1.  Types of Argumentation:
Inductive              Deductive
Analogical
Generalization
Causal

2.  Types of Argumentation for the Existence of God
A posteriori <------------- Deductive ------------> A Priori
Cosmological                                                     Ontological
Descartes                                                             Anselm
Aquinas                                                                 Descartes
 
 

3.  Anselm

1.  God is, by definition, the being than which nothing greater can be conceived.
2.  Therefore, God exists at least in the understanding as an idea.
3.  To exist in the understanding and to exist extramentally are different things.
4.  If the GCB exists only in the understanding, then there is a greater GCB which exists
in reality.  This implies that there is a being greater than the greatest, which is
absurd.* Reductio - see below.
5.  Therefore, the GCB exists in reality.

Note from ch. 4 of Anselm's Proslogium
God can be conceived not to exist only as a word.  The analogy is this: No person who knows what fire and water are can conceive fire to be water.  So no one who knows what God is can conceive God not to exist.

Significance - the only one of the arguments for the existence of God to focus on the attributes of God.

Procedure - reductio ad absurdum

Guanilo - Greatest Conceivable Island objection