I am surprised that this never came up in any of the threads I read.
The Ontological argument for the existence of god was first conceived off by St. Anselm.
It argument derives the existence of God from the concept of a being than which no greater can be conceived. St. Anselm reasoned that, if such a being fails to exist, then a greater being — namely, a being than which no greater can be conceived, and which exists — can be conceived. But this would be absurd: nothing can be greater than a being than which no greater can be conceived. So a being than which no greater can be conceived — i.e., God — exists.
Fromn then on it developed into a Model Onthological Argument, which uses model logic.  A borrowed copy of which I will post in short here:
	Quote:
	
	
		| 1.We define g to be something for which, if it exists, its existence is necessary. 2. Either the existence of g is necessary, or it is not.
 3. If the existence of g is not necessary, the it is necessary that the existence of g is not necessary.
 4. Either it is necessary that g exists, or it is necessary that it is not necessary that g exists (follows from 2 and 3).
 5. If it is necessary that it is not necessary that g exists, then it is necessary that g does not exist (follows from 1).
 6. Either it is necessary that g exists, or it is necessary that g does not exist (follows from 2 and 5).
 7. It is not necessary that g does not exist (justification?).
 8. It is necessary that g exists (follows from 6 and 7).
 9. If it is necessary that g exists, then g exists.
 10. g exists (follows from 8 and 9).
 
 It means that if we define g to be something whose existence is necessary (1), and assume that there are things whose existence is necessary (7), then it logically follows that g exists (10).
 
 Now all we have to do is establish that there is, in fact, something whose existence is necessary. Then we can name it God.
 
 - the above was written by Death Monkey.
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 More detail can be found here:
http://www-phil.tamu.edu/~b-everman/.../intro/God.pdf
Tell me what you guys think.  As I am still trying to make heads or tails out of it.
- edit - link fixed