The 一 and 不 Tone Changes: Rules That Finally Make Sense
Most Mandarin tone rules are simple enough to memorize but easy to forget in real speech. The trickiest pair of all might be 一 and 不 — two tiny syllables that change their tone depending on what comes next. If you have ever been corrected for saying 一个 as yī gè, this guide is for you.
The 一 (yī) tone change rule
In a dictionary, 一 is first tone: yī, meaning “one.” But in actual speech it almost never stays that way. The tone change rules for 一 are simple:
- Before a fourth tone, say it as second tone: 一个 yí gè
- Before tones 1, 2, or 3, say it as fourth tone: 一天 yì tiān, 一年 yì nián, 一起 yì qǐ
- When it means “first” in a sequence or an ordinal, keep first tone: 第一 dì yī, 星期一 xīng qī yī
My own aha moment: a student once asked why the teacher’s 一个 sounded nothing like the textbook’s yī gè. It wasn’t the teacher being sloppy — it was the rule working. 一个 is always yí gè in natural speech.
The 不 (bù) tone change rule
不 means “no” or “not” and is fourth tone on its own: bù. It changes in exactly one situation — before another fourth-tone syllable, it becomes second tone:
- 不是 bú shì — not be / it isn’t
- 不要 bú yào — don’t want
- 不错 bú cuò — not bad, pretty good
- 不客气 bú kè qi — you’re welcome
Before tones 1, 2, or 3, 不 keeps its fourth tone: 不吃 bù chī, 不难 bù nán, 不好 bù hǎo. And when 不 sits between two repeated words in an A-not-A question like 好不好, it goes neutral: hǎo bu hǎo.
Bonus: the disappearing 一
When 一 lands between two repeated verbs, it loses its tone entirely: 看一看 kàn yi kàn, 想一想 xiǎng yi xiǎng. Say it light and quick — like a breath, not a syllable.
| Word | Before tone 1/2/3 | Before tone 4 | Mid-word |
|---|---|---|---|
| 一 | yì (一天) | yí (一个) | neutral (看一看) |
| 不 | bù (不吃) | bú (不是) | neutral (好不好) |
Why this matters for how you sound
If you say yī gè, you will still be understood — but you will sound like a robot reading a dictionary. These two syllables are among the highest-leverage tone changes in Mandarin because they appear in nearly every sentence a learner says.
My advice: don’t memorize word by word. Learn the two rules once, then drill them inside real phrases. When you listen to native audio in 2026, train your ear to expect the changed forms — yí/yì and bú/bù — not the dictionary forms.
One last thing: when you type on a phone or computer, you type yi and bu and the input method inserts the right character. The tone change happens in your mouth, not in the text — so the only way to practice it is out loud.