ANSELM OF CANTERBURY'S ONTOLOGICAL ARGUMENT AS GIVEN BY ALVIN PLANTINGA:

- P1. God exists in the understanding but not in reality. (Assumption for reductio ad absurdum.)

- P2. Existence in reality is greater than existence in the understanding alone.

- P3. A being having all of God's properties plus existence in reality can be conceived.

- P4. A being having all of God's properties plus existence in reality is greater than God. (From P1 and P2.)

- P5. A being greater than God can be conceived. (From P3 and P4.)

- P6. It is false that a being greater than God can be conceived.

- P7. It is false that God exists in the understanding but not in reality. (From P1, P5 and P6.)

- P8. God exists in the understanding. (Even "the Fool" agrees.)

- ∴ God exists in reality. (From P7 and P8.)

Gaunilo's criticism
Anselm's response to Gaunilo
Alvin Plantinga's response to Gaunilo
Thomas Aquinas' criticism
Immanuel Kant's criticism
Philosophers supporting Kant
Philosophers opposing Kant
Peter van Inwagen's criticism
Richard Dawkins's criticism
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RENÉ DESCARTES' ONTOLOGICAL ARGUMENT AS GIVEN BY PETER VAN INWAGEN:

- P1. A perfect being has all perfections.

- P2. Existence is a perfection.

- ∴ A perfect being has existence. (From P1 and P2.)


Immanuel Kant's criticism
Peter van Inwagen's criticism

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ALVIN PLANTINGA'S ONTOLOGICAL ARGUMENT BASED ON THE VERSION GIVEN BY PETER VAN INWAGEN:

- P1. A perfect being is possible.

- P2. A perfect being has all perfections. (Definition of a perfect being.)

- P3. Necessary existence is a perfection.

- P4. Something that is possible and has the property of necessary existence must necessarily exist. (Based on modal axiom S5.)
- ∴ A perfect being exists


Criticism of Plantinga's ontological argument