 The notion of a referential NP has played a central role in philosophical discussions about ontological commitment; it is an important notion in semantics and also plays a role in syntactic theory. Names and definite NPs can serve as referential NPs, as can specific indefinites and certain determinerless (bare) plurals and mass nouns. Only certain syntactic positions are reserved for referential NPs, such as the subject or the object position of extensional predicates, as opposed to intensional predicates like look for, intentional predicates like imagine, and existence predicates like exist and occur. There are various syntactic and semantic criteria for referential NPs. For philosophers, since Frege, they include the ability of an NP to support anaphora, to be replaceable by quantificational NPs, and to serve as an argument of ordinary (i.e., extensional) predicates (Frege 1892; Hale 1987). For syntacticians, referential NPs also must satisfy certain syntactic conditions: they are generally taken to have the more complex structure of a determiner phrase (DP) rather than just that of what syntacticians take to be an NP, NPs being able to be used only predicatively (Abney 1987; Borer 2005).