An important role in English grammar is played by determiners – words or phrases that precede a noun or noun phrase and serve to express its reference in the context. Determinative is a lexical category whereas determiner is a grammatical or syntactic function. In traditional grammar, determinatives form a subclass of adjectives. In the Cambridge Grammar of English Language, determinatives are considered to be a distinct primary lexical category (part of speech). Just as the determiner function is not always realised by determinatives, so many of determinatives can have other functions that that of determiner. The determinative three is determiner is three books, but modifier in these three books. Similarly, determinative much is determiner in much happiness but a modifier in much happier.