Descriptions of the structural or syntactic properties of verbal behavior. Sequential grammars appeal only to the discriminative effects of prior verbal stimuli ; they are inadequate for dealing with most important structural features of verbal behaviour and are largely obsolete. Phrase-structure grammars describe structures in terms of the relations among sentence constituents (e.g., noun phrases and verb phrases), whereas transformational grammars describe them in terms of relations among different sentences (e.g., active and passive voice); these two types of grammars, one intrasentence and the other intersentence, are complementary. (Other types of grammars, such as case grammars, explicitly appeal to semantic features in defining structural relations.)