Anselm, Proslogion

In his Proslogion, Anselm give a proof for the existence of God.  Of the major parts of this proof, Chapters 2 and 3 are likely the most important to his argument.  Chapter 2 is "That God truly exists.  Chapter 3 is "That he cannot be thought to not exist".  In chapter 2, Anselm makes an important move; namely, that nothing greater than God can be thought to exist. He then goes on to say "that which is greater cannot be thought cannot exist only in the understanding.  For if it exists only in the understanding, it can be thought to exist in reality, as well, which is greater."

I must admit, I'm a bit confused with the move Anselm is trying to make. A sounds a bit like the greatest thing that can be thought can be understood therefore must necessarily exist.  Obviously, since it's the greatest thing that can be thought, it can not be thought that there is that which is greater. Regardless, his point is that God exists.  That's really all we need to get to his more important point which is "That he cannot be thought not to exist."

Anselm doesn't think that anyone could think of God as nonexistent.  Certainly it is absurd to conceive of something from nonexistence.  If nonexistence is some sort of property of an object, then the object doesn't exist, and therefore has no properties.  It reminds me of Descartes ontological argument, which, though not a logical proof, simply can not be wrong.  If he thinks, he is.  If he thinks he is, he couldn't have thought in the first place.  Same logic applies here, wherein if God is thought to not exist, then he isn't thought.  The problem I have with this is that it leads that God CERTAINLY exist. I'm not so sure.  Certainly, it follows that God may exist or could exist or is conceivable of existing.  But I'm not sure that conceiving in the mind necessitates existence.  That seems to be the move Anselm is trying to make.  And in terms of 'seeming', it seems to be wrong.