Tone 7(55)is merging with Tone 10(33)in the Menglian variety of the Dai language.The premise of this tonal change is the disappearance of the two distinctive segmental features,voicing contrast of consonants and length contrast of vowels.The specific cause for this tonal merger is that tone languages such as Chinese and Kam-Tai languages have the tonal pattern of"nonchecked and checked tones having identical tone values",which has a restrictive effect on generation of new tone values for the checked tones beyond tone values of non-checked tones.For the merging of Tone 7 and Tone 10,the starting point is the lowering of Tone 7(55)induced by language contact,and the checked tone is obliged to follow the parallel tonal change occurred in non-checked tones,that is,Tone 1(55)→Tone 6(33).Affected by the three parameters of pitch,segment,and length,a phonological checked tone has the same tone value with the non-checked ones;however,they are phonetically different,and it is advisable in phonological description not to classify the non-checked and checked tones with the same tonal values as one tone category.
Dai languagetone category mergingtonal evolutionchecked tone
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