If there's one tone rule that trips up every Chinese learner, it's third tone sandhi. You learn that the 3rd tone goes "down then up" (ˇ), but in real speech, it almost never does that. The 3rd tone is a shape-shifter — it changes depending on what comes after it.
Understanding these rules is the difference between sounding like a textbook robot and sounding like someone who actually speaks Chinese.
What Is Tone Sandhi?
"Sandhi" comes from Sanskrit and means "joining." Tone sandhi refers to systematic tone changes that happen when tones appear next to each other in connected speech. English has something similar — we change pronunciation based on context all the time (think "the apple" vs "the book"), we just don't think about it.
In Chinese, the most important sandhi rules involve the 3rd tone.
Rule 1: 3rd + 3rd → 2nd + 3rd
This is the big one. When two 3rd tones appear in sequence, the first one changes to a 2nd tone:
| Written | Pronounced | Example |
|---|---|---|
| nǐ hǎo | ní hǎo | 你好 (hello) |
| wǒ hěn | wó hěn | 我很 (I very) |
| yǔ fǎ | yú fǎ | 语法 (grammar) |
| mǎi mǎ | mái mǎ | 买马 (buy a horse) |
The pinyin still writes the original tones, but you say it with the changed tone. This is why beginners often think native speakers are "mispronouncing" these words — they're following sandhi rules that textbooks mention once and never drill.
Three or More 3rd Tones in a Row
When three or more 3rd tones appear consecutively, the grouping determines which ones change:
Two common patterns:
-
2 + 1 grouping: 展览馆 (zhǎn lǎn guǎn) → zhán lǎn guǎn (exhibition hall)
- First two form a unit, first changes: "zhán lǎn" + "guǎn"
-
1 + 2 grouping: 小老虎 (xiǎo lǎo hǔ) → xiǎo láo hǔ (little tiger)
- Last two form a unit, middle one changes: "xiǎo" + "láo hǔ"
The grouping depends on the semantic/grammatical structure of the phrase. Adjective + noun pairs typically group together.
Rule 2: The "Half Third" Tone
Here's what most textbooks don't tell you clearly: the full "dipping" 3rd tone (down-then-up) is actually rare in natural speech. In most contexts, the 3rd tone is pronounced as a half third — it goes down but doesn't come back up.
The full 3rd tone only appears:
- At the end of a sentence or phrase
- Before a pause
- When a word is spoken in isolation
In all other positions (before 1st, 2nd, 4th, or neutral tone), the 3rd tone is half-third: just a low, falling pitch.
| Context | Pronunciation | Example |
|---|---|---|
| 3rd + 1st | Half-3rd + 1st | 北京 (běi jīng) — "bei" stays low |
| 3rd + 2nd | Half-3rd + 2nd | 旅行 (lǚ xíng) — "lü" stays low |
| 3rd + 4th | Half-3rd + 4th | 考试 (kǎo shì) — "kao" stays low |
| 3rd alone | Full 3rd | 好 (hǎo) — dips down then up |
This is why native speakers seem to "swallow" the 3rd tone. They're not being lazy — they're using the natural half-third that's appropriate in connected speech.
Rule 3: 不 (bù) Tone Sandhi
The word 不 (bù, "not") is 4th tone by default, but it changes to 2nd tone before another 4th tone:
| Context | Change | Example |
|---|---|---|
| bù + 4th tone | bú + 4th | 不是 (bú shì) — "not is" |
| bù + 1st tone | bù + 1st | 不吃 (bù chī) — "not eat" |
| bù + 2nd tone | bù + 2nd | 不行 (bù xíng) — "not okay" |
| bù + 3rd tone | bù + 3rd | 不好 (bù hǎo) — "not good" |
Rule 4: 一 (yī) Tone Sandhi
The number 一 (yī, "one") is even more complex:
| Context | Change | Example |
|---|---|---|
| yī + 4th tone | yí + 4th | 一个 (yí gè) — "one (measure word)" |
| yī + 1st/2nd/3rd | yì + tone | 一天 (yì tiān) — "one day" |
| Counting or alone | yī | 一二三 (yī èr sān) — "1 2 3" |
Why Sandhi Matters for Sounding Natural
Native speakers process sandhi unconsciously. When you don't follow these rules, your speech sounds "off" even if individual tones are technically correct. It's like speaking English with perfect pronunciation but wrong stress patterns — people can understand you, but something feels unnatural.
Sandhi is what separates technically correct pronunciation from natural-sounding pronunciation.
How to Practice Sandhi
- Start with 3rd + 3rd pairs — drill common words like 你好, 你们, 可以, 所以, 只有
- Practice the half-third — say phrases like 北京, 旅行, 考试 with a low (not dipping) 3rd tone
- Drill 不 and 一 patterns — create sentences with these words in different tone contexts
- Use AI feedback — TonePerfect detects whether your tone changes match the expected sandhi patterns
The key is repetition with feedback. Your brain needs to automate these rules so you don't have to think about them in real conversation.
Practice Sandhi Now
TonePerfect includes dedicated sandhi practice exercises covering all major patterns. The AI evaluates not just your base tones but whether you're applying the correct sandhi changes.
Try it on iOS, Android, or Web.
Mastering sandhi is what takes you from "good pronunciation" to "sounds like a native speaker." It's the detail that makes the difference.