 The notion of a referential NP also plays a central role in the tradition of Montague Grammar, where referential NPs are taken to be of type e, the type of entities (Montague 1974). Montague himself, though, also proposed type-lifting referential NPs to the type of individual concepts (of type \(\langle\langle e, t\rangle, t\rangle\)). This was meant to allow for semantic uniformity with respect to NPs that for Montague must stand for individual concepts, such as the rising temperature, the golden mountain, and the mathematician John claims to be (but see  §3.1.1).  The move no longer maintains a straightforward notion of a referential NP and thus a criterion for entities being part of the ontology of natural language.