The Tone Changes Rules of “不”
1. 不 is a 4th tone syllable by itself.
不 （bù）
2. The tone doesn’t change when 不 is followed by a 1st tone, 2nd tone or 3rd tone syllable.
e.g.
| 不 + 1st Tone | 不吃 （bù chī） |
| 不 + 2nd Tone | 不行 （bù xíng） |
| 不 + 3rd Tone | 不想 （bù xiǎng） |
3. 不 becomes the 2nd tone when it’s followed by a 4th tone syllable.
e.g.
| 不 + 4th Tone | 不要 （bú yào） |
4. When 不 is in the between of “A 不 A” pattern phrase，不 will be the neutral tone.
e.g.
| A 不 A | 好不好 （hǎo bu hǎo） |