Tonal Erosion in a Minority Ethnic Language and Its Implications for Language Education: Evidence from Intergenerational Tonal Change in Phuan, Northeastern Thailand

Abstract

The Phuan language, a Tai-family language spoken by an ethnic minority community in northeastern Thailand, is critically endangered due to sustained contact with Northeastern Thai (Isan) and Standard Thai. As the Phuan-speaking population ages and younger generations shift toward dominant languages, the prospects for intergenerational language transmission and community-based language education are diminishing. This study investigates tonal change in progress in Phuan across four provinces—Loei, Nong Khai, Udon Thani, and Bueng Kan—through intergenerational comparison using Labov’s (1972) apparent-time method, with the dual aim of documenting ongoing phonological change and informing evidence-based language education planning for minority communities. Data were collected from 48 informants equally divided between an elderly group (55–65 years) and an adolescent group (15–25 years) across eight districts. Tonal analysis employed Gedney's (1972) tone box framework alongside 60 elicitation words and 20 analogous-set words, with acoustic analysis performed using Praat version 6.2.03 and fundamental frequency (F0) values converted to semitones (ST). Results reveal that tonal change is actively underway in all eight research sites. A Tonal Change Index (TCI) was computed for each district, showing that Ban Phue District (Udon Thani) exhibits the highest degree of change (TCI = 1.00), while Pho Tak District (Nong Khai) shows the greatest tonal retention (TCI = 0.33). The direction of change consistently moves toward fewer tonal distinctions, reflecting contact-induced convergence toward Isan and Standard Thai. These findings carry direct implications for minority language education policy, heritage language curriculum design, and teacher training in multilingual communities across Southeast Asia.