The Vowels of Cheju

o/√ merger; and (4) at least for the urban Cheju speakers, the merger is best accounted for by the merger-by-transfer model, a unidirectional change in which one phonemic category becomes another (cf. Labov, 1994). Further, when our data are compared with other acoustic data available (including studies of the standard Korean in the 1960s and 1990s), it suggests that the directionality of the diachronic sound change is guided by both auditorily and articulatorily based principles such as contrast maximization and effort minimization principles.