Bo, po and duo, tuo

Pinyin doesn't always specify finals in a straightforward way. For example it is difficult to see that wei and dui have the same final -uei, the former substituting u for semi-vowel w, the latter omitting the e. In Views on initials and finals of Mandarin in Pinyin I've tried to show those peculiarities by grouping forms under their actual final, not just their spelling. What I didn't do was merging columns -o (bo, po, mo, fo) and -uo (duo, tuo, ...).

But as Y.R. Chao indicates "there is a special form for labial initials, namely, 波 bo, 坡 po, 摸 mho, 脖 bor, 婆 por, 摩 mo, 佛 for, etc. This is only graphical, and the actual pronunciation is still, buo, puo, and so on." (A Grammar of spoken Chinese, 1968, p. 30). He adds: "After the labials: b, p, m, f, this final is written o, but there is still a trace of u before and also an unrounding at the end." (Mandarin Primer, 1948, p. 24). Though said about Gwoyeu Romatzyh this translates directly to Pinyin.

This is interesting as Hànyǔ Pǔtōnghuà Yǔyīn Biànzhèng (汉语普通话语音辨正, 2003, ISBN 7-5619-0622-6) states: "o这个字母只代表一个元音:[o]" and "[o]后、半高、圆唇元音。例如“波、摸、佛、磨”等字的韵母。" "The character o does only represent one sound: [o]" and "o, back, half high vowel with rounded lips. For example: 'bo, mo, fo, mo' and other characters with same final." And then in contrast: "uo[uo]例如“我、活、多、说”等字的韵母。" "uo [uo], for example wo, huo, duo, shuo and other characters with same final." So it gives different IPA values for both finals.

In addition to that Xiàndài Hànyǔ Cídiǎn (现代汉语词典) has entries lo with lonely character 咯 (also spelled luo) and luo, separating spellings, which for Chao would be the same.