Abstract:
This thesis is a diachronic study of /laeaew/, /yuu/ and /yuulaeaew/ from the Sukhothai period to the present. The data elicited is based on published documents between 1826 B.E. 2546 B.E. According to the study, it is found that the functions of /laeaew/ are not identical in the 6 different periods. In the Sukhothai period /laeaew/ had 3 functions that is verbs, perfective aspect markers and conjunctions and the 4 new functions{7f2014}idiomatic phrases functioned as adverbs, idiomatic phrases functioned as verbs, idiomatic phrases functioned as time markers and discourse markers are evolved at present. A semantic analysis indicates that /laeaew/ has 21 meanings including 4 content meanings and 17 functional meanings, but the meaning which has been grammaticalized to functional meanings is the meaning "finish". As for /yuu/, it is found that the functions of /yuu/ are not identical in the 6 different periods. In the Sukhothai period /yuu/ had 1 function that is verbs and 3 new functions-- continuative/progressive aspect markers, idiomatic phrases functioned as adverbs and conjunctions are evolved in the present. A semantic analysis shows that /yuu/ which have been grammaticalized to functional meanings are the meaning "to stay, to live" and "to be in/at". In the case of /yuulaeaew/, the finding shows that it functions only as a post-verbal auxiliary in every periods. In the Ayudhaya period, it co-occurs with 2 types of verbs whereas at the present period, /yuulaeaew/ can co-occur with various verbs. A semantic study points out that /yuulaeaew/ is a combination of the continuative/progressive aspectual meaning of /yuu/ and the perfective aspectual meaning of /laeaew/. Later on, the semantic feature 'certainty' is added to the item in the reign of King Rama I - King Rama III. Nowadays, it is found that /yuulaeaew/ also functions as a discourse marker in a daily conversation with the meaning of 'certainty' and the post-verbal auxiliary with the aspectual meaning still can be found. The findings suggest that the process of grammaticalization of /laeaew/, /yuu/ and /yuulaeaew/ do not occur at the same period of time. The development of /laeaew/ into function words start earlier than the other 2 items as it is found as a post-verbal auxiliary and a conjunction since the Sukhothai period whereas /yuu/ has functioned as a post-verbal auxiliary in Ayudhaya period. As for /yuulaeaew/, the item is found as a post-verbal auxiliary in the Ayudhaya period as it grammaticalized from 2 function words--continuative/progressive aspect marker /yuu/ and perfective aspect marker /laeaew/. The grammatical process found in the data coincide with the universal phenomenon of grammaticalization in terms of unidirection and gradual change