平仄或說 = A Note on the Level

In the Late Southern Dynasties (6(superscript th) century AD), for rhetorical purposes, Chinese literati induced the four tonal categories (si-sheng) into two groups: the level tone and the other three tones (rising, departing, entering). These two groups subsequently developed into the so-called level-oblique distinction, and the original tonal feature of this distinction was not investigated enough. In the late 20(superscript th) century some scholars succeeded in the reconstruction of tonal values of the Middle Tang period, and presumed that the feature of level-oblique distinction of Middle Tang was: [level-low, oblique-high]. Such reconstruction of the tones can explain why the Northern Chinese dialects (Mandarin dialects) in the process of devoicing, developed into voiceless aspirates in the level tone, voiceless non-aspirates in the oblique tones.Both of the four-tone system and the level-oblique distinction disappeared during the 8-11(superscript th) centuries AD, and the most important cause of this development was the evolution of Yin-Yang registers.