Quine proposed that "to be is to be the value of a variable". However, he also devised predicate functor logic (PFL), which effectively gives a recipe for eliminating bounded variables.
How should one reconcile predicate functor logic with Quine's own ontological theory?
While one might say that insofar as PFL and first order logic (FOL) are equally expressive, PFL has the same ontological commitment as FOL, but it appears to me that the argument could also go the other way round. If they are mere "notational variants" of each other, then all we can conclude is that PFL and FOL have the same ontological commitments. It might be that, contrary to appearances, the existential quantifier in FOL is not ontologically committal after all since it is merely a cropping predicate functor, as revealed by its translation in PFL.