Dating vowel lengthening in Thai

This paper dates vowel lengthening in Thai, which affected words that originally had a long vowel such as cʰaːw⁴ ‘morning’, naːm⁴ ‘water’, maːj⁴ ‘wood’, and daːj³ ‘to acquire’. Analysis of data from rhymming patterns in poetry, and from dictionaries and grammar books for foreigners shows that the vowel lengthening began in the late 24th century B.E. [ca A.D. 1850] and reached completion in the late 25th century B.E. [ca A.D. 1950]. Moreover, the paper also discusses factors that caused the change including syllable structure and the linguistic contexts in which the words occur.