Each chapter in The Grammar Book, Second Edition, is designed to lead readers systemati-cally from an understanding of the grammar structure to an ability to use this understanding in the ESL/EFL classroom. After the first two introductory chapters, each chapter includes | 8ö The Grammar Book An adverbial clause can be expanded to include an adverbial subordinator adv sub followed by a new sentence S 9. Advl CL adv sub S This rule reintroduces S a constituent already present in rule 1. To expand the new S we would go back to rule 1 and begin the process all over again. In other words phrase structure rules are recursive and can be applied as often as needed. Let us consider the tree diagram for a sentence with an adverbial clause Perhaps the boys left before their father could find them. Another possible expansion of the adverbial in rule 8 is an adverbial phrase Advl P which is rewritten as follows 10. AdvIP intens ADV This rule means that an adverbial phrase contains an obligatory adverb ADV optionally preceded by one or more intensifiers intens. An intensifier occurs not only before adjectives as you saw earlier in rule 5 but also before adverbs. The following sentence and tree diagram illustrate a case where the optional intensifier has been selected to modify an adverb Perhaps the boys worked very quickly. very quickly Chapter 5 Introduction to Phrase Structure 87 The superscript n after the optional intensifier allows for more than one intensifier to occur. As is also the case with adjective phrases in rule 5 some intensifiers may be repeated while other series of intensifiers can consist of different lexical items very very quickly really quite eagerly Finally an optional adverbial may also be expanded as a prepositional phrase. Rule 6 which was introduced earlier and which is repeated here would apply in such a case 6. PrepP - Prep NP Wc are now in a position to more fully specify the tree diagram for the following sentence Perhaps they eat lunch in the city. Structural Variation in Prepositional Phrases Note that in sentence-final adverbials prepositions are used to give adverbial function to nouns with temporal or locative meaning. As a general rule nouns do not function on their own as adverbs in English. For example take
