Anselms Ontological Proof

Anselm's Ontological Proof -->  his goal was to refute the fool that in his heart says there is no God

1) We have an understanding of God who is "that than which nothing greater can be conceived" (TTWNGCBC)

2) If God existed only in our understanding (A), and not outside our mind then God would not be the greatest possible being (B)

3) It is greater to exist outside the mind than to exist only inside the mind

4) God is "that than which nothing greater can be conceived"

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Therefore:  God exists outside our minds and not just in our understanding

Form of the argument -- Modus Tollens --valid

If A, then B

Not B

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TF: Not A

Gaunilos critcisim:  "The greatest possible island"

Just because you can imagine the greatest possible island doesn't mean it exists. (aka Reductio ad absurdum --> Latin: "reduction to the absurd").  Anslem is just defining God into existence, but you can define anything into existence. 

Anslem responds by saying a definition requires identifying that which is essential.  Islands differ from God in their essential properties.  It is essential to being a Martian, that one hail from Mars.  it is essential to being an island that it be a body of land surrounded by water.  Being greatest is not essential to being a Martian or an island, but it is essential to being God.

St. Thomas Aquinas, objected to Anselm's argument by noting that because the essence of God is his existence, the ontological argument would only be meaningful to someone who knew the essence of God completely. Since only God could completely know his own essence, only God can use the ontological argument to prove his own existence to himself.

Hume's criticism was that you can't go from a definition (a priori, relation of ideas) to a fact of the matter.  Hume is a little wrong -->  we can say a priori that incoherent things cannot exist, so he would need to restate that you can't go from a definition to a priori knowledge of existent facts.

Kants criticism was that there is something wrong with the grammar of the argument.  "Exists" is not a predicate.  You have to exist to bear predicates (properties).  If you imagine a rose, nothing in your mind changes when you add "existence" as a predicate.  There is no difference between a rose and a "really existing" rose.  Secondly, to be an "adequate" concept, the concept must contain everything the object contains.