 Noun phrase

A noun phrase is a grammatical unit conventionally analyzed as headed by a noun, potentially together with dependents that modify or specify it. A single noun or pronoun can also form a minimal noun phrase under this analysis.^[ref]

In The small bird landed, the words the small bird form a noun phrase containing the head bird, the adjective small and a determiner. The whole unit occupies the subject position. Replacing it with it gives It landed, illustrating that a multiword expression can occupy a position also available to one word.

Such substitution is useful evidence for a grammatical constituent, but one test alone does not settle every structural question. A clear syntax states how the proposed head and dependents combine and tests the same account across further constructions. Counting spaces therefore measures a different property from counting noun phrases.