This article investigates the development of the word /jaŋ/ from the Sukhothai period right up until the present time using grammaticalization theory. Findings indicate that the historical development of /jaŋ/ has two main pathways: (1) the lexical... verb /jaŋ/ meaning “to exist” as the original word, and then developed into three grammatical words which are the auxiliary, conjunction, and causative marker, and (2) the transition from the lexical verb /jaŋ/ meaning “to stay