Tone sandhi is a phonological change occurring in tonal languages, in which the tones assigned to individual words or morphemes change based on the pronunciation of adjacent words or morphemes.

For example 不是:

  • the original tone for each character is: bù shì (4 4)

  • After tone sandhi: bú shì (2 4)

Some say that it can be confusing to write it as if it is written, it would be confusing to know what the original tone is supposed to be.

Is there an standard practice to address this?

  • there also is the matter of tone changes to other than neutral occurring on 一、七 depending on tone on the following character, in which case nevertheless the original tone mark is preserved (discussed at this site before)
    – user6065
    Commented Sep 27, 2017 at 23:41
  • Just one note. Neutral tone is different. Neutral tone has been clearly addressed in dictionary, while tone sandhi is not addressed in any formal dictionaries.
    – dan
    Commented Sep 27, 2017 at 23:58
  • exactly, tone sandhi refers to 33 changing to 23, besides tone change on 一/七 there also is on 不,this all has been discussed before, in fact below answer has been given before
    – user6065
    Commented Sep 28, 2017 at 0:34

2 Answers 2


Tone Sandi rule should merely apply to spoken. In written, you should always put original tones in any forms of exams except that those exams are testing the rule itself.

In fact, I doubt most of natives are aware of the existence of Tone Sandi indeed. But they do apply the rule naturally in practice. I suggest you study by phrase, not by character. That way you will know how each character will be used and the way to pronounce in practice.

  • Never realize that. In fact, I never thought too much about neutral tone, though I know it is 轻声.
    – sfy
    Commented Oct 16, 2017 at 10:55

Standard practice is not to change the tone diacritics to represent tone sandhi. So bù shì keeps the fourth tone on in spite of the pronunciation as bú shì. The same applies to the tones on 一 / yī, even though some learners dictionaries diverge from this rule. The rule also applies to third-tone sandhi.

See for example Tone change rules in the Chinese Pronunciation Wiki.

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