Modal auxiliary verbs are a type of verb that expresses the speaker’s attitude and opinion towards a proposition or an event. This paper investigates the syntactic features of modal auxiliary verbs in different languages from the aspects of semantic constraints, the deletion of complement clauses, constituent movement, pseudo-cleft construction and temporal and aspect markers, and analyzes relevant hypotheses of modal auxiliary verbs under the framework of generative grammar. We challenge the assumption that modal verbs are raising verbs, argue that modal auxiliary verbs should be analyzed as raising or control verbs.