Phonetic and systemic biases in tonal contour changes in Bangkok Thai

Understanding phonetic and systemic motivation is a crucial element in the study of sound change. However, our understanding is largely limited to segmental changes. Working within the phonetically-based approach to sound change, this article accounts for the tonal contour changes in Bangkok Thai during the 20th century in terms of biases that exist in human speech. It proposes that the changes are explicable by known patterns of phonetic variation and sys-temic constraints that introduce biases into the process of phonologization. In this account, the tonal contour changes, like most cases of segmental changes, can be regarded as linguistically-motivated.