new manner, through the Son and the Spirit, and might now be known openly in His proper Names and Persons.⁵ Strip away the order of the three and you have no Gospel, only the old confession of One refusing to reckon the Son beside Him. Strip away the one substance and you have three gods. I keep both, and the whole treatise is the keeping.

The position in brief

God is one substance, and the one substance is distributed, not divided, into three Persons, Father, Son and Spirit, who differ in degree, form and aspect and not in substance, as the root, the shoot and the fruit are one tree and the sun, the ray and the point are one light.⁶⁷ The Son is a portion of the whole, for the Father is the whole substance; this is derivation, not diminution, and the Word came forth from God as God, not as nothing.

In Christ two substances, divine and human, stand unconfused in one Person, and it was the Son, not the Father, who suffered; Praxeas drove out the Paraclete and crucified the Father.⁸⁹¹⁰

Sources

three, however, not in condition, but in degree; not in substance, but in form; not in power, but in aspect; yet of one substance, and of one condition, and of one power, inasmuch as He is one God, from whom these degrees and forms and aspects are reckoned
Against Praxeas
I have already explained, on the ground of Personality, not of Substance-in the way of distinction, not of division.
Against Praxeas
Now this is not a separation; it is nothing but the divine dispensation.
Against Praxeas
the Father and the Son, which we maintain without destroying their inseparable union-as (by the examples) of the sun and the ray, and the fountain and the river
Against Praxeas
Now, what difference would there be between us and them, if there were not this distinction which you are for breaking down?
Against Praxeas
For God sent forth the Word, as the Paraclete also declares, just as the root puts forth the tree, and the fountain the river, and the sun the ray. For these are probolai/, or emanations, of the substances from which they proceed.
Against Praxeas
And indeed it is not once only, but three times, that we are immersed into the Three Persons, at each several mention of Their names. Chapter XXVII.-The Distinction of the Father and the Son, Thus Established, He Now Proves the Distinction of the Two Natures, Which Were, Without Confusion, United in the Person of the Son. The Subterfuges of Praxeas Thus Exposed.
Against Praxeas
Nothing, however, is alien from that original source whence it derives its own properties. In like manner the Trinity, flowing down from the Father through intertwined and connected steps, does not at all disturb the Monarchy, whilst it at the same time guards the state of the Economy. Chapter IX.-The Catholic Rule of Faith Expounded in Some of Its Points.
Against Praxeas
Jesus, therefore, cannot at this rate be God for He has ceased to be the Word, which was made flesh; nor can He be Man incarnate for He is not properly flesh, and it was flesh which the Word became. Being compounded, therefore, of both, He actually is neither; He is rather some third substance, very different from either.
Against Praxeas
They are your divinities upon whom these base deeds of Jupiter were done. But the Son of God has no mother in any sense which involves impurity; she, whom men suppose to be His mother in the ordinary way, had never entered into the marriage bond. But, first, I shall discuss His essential nature, and so the nature of His birth will be understood.
The Apology

Where the argument is made

Against Praxeas in full (c. 213), especially 2 on the one substance distributed into a Trinity of three Persons, 8-9 on the root, shoot and fruit and the sun, ray and point, 9 and 14 on the Father as the whole substance and the Son as a portion and derivation, 27 on the two substances in Christ unconfused, 29 on who suffered
Apology 21 on the Word as ray from the sun
Against Hermogenes 3 on God's having been Father not always
On the Flesh of Christ and On the Resurrection on the reality of the two natures

How the argument was received

The first Latin grammar of the Trinity, which the councils of the fourth century used and whose language of degrees and portions they had to leave behind.