Tone Sandhi Rules Explained: When Mandarin Tones Change
You can produce mā, má, mǎ, mà on demand. Then you open a real audio file, hear a native speaker say nǐ hǎo, and freeze. That was not “nǐ hǎo” with two clean third tones. It was “ní hǎo” - a second tone followed by a third. Your textbook never warned you.
That change is called tone sandhi (变调, biàndiào): a small set of rules Mandarin applies when syllables collide inside a word or short phrase. Learners need the rules by name, otherwise they miscount syllables, misjudge what they hear, and eventually misjudge what they say.
This guide explains every sandhi rule you will meet in your first year of Mandarin. It is the same rule set we tune the audio exercises against in ReadDeck, and small enough to memorise in an afternoon.
What tone sandhi is (and what it is not)
Tone sandhi is phonological, not orthographic. Dictionary pinyin shows the citation tone - the tone a syllable has in isolation. The sandhi tone is what you actually say when the syllable sits next to certain other tones in connected speech. Pinyin rarely marks the sandhi form; you have to know it from the rule or recognise it by ear.
Two corollaries to lock in: the change is predictive, not random (know the neighbouring tone and you can predict the change), and the change is local (sandhi applies within a word or a tight phrase and does not normally jump across pauses, comma breaks, or strong emphasis).
Sandhi is not the same as tone merger, neutralisation, or intonation. Intonation in Mandarin is real but small; tone sandhi is the grammar of how syllables reshape each other when they meet.
The table below summarises the three rules that cover roughly 95 percent of the changes you will ever hear.
The master tone-sandhi rules table
| Word or tone | Citation tone | Sandhi condition | Sandhi tone | Worked example |
|---|---|---|---|---|
| 3rd tone (any syllable) | 3rd (ǎ) | followed by another 3rd tone | first becomes 2nd (á) | nǐ hǎo 你好 - ní hǎo |
| 3rd tone (any syllable) | 3rd (ǎ) | followed by 1st, 2nd, or 4th tone | half third - low falling, no rise | hěn hǎo 很好 - hěn drops low |
| 不 (bù) | 4th (bù) | followed by another 4th tone | becomes 2nd (bú) | bù shì 不是 - bú shì |
| 不 (bù) | 4th (bù) | anywhere else | stays 4th (bù) | bù hǎo 不好 - stays bù hǎo |
| 一 (yī) | 1st (yī) | followed by a 4th tone | becomes 2nd (yí) | yí gè 一个 - yí gè |
| 一 (yī) | 1st (yī) | followed by 1st, 2nd, or 3rd tone | becomes 4th (yì) | yī tiān 一天 - yì tiān |
| 一 (yī) | 1st (yī) | alone, in counting, or ordinal | stays 1st (yī) | yī, èr, sān 一二三 |
Memorise that table first. Everything that follows is detail.
Hear each worked example from the master table:
Rule 1: Third-tone sandhi (3rd + 3rd becomes 2nd + 3rd)
This is the single most important tone change in Mandarin. When two third tones meet, the first one becomes a second tone (rising).
| Citation form | Sandhi form | Meaning |
|---|---|---|
| nǐ hǎo 你好 | ní hǎo | hello |
| lǎo shǔ 老鼠 | láo shǔ | mouse |
| kě yǐ 可以 | ké yǐ | may / can |
| hěn hǎo 很好 | hén hǎo | very good |
| wǒmen 我们 | wómen | we |
| yǔfǎ 语法 | yúfǎ | grammar |
The pattern is mechanical. Find two consecutive third-tone syllables; change the first to second tone.
Three third tones in a row
Real sentences occasionally stack three third tones. The textbook rule is that sandhi “shifts rightward”: the first syllable becomes second, then the next pair re-applies the rule. The most common surface pattern is 2nd + 3rd + 3rd, with the final syllable staying third.
- zhǎn lǎn guǎn 展览馆 (exhibition hall) - pronounced zhán lǎn guǎn.
- hěn hǎo kàn 很好看 (very good-looking) - pronounced hén hǎo kàn.
A two-and-two grouping is also common. Do not memorise the variation; train your ear to recognise “third-tone stacks change shape” and the specifics will sort themselves out.
The half-third tone before non-third tones
The flip side of third-tone sandhi is the rule many textbooks skip. When a third tone sits before a 1st, 2nd, or 4th tone, it compresses into a half-third tone - a low falling note with no rising tail.
- hěn hǎo 很好 - hěn drops to a low fall, not a full dip-and-rise.
- wǒ qù 我去 - wǒ is a low fall, not a textbook third.
- mǎi le 买了 - same.
The pinyin spelling still writes hěn, wǒ, mǎi. Only the acoustic shape changes. If you keep producing the full dip-and-rise on every 3rd-tone syllable, your speech will sound slow and over-pronounced. Native speakers compress.
Rule 2: The 不 (bù) tone change
The negation 不 is normally fourth tone: bù. It becomes bú (second tone) only when it sits directly before another fourth tone.
| Citation | Sandhi | Meaning |
|---|---|---|
| bù shì 不是 | bú shì | is not |
| bù duì 不对 | bú duì | incorrect |
| bù qù 不去 | bú qù | does not go |
| bù yào 不要 | bú yào | do not want |
| bù huì 不会 | bú huì | cannot |
| bù gàn 不干 | bú gàn | will not do |
When 不 sits before a 1st, 2nd, or 3rd tone, it stays fourth: bù hǎo 不好, bù lái 不来, bù mǎi 不买.
The common English-speaker trap is over-application. bù xíng 不行 is pronounced bù xíng, not bú xíng, because the next syllable is second tone. Drill the rule, then drill the exceptions.
Two more exceptions: a standalone “No!” - just 不 by itself - stays fourth, and 不 at the end of a sentence or before a pause stays fourth. Sandhi only applies inside a tight two-syllable phrase.
Rule 3: The 一 (yī) tone change
The numeral 一 is normally first tone: yī. It behaves like a chameleon, with two distinct sandhi rules.
一 before a 4th tone becomes 2nd tone
| Citation | Sandhi | Meaning |
|---|---|---|
| yī gòng 一共 | yí gòng | altogether |
| yī yàng 一样 | yí yàng | same |
| yī dìng 一定 | yí dìng | certainly |
| yī kuài 一块 | yí kuài | one piece / together |
| yī shù 一束 | yí shù | one bunch |
| yī zhèn 一阵 | yí zhèn | a gust, a fit |
一 before any other tone becomes 4th tone
| Citation | Sandhi | Meaning |
|---|---|---|
| yī tiān 一天 | yì tiān | one day |
| yī bān 一般 | yì bān | general |
| yī qǐ 一起 | yì qǐ | together |
| yī bǎi 一百 | yì bǎi | one hundred |
| yī nián 一年 | yì nián | one year |
| yī zǔ 一组 | yì zǔ | one group |
When 一 stays first tone
Three situations keep 一 as yī and ignore both sandhi rules:
- Counting in sequence: yī, èr, sān 一二三. Each number keeps its citation tone.
- Ordinal use: dì yī 第一 (first). The ordinal “first” reads as yī, even before a fourth tone.
- Final position or before a pause: wǒmen shì yī 我们是一 (we are one). At the end of the phrase, the change is suspended.
A note on spelling: dictionary entries often write 一 as yī even when the spoken form is yì or yí, because the spelling shows the citation form. Trust the rule, not the spelling.
The neutral tone and other small changes
Beyond the three big rules, Mandarin has a cluster of smaller sandhi behaviours. None are individually as important as third-tone sandhi, but together they account for a lot of the difference between textbook Mandarin and natural Mandarin.
Neutral tone (轻声, qīngshēng)
Some syllables lose their tone and become short, light, and unstressed. Common cases:
- Reduplicated nouns: māma 妈妈 (mother), bàba 爸爸 (father). The second syllable is neutral.
If you produce every syllable with full tonal weight, you will sound stilted, even if your tones are technically correct.
Adjective reduplication
When an adjective is reduplicated for emphasis (piàopiàoliangliang 漂漂亮亮, “very pretty”), the repeated syllables often shift toward first tone, and the trailing syllable may go neutral. This is one of the most common ways Mandarin speakers intensify an adjective.
Common exceptions and natural-speech variations
Textbook sandhi is the idealised version. Real Mandarin is messier. Six things to remember:
- Sandhi does not cross strong prosodic boundaries. A pause or comma resets the rules.
- Emphasis suspends sandhi. If a speaker stresses a word, they restore the citation tone.
- Fast speech drops sandhi. Native speakers in casual chat sometimes say nǐ hǎo without the change.
- Phone numbers, addresses, and prices ignore sandhi. Learners who sandhi their phone numbers sound stilted.
- Regional Mandarin varies. Taiwan Mandarin and Mainland Mandarin handle neutral tones and the half-third tone slightly differently. The big three rules are universal.
- Children’s speech and careful speech reduce sandhi. Slow, didactic speech restores citation tones.
If a textbook example and a real recording disagree, trust the recording. Sandhi lives in the ear, not the page.
How native speakers actually use these rules
The gap between textbook and natural speech shows up most in three places.
Greetings and formulaic phrases. The textbook says nǐ hǎo is third plus third, pronounced ní hǎo. In practice, native speakers compress the first syllable so far it almost becomes a neutral tone, and the second syllable is the only one with clear pitch.
不好, 不是, 不要. Learners reach for sandhi on all three. In natural speech, the bù in bù hǎo is a low, short fourth tone with no stretch; the textbook tone is rarely fully produced. bú shì and bú yào are clearer because the rule fires.
The hidden half-third. The single biggest difference between a learner’s speech and a native speaker’s speech is whether the learner compresses third tones before non-third tones. If you keep producing the full dip on every hěn, wǒ, mǎi, kě, your speech sounds slow and wooden. Compress, and you instantly sound faster.
The fix is ear-based: listen to the same sentence at 0.75x and 1x speed, and pay attention to how the hěn in hěn hǎo shrinks.
A five-minute daily practice routine
Sandhi rules decay fast without practice. The routine below keeps them alive without burning out:
- Minute 0-1: warm-up. Hum the four tones on an “ah” vowel, twice through. Run the master rules table from memory once, aloud.
- Minute 1-2: third-tone pairs. Drill six: nǐ hǎo, hěn hǎo, kě yǐ, lǎo shǔ, wǒmen, yǔfǎ. Focus on the first syllable becoming second.
- Minute 2-3: 不 pairs. Drill six: bú shì, bú duì, bú qù, bú yào, bú huì, bù hǎo. The rule fires only on the first five.
- Minute 3-4: 一 pairs. Drill six: yí gè, yí yàng, yí dìng, yì tiān, yì bǎi, yì qǐ. yí before fourth tone, yì otherwise.
- Minute 4-5: live audio. Play a one-minute native clip and mark every sandhi you hear. Audio Deck ships transcripts alongside audio so this step is friction-free.
After two weeks, the patterns are muscle memory. After six weeks, you will catch the half-third tone in passing without thinking.
FAQ: Mandarin tone sandhi
Do I really need to learn tone sandhi?
Yes. Without the rules you will say nǐ hǎo with two third tones and instantly mark yourself as a textbook learner. The three big rules are about thirty minutes of study. They pay back for the rest of your Mandarin life.
Does sandhi change the meaning of a word?
Not at the lexical level. nǐ hǎo and ní hǎo are the same word; the second is just the natural pronunciation. But over- or under-applying sandhi sounds unnatural.
What about the half-third tone?
The half-third is the third tone compressed to a low fall, with no rising tail. It appears whenever a third tone sits before a non-third tone. Most textbooks mention it in passing. It is one of the highest-leverage habits a learner can pick up, because compressing third tones is what makes speech sound natural-paced.
Does Taiwan Mandarin follow the same rules?
The three big rules are essentially identical in Taiwan Mandarin and Mainland Mandarin. They differ in neutral-tone patterns, stress, and the realisation of the half-third tone.
How does sandhi interact with other Sinitic languages?
Standard Mandarin (Pǔtōnghuà) is the reference for the three big rules. Other Sinitic languages - Cantonese, Shanghainese, Hokkien - have their own tone-change rules and tone inventories (Cantonese has six to nine contrastive tones). If you learn a regional variety later, expect a different but analogous system.
Hear real sandhi in ReadDeck
The fastest way to internalise tone sandhi is to hear it in context. ReadDeck is built around exactly that loop. The library ships with audio-first lessons, every word is tappable for isolated pronunciation, and the FSRS review system schedules tone and sandhi drills at the moment your ear is about to forget them. It is free, offline, and Mandarin-only.
If you have ten minutes today, open the Mandarin tones hub, pick a four-tone drill pack, and run through twenty minimal pairs followed by the master sandhi table above. To check how your sandhi pronunciation lands in a graded setting, HSK Quiz runs free listening mocks scored against the official HSK pass mark. Train your ear every day and the sandhi rules will click within a month.