Is a Necessary Being Really Necessary?

The Ontological Argument maintains that the existence of an absolutely necessary being cannot be denied without self-contradiction. This concept of God, Kant says, is logically possible (i.e., it does not contain a contradiction), but we can never establish that something [exists] from a mere analysis of the corresponding concept. Real possibility can never be inferred from logical possibility. Indeed, a concept may be logically possible and yet cognitively empty, if it is impossible to conceive what it would be like to experience such a being.

This latter point is important because, according to the Ontological Argument, if we can possibly conceive of an absolutely necessary being (God), then God must necessarily exist. Why? Because it would supposedly be contradictory to deny the existence of a being whose existence is absolutely necessary. If it is possible for the most real being to exist, then it must necessarily exist, because existence is part of [what] it means to be "most real."

This argument is fallacious, according to Kant, because it treats "existence" as a real predicate, incorporates this predicate into the definition of "God," and then "proves" the existence of God by unpacking this definition. But if the existence of God follows necessarily from our definition of "God," then to declare that "God exists" is to utter a tautology, since this restates what is already included within our definition of "God."

We should understand that "existence" (or "being") is not a real predicate; "existence" is not an attribute or quality that adds something new to our concept of something else. Rather, "existence" functions as the copula ("is," "are," etc) of a judgment, indicating the relationship of the predicate to the subject.

--George H. Smith, Why Atheism?