Recently I started to learn Pinyin. The system is relatively easy to follow but some ambiguity does exist. For example, I found the usage of finals o and uo confusing: why the Pinyin for 波 is bo1, not buo1? and 多 is duo1 instead of do1? Would appreciate if someone could give the reason for such usage.

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    It's a good question. I've been learning Chinese for 3 years and a half and I can't really hear the difference between "mou" and "mo" (both these sounds exist in Chinese).
    – musialmi
    Commented Mar 29, 2020 at 14:25
  • This point is well explained in episode 14 on labial initials in the (paywalled) Chinesepod series "Say it Right." And I am sure I have seen it explained in other places. But I am not sure enough of the details to explain it, and I cannot find a good explanation free on line now, Commented Mar 29, 2020 at 16:13
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    Since "buo" and "do" don't exist. I would guess this is just a spelling convention, similar to how you don't write the two dots on the ü when it's after "q", "j", "x", but do write them when it's after "l" or "n".
    – Sweeper
    Commented Mar 29, 2020 at 16:25
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    @techie11 Yes, basically. I don't know what "inherent" would mean. But in Mandarin b, p, m, f, all need a u on-glide before o, so pinyin leaves it implicit. Commented Mar 29, 2020 at 23:32
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    @musialmi The question is about -uo and -o, not -ou and -o. The latter, which you wrote, are definitely different sounds and there are innumerable minimal pairs you'd confuse if you mix them up. Can you hear the difference between duo and dou, you should be able to hear the difference between mo and mou too.
    – Olle Linge
    Commented Mar 30, 2020 at 10:41

3 Answers 3


For all practical purposes, you can think of this as a spelling convention. The finals are pronounced the same, even if all finals are to some extent influenced by the preceding initial.

In Pinyin, there is (almost) no overlap between these two spellings, so any given initial that can be followed by -uo can never be followed by -o and vice versa.

The actual pronunciation is arguably also identical, even though this always sparks emotional arguments when mentioned to native speakers with no training in phonetics (they typically claim that there's an obvious difference). This could be either because they are influenced by orthography (the way the word is spelt influences how they perceive it) or that the coarticulation going on with the preceding syllable in combination with the spelling makes them take note of the difference more than they otherwise would have. The phenomenon that spelling influences how native speakers pronounce words is not uncommon, see for example this list on Wikipedia for examples when this happens in English.

In many narrow transcriptions of Mandarin syllables (such as the one in Duanmu San's The Phonology of Chinese (2007) or Lin Yen-Hwei's The Sounds of Chinese (2007), the -uo and -o finals are transcribed exactly the same way: [ᵂoo], e.g. [pᵂoo] for bo and [tᵂoo] for duo.

This means that the sound is treated as a glide, which in one case gets its own letter in Pinyin, but in the other cases (after b, p, m and f) is merely implied.

I don't know the historical reason for this, though. If you listen to the syllables spelt with only -o, there's a clear glide in there, which is also easy to see if you look at spectrograms in e.g. Praat.

Finally, I said at the beginning that there is almost no overlap between these finals. That's because we do have both wo (which could be thought of as uo) and o, which are clearly different sounds. Since none of these have a normal initial, maybe you could say there's overlap, even though they are spelt differently.

However, while the first is very common (e.g. 我), the second is very rare and could be argued to not be a standard syllable at all. It's normally only used for modal particles like 喔.

I have done several projects that involve recording native speaker audio for all possible syllables in Mandarin, and most recorders (educated native speakers) don't know what to do with o or simply read it as wo, further hinting that this is not a normal syllable.

For a clear distinction, check the Pinyin chart over at Chinese Pronunciation Wiki.

Possibly, lo also follows this pattern, which would create an overlap with luo, but then again, lo is used in a similar way to o and not really as a full syllable. It should be abundantly clear that bo, po, mo, fo are not pronounced as lo or o, further indicating that it's mostly about spelling.

I have answered several similar questions here and have collected other potential tricky Pinyin issues here: A guide to Pinyin traps and pitfalls: Learn Mandarin pronunciation.


  • Duanmu, S. (2007). The phonology of standard Chinese. Oxford University Press.
  • Lin, Y. H. (2007). The Sounds of Chinese. Cambridge University Press.
  • thanks for the elaboration. I believe, even though o is qualified as a final on the Pinyin chart, it's actually not used as a final to be attached to any initials other than bpmfw: it's mainly an element to form other composite finals such as ou, uo, ao, etc. It's easier to just think that b,p,m,f,w all have a diminutive 'u' sound in their pronunciation, hence, uo in this case is "simplified" as o.
    – techie11
    Commented Mar 30, 2020 at 14:52
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    This answer is all true, except these are not traps or pitfalls of pinyin. They are rules of pinyin, well known to phonologists. They are traps and pitfalls of deliberately oversimplified textbook descriptions of pinyin. Commented Mar 30, 2020 at 14:52
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    @ColinMcLarty Well, these are certainly problems for students. Obviously, the article is not aimed at people who have studied Mandarin phonetics and phonology. It's a collection of things that students tend to miss, partly because of lack of proper explanations in textbooks and courses.
    – Olle Linge
    Commented Mar 30, 2020 at 15:04
  • I wonder if you have any thoughts on e.g. 蘿蔔 with neutral tone bo? To my untrained ears it still sounds like a diphthong [pwo], in contrast to other neutral tone syllables like 得 where the full tone is a diphthong [tɯ̯ʌ] but neutral tone is a monophthong [tɤ].
    – gnucchi
    Commented Sep 18, 2020 at 19:08

Please check out this article. It has been decided in 1920 that it should be bo not buo , fo not fuo, and so on.


Excerpt from the article follows:

「ㄅㄛ、ㄆㄛ、ㄇㄛ、ㄈㄛ的注音符號裡面沒有ㄨ,為什麼許多人發音的時候都有 ㄨ呢?」這是除了ㄈㄥ之外,另一個常見的發音問題。

要解釋這個疑問,只要看民國九年十二月「國語統一籌備會」所撰〈修正《國音字 典》之說明〉(收錄於商務印書館出版《校改國音字典》書末)即可知其梗概:

唇音各聲母與韻母拼合,原案根據韻書,有用開口呼之韻母者,有用合口呼之韻母 者,如「剝」「駁」音「ㄅㄛ」,「撥」「鉢」音「ㄅㄨㄛ」;「煩」「繁」音 「ㄈㄨㄢ」,「凡」「帆」音「ㄈㄢ」之類;編《字典》時,因唇音聲母本已合口, 故遇原案中唇音與合口呼韻母拼合之字,除「ㄨ」韻以外一律改用開口呼韻母。

文中所謂「唇音各聲母」,即指ㄅㄆㄇㄈ。在民國二年「讀音統一會」制定的注音 字母方案中,唇音聲母有些和開口呼韻母拼合,如「剝」「駁」音「ㄅㄛ」、 「凡」「帆」音「ㄈㄢ」;有些和合口呼韻母拼合,如「撥」「鉢」音「ㄅㄨ ㄛ」、「煩」「繁」音「ㄈㄨㄢ」。

  • Hi Joe, please don't post link-only answers, as with time the links may break or become invalid. It would be better to add a summary, an excerpt or some more info to your answer. Thanks!
    – blackgreen
    Commented Sep 14, 2020 at 12:23
  • Hi, as I reread your answer, I think you managed to convince me. I am happy to remove my answer. Even though I still think some of the pronunciations does not exist now a days, your answer is the most sound one. I encourage you to explain a little bit more in English so that the info can get to entrance level learners as well. Best.
    – River
    Commented Sep 18, 2020 at 14:41
  • @River, thanks for the suggest. Though I'm interested in linquistics, I'm not a linquist. It'd be difficult for me to translate the excerpt into English. Sorry.
    – joehua
    Commented Sep 19, 2020 at 0:12

Let make the answer simple, for uo and o, you can only choose 1 for a 声母:

  • b, p, f only combine with o, e.g. 波, 博, 婆, 佛,
  • l only combine with `uo', e.g. 罗, 落,

In fact, o sounds like , uo sounds like 乌窝

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