 Though Quine’s (1948) well-known paper “On what there is,” raises serious ontological questions for intentional-object theories, both Parsons and Zalta have provided answers to Quine’s queries, in their respective work.  Nonetheless, to this day, many contemporary philosophers have been reluctant to embrace intentional-object theories for two related reasons.  First of all, they have been eager to avoid what they see as the heavy ontological commitments incurred by intentional-object theories.  Secondly, the ontology of non-existent and abstract objects has seemed difficult to square with the ontology of the contemporary natural sciences according to which the world contains only concrete objects that exist in space and time. (See Section 9 for further discussion.)