  Nominalism comes in at least two varieties. In one of them it is the rejection of abstract objects; in the other it is the rejection of universals. Philosophers have often found it necessary to postulate either abstract objects or universals. And so Nominalism in one form or another has played a significant role in the metaphysical debate since at least the Middle Ages, when versions of the second variety of Nominalism were introduced. The two varieties of Nominalism are independent from each other and either can be consistently held without the other. However, both varieties share some common motivations and arguments. This entry surveys nominalistic theories of both varieties.