01The record
Anselm's argument (Proslogion 2-3, c. 1078) proceeds entirely from the concept of God, requiring no observation of the world at all.
Ontological
The Ontological Argument (Anselm, Plantinga)
Anselm's argument from the Proslogion (c. 1078) has never been decisively refuted or widely accepted; Alvin Plantinga's 1974 modal restatement is formally valid, so the entire dispute now rests on whether one premise — that a maximally great being is possible — is true.
medium confidencePhilosophical
THE CLAIM
Anselm's argument from the Proslogion has never been decisively refuted or widely accepted
- 1Anselm's argumentThe record
- 2Gaunilo's Lost Island parody failsThe record
- 3Plantinga's modal versionThe record
- 4Treating necessary existenceThe record
- 5Godel's version was machine-verifiedThe record
- 6The argument's lasting result is a narrowingThe record
WHERE IT STANDS
How far this gets
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The span, dated
c. 1078
Anselm writes the Proslogion
God is defined as that than which nothing greater can be conceived. No appeal to the world, to causation, to design, or to any observation whatever — it runs entirely on the concept.
c. 1080
Gaunilo's lost island
"On Behalf of the Fool," written in Anselm's own lifetime, substitutes an island than which no greater island can be conceived. Anselm's answer: an island's greatness has no intrinsic maximum — any island can be improved by another palm tree.
1781
Kant: being is not a predicate
Critique of Pure Reason, A598/B626. A hundred real dollars contain not a coin more than a hundred possible ones. Widely thought fatal to Anselm's version.
1974
Plantinga recasts it in modal logic
The Nature of Necessity, ch. 10. Necessary existence is treated as a modal property rather than a predicate bolted onto a concept, which sidesteps Kant. Plantinga's own verdict is modest: the argument does not compel assent, but shows that accepting its conclusion is rationally permissible.
1987
Gödel's proof published
Kurt Gödel's formal ontological proof in modal logic, drafted by 1941, published after his death.
2013
A machine checks it
Christoph Benzmüller and Bruno Woltzenlogel Paleo formalised Gödel's proof in higher-order logic and verified it with automated theorem provers.
Anselm's original
Writing at Bec around 1077-78, Anselm defines God as that than which nothing greater can be conceived. Even the fool of Psalm 14:1 who says there is no God understands the phrase, so the being exists at least in his understanding.
But a being that exists in reality is greater than one existing in the understanding alone. So if that than which nothing greater can be conceived existed only in the understanding, a greater could be conceived — which is a contradiction. Proslogion 3 pushes further: such a being cannot be conceived not to exist, and therefore exists necessarily.
The argument is remarkable for what it does not use. There is no appeal to the world, to causation, to design, or to any observation whatever. It runs entirely on the concept.
Plantinga's modal version
In The Nature of Necessity (Oxford, 1974, ch. 10) Alvin Plantinga recast the argument using possible-worlds semantics and the modal system S5:
1. It is possible that a maximally great being exists. 2. Maximal greatness entails maximal excellence in every possible world. 3.
So there is a possible world in which a maximally great being exists. 4. In S5, what is possibly necessary is necessary. 5. Therefore a maximally great being exists in every possible world, including this one.
The inference is valid; that is not disputed. Plantinga's move is that necessary existence is treated as a modal property rather than as an ordinary predicate bolted onto a concept, which sidesteps Kant.
Plantinga's own verdict is modest and worth repeating: the argument does not compel assent, but it shows that accepting its conclusion is rationally permissible. That is a smaller claim than a proof, and he makes it deliberately.
Godel's version and the machine check
Kurt Godel worked out a formal ontological proof in modal logic, drafted by 1941 and published after his death in 1987. In 2013 Christoph Benzmuller and Bruno Woltzenlogel Paleo formalized it in higher-order logic and ran it through automated theorem provers. The provers confirmed that the conclusion follows from Godel's axioms — and also that those axioms entail modal collapse, the result that every truth is necessary.
That is a genuine finding on both sides of the ledger, and it is the most concrete modern development in this argument's history.
What the argument is actually for
Nobody is converted by it, and its defenders say so. Its real payload is this: if God's existence is even possible, it is necessary. Theism cannot be a merely contingent truth.
The God of Exodus 3:14 and Psalm 90:2 — from everlasting to everlasting — is either impossible or actual. There is no third option, and that narrowing is the argument's permanent contribution.
Scripture on this
Exodus 3:14 — I AM THAT I AM — God identified with being itself.
Psalm 90:2 — From everlasting to everlasting, thou art God.
Psalm 14:1 — The fool Anselm addresses directly in Proslogion 2.
1 Timothy 6:16 — Who only hath immortality — existence that is not derived.
Malachi 3:6 — I am the LORD, I change not — necessity expressed as constancy.
Revelation 1:8 — Which is, and which was, and which is to come, the Almighty.
6 pieces of evidence
What this establishes
- 02The record
Gaunilo's Lost Island parody fails because island-greatness has no intrinsic maximum, while necessary existence belongs to the concept of a maximally great being.
- 03The record
Plantinga's modal version (The Nature of Necessity, 1974) is formally valid in S5 — the only live question is whether its possibility premise is true.
- 04The record
Treating necessary existence as a modal property rather than a predicate added to a concept avoids Kant's objection that being is not a real predicate.
- 05The record
Godel's version was machine-verified as valid by Benzmuller and Paleo in 2013 — and the same analysis exposed its modal-collapse cost.
- 06The record
The argument's lasting result is a narrowing: God's existence is either impossible or necessary, never merely contingent.
1 objection taken at full strength
The objections, answered
THE OBJECTION01Gaunilo of Marmoutiers replied in Anselm's own lifetime with "On Behalf of the Fool," substituting an island than which no greater island can be conceived — and observing that the same reasoning would conjure it into existence.
THE ANSWER
Anselm's answer is that the parody fails on the terms of the argument. An island's greatness has no intrinsic maximum: any island can be improved by another palm tree. Necessary existence is not part of what an island is, but it is part of what a maximally great being is.
6 passages
Key verses
Berean Standard Bible
God said to Moses, “I AM WHO I AM. This is what you are to say to the Israelites: ‘I AM has sent me to you.’”
Exodus 3:14
“Before the mountains were born or You brought forth the earth and the world, from everlasting to everlasting You are God.”
Psalm 90:2
“The fool says in his heart, “There is no God.” They are corrupt; their acts are vile. There is no one who does good.”
Psalm 14:1
“He alone is immortal and dwells in unapproachable light. No one has ever seen Him, nor can anyone see Him. To Him be honor and eternal dominion! Amen.”
1 Timothy 6:16
“Because I, the LORD, do not change, you descendants of Jacob have not been destroyed.
Malachi 3:6
“I am the Alpha and the Omega,” says the Lord God, who is and was and is to come—the Almighty.
Revelation 1:8
THE RECEIPTS
Sources
- Anselm of Canterbury, Proslogion (1078)
- Gaunilo of Marmoutiers, Pro Insipiente (1080)
- Immanuel Kant, Critique of Pure Reason, A598/B626 (1781)
- Alvin Plantinga, The Nature of Necessity, ch. 10 (1974)
- Rene Descartes, Meditations on First Philosophy, V (1641)
- Christoph Benzmuller & Bruno Woltzenlogel Paleo, arXiv:1308.4526 (2013)
- Graham Oppy, Stanford Encyclopedia of Philosophy (2023)
◈Contested pointscontested
Kant's objection
Immanuel Kant, in the Critique of Pure Reason (1781, A598/B626), argued that being is not a real predicate — not a concept of something that could be added to the concept of a thing. A hundred real dollars contain not a coin more than a hundred possible ones. On this view Anselm defines a being that would exist if it existed, which is empty.
Kant's objection is widely thought to be fatal to Anselm's version. It is not obviously fatal to Plantinga's.
- The parody runs in reverse. It seems equally intuitive that possibly no maximally great being exists — and in S5 that premise proves, by identical reasoning, that God exists in no possible world. The possibility premise simply is the conclusion, restated in modal vocabulary.
- Nobody has shown maximal greatness to be coherent. 'Possible' here means metaphysically possible, not merely conceivable, and the classical puzzles about omnipotence, and about whether omniscience is compatible with creaturely freedom, leave that unsettled.
- Kant's objection stands against Anselm's original: defining a thing as existing adds nothing to the concept, and no analysis of a concept can settle whether anything answers to it.
- Godel's formalization was proved to entail modal collapse — every truth becomes necessary, and contingency vanishes. Most logicians read that as a reductio of the axioms rather than a triumph.