Tone Sandhi Explained: Why 你好 Isn't Pronounced nǐ hǎo
You've memorized the 4 tones. You can say nǐ (3rd tone) and hǎo (3rd tone) perfectly in isolation. Then you put them together — and every textbook tells you it's pronounced ní hǎo, not nǐ hǎo. What's going on?
Welcome to tone sandhi (变调, biàndiào) — the set of rules that govern how tones change when placed next to each other. These aren't optional or dialectal. They're how native speakers actually speak. If you ignore sandhi, you'll sound robotic at best and incomprehensible at worst.
What Is Tone Sandhi?
Tone sandhi is the phenomenon where a tone changes its pronunciation depending on the tone that follows it. It happens in all tonal languages (Mandarin, Cantonese, Vietnamese, Thai) but each language has different rules. Mandarin's sandhi system is relatively simple — only a handful of rules — but they're high-frequency, meaning they affect words you use every day.
Rule 1: The 3rd Tone Rule (Most Important)
Two 3rd Tones → 2nd + 3rd
When two 3rd tone syllables appear together, the first becomes a 2nd tone.
| Written | Spoken | Meaning |
|---|---|---|
| nǐ (3) + hǎo (3) | ní (2) + hǎo (3) | hello 你好 |
| hěn (3) + hǎo (3) | hén (2) + hǎo (3) | very good 很好 |
| kě (3) + yǐ (3) | ké (2) + yǐ (3) | can / may 可以 |
| shuǐ (3) + guǒ (3) | shuí (2) + guǒ (3) | fruit 水果 |
This is why 你好 is pronounced ní hǎo. Every beginner learns this the hard way.
Three or More 3rd Tones
With three or more 3rd tones in a row, things get flexible. The general pattern: all but the last become 2nd tone:
| wǒ (3) + hěn (3) + hǎo (3) | → wó hén hǎo | I'm very good 我很好 |
| wǒ (3) + yě (3) + hǎo (3) | → wó yé hǎo | I'm also good 我也好 |
Rule 2: 不 (bù) — The "Not" Word
不 + 4th Tone → 2nd Tone
The word 不 (bù) is normally 4th tone. But before another 4th tone syllable, it becomes 2nd tone (bú).
| Written | Spoken | Meaning |
|---|---|---|
| bù (4) + duì (4) | bú (2) + duì (4) | incorrect 不对 |
| bù (4) + shì (4) | bú (2) + shì (4) | is not 不是 |
| bù (4) + yào (4) | bú (2) + yào (4) | don't want 不要 |
Before any other tone (1, 2, or 3), 不 stays as 4th tone:
- bù gāo (不高, not tall) — stays 4th before 1st tone
- bù lái (不来, not coming) — stays 4th before 2nd tone
- bù hǎo (不好, not good) — stays 4th before 3rd tone
Rule 3: 一 (yī) — The "One" Word
一 Changes Based on What Follows
一 (yī) is the most versatile sandhi word. It changes depending on the tone of the next syllable:
| Context | Written | Spoken | Meaning |
|---|---|---|---|
| 一 + 4th tone → 2nd | yī (1) + gè (4) | yí (2) + gè (4) | one (of something) 一个 |
| 一 + 4th tone → 2nd | yī (1) + dìng (4) | yí (2) + dìng (4) | definitely 一定 |
| 一 + 1st/2nd/3rd → 4th | yī (1) + tiān (1) | yì (4) + tiān (1) | one day 一天 |
| 一 + 1st/2nd/3rd → 4th | yī (1) + nián (2) | yì (4) + nián (2) | one year 一年 |
| 一 + 1st/2nd/3rd → 4th | yī (1) + qǐ (3) | yì (4) + qǐ (3) | together 一起 |
Exception: When counting or reciting numbers, 一 stays 1st tone (yī, èr, sān...).
Rule 4: The Half 3rd Tone
3rd Tone Before Non-3rd → "Half" 3rd
In natural speech, a 3rd tone only does its full "dip and rise" at the end of a phrase. Before a 1st, 2nd, or 4th tone, it becomes a "half 3rd" — it dips low but doesn't rise back up.
| Context | Example | How It Sounds |
|---|---|---|
| 3rd + 1st | hěn gāo (很高, very tall) | hěn drops low, stays low. gāo is high flat. |
| 3rd + 2nd | hěn máng (很忙, very busy) | hěn drops low. máng rises. |
| 3rd + 4th | hěn dà (很大, very big) | hěn drops low. dà falls. |
This isn't an explicit "rule" you need to memorize — it happens naturally when you speak at normal speed. But it explains why your carefully articulated 3rd tones sometimes sound unnatural.
How to Practice Tone Sandhi
- Learn the rules, then forget them. Native speakers don't think about sandhi — they've internalized it. Your goal is the same: know the rules intellectually, then drill them until they become automatic.
- Focus on the high-frequency cases first. 你好, 不是, 一个 — these appear in almost every conversation. Master these and you've covered 80% of real-world sandhi.
- Listen more than you read. Sandhi is an auditory phenomenon. Reading about it helps, but hearing it in context is what makes it stick.
- Drill tone pairs, not isolated syllables. The confusion always happens at the boundary between two tones. Practice transitions, not individual tones.
🎧 Practice Tone Sandhi in Context
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