Full Idea
No one thinks that the proposition that something exists that transcends all possible experience harbours a logical inconsistency. Its denial cannot therefore be an analytic proposition, so it must be synthetic, though only knowable on a priori grounds.
Gist of Idea
Assertions about existence beyond experience can only be a priori synthetic
Source
José A. Benardete (Metaphysics: the logical approach [1989], Ch.18)
Book Reference
Benardete,José A.: 'Metaphysics: The Logical Approach' [OUP 1989], p.135