This dissertation presents a study of three linguistic areas--morphology, syntax and semantics--of what have traditionally been called auxiliaries or auxiliary verbs in Thai, but what I call temporal verbs. My morphological analysis offers answers to long-term questions: What is the grammatical category of temporal verbs? What is the structure of sequences of these elements? And how are their syntactic discontinuities to be handled? My syntactic analysis investigates all possible positions of temporal verbs in both Subject-Verb-(Complement) and Verb-Subject-(Complement) sentences (Sookgasem 1989). Using Head-Driven Phrase Structure Grammar (Pollard & Sag 1987) for my analysis, I focus on three interesting points: First, a problem with the H...