On the mid vowel phoneme in Mandarin phonology

The classification of the mid vowel phoneme in Mandarin phonology has always been a controversial issue. On the foundation of previous researchers’ opinions, this paper analyzes and discusses Mandarin's mid vowels from a phonological perspective and an experimental phonetics perspective, proposing that the vowel system hierarchy should be considered in the process of classifying the mid vowel phoneme. Only one phoneme, written as /ə/, is necessary to represent the mid vowel in Mandarin phonology. The phoneme of the mid vowel, /ə/, is a first-class Mandarin vowel, and all second-, third- and fourth-class mid vowels are its allophones.