In a nutshell, he suggests that "...the entire notion of a supernatural being is incomprehensible" because nothing can exist apart from that which exists naturally.
To be is to be something as opposed to nothing, and to be something is to be something specific. If a god is to have any characteristics (which it must to exist), these characteristics must be specific - but to assign definite attributes, to say that a being is this as opposed to that, is to limit the capacities of that being and to subject it to the uniformity imposed by those capacities. A supernatural being, if it is to differ in kind from natural existence, must exist without a limited nature - which amounts to existing without any nature at all (p. 41).The theist who is not ready to concede defeat has one obvious place of retreat. He or she will claim that his or her god is unknowable. Of course! Theists make this claim all the time. Their god is not merely unknown in the present time but unknowable in principle. The human mind simply cannot comprehend their god.
As Smith suggests, this shifts the discussion away from metaphysics and back to epistemology. However, before making this shift, it is important to understand that the theist is now admitting that his or her god (and any other supernatural entity) is beyond comprehension of the human mind. Is this really what theists believe? Perhaps it gets them around the many metaphysical problems with their god, but it may well come back to haunt them.
How might the concession that their god is unknowable haunt the theist? Consider the following dialogue which Smith provides:
Theist: "I believe in god."The hole into which the theist has dug himself/herself should now be apparent. The theistic belief claim (i.e., god exists) has been effectively neutered and is now thoroughly void of meaning.
Atheist: "What is 'god'?"
Theist: "I don't know."
Atheist: "But what is it that you believe in?"
Theist: "I don't know that either."
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