Anselm: the classic argument

In the Proslogion, Anselm defines God as that than which nothing greater can be conceived. His reasoning:

• Even 'the fool' who denies God has this idea in his understanding.
• But a being that exists in reality is greater than one that exists in the mind alone.
• So if the greatest conceivable being existed only in the mind, we could conceive a greater one (that also exists in reality) — a contradiction.
• Therefore God must exist in reality.

Second form: Anselm adds that God cannot even be conceived not to exist — God has necessary existence, unlike contingent things.

Anselm definition

The crucial step

Descartes: the perfect being

Descartes gives his own version. God is a supremely perfect being. 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 God's essence, as necessarily as three angles belong to a triangle, or a valley to a mountain.
• We cannot conceive of God without existence any more than a triangle without its angles.

Gaunilo: the perfect island

A monk, Gaunilo, replied 'on behalf of the fool'. He parodies Anselm: imagine the most perfect island conceivable. By Anselm's logic, since a real island is greater than an imagined one, this perfect island must exist — which is absurd.

Gaunilo's point: you cannot define things into existence. Anselm replied that the argument only works for God, the necessary being, not for contingent things like islands.

Gaunilo parody

Defend or attack?

Tap a name or idea, then whether it defends or attacks the ontological argument.

Kant: existence is not a predicate

Kant gives the most famous objection: existence is not a predicate — not a property that adds to the concept of a thing.

• Saying a thing exists tells us it is instantiated in reality; it does not describe or enlarge the concept.
• Kant's example: a hundred real thalers (coins) contain no more in concept than a hundred imagined ones — existence adds nothing to the idea.
• So you cannot include 'exists' in the definition of God and thereby prove God real.

Kant objection

Malcolm: necessary existence

Norman Malcolm accepts Kant's point about the first form, but defends Anselm's second form. He argues God's existence is either impossible or necessary:

• God, if God exists, cannot be contingent (dependent) — that would not be the greatest being.
• God's existence is not impossible (the concept is not self-contradictory).
• Therefore God's existence is necessary.

Evaluate: critics say Malcolm still moves illegitimately from the concept of a necessary being to its real existence — the same gap Kant identified.

Who claims what?

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Malcolm move

The big ideas to take into the exam

The ontological argument shows the promise and peril of pure reason. Press Finish for your score.