Anselm of Canterbury formulated the first ontological argument in the Proslogion (1078). He argued that "God" is rightly defined as "that than which nothing greater can be conceived." If God exists only in the mind and not in reality, then one could conceive of a greater being — one that exists in both mind and reality. Therefore, the definition of God entails His existence.\n\nThe argument provoked immediate objection (Gaunilo's "Perfect Island" parody) and has been debated ever since. Descartes, Leibniz, and Gödel each produced variants. The most-discussed modern version is Alvin Plantinga's modal ontological argument: (1) a maximally great being is possible in at least one possible world; (2) if a maximally great being exists in any possible world, it exists in every possible world; (3) therefore, a maximally great being exists in the actual world.\n\nThe argument's philosophical weight is contested. Critics (notably Richard Gale) argue that the possibility premise begs the question. Defenders (Plantinga himself) acknowledge the argument does not compel the skeptic but show that theism can be defended as rationally permissible. It functions better as an analysis of what "God" means than as a persuasive first apologetic.
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The Ontological Argument (Anselm, Plantinga)
Anselm's ontological argument contends that a being than which none greater can be conceived must exist in reality, not merely in the mind; Alvin Plantinga's modal reformulation shows that if a maximally great being is even possible, it exists.
Key arguments
- Anselm's original form is a reductio ad absurdum on the concept of God.
- Plantinga's modal version relies on S5 modal logic.
- The contested premise is the possibility of a maximally great being.
- The argument is often deployed defensively rather than offensively.
Key verses
- Psalm 14:1
- Exodus 3:14
- Hebrews 6:13
Sources
- Anselm — Proslogion (1078)
- Alvin Plantinga — The Nature of Necessity (1974)
- Richard Gale — On the Nature and Existence of God (1991)