Ontological arguments
for God’s existence:
 Derived
from the Greek terms ontos
(being) and logos(reason or rational
account)
 First developed by Saint Anselm of
Canterbury, the argument takes a variety
of forms
 The common theme among them is that
they begin a priori – proceeding from the
mere concept of God – and conclude that
God must exist
1. Everyone is able to understand by the
term “God” a being than which none
greater can be conceived
2. So, a being than which none greater can
be conceived exists in the mind (the
understanding) when one hears about
such a being
3. We can conceive of a being than which
none greater can be conceived which
exists both in the mind and in reality
4. To exist in reality is better than to exist
in the mind alone
5. If, therefore, a being than which none
greater can be conceived exists in the
mind alone and not in reality, it is not a
being than which none greater can be
conceived
6. Therefore, a being than which none
greater can be conceived exists in
reality.
1. Everyone is able to understand by the term
2.
3.
4.
5.
6.
7.
“Perfect Island” the greatest possible island(GPI).
So, a GPI exists in the mind
We can conceive of a GPI that exists in the mind
and reality
Existence in reality is greater than existence in the
mind alone
If a GPI exists in the mind alone, then it is not the
GPI
Thus, a GPI exists in reality
But since a GPI does not exist in reality, the
argument structure (which Anselm also utilizes)
must be flawed
 Existence
is not a predicate such that it is
a property which can be affirmed of a
thing
 Existence does not add to the concept of
a thing; rather, existence is the
instantiation of a thing
 The example of a black, existing cat
1.
2.
3.
4.
5.
It is possible that a being exists which is
maximally great (a being we can call God)
So, there is a possible world in which a
maximally great being exists
A maximally great being is necessarily
maximally excellent in every possible world(by
definition)
Since a maximally great being is necessarily
maximally excellent in every possible world,
that being is necessarily maximally excellent in
the actual world
Therefore, a maximally great being exists in the
actual world
 God’s
existence is a logical or
metaphysical impossibility
 Possible
worlds and the semantics they
employ are problematic
 Fairies, ghosts, gremlins
and unicorns
can be made “plausible” through the
same argumentation (similar to “Perfect
Island”)
1. It is possible that a special fairy exists
2. So, there is a possible world in which a special
fairy exists
3. A special fairy is necessarily a tiny woodland
creature with magical powers in every possible
world
4. Since a special fairy is necessarily a tiny
woodland creature with magical powers in
every possible world, that fairy is necessarily a
tiny woodland creature with magical powers in
the actual world
5. Therefore, a special fairy exists in the actual
world

Is it greater to exist than to not exist, as
Anselm claimed? How does your answer
affect Anselm’s argument?

Can you conceive of God’s non-existence? If
so, what follows from this regarding the
ontological argument?

How does the ontological argument differ
from other classic arguments for the
existence of God?