  Thus Nominalism, in both senses, is a kind of anti-realism. For one kind of Nominalism denies the existence, and therefore the reality, of universals and the other denies the existence, and therefore the reality, of abstract objects. But what does Nominalism claim with respect to the entities alleged by some to be universals or abstract objects, e.g. properties, numbers, propositions, possible worlds? Here there are two general options: (a) to deny the existence of the alleged entities in question, and (b) to accept the existence of these entities but to argue that they are particular or concrete.