How to pronounce 一杯水。 (yì bēi shuǐ.)

How tone change works for 一 and 不

A practical guide to how 一 and 不 change tone depending on the following syllable in Mandarin speech.

我不是。 (wǒ bú shì.)

Because shì is fourth tone, 不 changes to bú in the middle of the sentence.

不要去。 (bú yào qù.)

Say 不要去。 (bú yào qù.) as a full chunk and let 一 or 不 change tone according to the following syllable.

一个人。 (yí gè rén.)

Say 一个人。 (yí gè rén.) as a full chunk and let 一 or 不 change tone according to the following syllable.

一个 (yí gè)

Because gè is fourth tone, 一 changes to a rising yí in connected speech.

一杯 (yì bēi)

Before a first tone like bēi, 一 falls as yì rather than staying flat.

一定 (yí dìng)

The first syllable rises because dìng is fourth tone.