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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
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anything?
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Distinguish sensible/observable from
nonsensible/nonobservable objects
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Note that sensation/observation is a form
of thought; sensations are ideas
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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
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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
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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
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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
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It is greater to exist than not to exist
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So, x is conceived to be greater than God
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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
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Hence, the assumption that God does not exist must be false
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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
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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
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e.g. mathematics
 Also
 Fido is a dog
 Dogs = canine’s (def)
 So, Fido is a canine
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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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