The Ontological Argument

The a priori argument that the existence of God can be derived from the concept of God as a being than which none greater can be conceived.

Definition

An argument that purports to establish God's existence from the analysis of the concept of God alone, without reliance on any empirical premise about the world.

Scope

This topic covers Anselm's original formulation in the Proslogion, Descartes's version grounding existence in the divine essence, Kant's objection that existence is not a predicate, and twentieth-century modal reformulations by Hartshorne, Malcolm, and Plantinga. It covers the parody objections, such as Gaunilo's perfect island, and the dispute over whether possibility premises beg the question.

Core questions

• Can existence, or necessary existence, be a property that a concept entails?
• Is the argument viciously circular, smuggling existence into the definition of God?
• Do parody arguments for a perfect island or a necessary devil show the form to be invalid?
• Does the modal version succeed only by assuming the very possibility it needs to prove?

Key theories

Modal ontological argument

Plantinga argues that if a being with maximal greatness — including necessary existence and maximal excellence in every possible world — is even possible, then it exists in every world and hence actually; the argument's force rests entirely on the possibility premise.

Anselmian premise that existence in reality is greater

Anselm holds that a being existing in reality is greater than one existing in the understanding alone, so the greatest conceivable being must exist in reality on pain of contradiction; Malcolm distinguishes a second Anselmian argument turning on necessary existence.

History

Anselm formulated the argument in the eleventh-century Proslogion; the monk Gaunilo replied with the perfect-island parody. Descartes revived it in the seventeenth century, and Kant delivered the influential objection that existence is not a real predicate. Hartshorne, Malcolm, and Plantinga recast it in modal logic in the twentieth century, and Oppy provided a comprehensive critical survey.

Debates

Whether existence is a predicate

Kant's objection that 'exists' adds nothing to a concept is widely held to defeat the original argument; modal defenders reply that the relevant property is necessary existence, but critics such as Mackie hold the reformulation merely relocates the difficulty.

Whether the possibility premise begs the question

Plantinga concedes that one who already doubts God's existence has equal reason to deny that a maximally great being is possible; Oppy argues this renders the modal argument dialectically ineffective even if formally valid.

Key figures

• Anselm of Canterbury
• Gaunilo of Marmoutiers
• René Descartes
• Immanuel Kant
• Norman Malcolm
• Charles Hartshorne
• Alvin Plantinga

Seminal works

• plantinga1974
• oppy1995
• malcolm1960

Frequently asked questions

Why is it called an a priori argument?

Because it claims to establish God's existence by reasoning from the concept of God alone, without any premise drawn from observation of the world, unlike the cosmological and teleological arguments.

What is Gaunilo's island objection?

Gaunilo argued that the same reasoning would prove the existence of a perfect island, which is absurd; defenders reply that islands have no intrinsic maximum of greatness, so the parody does not apply to the unique concept of a greatest possible being.