  In addition, the structuralists had attempted to capture the  syntactic properties of languages in terms of simple rewrite rules  known as ‘phrase structure rules.’ Phrase structure rules describe the internal syntactic structures of sentence types;  interpreted as rewrite rules, they can be used to generate or  construct sentences. Thus, the rule S → NP VP, for instance,  says that a sentence symbol S can be rewritten as the symbol NP  followed by the symbol VP, and tells you that a sentence consists of  a noun phrase followed by a verb phrase. (This information can be  represented via a tree-diagram, as in Fig. 1a, or by a phrasemarker  (or labeled bracketing), as in Fig. 1b.)