Tone Sandhi in Mandarin: The Tone Change Rules Explained

沉浸 TeamAugust 12, 20265 min read

Tone sandhi is the set of rules that change a syllable's tone depending on the tone that follows it. It's why 你好 (written nǐ hǎo) is pronounced ní hǎo, and why 不 sometimes sounds like bú. Mandarin has only three sandhi rules worth learning, plus one pronunciation habit (the half-third tone) that explains why native speech sounds smoother than your textbook's tone diagrams. This guide covers all four, with words you can practice on.

First, the reassuring part: sandhi isn't an extra memorization burden. The rules exist because the changed versions are easier to say. Your mouth will start doing most of this on its own once you've heard enough Mandarin; the rules just tell you what to listen for. (If tones themselves are still new, start with our complete guide to Chinese tones and come back.)

Rule 1: two 3rd tones in a row, the first becomes 2nd

When a 3rd tone is followed by another 3rd tone, the first one turns into a 2nd (rising) tone:

你好 (nǐ hǎo, hello) is said ní hǎo
可以 (kěyǐ, can) is said kéyǐ
所以 (suǒyǐ, therefore) is said suóyǐ
洗澡 (xǐzǎo, to shower) is said xízǎo

Why? Try saying two full low tones back to back. It's like doing two squats mid-sentence. Raising the first one keeps the sentence moving.

Two details worth knowing:

The spelling doesn't change. Pinyin keeps writing nǐ hǎo; you're expected to apply the rule when speaking. That's the convention almost everywhere.
In longer runs of 3rd tones (like 我也很好, wǒ yě hěn hǎo), speakers group words naturally and raise all but the last 3rd tone in each group: wó yé hén hǎo is a normal way to say it. Don't overthink chains; follow the word groupings and it falls out on its own.

Rule 2: 不 (bù) becomes bú before a 4th tone

不 (not) is a 4th tone word, but two falling tones in a row feel like slamming a door twice. So before another 4th tone, 不 rises instead:

不是 (not to be): bú shì
不对 (not right): bú duì
不去 (not going): bú qù

Before 1st, 2nd, and 3rd tones it stays bù: 不吃 (bù chī), 不忙 (bù máng), 不好 (bù hǎo). Some textbooks write the change (bú shì), others keep bù everywhere; the pronunciation is the same either way.

Rule 3: 一 (yī) changes by what follows it

一 (one) has three faces:

yí before a 4th tone: 一个 (yí ge, one), 一定 (yídìng, definitely)
yì before 1st, 2nd, or 3rd tones: 一天 (yì tiān, one day), 一年 (yì nián, one year), 一起 (yìqǐ, together)
yī, its original 1st tone, when counting or at the end of a phrase: counting 一, 二, 三 (yī, èr, sān), numbers like 第一 (dì yī, first), and in dates and phone numbers.

The pattern mirrors 不: avoid two identical strong tones colliding, keep the sentence flowing.

The half-third tone (why real speech sounds smoother)

Here's the habit that isn't usually printed in the rules list but shapes how Mandarin sounds. When a 3rd tone comes before any tone other than another 3rd, it doesn't do the full textbook dip-and-rise. It just goes low and stays low, with no rise. That's called the half-third tone:

老师 (lǎoshī, teacher): lǎo is a low, level "lao," no rise
很 (hěn, very) in 很忙 (hěn máng): low, then move on
买 (mǎi, to buy) in 买东西 (mǎi dōngxi, to shop): low, no scoop upward

In practice this means the full dipping 3rd tone is the exception (it appears when the syllable stands alone or ends a phrase), and "3rd tone = low tone" is the better everyday model. We make that case in detail in our 3rd tone guide.

How to practice sandhi without memorizing charts

Anchor each rule to one word you say daily. 你好 for Rule 1, 不是 for Rule 2, 一个 for Rule 3. Say them correctly and the rules generalize on their own.
Listen for sandhi in real audio. Play any native sentence with 不 or a 3rd-tone pair in it and confirm you can hear the change. Graded stories with audio give you hundreds of natural examples at your level.
Get feedback on real sentences. Chenjin's Tone Coach compares your recording to native audio and scores against the tones speakers use in connected speech, sandhi included, so saying ní hǎo for 你好 counts as correct, and the analysis explains which rule applied. That closes the gap between knowing the rule and saying it.

Frequently asked questions

What does "sandhi" mean?

It's a linguistics term (borrowed from Sanskrit) for sounds changing because of their neighbors. English has sandhi too: "a" becomes "an" before a vowel. Mandarin's tone sandhi is the same idea applied to tones.

Do I have to write the changed tones in pinyin?

No. Standard pinyin writes the original tones (nǐ hǎo, yī gè) and trusts the speaker to apply the rules. Some beginner textbooks mark the changes for 不 and 一 as training wheels. Read either style; speak the changed version.

Is there sandhi with the neutral tone?

The neutral tone doesn't trigger the 3rd-tone rule (it has no full tone of its own). A 3rd tone before a neutral tone usually stays low, like the half-third: 我们 (wǒmen, we) is a low wǒ plus a light men. Nothing new to learn there beyond keeping 3rd tones low.

What about 一 in 一样 or 不 in 不客气?

They follow the rules on this page: 一样 (yíyàng, the same) has yí before a 4th tone; 不客气 (bú kèqi, you're welcome) has bú before the 4th-tone kè. Once you've drilled a handful of these, new cases sound obvious before you've reasoned them out.

Want to hear the rules in action? Create a free Chenjin account: read graded stories with native audio, then check your own 你好 against a native speaker's pitch curve in Tone Coach.