  The nominalist about universals rejects universals — but what are they? The distinction between particulars and universals is usually taken to be both exhaustive and exclusive, but whether there is such a distinction is   controversial.[5]   The distinction can be drawn in terms of a relation of instantiation: we can say that something is a universal if and only if it can be instantiated (whether it can be instantiated by particulars or universals) — otherwise it is a particular. Thus while both particulars and universals can instantiate entities, only universals can be instantiated. If whiteness is a universal then every white thing is an instance of it. But the things that are white, e.g. Socrates, cannot have any  instances.[6]