  Some of the objections to platonism in art ontology are versions of longstanding criticisms of the postulation of abstract objects, such as the objection that the instantiation relation between universals and their particular manifestations leads to a regress, or is obscure or inexplicable. Other objections are raised by philosophers who do not reject all postulations of knowable abstract objects, but who nonetheless find that works of art are not adequately classified as such items.