Noun phrases are composed of four kinds of elements;
Knowledge of the internal structure of noun phrases is useful for identifying a word as a noun, since only a noun (or a pronoun) can serve as the head of a noun phrase. One way of showing this is to construct test frames with empty slots like the following (square bracket indicate the boundaries of the phrase).
[The new ___ ] seemed good.
The test frame contains a determiner and a premodifier before the empty slot. The only element that can fill the empty slot has to be the head of the noun phrase, hence a noun (disregarding, for the moment, the fact that words from certain other word classes, for instance pronouns, can head noun phrases too).
In the following sections we focus on the classes of elements, mostly nouns, that can function as heads of noun phrases, and on determiners. Modifiers are dealt with in the sections on adjective phrases and prepositional phrases, since these two are the most common realisations of the modifier function.