Mandarin tone sandhi rules
Third tone · 不 bù · 一 yī
Tone sandhiis when a tone changes because of the tone beside it. The word’s dictionary tone stays the same, but the way you say it shifts so the syllables flow. Three cases cover almost everything a beginner meets: the third-tone rule, the word 不 (bù), and the word 一 (yī).
Pinyin colour key: tone 1 (high flat), tone 2 (rising), tone 3 (dipping), tone 4 (falling), neutral.
1. Third-tone sandhi: two thirds in a row
This is the most important rule in the language. When one third tone is immediately followed by another third tone, the first one is pronounced as a second (rising) tone. The classic example is the first thing everyone learns:
“hello” — 你 (nǐ, third) becomes ní (second) because 好 (hǎo) is also a third tone. The second syllable keeps its third tone.
A few more of these everyday pairs:
With three or more third tones in a row, native speakers group the syllables and apply the rule within each group, which can vary. As a beginner, getting two-in-a-row right is what matters.
2. The 不 (bù) rule
不means “not” and is normally a fourth tone (bù). But before another fourth tone it changes to a second tone (bú). Before tones 1, 2 and 3 it stays bù.
3. The 一 (yī) rule
一means “one” and is first tone (yī) on its own, when counting, or at the end of a word. In combination it changes:
- Before a fourth tone → second tone (yí). e.g. yídìng一定 “definitely”.
- Before a first, second, or third tone → fourth tone (yì). e.g. yìqǐ一起 “together”.
- On its own / counting → first tone (yī). e.g. yī, yī…
Sandhi is easier by ear than by rule
ToneDeck plays these phrases the way they are actually said, so the change becomes a sound you recognise instead of a rule you recite. HSK 1 is free.
Start freeQuick recap
- • Third + third → first becomes second (rising).
- • 不 before a fourth tone → bú (second), otherwise bù (fourth).
- • 一 before a fourth → yí; before 1/2/3 → yì; alone → yī.
Frequently asked questions
What is tone sandhi in Mandarin?+
Tone sandhi is when a tone changes because of the tone next to it. The written (dictionary) tone stays the same, but the spoken tone shifts to make the word flow. The main cases are two third tones in a row, and the special words 不 (bù) and 一 (yī).
Why is nǐ hǎo pronounced ní hǎo?+
Both 你 (nǐ) and 好 (hǎo) are third tones. When two third tones come together, the first one changes to a second (rising) tone. So 你好 is written nǐ hǎo but pronounced ní hǎo. The dictionary spelling does not change.
How does 不 (bù) change tone?+
不 is normally a fourth tone (bù). But when it comes directly before another fourth tone, it changes to a second tone (bú). For example 不是 is bú shì, not bù shì. Before tones 1, 2, and 3 it stays bù.
How does 一 (yī) change tone?+
一 is first tone (yī) when counting or at the end. Before a fourth tone it becomes second tone (yí), as in 一定 yídìng. Before first, second, or third tones it becomes fourth tone (yì), as in 一起 yìqǐ.
Do I write the changed tone or the original tone?+
In standard pinyin you usually write the original dictionary tone (nǐ hǎo, bù, yī) and apply the change when speaking. Some teaching materials mark the changed tone to help beginners. Either way, say the changed tone aloud.
Related
The tone behind the most important sandhi rule.
Drill two-syllable tone combinations.
Back to Mandarin tones explained.