Several problematic syntactic constructions are examined in order to determine if the grammar of Thai requires the postulation of a verb phrase expanding to two main verbs. In Chapters I to IV, alleged mUltiple verb sequences are shown to consist of a verb plus an element belonging to one of the following syntactic categories: 'modal', preposition, and complementizer. In contrast, Chapter V is concerned with 'verb series' that derive from distinct underlying verb phrases. For the specific Thai constructions investigated in this study, it is concluded that there is no evidence to motivate a phrase structure rule that generates an optional second verb.