That which has no form cannot be conceived – and vice versa. It’s easy to see that this is so when we try to think of what a square circle is like, or a four-sided triangle.
But, let’s talk about God.
To put the same thing another way: that than which no greater can be conceived by any mind cannot be conceived by any mind. If that than which no greater can be conceived could be conceived by any mind, then that mind would insofarforth understand how its conception of that thing could be surpassed, and would realize that in conceiving of it he had not yet quite conceived of that than which no greater can be conceived. He would realize that he had not been thinking of the unsurpassable. He would, i.e., realize that he had been thinking, not of God, but rather of something like Gaunilo’s Island, than which always some greater island might be conceived.
So, here’s the shocking consequence of these considerations: Not even God can conceive himself.