Saint Anselm and the Ontological Argument — God, Existence, and the Limits of Reason

Introduction — Where We Are in Medieval Philosophy

The previous lecture examined the faith-reason controversy through two extreme figures: Peter Abelard, who used reason so confidently that his conclusions were condemned by the Church, and Saint Bernard of Clairvaux, who rejected reason so thoroughly that he contradicted himself in the very act of arguing against it.

The lesson from both failures was the same: neither extreme is tenable. Following reason all the way leads to results that contradict orthodox Christian teaching. Abandoning reason entirely is not actually possible — even saying ‘don’t use reason’ requires using reason. Something between the two extremes was needed: a position that takes faith seriously as the primary authority while also using reason genuinely and confidently within proper limits.

Saint Anselm of Canterbury provides the most historically important version of this middle position. He reformulated Augustine’s famous phrase — ‘I do not know in order to believe; I believe in order to know’ — into the principle that would define his entire philosophical project. And within that project, he produced the single most discussed argument for God’s existence in the history of philosophy.

Anselm’s formula:  ‘I believe in order to understand.’ (Credo ut intelligam.) Faith is first: a Christian should not doubt what the Church teaches. But having faith, one should use reason to seek understanding of what faith holds. ‘If he can understand it, let him thank God. If he cannot, let him not raise his head in opposition but bow in reverence.’ Reason operates within faith and in its service — never against it.

1. Anselm — Life and Position

Anselm was born in Italy in 1033 into a noble family. Against his father’s wishes, he became a Benedictine monk at the monastery of Bec in Normandy, France. He eventually became its abbot, and was later summoned — reluctantly — to serve as Archbishop of Canterbury in England, the highest ecclesiastical office in the country. He served in this position until his death in 1109, a tenure marked by persistent political conflict between the English crown and Rome. He died at seventy-six and was eventually canonised.

Anselm’s philosophical goal was precise: to provide rational arguments for the Christian teachings he already held on faith. He was not using reason to discover whether Christianity was true — he was already entirely confident that it was. He was using reason to understand what faith already guaranteed. In his era, the boundaries between what reason could prove and what required revelation had not yet been clearly drawn. Anselm was so confident in reason that he believed he could provide ‘necessary reasons’ not just for God’s existence but for doctrines such as the Trinity and the Incarnation — conclusions that later theologians would regard as beyond the competence of unaided reason.

His most famous work was originally titled Faith Seeking Understanding — a perfect expression of his programme. It was later given the Latin title Proslogium. The ontological argument it contains was, by Anselm’s own account, the result of sustained prayer and reflection — an insight that offered itself to him after many previous attempts to formulate a single self-sufficient proof for God’s existence.

2. What Is Ontology? — Why This Argument Has This Name

The term ‘ontological argument’ was not used by Anselm himself. It was coined by Immanuel Kant in the eighteenth century when he was analysing and criticising it. The name comes from the Greek word ontos, meaning being or existence.

Ontology is the branch of philosophy concerned with the nature of existence itself: what exists in this reality, and what does it mean for something to exist? It is a branch of metaphysics, which asks broader questions about the nature of reality — questions about time, numbers, causation, the soul, the mind. Ontology focuses specifically on the existence question: what is there? What kinds of things exist? What are the conditions for existence?

Kant called Anselm’s argument ‘ontological’ because — unlike the arguments of Thomas Aquinas, which begin from observations about the world — Anselm’s argument begins directly from the concept of what God is (God’s nature, God’s being) and moves from there to the conclusion that God exists. It is a pure conceptual argument: it requires no observation of the world, no experience, no evidence from outside the mind. It needs only one thing: a definition.

What makes this argument unique in the history of philosophy:  Almost every other proof of God’s existence begins from something in the world: the world exists, therefore something caused it; things in the world are ordered, therefore something designed them; things change, therefore something set them in motion. Anselm’s argument bypasses the world entirely. It begins from the concept of God and derives God’s existence from that concept alone. This is why it is philosophically fascinating — and why it has been debated for nearly a thousand years.

3. The NGC Definition — Two Differences That Change Everything

Before any argument can be given, the subject of the argument must be defined precisely. Anselm’s definition of God is the entire foundation of the ontological argument. Every subsequent step depends on it. And the definition is easily stated and easily misunderstood.

God is that than which nothing greater can be conceived.

— Saint Anselm of Canterbury, Proslogion

Many books — including serious philosophy textbooks — give a subtly incorrect version of Anselm’s definition. Before examining the argument, it is worth pausing on the two differences between the correct definition and the incorrect versions.

The abbreviation: Anselm’s definition is often abbreviated as NGC — Nothing Greater Can be Conceived. N = Nothing, G = Greater, C = Conceived. This shorthand is useful for following the argument’s steps.

4. Why No ‘We’ — The Removal of Psychological Limitation

The human mind has limits. Our imagination is bounded by our experience. A person who has only ever seen colours might struggle to imagine a completely new sense modality. A person who has only experienced finite things — objects, events, relationships — will find it very difficult to genuinely imagine the infinite.

If Anselm’s definition said ‘God is the greatest being we can conceive,’ then God would be defined relative to the limits of human cognitive capacity. However talented, however trained, the human mind that is doing the conceiving would impose a ceiling on what God could be. If human imagination can reach only to level X, then God (as ‘we can conceive’) would be capped at level X.

Anselm explicitly refuses this. God is not limited by what a particular mind, or all minds together, can imagine. The definition does not ask ‘what can you conceive?’ — it asks ‘can something greater be conceived?’ The question is not about the conceiver’s capacity; it is about the conceivability of greatness. And this question is asked repeatedly: whatever you have conceived, ask again — can something greater be conceived? If yes, that was not yet God. Keep going until the answer is no. That is God.

The runaway question: Suppose you say: ‘God is very powerful.’ I ask: ‘Can something more powerful be conceived?’ Yes. So that was not God. You say: ‘God is extremely powerful.’ Can something more powerful be conceived? Again yes. You say: ‘God is maximally powerful.’ Now I ask: can something more powerful be conceived? And here the question runs out — not because your imagination has reached its limit, but because power beyond the maximum is logically incoherent. The phrase ‘nothing greater can be conceived’ establishes its stopping point logically, not psychologically.

5. Why Negative — The Removal of Language Limitation

The second distinctive feature of Anselm’s definition is its negative form: ‘nothing greater can be conceived,’ not ‘God is the greatest.’ This connects to a philosophical tradition that runs through Eriugena and back through the entire mystical-theological tradition: the recognition that positive predicates always impose limitations on what they describe.

Every word we use for a positive quality — good, powerful, wise, great — derives its meaning from its contrast with the opposite. ‘Good’ means something because ‘bad’ also means something. ‘Powerful’ is understood in contrast to ‘weak.’ ‘Wise’ in contrast to ‘foolish.’ These words carry their meanings within a system of contrasts.

But God has no opposite. Nothing stands to God the way ‘bad’ stands to ‘good.’ Saying ‘God is good’ in the same sense that a kind person is good, or a pleasant day is good, implicitly places God in the same system of contrasts that operates for ordinary things. And that is inadequate.

By using a negative formulation — ‘nothing greater can be conceived’ — Anselm avoids adding a positive attribute to God. He is not saying God has greatness in the way a mountain has height. He is saying that whatever greatness can be conceived, God is beyond it. The definition points beyond language rather than being limited by language — the apophatic (via negativa) approach.

6. The Great Chain of Being — Setting Up the Hierarchy

Anselm’s argument assumes a framework that was so obvious in his context that he never argues for it — it was simply part of the intellectual air he breathed: the Great Chain of Being. This is the idea that reality is not a flat collection of equal things, but a hierarchy in which beings have different levels of perfection, reality, and value.

• Stones: at the base — exist, but have no life, no sensation, no reason.
• Plants: above stones — exist and live, but have no sensation or reason.
• Animals: above plants — exist, live, and sense, but have no reason.
• Human beings: above animals — exist, live, sense, and reason.
• Angels: above humans — rational beings without the limitations of matter and mortality.
• God: at the summit — that than which nothing greater can be conceived.

In this hierarchical picture, moving up the chain means moving toward greater perfection, greater reality, greater value. And Anselm’s question is: what occupies the very summit of this chain? What is the being beyond which no greater being can be conceived?

Once you are working within this framework, the argument takes a natural shape. Look at a human being. Is a human being the NGC? Clearly not. A human is mortal — so a non-mortal being would be greater. A human has limited knowledge — so a more knowing being would be greater. A human has limited power — so a more powerful being would be greater. Therefore a human is not God.

Continue up the chain: is there a level at which you cannot conceive of anything greater? That level, by definition, is God. This is not a new discovery; it is what the word ‘God’ has always meant in Anselm’s framework. The NGC definition is not introducing a new concept — it is making the existing concept precise.

7. The Argument — Step One: Understanding vs Reality

With the definition in place, the argument can begin. It has a distinctive logical structure: it is a reductio ad absurdum — it assumes the opposite of what it wants to prove, derives a contradiction from that assumption, and concludes that the assumption must be false.

The Painter Analogy — Understanding Without Reality

To clarify the distinction between something existing ‘in the understanding’ versus existing ‘in reality,’ Anselm uses the example of a painter who has conceived a painting in their mind but has not yet executed it.

The painter and the painting: Before a painter puts brush to canvas, the painting exists in the painter’s understanding — the painter has a clear and complete idea of what they intend to create. But the painting does not yet exist in reality. After the painter has actually created it, the painting exists in both the understanding (the painter still has the idea) and in reality (the canvas with paint). The point: these are two genuinely different modes of existence, and existing in reality is an additional condition beyond existing merely as a mental idea.

Applying this to God: suppose God exists only in the understanding — as an idea in the mind — but not in reality. Then we can conceive of something even greater: a being exactly like our concept of God, except that it also exists in reality. A God who actually exists is greater than a God who is merely an idea. But then the God we started with — the one who only exists in the understanding — is not the NGC. Because we just conceived of something greater. This is a contradiction.

The contradiction proves that the initial assumption — God exists only in the understanding — must be false. Therefore God exists in reality.

The Bachelor Analogy — How the Argument Claims to Work

Anselm’s argument claims that simply understanding the concept of God is enough to know that God exists. The philosopher might compare this to how we understand other definitional truths.

The bachelor analogy: If I know what a bachelor is — an unmarried man — I know automatically that all bachelors are unmarried. I don’t need to survey any bachelors or observe them. It follows from the definition. ‘Unmarried’ is entailed by ‘bachelor.’ Anselm claims something analogous: that ‘exists in reality’ is entailed by ‘that than which nothing greater can be conceived.’ Understanding the NGC means understanding that it must exist, just as understanding ‘bachelor’ means understanding that the person is unmarried.

Whether this analogy holds is precisely what the debate is about. For ‘bachelor,’ the definitional truth tells us nothing about whether any bachelors actually exist in the world. It just tells us that IF something is a bachelor, it is unmarried. The question is whether Anselm’s argument genuinely establishes God’s existence, or whether it only establishes: IF something is the NGC, it exists. These are very different conclusions.

8. The Argument — Step Two: Contingent vs Necessary Existence

Anselm does not stop at establishing that God exists. He takes a further step — one that is found in his third chapter of the Proslogium and that many textbooks omit. He argues that God does not merely exist, but exists necessarily.

To see why, consider the difference between two kinds of existing things:

• Contingent beings exist — but they could have not existed. The Empire State Building exists, but it might never have been built. You exist, but you might not have been born. Stars exist, but specific stars might not have formed. These beings are real, but their existence is not guaranteed by what they are; they depend on circumstances, causes, and conditions that might not have obtained.
• Necessary beings exist in a different way — their non-existence is impossible. Mathematical truths are like this: 2+2=4 cannot fail to be true; the number four necessarily is what it is. If God is the NGC, then God must be necessary in this sense: a being whose non-existence is impossible is greater than a being whose non-existence is possible.

Why is necessary existence greater? Because a contingent being’s existence depends on other things — on conditions being met, on causes producing it, on lucky circumstances. A being that depends on other things for its existence is in some way less than fully independent. The NGC cannot depend on anything for its existence — there is nothing ‘above’ or ‘beyond’ the NGC for it to depend on. Therefore the NGC must be self-sufficient, uncaused, and in that sense necessary.

The impossibility of God not existing: If you say ‘it is possible that God does not exist,’ you are implying that God is the kind of being whose existence depends on conditions, like the Empire State Building. But the NGC cannot be like that — something even greater could be conceived (a being whose existence is not conditional). Therefore the NGC must be necessarily existent. God’s non-existence is not just false — it is logically impossible. It is as impossible as 2+2 equalling 5. The ‘fool’ who says in his heart ‘there is no God’ is not just wrong — he is contradicting himself without knowing it.

9. Gaunilo’s Two Objections

Almost as soon as Anselm published his argument, a contemporary monk named Gaunilo wrote a famous critique titled ‘On Behalf of the Fool’ — taking up the perspective of the person who says in their heart ‘there is no God.’ Gaunilo was himself a Christian and had no wish to disprove God’s existence. He wanted to show that Anselm’s argument contained a logical flaw. His two objections remain the most important criticisms of the ontological argument.

Objection One — Do We Have a Clear Concept?

Gaunilo’s first objection strikes at the very beginning of the argument: before we can argue from the concept of God to God’s existence, we need to be sure we actually have a coherent, precise concept to work with.

Anselm defines God as ‘that than which nothing greater can be conceived.’ This phrase is impressive. When we hear it, we feel something — a sense of awe, of greatness beyond imagining, of something ultimate. But Gaunilo asks a very precise question: is this a genuine, logically determinate concept, or is it only a powerful emotional response dressed up in the language of a concept?

The beautiful view example: Tell ten different people: ‘Imagine the most beautiful view in the world.’ One person imagines the Himalayas at dawn. Another imagines a sunset over the Pacific Ocean. A third imagines the green valleys of Ireland. A fourth imagines the Northern Lights. Each person imagines something different. The phrase ‘most beautiful view’ generates a strong emotional reaction — beauty, wonder, appreciation — in all of them. But they are not all imagining the same thing. The phrase does not pick out a single, determinate mental content. It triggers a feeling, not a concept.

Gaunilo argues that ‘the being than which nothing greater can be conceived’ may work the same way. We are finite beings, limited to finite experiences. We can compare things — this mountain is grander than that hill, this piece of music is more beautiful than that one. From these relative comparisons, we might try to extrapolate to an absolute perfection: the most powerful, the most good, the most beautiful, beyond all limit. But is this extrapolation a genuine concept of an infinite being — or is it only a feeling of ‘something very, very great, projected outward without limit’? If it is the latter, then Anselm’s argument starts from a vague emotional impression and tries to derive a rigorous logical conclusion from it. The argument would fail not at a later step but at its very first step.

Objection Two — The Perfect Island

Gaunilo’s second objection is his most famous. It does not attack the concept of God directly. Instead, it attacks the logical form of the argument by showing that the same form, applied to something else, leads to an absurd conclusion.

The Perfect Island: Imagine the most perfect conceivable island. It has the most beautiful beaches, the most pleasant climate, the clearest water, the most spectacular landscapes — everything that could make an island perfect, this island has. Call it the Perfect Island. It exists in our understanding. Now apply Anselm’s logic: a Perfect Island that also exists in reality is greater than one that exists only in the understanding. Therefore, to be truly the most perfect island, it must exist in reality. Therefore the Perfect Island exists in reality.

Gaunilo does not believe the Perfect Island actually exists. His point is philosophical: if Anselm’s argument were a valid form of reasoning, it would apply not just to God but to any ‘most perfect’ thing — the most perfect island, the most perfect painting, the most perfect detective. In each case, the same logical structure would conclude that the ‘most perfect’ version must exist in reality. But this is clearly absurd. We all know that inventing the phrase ‘most perfect island’ does not create an island. If the argument proves too much — if it would prove the existence of perfect islands, paintings, and detectives — then something is wrong with the argument itself.

10. Anselm’s Reply to Gaunilo

Anselm’s response to the Perfect Island objection is philosophically interesting and partially successful. He argues that the analogy between the Perfect Island and God fails because ‘perfect’ or ‘most great’ means something entirely different in the two cases.

An island is a particular kind of thing — a landmass surrounded by water, with certain possible features: beaches, vegetation, climate, wildlife. Its perfection is island-perfection: the best possible beach, the best possible climate. But no matter how perfect, the island remains a finite, particular, located thing. It is in one place, not another. It has this landscape, not all landscapes. It is limited by what islands can be.

God, as the NGC, is not the best member of any category. God is not the best being in the universe the way a Perfect Island would be the best island. God transcends all categories, all finite limitations, all classification by type. The NGC is not ‘things’ taken to their limit — it is the being beyond all things, beyond all limits, beyond all categories.

Therefore, Anselm argues, you cannot use his logical form on finite things like islands, because ‘most perfect’ in that context always remains within a finite class. But God = NGC is not within any finite class. The argument only works for the specific case of the NGC — the only concept that genuinely points beyond all finitude and all limitation.

The problem Anselm cannot fully escape: His reply to the island objection is logically sound as far as it goes. But notice where it leads. By saying that the NGC is beyond all finite categories — beyond all limited conceptions — Anselm is effectively admitting that human minds cannot form a clear, determinate concept of the NGC. And this is exactly what Gaunilo’s first objection claimed. Anselm’s reply to the second objection returns us, unavoidably, to the first objection.

11. The Deeper Question — Can Reason Reach Reality Through Concepts Alone?

Behind both of Gaunilo’s objections lies a more fundamental question — one that the ontological argument forces into the open and that philosophy has never fully resolved. Can reason alone, by analysing the content of a concept, establish what exists in reality?

This is the real question at the heart of the ontological argument. And Anselm is not the only one who has to answer it.

The triangle and chess examples reveal a general principle that many philosophers have defended: logical necessity and actual existence are different things. Logical necessity tells us about the relationships between concepts — if this, then that. Actual existence tells us about what is in the world. And the gap between these two cannot be crossed by logic alone; it requires some contact with the world, some observation or evidence that the concepts apply to anything real.

If this is right, then Anselm’s argument — however elegant its logical structure — cannot establish God’s actual existence. It can establish: IF there is a being answering to the NGC description, that being necessarily exists. But the ‘if’ cannot be removed by analysis alone.

The detective analogy: Define the perfect detective as the one who can solve every mystery. Now apply Anselm’s logic: a perfect detective who exists in reality is greater than one who exists only in the mind. Therefore the perfect detective must exist in reality. But we all know this is absurd. Defining something as ‘perfect’ at solving mysteries does not bring a detective into existence. The definition tells us what such a detective would be like; it does not establish that any such detective is real.

12. The Platonic Realism Connection

The ontological argument does not exist in philosophical isolation. It connects directly to the debate about universals that occupied the previous lecture — specifically, to the question of whether universal concepts correspond to something in reality or are only mental constructions.

Anselm was a Platonic realist. He believed that when the mind grasps a universal concept — beauty, justice, equality, humanity — it is not merely creating a private mental image. It is connecting to something objective: a real form, a real universal, that the concept refers to. The knowing mind and the universal it knows are genuinely connected.

Within this Platonic framework, the ontological argument becomes much more plausible. If concepts genuinely refer to real universals — if thinking about absolute perfection means the mind is in contact with something real — then following the concept of the NGC through to its logical implications might genuinely tell us something about what exists. The connection between the concept and reality is already guaranteed by realism.

But if you are a nominalist — if you believe universals are only names, and concepts are only mental constructions with no guaranteed reference to anything outside the mind — then the ontological argument fails at its very first step. You are working entirely within concepts; you cannot derive existence from concepts alone, because concepts have no automatic connection to reality.

This is why the ontological argument has divided philosophers along the same lines as the debate about universals. Realists tend to find the argument plausible; nominalists and conceptualists tend to find it obviously flawed. And this is not coincidental — the two debates are expressions of the same underlying question about the relationship between thought and reality.

Hegel’s view: Hegel held that the distinction between thought and its objects is itself a distinction within thought — because the only way the mind can ever know anything is through its own states. From this, he concluded that consistently reasoned thinking is not just valid but true — that the structure of rational thought mirrors the structure of reality. On these premises, the ontological argument is entirely correct: the totality of consistent thoughts is the totality of what is real. Most philosophers do not accept Hegel’s premise — but his sympathy for the ontological argument shows how the argument depends on deep assumptions about the mind-reality relationship.

13. Why the Debate Has Not Ended

Anselm presented his argument in approximately 1078. It is now nearly a thousand years later. The debate has not ended. Philosophers still disagree about whether the argument succeeds. This longevity is not because the question is simply too hard to settle — it is because the argument touches questions that remain genuinely open.

Every generation of philosophers has rediscovered the argument in their own terms:

• Descartes (17th century): Reproduced a version of the ontological argument as part of his own proof of God’s existence in the Meditations. If we have a clear and distinct idea of a perfect being, it must exist.
• Leibniz (17th century): Modified and defended the argument, adding the requirement that the concept of God must first be shown to be logically possible (non-contradictory) before the argument can proceed.
• Hume (18th century): Argued that existence is not a predicate — that adding ‘exists’ to a concept adds nothing to the concept itself. A real hundred dollars and an imagined hundred dollars differ in what they can do for you, not in the concept of a hundred dollars.
• Kant (18th century): Made the decisive classical refutation: existence is not a predicate. The concept of a hundred dollars does not change when the dollars are real versus merely imagined. Adding ‘exists’ to a concept never enriches the concept — therefore the ontological argument cannot derive existence from a concept.
• Modern logic (20th century): Godel produced a formal modal logic version of the argument. Philosophers such as Alvin Plantinga have defended versions using possible worlds semantics. The debate continues in highly technical form.

The reason the argument refuses to die is that it touches one of the genuinely deepest questions in all of philosophy: Can pure reason, without any input from experience, give us knowledge of what exists? This question — which Kant called the question of whether synthetic a priori knowledge is possible — runs through the entire history of philosophy from Anselm through Kant to the present.

14. The Significance for Faith and Reason

The ontological argument is not just an interesting puzzle about God. It is the place where the medieval faith-reason controversy becomes most philosophically sharp.

Anselm’s formula — ‘I believe in order to understand’ — expresses his compromise: faith first, reason second. But the ontological argument represents his attempt to show that, for someone who already has faith, reason can produce genuine and rigorous understanding. If the argument works, then faith and reason are genuinely harmonious: what faith holds as certain can be proven by reason to be necessarily true.

If the argument does not work — if it turns out that existence cannot be derived from the analysis of a concept, and that reason cannot independently reach God — then the faith-reason relationship is in a different and more precarious position. Faith would be affirming what reason cannot prove. The two would coexist, but their relationship would need to be rethought.

This is precisely why the ontological argument matters so much for medieval philosophy. It was Anselm’s most ambitious attempt to show that faith and reason point to the same truth. The success or failure of that attempt has implications for the entire faith-reason controversy — not just for the specific question of whether God exists.

Thomas Aquinas, coming a century and a half after Anselm, would decide that the ontological argument does not work — and would offer five different arguments for God’s existence that begin not from a concept but from observations about the world. His decision represents a careful response to exactly the problem that Anselm’s argument reveals: that reason, when it tries to go purely from concepts to existence, may not be able to make the journey.

Conclusion

The ontological argument is the most audacious argument in the history of philosophy of religion. It asks: can we prove that God exists without observing the world — purely from the definition of God? Can the human mind, by thinking carefully about what God must be, arrive at the certain knowledge that God is?

Anselm’s answer was yes. God is the being than which nothing greater can be conceived. If such a being existed only as an idea, something greater could be conceived — the same being, but also existing in reality. But then the original being was not the NGC. Contradiction. Therefore the NGC must exist in reality. And not just exist, but exist necessarily — because a contingent God would not be the NGC.

Gaunilo’s objections were two: first, we may not have a genuine, precise concept of the NGC at all — only an emotionally powerful but vague idea. Second, the same logical form applied to a perfect island yields an absurd conclusion — therefore something is wrong with the form. Anselm replied: a perfect island is finite; the NGC is not; the analogy fails. But this reply returns us to the first objection.

Beneath these specific debates lies the deepest question: can reason alone — by analysing what a concept means — establish what exists? The triangle proof does not prove triangles exist. The chess analysis does not prove the position is on a real board. Can the analysis of NGC establish that God exists? This question was not settled by Anselm and Gaunilo. It was not settled by Descartes or Leibniz. Kant’s critique — that existence is not a predicate — came closest to a decisive answer, but even this is disputed.

What makes the ontological argument permanently important is not that it solves the question but that it identifies it with the utmost precision. It shows exactly where the tension between reason and reality lies, exactly what would need to be true for pure reasoning to reach existence, and exactly what the deepest assumptions of the faith-reason controversy ultimately come down to. For that reason, the argument Anselm wrote in three pages in the eleventh century remains alive, actively discussed, and genuinely unresolved today.

Frequently Asked Questions