Full Idea
We think of a thing when we say the world, and in another way when we think of the very thing itself. In the second sense God cannot be thought of as nonexistent. No one who understands can think God does not exist.
Gist of Idea
The word 'God' can be denied, but understanding shows God must exist
Source
Anselm (Proslogion [1090], Ch 4)
Book Reference
'The Existence of God', ed/tr. Hick,John [Macmillan 1964], p.27
A Reaction
It seems open to the atheist to claim the exact opposite - that you can commit to God's existence if it is just a word, but understanding shows that God is impossible (perhaps because of contradictions). How to arbitrate?