Anselm's Proof for the Existence of God

Proslogion

Proslogion Ch. 2

1. Suppose there is something in the understanding, of which nothing greater can be conceived.
   
   
2. However, if this something is only in the understanding, then there is something which is greater than it - namely, the same thing in reality. This is because something that is real is greater than something that exists only in the understanding.
   
   
3. However, there is a contradiction if the thing doesn't exist, for then it would be something of which nothing greater can be conceived, but there would be something greater.
   
   
4. Therefore, if this something exists in the understanding, it must exist in reality.

Proslogion Ch. 3

1. We can conceive of a being which cannot be conceived not to exist, and it is greater than one which can be conceived not to exist.
   
   
2. Now, if the [than which nothing greater can be conceived], can be thought to not exist, it negates its own nature (ie., there is something greater than it).
   
   
3. This is a contradiction. Therefore, there is a being than which none greater can be conceived, and it cannot even be conceived to not exist. This is God.