Originally posted 2014-01-17 01:32:12.
This is sometimes called the attempt to define god into existence, and was first proposed by Anselm of Canterbury (1033—1109). This original version was busted by Kant and Hume amongst others, but lo and behold, it resurfaced after several reworkings. While modern apologists are mightily proud of the shiny new gloss this has given the argument, it still devolves to the same thing:
A thing that can be imagined to exist, must exist, if it is imagined to have certain properties.
Clearly this is nonsense. However the dense fug of philosophical obscurantism is, as usual, used to hide the central argument, so let me expand what it says:
God is a being greater than which none can be conceived (unsubstantiated premise.)