Tertullian's opening assault on Marcion argues from the ground up that there can only be one God, dismantling the case for a second, higher deity before Marcion's actual doctrines are even addressed.
Book One of Tertullian's Against Marcion opens not with a survey of Marcion's teaching but with a demolition of its premise: that two gods, an inferior Creator and a superior stranger-god revealed in Christ, can coexist. Tertullian recounts that this is already his third attempt at the treatise, an earlier draft having been mangled and leaked by a disloyal copyist, and he uses that occasion to write a fuller, more rigorous version. From there he builds a chain of arguments that God's very definition -- supreme greatness -- excludes plurality, since two supreme things cannot both be supreme without one exceeding the other and so ceasing to be equal.
The book unfolds as a running case against a second, unknown god who appears in history only in the fifteenth year of Tiberius, with no antecedent creation, no world, no prior signs, and no witnesses -- unlike the Creator, who is known through the world he made and the prophets who spoke of him from Eden onward. Tertullian presses the absurdity of a god who owns nothing, made nothing, and yet is credited with the one 'great work' of redeeming man from someone else's world. He then turns the argument onto Marcion's prized attribute, the stranger-god's exclusive goodness, showing it to be neither natural, nor rational, nor perfect, since it saves only some and never judges, condemns, or enforces anything it commands. The book closes by opening the subject of Marcion's rejection of marriage, a doctrine Tertullian says will stand or fall on whether that condemnation is just.
Historically, this treatise is Tertullian's fullest surviving engagement with Marcionism, the second-century movement that split the God of the Old Testament from the Father of Jesus and produced its own edited canon of Luke and Paul. It matters as direct evidence for how mainstream Christian writers argued monotheism against a rival Christian cosmology, and as a witness to Marcion's own now-lost writings, which survive mainly through Tertullian's hostile paraphrase and rebuttal.
“Whatever I have done against Marcion up to now, let it stand or fall for itself; I am starting a new work out of an old one.”
— Adversus Marcionem 1 – Chapter 1
“The man from Pontus brings forward two gods, like two clashing rocks to wreck his own ship on: the one he could not deny to be the Creator, that is, ours; and the one he will never be able to prove, that is, his own.”
— Adversus Marcionem 1 – Chapter 2
“But Christian truth has flatly declared: if God is not one, he is not at all — since we rightly believe that whatever is not what it ought to be, simply is not.”
— Adversus Marcionem 1 – Chapter 3
“It was in Tiberius's fifteenth regnal year that Christ Jesus condescended to glide earthward out of the heavens, a spirit bringing salvati”
— Adversus Marcionem 1 – Chapter 19
“But God, as he is eternal and rational, is, I think, also perfect in all things: "You shall be perfect, as your Father who is in heaven is perfect."”
— Adversus Marcionem 1 – Chapter 24
It is the first of Tertullian's five books against the heretic Marcion, and it focuses on a single foundational question: can there be more than one God? Tertullian argues that the very concept of supreme greatness rules out a second, higher god alongside the Creator, before ever discussing Marcion's specific teachings about Christ or scripture.
Marcion of Pontus taught that the vengeful Creator-God of the Old Testament was a lesser being than the good, unknown Father revealed by Jesus, and he compiled his own canon of an edited Luke and ten Pauline letters to fit this scheme. Tertullian saw this as a direct threat to the unity of scripture and of God, and wrote this treatise, his longest surviving work, to refute it point by point.
In Chapter 1 he explains that his first draft was hurried and that he had already discarded a fuller second version when a disloyal associate copied it inaccurately and circulated it without his consent. He wrote this version to correct that damage and give the argument its proper, deliberate form.
He argues that 'supreme greatness' is by definition singular: if two beings both held it, one would necessarily be able to exceed or oppose the other, and neither would then truly be supreme. He extends this into a broader case that Marcion's god, lacking any antecedent creation or world of his own, cannot be shown to exist at all in the way the Creator plainly can.
He insists that any divine attribute must be natural, rational, and perfect to count as real, and argues Marcion's god's goodness fails all three: it rescues only some people, never judges or punishes sin, and forbids commandments it will never enforce, making it what Tertullian calls a 'phantom discipline.'
It ends by opening that subject: Chapter 29 states that Marcion's church only baptizes the virgin, widowed, unmarried, or divorced, and that his whole doctrine 'will stand or fall on the condemnation of marriage,' a topic Tertullian says he will now examine to see whether that condemnation is just.
No — Tertullian explicitly defers that to a later book, noting in Chapter 19 that 'a whole book will be given over to Christ, on his entire condition,' since he wants the question of God's unity settled first before turning to Christology.
It is one of the fullest ancient sources for reconstructing Marcion's actual arguments, since Marcion's own writings do not survive independently and are known largely through hostile quotation in works like this one. It also shows how early Christian writers defended a single, unified God against a rival Christian cosmology that split creation from redemption.
Ad Martyras · Ad Nationes 1 · Ad Nationes 2 · Adversus Marcionem 2 · Adversus Marcionem 3 · Adversus Marcionem 4 · Adversus Marcionem 5 · Adversus Praxean · Apologeticum · De Anima · De Baptismo · De Carne Christi