And assuredly that, than which nothing greater can be conceived, cannot exist in the understanding alone.
In other words, the concept of whatever exists in the understanding either exists in the understanding alone or it exists also in reality.
For, suppose it exists in the understanding alone: then it can be conceived to exist in reality; which is greater.
In other words, if God A exists in the understanding only, then God B which also exists in reality is greater or more perfect than God A which exists in the understanding only.
Therefore, God A is that than which a greater or more perfect can be conceived i.e. God B.
Therefore, if that, than which nothing greater can be conceived, exists in the understanding alone, the very being, than which nothing greater can be conceived, is one, than which a greater can be conceived. But obviously this is impossible.
In other words, that than which a greater or more perfect cannot be conceived [God B] is also that than which a greater or more perfect can be conceived [God A] because both A and B are Gods. This is a contradiction, a logical impossibility.
Therefore, God cannot exist in the understanding only.
Hence, there is no doubt that there exists a being than which nothing greater can be conceived, and it exists both in the understanding and in reality.
In other words, something than which nothing greater or more perfect can be conceived must exist in the understanding and also in reality.
Therefore, God exists in reality.
Why not the Jewish God?
Not all-knowing and not transcendent
The Jewish God is not all-knowing.
For example, He does not know Prophet Adam’s whereabouts, when Prophet Adam and his wife, Eve, ate from the tree of knowledge of good and evil.
Then the man [Prophet Adam] and his wife [Eve] heard the sound of the Lord God as He was walking in the Garden in the cool of the day, and they hid from the Lord God among the trees of the Garden. But the Lord God called out to the man, “Where are you?”[2]