What does it actually mean for God to be “one”? Most people accept monotheism as a matter of religious tradition or personal belief. But John Duns Scotus – the medieval philosopher-theologian known as the Subtle Doctor – went further. He argued that the oneness of God is not simply a matter of faith: it is a logical and metaphysical necessity. His doctrine of the Unicity of God stands as one of the most rigorous philosophical defenses of monotheism ever constructed, using the nature of will, love, and infinity to demonstrate that more than one God is not just unlikely, but conceptually impossible.
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Who was John Duns Scotus?
John Duns Scotus (c. 1266-1308) was a Scottish Franciscan friar, priest, and university philosopher whose influence extended across both Catholic and secular thought. He is considered among the most important philosopher-theologians of the High Middle Ages, alongside Thomas Aquinas, Bonaventure, and William of Ockham. The doctrines for which he is best known include the univocity of being – the idea that existence is the most abstract concept applicable to everything that exists – the formal distinction, and the concept of haecceity, the “thisness” that makes each individual thing uniquely itself.
His great work, the Ordinatio (also known as the Opus Oxoniense), is a detailed commentary on the Sentences of Peter Lombard and contains nearly all the philosophical arguments for which he is well known, including his renowned proof for God’s existence. It was within this ambitious framework that Scotus directly addressed a question most philosophers of his day considered settled by scripture: is there only one God – and if so, how do we know?
What is the “unicity” of God?
The term unicity refers not simply to oneness in number, but to a deeper philosophical claim: that the singular existence of God is a necessary feature of what it means to be God, not merely a theological assertion. Scotus makes a crucial distinction here. To say God is “one” in the way that there happens to be one sun in our solar system is very different from saying that God’s oneness is built into the very concept of divine being itself. For Scotus, it is the second, stronger claim that is true.
Before arriving at the question of unicity, Scotus builds an elaborate proof of God’s existence. According to the Internet Encyclopedia of Philosophy, his argument proceeds through a triple primacy: he first establishes that there is a first efficient cause, a preeminent being, and a first final cause. He then shows that only one nature can hold all three primacies simultaneously, and that any nature holding even one of these primacies must be infinite. The conclusion – that there is only one infinite being – then directly sets up the doctrine of unicity. As the Ordinatio makes clear, the very next question after proving God’s infinite nature is whether that nature can belong to more than one being. Scotus answers with a firm no, and provides multiple arguments to prove it.
The argument from infinite intellect
Scotus’s first major argument for unicity draws on the nature of infinite intellect. The reasoning works as follows: if two Gods existed, they would necessarily know each other with perfect completeness, since each possesses infinite understanding. But here a problem arises. For the first God to know the second, it must either know the second through the second’s own essence, or through something else.
If it knows God B through God B’s essence, then God A’s knowledge is in some way dependent on – and therefore comes after – God B’s essence. But that would mean God A is not truly first and self-sufficient. If, on the other hand, God A does not know God B through God B’s essence, then God A does not know God B in the most perfect way possible, which contradicts the premise of infinite intellect. As Scotus’s argument in the Opus Oxoniense shows, either horn of this dilemma undermines the claim that both beings are fully and equally divine. Therefore, there can be only one being with an infinite intellect – and that being is God.
The argument from infinite will
The second major argument concerns the nature of the divine will. In Scotus’s metaphysics, the will is not a passive feature of a nature but an active power capable of opposites – it can choose to act or not act, and in God’s case, it is entirely unlimited in scope. This is closely tied to his identification of God as strongly voluntarist: Scotus is associated with theological voluntarism, the tendency to emphasize God’s will as foundational to all philosophical and theological questions.
Now, suppose two Gods exist – call them God A and God B. Each possesses an infinite will. God A, as omnipotent, can will that something must exist. But God B, also omnipotent, can will that same thing not to exist. The result is a direct contradiction: the same thing would simultaneously have to exist and not exist. As the scholastic notes on the Opus Oxoniense explain, a multiplicity of Gods therefore necessitates a contradiction. Two infinite wills cannot coexist without one limiting or overriding the other, and the moment one infinite will limits another, neither remains truly infinite. The concept of multiple infinite wills is thus self-defeating.
The argument from natural love
Perhaps the most philosophically striking of Scotus’s arguments comes from the nature of love as a divine attribute. This argument depends on a principle Scotus considers foundational: every being, if it is not part of something greater than itself, naturally loves itself more than it loves anything else. This is what Scotus calls natural love – a love rooted in the very nature of a being, prior to any free choice.
Apply this to two hypothetical Gods. God A, being entirely distinct from God B and not part of any wider unity, naturally loves itself more than it loves God B. But here is the problem: since God B is infinitely good, an infinite will must love God infinitely. So God A’s infinite will is required to love God B as much as it loves itself – but its natural love directs it to love itself more. The result is an irresolvable contradiction within the very nature of the divine: the natural love and desire rooted in each being tend toward something infinite, and two infinitely good beings cannot both command the kind of total, supreme love that divine perfection demands from an infinite will. The two would each require to be loved absolutely and equally, yet natural love resists this perfect equivalence. Once again, the concept collapses under its own weight.
Why not just accept it on faith?
A significant feature of Scotus’s project is his explicit rejection of the view that God’s unicity can only be accepted on faith and never demonstrated by reason. Some of his contemporaries held that to prove God’s oneness would require knowing God’s essence, which human reason cannot access. Scotus disagrees. As the scholastic notes from the Opus Oxoniense record, he identified at least seven distinct ways to prove the unicity of God – drawing on infinite intellect, infinite will, omnipotence, and more. For Scotus, the Bible does not state that God is singular because unicity is unprovable; it states it because the people needed to be told what reason could, in principle, work out on its own.
This is entirely consistent with his broader philosophical stance. The Routledge Encyclopedia of Philosophy notes that Scotus’s proof of God’s existence is the most ambitious of the entire scholastic period precisely because it tries to integrate diverse lines of traditional argument into a single, sustained demonstration. Unicity is the capstone of that demonstration – the final logical step confirming that the infinite being whose existence has been proved cannot be replicated or multiplied.
The principle of perfection and unity
Running through all of Scotus’s arguments is a deeper metaphysical principle: perfection entails unity. Divine perfection – understood as infinite goodness, infinite will, infinite intellect, and omnipotence – is not compatible with division or multiplicity at the level of the divine nature itself. If there were two Gods, the differences between them would have to be accounted for somehow. Either they differ in their perfections, in which case neither is fully perfect; or they are perfectly identical in every attribute, in which case there is no real ground for calling them two distinct beings at all.
This is not merely a theological point. It reflects Scotus’s broader metaphysical framework in which being, unity, truth, and goodness are transcendentals – properties that go beyond any particular category of existence and apply to being as such. As the Internet Encyclopedia of Philosophy explains, Scotus identifies the unique being whose existence he proves as one that is first efficient cause, ultimate final cause, and most preeminent nature all at once – and concludes that there cannot be more than one such being with this triple primacy. The very structure of what it means to be the most perfect being rules out duplication.
Scotus and the broader medieval debate
It is worth placing Scotus’s argument in context. Medieval philosophers were not responding to modern polytheistic traditions in an anthropological sense; they were engaging with inherited philosophical arguments – some rooted in Neoplatonism, others in Aristotle – that could potentially be read as admitting multiple divine principles or emanations. Scotus’s contribution was to cut through these ambiguities with tight logical argument rather than scriptural authority alone.
His approach also differs meaningfully from that of Thomas Aquinas. While both agreed that knowledge of God must begin from creatures and proceed through effects to causes, Scotus believed certain predicates could be applied univocally – with exactly the same meaning – to both God and creatures, whereas Aquinas held that only analogical predication was possible. This difference matters for unicity: Scotus’s univocal framework allows him to reason more directly about what “infinite will” or “infinite intellect” must mean, and therefore what follows logically when you posit more than one such being. His arguments have a sharper logical bite precisely because he believes our concepts, when properly refined, genuinely apply to God.
The lasting significance of the argument
Scotus’s doctrine of unicity is not a peripheral point in his philosophy – it is the culmination of his entire natural theology. By the time he addresses it in the Ordinatio, he has already proved the existence of an infinite being and established its key attributes. The unicity argument then closes the case: this being is not only infinite and perfect, but necessarily singular. As Encyclopedia.com notes, his philosophy is fundamentally founded on love – and it is precisely this concept of love, rigorously examined, that reveals why even the most internally coherent version of polytheism cannot survive philosophical scrutiny.
For Scotus, monotheism is not a preference or a tradition. It is what reason, taken seriously and followed carefully, demands.
What do you think? If the existence of multiple infinite wills necessarily leads to contradiction, does that mean our very concept of “infinity” already contains within it the idea of uniqueness – and what might that imply for how we think about perfection in other domains? And is Scotus right that faith and reason ultimately point to the same conclusion about God’s oneness, or does his argument only work within a framework that already assumes certain theological premises?
References
- https://plato.stanford.edu/entries/duns-scotus/
- https://iep.utm.edu/john-duns-scotus/
- https://en.wikipedia.org/wiki/Duns_Scotus
- https://sarcanor.substack.com/p/duns-scotus-the-unicity-of-god-notes
- https://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/duns-scotus-john-bl
- https://www.rep.routledge.com/articles/biographical/duns-scotus-john-c-1266-1308/v-1/sections/proofs-for-the-existence-of-god
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