Anselm's Ontological Argument
uses reductio ad absurdum reasoning – attempts to establish a claim by showing that the opposite scenario would lead to absurdity or contradiction
“Fools” understand the definition of God - that than which nothing greater can be conceived but they create a logical contradiction saying that TTWNGCBC only exists in intellectu. To be “that than which nothing greater can be conceived” it must exist in re
Therefore, existing in re is part of the definition of God