What Are the Chinese Tone Rules and Tone Sandhi?

One of the trickiest aspects of Mandarin pronunciation is tone sandhi (变调 biàndiào) — the rules that govern when tones change based on the tones around them. Even if you've memorized the dictionary tone for every word, you'll sound unnatural if you don't apply these rules!

Third Tone Sandhi (The Most Important Rule)

When two 3rd tones appear in a row, the first one changes to a 2nd tone:

• 你好 nǐ + hǎo → ní hǎo (hello) — The first 3rd tone becomes 2nd
• 很好 hěn + hǎo → hén hǎo (very good)
• 可以 kě + yǐ → ké yǐ (can/may)
• 所以 suǒ + yǐ → suó yǐ (therefore)

一 (yī) Tone Changes

The word "one" (一) has three different pronunciations depending on context:

• yī (1st tone) — When counting, at the end of a word, or alone: 一二三 (yī èr sān)
• yí (2nd tone) — Before a 4th tone: 一个 yí gè (one [measure word])
• yì (4th tone) — Before 1st, 2nd, or 3rd tones: 一天 yì tiān (one day), 一年 yì nián (one year)

不 (bù) Tone Changes

The negative word 不 also changes tone:

• bù (4th tone) — Before 1st, 2nd, or 3rd tones: 不吃 bù chī (not eat), 不来 bù lái (not come)
• bú (2nd tone) — Before another 4th tone: 不是 bú shì (is not), 不要 bú yào (don't want)

Half Third Tone

In natural speech, the 3rd tone is rarely pronounced with the full dip-and-rise pattern. Before 1st, 2nd, or 4th tones, it becomes a "half third" — just the low dipping part without rising:

• 老师 lǎo shī — The lǎo is pronounced low without the rise
• 你们 nǐ men — The nǐ dips but doesn't rise