Tone Changes (Sandhi): The Third-Tone Shift, and How 不 and 一 Change

Tones aren't always pronounced exactly the way they're written. When certain syllables bump into each other, the tones shift a little to make the words easier to say. This is called sandhi. The spelling and the dictionary tone don't change, just the sound coming out of your mouth.

There are really only three patterns you need at this stage: what happens when third tones meet, and the special behavior of two very common words, 不 (bù) and 一 (yī).

The third-tone shift

When two third tones come in a row, the first one changes to a second tone. Two dipping tones back to back are a pain to say, so the first one rises instead.

The classic example is 你好 (nǐ hǎo), which is actually said ní hǎo. Same with:

• 很好 (hěn hǎo) → said hén hǎo (very good)
• 我也 (wǒ yě) → said wó yě (me too)

The writing stays as third tone in both spots, but your voice rises on the first one.

If three third tones stack up, you usually shift the first two, though it can depend on how the words group together. Don't overthink this one. Just remember the core rule: third + third, the first becomes second.

There's also a softer version. When a third tone is followed by any other tone (first, second, or fourth), the third tone often loses its rise and just stays low. This is the "half third tone." You don't have to aim for it on purpose. It tends to happen naturally when you stop forcing the full dip-and-rise.

How 不 (bù) changes

不 means "no" or "not," and its normal tone is fourth (bù). But when it's followed by another fourth tone, it switches to second tone (bú).

• 不是 (bù + shì) → said bú shì (is not)
• 不要 (bù + yào) → said bú yào (don't want)
• 不去 (bù + qù) → said bú qù (not going)

Before first, second, or third tones, it stays as bù:

• 不好 (bù hǎo) (not good)
• 不来 (bù lái) (not coming)

So the only thing to watch for is 不 + fourth tone → bú.

How 一 (yī) changes

一 means "one," and it's the trickiest of the three because it shifts in two directions depending on what follows.

On its own, or when counting, or at the end of a phrase, it stays as first tone: yī (as in yī, èr, sān for "one, two, three").

But in front of another syllable, it changes:

Before a fourth tone, 一 becomes second tone (yí):

• 一定 (yī + dìng) → said yí dìng (definitely)
• 一样 (yī + yàng) → said yí yàng (the same)

Before first, second, or third tones, 一 becomes fourth tone (yì):

• 一天 (yī tiān) → said yì tiān (one day)
• 一年 (yī nián) → said yì nián (one year)
• 一起 (yī qǐ) → said yì qǐ (together)

So 一 flips to second tone before a falling tone, and to fourth tone before everything else.

A note on what you'll see written

Most textbooks and dictionaries write 不 and 一 with their base tones (bù and yī) no matter what, and they expect you to apply the changes when you speak. Some learner materials mark the shifted tones for you. Either way, the underlying word is the same. Once you've said these a few dozen times, the shifts stop feeling like rules and start feeling automatic, which is exactly the point of sandhi.