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不 usually has a falling fourth tone, becomes rising bú before another fourth tone, and can be light and neutral in certain patterns.
Why does 不 (bù) sound different in different Chinese phrases? You learn it with a falling tone, then hear a rising sound in 不是 (bú shì), “is not”. This is a normal Mandarin tone change, often called tone sandhi. Start with the next syllable: its tone usually tells you how to pronounce 不. Then learn one useful exception for everyday questions.
When Does 不 Change from Bù to Bú?
In 不要糖 (bú yào táng), “no sugar”, 不 rises before the falling tone of 要 (yào).
When 不 (bù) comes directly before another fourth-tone syllable in connected speech, pronounce it with the rising second tone bú:
- 不是 (bú shì): is not; am not.
- 不要 (bú yào): do not want; do not.
- 不用 (bú yòng): no need.
- 不对 (bú duì): incorrect; not right.
Try 不是 (bú shì) slowly: let your voice rise on bú, then fall on shì. Keep the two syllables connected. The following syllable keeps its fourth tone; you change 不.
For example, 我不是老师。 (Wǒ bú shì lǎoshī.) means “I’m not a teacher.” The meaning of 不 stays negative even though its pitch changes.
When Does 不 Keep Its Fourth Tone?
Record short phrases so you can hear the contrast between bù and bú.
Before a first, second or third tone, 不 normally remains bù:
- 不吃 (bù chī): do not eat; followed by first tone.
- 不忙 (bù máng): not busy; followed by second tone.
- 不好 (bù hǎo): not good; followed by third tone.
It also keeps its fourth tone when said on its own. A common mistake is to turn every 不 into bú once you learn the change. Check the tone immediately after it instead.
✨ Did you know? Pinyin may show the dictionary form bù even where speech uses bú. This guide shows the spoken pronunciation to help you practise.
Why Is 不 Sometimes Neutral: Bu?
In relaxed questions, the middle 不 can be short and unstressed.
In A-not-A questions, the same verb or adjective appears on both sides of 不. The middle 不 is often pronounced lightly, without a full tone:
- 好不好？ (Hǎo bu hǎo?): Is that OK?
- 去不去？ (Qù bu qù?): Are you going or not?
This bu has no tone mark. Keep it short and unstressed rather than giving it a long, deliberate rise or fall. Full-toned pronunciations can also occur with emphasis; the neutral form is useful for relaxed everyday speech.
Compare 不去 (bú qù), “not going”, with 去不去 (qù bu qù), “going or not?” The sentence pattern matters as well as the following tone.
A Simple Way to Practise the 不 Tone Change
| Context | Say | Example |
|---|---|---|
| Before fourth tone | bú | 不是 · bú shì |
| Before tones 1, 2 or 3 | bù | 不吃 · bù chī |
| Unstressed middle of an A-not-A question | bu | 好不好 · hǎo bu hǎo |
Listen to one phrase below, repeat it, then record yourself. Alternate 不是 (bú shì) with 不吃 (bù chī) before practising a question. Aim for clear pitch and connected syllables; speed can come later.
For visitors, 不用，谢谢。 (Bú yòng, xièxie.), “No need, thank you”, is useful when declining an offer politely. Add a friendly tone of voice rather than making 不 unusually forceful. For the separate grammar question of when to choose a negative word, see 不 (bù) vs 没有 (méiyǒu).
Useful Chinese Words and Phrases
- 不是is not; am not
- 不用no need
- 不吃do not eat
- 不忙not busy
- 好不好？Is that OK?
A Short Everyday Conversation
Alex: 你去不去？
Nǐ qù bu qù?
Are you going or not?
Lin: 我不去，今天有点忙。
Wǒ bú qù, jīntiān yǒudiǎn máng.
I’m not going; I’m a bit busy today.
Alex: 明天去，好不好？
Míngtiān qù, hǎo bu hǎo?
Let’s go tomorrow. Is that OK?
Lin: 好，明天我不忙。
Hǎo, míngtiān wǒ bù máng.
OK, I’m not busy tomorrow.
Final Takeaway
Use bú before another fourth tone and bù before the first, second or third tone. In common A-not-A questions, listen for the short, neutral bu. Practise complete phrases so the pattern becomes familiar when you speak.