I don't have an idea in mind of a being that which is greater cannot be conceived.
God is ‘that than which nothing greater can beconceived’.
We form a notion of God beginning with theknowledge of less perfect things and raising our mind to the notion of amost perfect being.
If we conceived this being, then this being exists inreality, but only in thought.
We can reason from existence in thought to existence in reality in one case only. For there is only one being which cannot be thought not to be; namely, the being than which nothing greater can be thought.