1. Ontological arguments for God’s existence:
Chapter 6:
Ontological arguments
for God’s existence:

2. Ontological argument
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

3. Anselm’s ontological argument
Everyone is able to understand by the term “God” a being than which none greater can be conceived
So, a being than which none greater can be conceived exists in the mind (the understanding) when one hears about such a being
We can conceive of a being than which none greater can be conceived which exists both in the mind and in reality

4. Anselm’s argument continued
To exist in reality is better than to exist in the mind alone
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
Therefore, a being than which none greater can be conceived exists in reality.

5. Guanilo’s objection
Everyone is able to understand by the term “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

6. Kant’s objection
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

7. Plantinga’s modal argument
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

8. Objections 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”)

9. Martin’s special fairy argument
It is possible that a special fairy exists
So, there is a possible world in which a special fairy exists
A special fairy is necessarily a tiny woodland creature with magical powers in every possible world
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
Therefore, a special fairy exists in the actual world

10. Questions for discussion
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?