Grice on the unknowable infinite -- and the null class

R. B. JONES, this blog, notes:

"I find this observation rather puzzling when talking of NBG as a conservative extension of ZFC, since the existence of the empty set is usually taken to be an axiom of ZFC even though it can be derived from other axioms of ZFC.

In ZFC the existence of the empty set follows from the separation axiom schema, and from the replacement scheme (from which separation can be obtained).

To understand what is intended here, to make the claim intelligible. one really needs to know in what context infinity suffices to derive the existence of the empty set, since in the context of ZFC or NBG - {empty set, infinity} the existence of the empty set is already provable."

This may compare to Grice's idea that to KNOW INFINITY is senseless.

His example, in WoW:

"I KNOW THAT THERE IS AN INFINITE NUMBER OF STARS"