The ontological argument in Christianity
Christianity produced the classical ontological argument (Anselm, 1078) and has revived it repeatedly — from Descartes's clear-and-distinct formulation to Gödel's modal proof and Plantinga's possible-worlds reformulation.
The ontological argument is uniquely Christian in origin. Anselm of Canterbury, in his Proslogion (1078), reasoned that God — 'that than which nothing greater can be conceived' — cannot exist only in the understanding, because to exist in reality is greater than to exist only in thought. Therefore God must exist in reality. Every major medieval Christian philosopher weighed in: Thomas Aquinas rejected Anselm's form; Duns Scotus modified it; Bonaventure embraced it.
The argument had a second life in early modern philosophy. Descartes, in the Fifth Meditation, gave the cleanest seventeenth-century version: existence is a perfection, God has all perfections by definition, therefore God exists. Leibniz added a crucial missing step — a proof that the concept of God is coherent, without which the other steps do not go through. Kant's Critique of Pure Reason issued the canonical objection: existence is not a predicate, so listing 'exists' among God's perfections begs the question.
Twentieth-century Christian philosophers revived the argument in modal logic. Charles Hartshorne, Norman Malcolm, and Alvin Plantinga developed versions that trade on the distinction between necessary and contingent existence. Plantinga's modal ontological argument (1974) runs: it is possible that there exists a maximally great being (one that is omniscient, omnipotent, and morally perfect in every possible world); if such a being is possible, then it exists in some possible world; but a maximally great being exists in every possible world if it exists in any; therefore a maximally great being exists in the actual world. Critics grant the validity but press the possibility premise. Plantinga himself has said the argument's achievement is to show that belief in God is rational — not to prove God exists to an unwilling audience.
- Anselm of Canterbury— Proslogion (1078); original formulation
- René Descartes— Fifth Meditation; early modern version
- Alvin Plantinga— Modal ontological argument (1974)
- Kurt Gödel— Formal modal proof (posthumously published 1987)
“Therefore, Lord, not only are you that than which a greater cannot be conceived, but you are also something greater than can be conceived.”
“The ontological argument does not prove that God exists. What it shows is that, if it is even possible that God exists, then it is necessary that he does.”