Ontological arguments

A priori arguments and Anselm's Proslogion 2#

StandardAQA 7172 3.3 Metaphysics of God — Ontological argumentsDfE GCE Philosophy subject content

Anselm's Proslogion 2 as a reductio

Fig. 1Assuming God exists only in the mind contradicts the definition of God, so God exists in reality.

The ontological argument is unique among the arguments for God in being a priori and deductive: it appeals to no feature of the world (unlike the a posteriori design and cosmological arguments) but claims that God's existence follows from the CONCEPT of God alone, by reason. If it works, it delivers a necessary conclusion with the certainty of a mathematical proof; if it fails, it is often thought to fail in an instructive way, exposing something about the logic of existence. Its a priori character sets the terms of the debate: the argument cannot be attacked as Hume attacks design (weak analogy) or the cosmological argument (dubious causal principle), but only by challenging its logic or its treatment of existence.

Anselm, in the Proslogion (1078), begins from a definition of God as 'that than which nothing greater can be conceived' (aliquid quo nihil maius cogitari possit) — the greatest conceivable being. Crucially, Anselm claims even the atheist (the 'fool' of Psalm 14 who says 'there is no God') can UNDERSTAND this definition; in understanding the words, the fool has the concept of God in his understanding (in intellectu), whatever he believes about God's existence in reality (in re). So both theist and atheist agree that God, so defined, exists at least as an idea in the mind.

Proslogion 2 then argues by reductio. Suppose God exists only in the understanding and not in reality. But it is greater to exist in reality AND in the understanding than to exist in the understanding alone (a really existing thing is greater than a merely imagined one). So we could conceive of something greater than God — namely, a being just like God but also existing in reality. But this is a being greater than 'that than which nothing greater can be conceived' — a contradiction. So the supposition (that God exists only in the understanding) is false; God must exist in reality as well as in the understanding. The argument's engine is the definition plus the premise that existence-in-reality is a great-making feature: to deny God's real existence, while granting the concept, is to fall into contradiction.

Reconstructed formally: (P1) God is that than which nothing greater can be conceived. (P2) God exists at least in the understanding (even the fool grants the concept). (P3) A being that exists in reality as well as in the understanding is greater than one existing in the understanding alone. (P4) Suppose God exists only in the understanding. (P5) Then a greater being can be conceived (one existing in reality too). (P6) But this contradicts P1 (nothing greater than God can be conceived). (C) Therefore God exists in reality. The argument is valid (the reductio is well-formed); the whole debate is about soundness — in particular, about P3, the claim that existence (or existence-in-reality) is a great-making PROPERTY, which is exactly what Kant will deny.

Worked example

Reconstructing Proslogion 2

Set out Anselm's Proslogion 2 argument as explicit premises and a conclusion, and identify the premise most open to attack.

Definition
P1: God is that than which nothing greater can be conceived. P2: God exists at least in the understanding.
Great-making premise
P3: A being existing in reality and in the understanding is greater than one existing in the understanding alone.
The reductio
Suppose God exists only in the understanding; then a greater (really existing) being is conceivable, contradicting P1.
Locate the weak point
P3 assumes existence-in-reality is a great-making PROPERTY — the very claim Kant denies with 'existence is not a predicate'.

Result: The argument is valid; its soundness hinges on P3, the claim that real existence adds greatness — so the decisive evaluation must assess whether existence is a predicate at all.

Typical mistakes

Stating the argument as 'God is perfect, so God exists' without the reductio structure; the force comes from the contradiction generated by denying real existence.
Confusing 'in the understanding' (in intellectu, having the concept) with 'exists in reality' (in re); the argument moves from the former to the latter, and blurring them misstates it.

Active revision

Outline Anselm's ontological argument from Proslogion 2. (5-mark AO1 response)

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for philosophy (Department for Education)

Necessary existence: Proslogion 3 and Malcolm#

AdvancedAQA 7172 3.3 Metaphysics of God — Ontological argumentsDfE GCE Philosophy subject content

Malcolm's disjunctive syllogism

Fig. 2God's existence is impossible or necessary; it is not impossible; so it is necessary.

In Proslogion 3 Anselm gives a second, stronger argument, concerning not mere existence but NECESSARY existence. He reasons: a being that CANNOT be conceived not to exist is greater than one that CAN be conceived not to exist. God is that than which nothing greater can be conceived. So if God could be conceived not to exist, we could conceive of something greater (a being whose non-existence is inconceivable), which contradicts the definition. Therefore God cannot be conceived not to exist — God exists NECESSARILY, not contingently. This version is significant because it treats God's existence not as one more property added to a being, but as the special MODE of existence (necessity) proper to the greatest conceivable being: God is the kind of thing that, if it exists at all, exists necessarily.

Norman Malcolm (1960) revived and defended Proslogion 3, arguing that while Proslogion 2 falls to Kant (existence is not a predicate), Proslogion 3 does not, because NECESSARY existence, unlike mere existence, may be a legitimate great-making property. Malcolm's version runs: God's existence is either impossible or necessary (God, as the greatest conceivable being, cannot be a contingent being that merely happens to exist or not). God's existence is not impossible (the concept of God is not self-contradictory, unlike 'round square'). Therefore God's existence is necessary — God necessarily exists. The argument's logical form is a disjunctive syllogism: God's existence is impossible or necessary; it is not impossible; so it is necessary.

Malcolm's key move is the claim that God cannot be a contingent being. A contingent being's existence depends on something else and could fail to obtain; but the greatest conceivable being cannot depend on anything or be limited in that way, so God's existence, if possible at all, cannot be contingent — it must be necessary. This connects the ontological argument to the concept of God as a necessary being that also underlies the cosmological argument (the necessary being that grounds the contingent universe). The two arguments thereby illuminate each other: the cosmological argues to a necessary being from the world, the ontological analyses what necessary existence involves.

The decisive objection to Malcolm concerns the premise that God's existence is 'not impossible'. Malcolm needs the concept of God to be COHERENT (logically possible) — for only then can he move from 'impossible or necessary' to 'necessary'. But that God is a coherent, possible being is precisely what an atheist may deny, and what the coherence puzzles of the previous topic (omnipotence, omniscience-and-freedom) put in question. Moreover, critics (following Kant and Findlay) argue that 'necessary existence' may be incoherent or may be merely CONCEPTUAL necessity ('IF God exists, God exists necessarily') rather than the unconditional existence Malcolm wants; the argument may establish only that the concept of God includes necessary existence, not that anything answers to the concept. A balanced verdict is that Proslogion 3/Malcolm is the most resilient form of the ontological argument — it sidesteps the simplest version of Kant's objection by using necessary rather than mere existence — but that it succeeds only if the concept of God is granted to be genuinely possible, which is exactly what is in dispute, so it cannot compel a sceptic who doubts the coherence of the concept.

Worked example

Testing Malcolm's 'not impossible' premise

Explain why the coherence of the concept of God is the crux of Malcolm's argument.

The structure
God's existence is impossible or necessary; not impossible; therefore necessary — a valid disjunctive syllogism.
The vulnerable premise
The second premise, 'not impossible', asserts the concept of God is coherent (logically possible).
Why it matters
If the concept is incoherent (as the coherence puzzles might show), then God's existence IS impossible, and the syllogism concludes the opposite — God necessarily does not exist.
The dialectical result
Malcolm cannot simply assume coherence; a sceptic who doubts the concept blocks the argument, so it presupposes what is in dispute.

Result: Malcolm's argument is valid and avoids the simplest Kantian objection, but it turns entirely on the contested premise that the concept of God is coherent — so it cannot compel a doubter, and connects directly to the coherence-of-God debate.

Typical mistakes

Running Proslogion 2 and 3 together; the second concerns NECESSARY existence and is designed to survive objections to the first.
Overlooking the 'not impossible' premise; Malcolm's argument works only if the concept of God is coherent, which is contestable and is where the real weight lies.

Active revision

'Malcolm's version of the ontological argument succeeds where Anselm's Proslogion 2 fails.' Assess this claim. (25-mark essay)

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for philosophy (Department for Education)

Descartes' version#

StandardAQA 7172 3.3 Metaphysics of God — Ontological argumentsDfE GCE Philosophy subject content

Descartes: existence as a perfection

Fig. 3God has all perfections; existence is a perfection; so God has existence — the disputed premise is that existence is a perfection.

Descartes gives his own ontological argument in the Fifth Meditation, framed in terms of perfection rather than 'the greatest conceivable being'. He argues: I have a clear and distinct idea of God as a supremely perfect being — a being possessing all perfections. Existence is a perfection (a supremely perfect being that lacked existence would lack a perfection, and so would not be supremely perfect). Therefore existence belongs to the nature of a supremely perfect being just as necessarily as having three angles summing to two right angles belongs to the nature of a triangle. So I cannot conceive of God (a supremely perfect being) without existence, any more than I can conceive of a triangle without its properties; hence God necessarily exists.

Descartes' triangle analogy is central and revealing. Just as it is part of the essence of a triangle that its angles sum to 180 degrees — I cannot coherently think of a triangle lacking this — so, he claims, it is part of the essence of a supremely perfect being that it exists; existence is 'inseparable from' God's essence. The argument is thus a claim about what is contained in the concept of God: analysing the concept of a supremely perfect being reveals existence as one of its contents, so 'God exists' is (Descartes thinks) knowable a priori by inspecting the idea, as geometrical truths are.

The argument's distinctive premise is that existence is a PERFECTION. This is meant to be obvious: a thing is better, more perfect, for existing than for not existing, so a being with ALL perfections must have existence. But this is exactly the premise Kant will target: if existence is not a genuine property or perfection at all — if it adds nothing to a concept — then it cannot be one of the perfections a supremely perfect being must possess, and the argument collapses. Descartes' version therefore stands or falls, like Anselm's Proslogion 2, on the status of existence as a property.

Descartes' version also faces the objection, urged by Caterus and others in the Objections to the Meditations, that the argument at most shows a CONDITIONAL: IF God exists, then God exists necessarily (existence is part of the concept), but it does not show that God actually exists — one can always deny the antecedent by refusing to instantiate the concept. Just as 'a triangle has three sides' does not entail 'there exists a triangle', so 'God (the perfect being) has existence' does not entail 'there exists a God'; both are truths about concepts, not about what the world contains. Descartes replies that God is unique in that existence is contained in His essence in a way that makes the concept self-instantiating, unlike the triangle — but this simply restates the disputed claim that existence is a perfection built into God's essence. A balanced evaluation is that Descartes' version is elegant and makes vivid the idea that God's existence, if it follows at all, follows from God's essence; but it inherits Anselm's central vulnerability (existence as a predicate/perfection) and the Caterus objection that a definition cannot by itself guarantee instantiation — both of which the next two sections develop.

Worked example

The Caterus objection

Explain the objection that Descartes' argument establishes only a conditional, using the triangle analogy against him.

Descartes' claim
Existence is contained in the concept of a supremely perfect being, as three-sidedness is contained in the concept of a triangle.
Turn the analogy
But 'a triangle has three sides' does not entail 'a triangle exists'; it is a truth about the concept, not about the world.
Apply to God
Likewise 'the perfect being has existence' shows only that IF God exists, existence belongs to His essence — not that God exists.
Descartes' reply
God is uniquely self-instantiating because existence is a perfection in His essence — but this restates the disputed premise rather than answering the objection.

Result: The Caterus objection shows the argument yields at most a conditional; Descartes' reply that God is uniquely self-instantiating simply reasserts that existence is a perfection, which is precisely what Kant will deny.

Typical mistakes

Confusing Descartes' ontological argument (from the concept of a perfect being) with his trademark/causal argument (from the idea of God as an effect requiring a cause); both appear in the Meditations but are distinct.
Treating the triangle analogy as establishing existence; it establishes only what is CONTAINED in the concept, which is the Caterus objection's point.

Active revision

Explain Descartes' ontological argument and one objection to it. (12-mark AO1 response)

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for philosophy (Department for Education)

Gaunilo's perfect island#

StandardAQA 7172 3.3 Metaphysics of God — Ontological argumentsDfE GCE Philosophy subject content

Gaunilo's parody

Fig. 4The same form 'proves' a perfect island exists — an absurdity — so Anselm replies the island is merely contingent.

Gaunilo of Marmoutiers, a contemporary monk, gave the first great objection to Anselm in 'On Behalf of the Fool'. His strategy is a PARODY (or reductio by analogy): he constructs an argument with the same form as Anselm's but an absurd conclusion, to show the form must be invalid. Imagine the most perfect (or 'most excellent') island conceivable — an island than which no greater island can be conceived, with every perfection an island could have. By Anselm's reasoning, an island that exists in reality is greater than one existing only in the understanding; so if the most perfect island existed only in the mind, we could conceive of a greater (one existing in reality), contradicting its definition; therefore the most perfect island must exist in reality.

But this conclusion is patently absurd — we cannot conjure a perfect island into existence merely by defining it as the greatest conceivable island. Since Anselm's reasoning, applied to the island, yields an absurdity, and the reasoning is the same as that applied to God, the reasoning must be fallacious in both cases. Gaunilo's general point is that you cannot define ANYTHING into existence: from the mere concept of the greatest possible F (island, being, pizza), it does not follow that any F exists in reality. The argument illegitimately moves from a concept in the understanding to existence in reality.

Anselm's reply (in his Response) is that the parody fails because the argument works ONLY for 'that than which nothing greater can be conceived' — a being with NECESSARY existence — and not for contingent things like islands. An island is a contingent thing: however perfect, it could always be improved (add another palm tree, more treasure), so there is no intrinsic maximum, no 'greatest conceivable island'; and an island can always be conceived not to exist, so it lacks necessary existence. God alone is the being whose non-existence is inconceivable (Proslogion 3), so the argument's crucial premise — that the being's non-existence would make it less than the greatest conceivable — applies only to God. The reductio does not transfer, because islands are the wrong kind of thing.

Evaluation weighs whether Anselm's reply succeeds. In its favour: the reply does identify a real disanalogy — islands are contingent and admit no intrinsic maximum of perfection, whereas the concept of God is of a being that, if it exists, exists necessarily and is maximally great by its nature. Gaunilo's parody arguably applies most directly to Proslogion 2 (mere existence) and is answered by moving to Proslogion 3 (necessary existence), which cannot be run for a contingent island. Against the reply: it may concede too much, for it shows that the ontological argument works, if at all, only for a being with necessary existence — and whether there can BE such a being, whether the concept of a necessarily existing being is coherent, is exactly the question at issue (Malcolm's 'not impossible' premise). So Gaunilo's parody, though answerable, usefully forces the argument back onto the harder ground of necessary existence and the coherence of the concept, where Kant's objection awaits. A judicious verdict is that Gaunilo does not by himself refute the argument (Anselm's disanalogy is genuine), but that he shifts the burden decisively: the theist must show not merely that existence is great-making, but that a necessarily existing being is possible — which the argument cannot establish from within itself.

Worked example

Assessing Anselm's reply to Gaunilo

Does Anselm's reply successfully distinguish God from Gaunilo's island?

The parody
Applied to 'the greatest conceivable island', Anselm's reasoning absurdly concludes the island exists.
Anselm's disanalogy
Islands are contingent and admit no intrinsic maximum (always improvable), and can be conceived not to exist; God alone has necessary existence.
The strength
The disanalogy is real: 'greatest conceivable island' arguably has no coherent maximum, while 'greatest conceivable being' is defined as necessarily existing.
The concession
But the reply admits the argument works only for a necessarily existing being — whose possibility (coherence) is exactly what is disputed.

Result: Anselm answers Gaunilo by a genuine disanalogy (contingent island vs necessary being), but at the price of resting the argument on the coherence of a necessarily existing being — so the parody is deflected onto Malcolm's and Kant's terrain rather than refuted outright.

Typical mistakes

Treating Gaunilo's island as a knock-down without Anselm's reply; a fair evaluation must engage the contingent/necessary disanalogy.
Missing that the parody is aimed at the FORM of the argument; Gaunilo grants the premises' form and shows it 'proves' too much, so it is a formal objection, not a denial of God.

Active revision

'Gaunilo's island shows that the ontological argument is fallacious.' Discuss. (25-mark essay)

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for philosophy (Department for Education)

Kant: existence is not a predicate#

AdvancedAQA 7172 3.3 Metaphysics of God — Ontological argumentsDfE GCE Philosophy subject content

Existence versus a genuine predicate

Fig. 5A predicate like 'omnipotent' adds content; 'exists' merely posits an instance — so it cannot be a defining perfection.

Kant delivered what is widely regarded as the decisive objection to the ontological argument: existence is not a real predicate (property). When I say something exists, I do not add a further property to my concept of it; I merely POSIT that an instance of the concept obtains — that something in reality answers to it. Kant's illustration: '100 real thalers contain no more than 100 possible thalers'. The concept of 100 real coins and the concept of 100 possible (merely imagined) coins are exactly the same in content — the real coins do not have an extra property, 'existence', that the imagined ones lack; the difference is only that in the one case there is, and in the other there is not, an object corresponding to the concept. Existence 'adds nothing' to the concept of a thing.

This dismantles the ontological argument at its root. Both Anselm's Proslogion 2 (existence-in-reality is a great-making feature) and Descartes' version (existence is a perfection) require existence to be a PROPERTY that a being can have or lack, and that adds greatness or perfection. If Kant is right that existence is not such a property, then it cannot be one of the great-making features or perfections built into the concept of God; 'God exists' cannot be an analytic truth deducible from the concept of God, but must be a SYNTHETIC claim about whether anything in reality answers to the concept — which cannot be settled by analysing the idea. So the argument's attempt to derive existence from the concept commits a category mistake: it treats 'exists' like 'is omnipotent', a defining predicate, when it is really a matter of instantiation.

Bertrand Russell's theory of descriptions reinforces Kant with the tools of modern logic. Grammatically, 'exists' looks like a first-order predicate ('God exists' seems to have the form 'God is F', like 'God is wise'). But logically, Russell argues, 'exists' is a SECOND-order predicate, a quantifier: to say 'God exists' is to say 'there is exactly one x such that x is omnipotent, omniscient...' — it says of a CONCEPT that it is instantiated, not of an OBJECT that it has a property. 'Cows exist' means 'the concept cow has instances'; 'unicorns do not exist' means 'the concept unicorn has no instances' (and is not the puzzling claim that certain objects, unicorns, have the property of non-existence). On this analysis, existence simply is not the sort of thing that can be a defining property of God, so it cannot be smuggled into the definition — the grammatical surface that made the ontological argument seem to work is logically misleading.

Evaluation weighs the objection's power against the theist's replies. Kant's objection is generally regarded as fatal to Proslogion 2 and Descartes' version, which explicitly treat existence as a great-making property or perfection. The most serious reply is Malcolm's: NECESSARY existence, unlike mere existence, MAY be a genuine predicate, since it concerns not whether the concept is instantiated but the MODE (necessary vs contingent) in which the being exists — and a being's mode of existence does seem to be a feature of it. So Proslogion 3/Malcolm sidesteps the simplest form of Kant's objection. But two points blunt even this. First, it is contested whether 'necessary existence' is a coherent predicate or reduces to the harmless conceptual truth 'if God exists, God exists necessarily' (which does not entail that God exists). Second, and most decisively, Malcolm's argument needs the further premise that God is POSSIBLE (coherent), which the ontological argument cannot itself establish. The considered A-Level judgement is therefore that the ontological argument fails as a proof: Kant's objection sinks the existence-versions decisively, and although the necessary-existence version evades it, that version cannot deliver a real existence claim without independently establishing the coherence of the concept of God — which is exactly what is in dispute. The argument may succeed in ARTICULATING the theist's concept of God as a necessary being, but it cannot COMPEL a non-believer, because it presupposes the very possibility it aims to instantiate. This connects the topic to the coherence-of-God debate and, by contrast, to the a posteriori arguments, which try to establish God from features of the world rather than from the concept alone.

Worked example

Model 25-mark plan: does the ontological argument work?

Plan an essay defending a judgement on whether the ontological argument succeeds.

Thesis
The ontological argument fails as a proof: Kant sinks the existence-versions, and Malcolm's necessary-existence version presupposes God's possibility.
AO1
Reconstruct Proslogion 2 and 3, Descartes' perfection version, and Malcolm's disjunctive syllogism.
Objections
Gaunilo's island (answered by necessity); Kant that existence is not a predicate (so 'God exists' is synthetic); Russell on 'exists' as a quantifier.
Reply and rejoinder
Malcolm answers Kant (necessary existence may be a predicate), but needs the premise that God is possible — precisely what is in dispute.
Judgement
Conclude the argument cannot compel the sceptic: it presupposes the coherence of the concept it aims to instantiate, though Proslogion 3 clarifies the theist's God as a necessary being.

Result: A defensible judgement: the ontological argument does not prove God to a doubter (Kant defeats the existence-versions; the necessary-existence version presupposes coherence), but it valuably articulates God as a necessarily existing being — a conceptual gain, not a proof.

Typical mistakes

Paraphrasing Kant as 'you cannot define things into existence' without the technical claim that existence adds nothing to a concept — the technical point is where the force lies.
Assuming Kant refutes ALL versions; Malcolm's necessary-existence version is designed to evade him, so a full evaluation must engage it before concluding.

Active revision

'Kant's objection that existence is not a predicate destroys the ontological argument.' Is this claim true? Defend your answer. (25-mark essay)

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for philosophy (Department for Education)

Key points

Reconstructing Proslogion 2

Key points

Testing Malcolm's 'not impossible' premise

Key points

The Caterus objection

Key points

Assessing Anselm's reply to Gaunilo

Key points

Model 25-mark plan: does the ontological argument work?

Sources

Ontological arguments

Key points

Reconstructing Proslogion 2

Key points

Testing Malcolm's 'not impossible' premise

Key points

The Caterus objection

Key points

Assessing Anselm's reply to Gaunilo

Key points

Model 25-mark plan: does the ontological argument work?

Sources