Born to a noble family in Italy As a young man, joins the Benedictine Order in

Normandy, France, residing in the monastery there for 30 years – 15 as Abbot

Thereafter, named Archbishop of Canterbury, England for final 16 years of his life.

Aims to establish the existence of God on the basis of reason rather than faith

Arguments for the existence of God raise the general question: how do we prove the existence of anything?

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Distinguish sensible/observable from nonsensible/nonobservable objectsNote that sensation/observation is a

form of thought; sensations are ideasEmpirical proof of the existence of X

from observation of X is a proof of the existence of X from a “sensory idea” of X

can we prove the existence of X from ideas, sensory or not?

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It is important to keep this point in mind when considering Anselm’s ontological argument for the existence of God since Anselm’s critics fault his argument saying that it attempts to prove the existence of X from the mere idea of X

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Ontology = the study of being/existence Anselm’s argument for the existence of God

came to be called “The Ontological Argument” by Immanuel Kant (German Philosopher: 1724 – 1804)

The argument presented next is in the form of Reductio ad Absurdum Arguments of this form attempt to prove X by

demonstrating that if X were false something impossibly absurd would be true. Thus, X must be true

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The Ontological Argument By definition: God = that than which nothing greater can be

thought (conceived) In order to derive a contradiction: Assume that God does not

exist It is possible to conceive of something, x,  exactly similar to

God except that x exists It is greater to exist than  not to exist So, x is conceived to be greater than God But this contradicts the identity or definition specified in the

first line of the argument This contradiction depends on the assumption that God does

not exist Hence, the assumption that God does not exist must be

false Hence, God exists!

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Gaunilo was a monk and a contemporary of Anselm.

Gaunilo believed in the existence of God as a matter of faith rather than reason

Gaunilo attempted to refute the Ontological Argument by showing that the argument is invalid (def.)

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In the ontological argument:  replace the definition of God with a definition of “the perfect island”

The perfect island =the island than which none greater can be conceived

The resulting proof "proves" the existence of the perfect island if the ontological argument proves anything

But it is absurd to suppose that we have proven the existence of the perfect island

So, by parallel reasoning, the ontological argument proves nothing

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Definitions in Proofs In comparing Anselm and Gaunilo, we

must ask under what conditions it is legitimate to use definitions (or expressions of our ideas/concepts of things)

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We do use definition in proofs of many things e.g. mathematics

Also

Fido is a dog

Dogs = canine’s (def)

So, Fido is a canine

So, why not use definitions in ontological proofs?

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The Ontological Argument is a priori. Are proofs regarding existence invalid? Are only a posteriori (empirical) proofs regarding existence valid?

If so, why?

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