Tone sandhi is the name for the way Mandarin tones change when syllables are spoken together. The rules are few, they are regular, and they are the reason a learner who "knows the tones" can still sound like a recording played one syllable at a time. Here they are with audio, starting with the one you use in the first word you ever learn.
Rule 1: third + third becomes second + third
When two third-tone syllables meet, the first turns into a second tone.
- 你好 nǐ hǎo → said ní hǎo. Hear it on nǐ hǎo.
- 可以 kěyǐ → kéyǐ
- 老虎 lǎohǔ → láohǔ
- 很好 hěn hǎo → hén hǎo
The pinyin on the page does not change. Dictionaries and textbooks write the underlying tones and expect you to apply the rule as you speak.
Three or more third tones in a row. Group them the way the meaning groups them. 我很好 wǒ hěn hǎo is usually (我)(很好) → wǒ hén hǎo, with the first syllable staying low because it stands apart. 展览馆 zhǎnlǎnguǎn (exhibition hall) is one word, so both leading syllables rise: zhánlánguǎn. When in doubt, pause after the subject and apply the rule inside each group.
Rule 2: the "half third" tone, which is most third tones
Before any tone other than a third, a third tone loses its rise and becomes a short low tone. This is not an exception; it is what the third tone sounds like most of the time.
- 老师 lǎoshī: lǎo is low and flat, then shī is high. No rise in lǎo.
- 请问 qǐngwèn: qǐng is low, wèn falls.
- 美国 Měiguó: měi low, guó rises.
- 好吗 hǎo ma: hǎo low, ma light.
The full falling-rising shape (the V in the textbook diagram) only appears when the third tone is alone or ends a phrase and the speaker is being deliberate. If you produce the V everywhere, native speakers hear a strange sing-song emphasis on every other syllable. The fix is a reframe: the third tone is the low tone. Drop to the bottom of your range, stay there, and let the rise happen only at the end of a sentence.
Rule 3: 不 bù changes before a fourth tone
不 is a fourth tone by itself and before first, second and third tones. Before another fourth tone it becomes second tone bú.
- 不是 bù shì → bú shì (is not)
- 不要 bù yào → bú yào (don't want)
- 不对 bù duì → bú duì (wrong)
- but 不好 bù hǎo, 不来 bù lái, 不吃 bù chī keep bù
Rule 4: 一 yī changes almost everywhere
一 is first tone when counting or standing alone (yī, èr, sān). In a phrase:
- before a fourth tone it becomes second: 一个 yī gè → yí gè, 一样 → yíyàng
- before first, second or third it becomes fourth: 一天 → yì tiān, 一年 → yì nián, 一起 → yìqǐ
Full detail and more examples: 一 and 不 tone change rules.
Why sandhi is worth a week of your life
Sandhi words are the most common words in the language: 你好, 可以, 不是, 一个, 我想, 请问. A learner who says each syllable with its dictionary tone is correct on paper and wrong in every conversation. Getting these four rules automatic is the fastest single upgrade to sounding natural, and it takes days, not months, because the rules never vary.
How to practise it
- Ear first. Listen to nǐ hǎo said naturally and notice the first syllable rising. If you cannot hear it yet, play it against nǐ alone on the pinyin chart.
- Ten pairs a day. 你好, 可以, 老虎, 很好, 我想, 展览, 不是, 不要, 一个, 一样. Say each five times, slowly, then at speed.
- Read short sentences aloud and mark every place a rule applies before you speak. 我可以不去吗 → wǒ kéyǐ bú qù ma.
- Check yourself. The free test and the practice tool score each syllable's tone, so a nǐ hǎo said as 3-3 shows up as a low score on the first syllable. That is the feedback a textbook cannot give.
Common mistakes
- Applying 3+3 to the pinyin in your head but not in your voice. Say it out loud; the rule is physical.
- Rising on the second syllable too. In ní hǎo only the first syllable rises; the second stays low.
- Over-applying 一 rules. In dates, phone numbers and counting, 一 stays first tone: 一月 yī yuè, 一二三 yī èr sān.
- Forgetting 不 before fourth tones in fast speech. bù shì said with two fourth tones sounds like an angry "NO. IS."
A seven-day plan
Day 1–2: listen only, 3+3 pairs. Day 3: say 3+3 pairs, record. Day 4: half-third words (老师, 请问, 美国). Day 5: 不 and 一. Day 6: mixed sentences. Day 7: run five sentences through the pronunciation checker and drill whatever scored lowest.
Frequently asked questions
Does the pinyin spelling change when the tone changes? No. nǐ hǎo is written with two third-tone marks and pronounced ní hǎo.
Is the half third a separate tone? No, it is the ordinary third tone in its usual position. Think of the full V as the special case.
Do native speakers ever break these rules? Slow, emphatic speech can keep two full third tones; songs ignore tones entirely. In normal speech the rules hold.
Does sandhi apply across word boundaries? Yes for 3+3 when the words belong to one phrase (很好 → hén hǎo). Pauses cancel it.
Say a few sandhi words into the mic and see which syllable slipped: free 2-minute tone test.