Tone changes for "bu"

Also known as: tone sandhi and 变调规则 (biàndiào guīzé).

There are certain circumstances under which a Chinese word or character's normal tone will regularly change to a specific different tone. These tone changes (also called tone sandhi) must be learned in order to pronounce Chinese correctly.

There are three main tone change rules that every learner needs to know. These rules are not normally reflected in the tone marks of pinyin; you just have to know them.

Tone Change Rule for 不 (bù)

When followed by a 4th tone, 不 (bù) changes to 2nd tone (bú).

Examples of the 4→2 Tone Change

Remember, normally you do not write the tone change. We're just doing it here to make it extra clear.

Audio Chinese We Write We Say English
不 对 bù duì duì incorrect; wrong
不 要 bù yào yào to not want; do not (do something)
不 在 bù zài zài to not be (in a place)
不 是 bù shì shì to not be
不 去 bù qù to not go

Examples of NO Tone Change

Remember, 不 (bù) only changes when followed by a 4th tone. Here are examples when it doesn't change.

So there is no difference between what we say and what we write (no tone change) in the table below.

Audio Chinese We Write We Say English
不 好 bù hǎo bù hǎo not good, no good
不 想 bù xiǎng bù xiǎng to not think; to not miss
不 忙 bù máng bù máng not busy
不 能 bù néng bù néng cannot
不 一样 bù yīyàng bù yīyàng not the same, different


There are no exceptions to this rule. Just remember that it only applies to the character 不 (bù), and it's still written "bù."

Why Tone Changes Are Not Written

Normally the tone changes above are not written in the pinyin; you are supposed to just know the rule and apply it if you say the word(s) aloud. The reason for this is that in many cases if the tone change is written, you will be confused as to what the “normal” tone of a character is actually supposed to be. For example, you might wonder, “is this a third tone written as a second tone because it’s followed by a third tone, or is this character always a second tone?” Always writing the original tones solves this problem. But it also means that you really need to know your tone change rules. Learn them well!

An Alternative Way to Indicate Tone Changes

Some textbooks or software (such as Wenlin) indicate a tone change with a small dot under the letter with the tone mark. This can be nice for beginners, but it is not part of standard pinyin.

Sources and further reading