1.  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? 1

2.  Distinguish sensible/observable from nonsensible/nonobservable objects  Note that sensation/observation is a form of thought; sensations are ideas  Empirical 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? 2

3.  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 3

4.  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 4

5. 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! 5

6.  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.) 6

7.  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 7

8. 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) 8

9.  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? 9

10.  The Ontological Argument is a priori. Are proofs regarding existence invalid? Are only a posteriori (empirical) proofs regarding existence valid?  If so, why? 10