5.4.2 Syntactic categories

　 A syntactic category is a class of expressions that substitute for one another without loss of grammaticality. For example, in the sentence A naughty boy broke the window, a naughty boy can be replaced by he, a man, John, the man who has just left, and so on. All these belong to the same syntactic category called Noun Phrase (abbreviated as NP). The rest of the sentence, broke the window, is called Verb Phrase (VP). Other syntactic categories are Sentence (S), Determiner (Det), Adjective (Adj), Pronoun (Pro), Verb (V), Auxiliary Verb (Aux), Prepositional Phrase (PP), and Adverb (Adv).