How to pronounce 不要去。 (bú yào qù.)

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.

一杯水。 (yì bēi shuǐ.)

The first syllable falls as yì before the high flat bēi.

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.