Chinese Pinyin: Sandhi of the "一" (yī) | Free Online Learning Chinese

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In the Mandarin Chinese Pinyin system, the character '一' (yī) retains its original first tone (high level tone) only when it is used as an ordinal number, at the end of a sentence, or read in isolation. When '一' appears before other tones, it undergoes tone sandhi (tone change).

1. '一' Before Fourth Tone

When '一' appears before a fourth tone, it changes to a second tone, and the pitch contour shifts from 55 to 35.

Examples:

一半 [one half]：yíbàn
一旦 [once, in case]：yídàn
一定 [certainly]：yídìng
一度 [once, for a time]：yídù
一概 [all inclusive]：yígài
一共 [altogether]：yígòng

2. '一' Before Non-Fourth Tone

When '一' precedes any tone other than the fourth tone (i.e., a first, second, or third tone), its tone changes to a fourth tone, and the pitch contour shifts from 55 to 51.

Before a first tone:

一般 [general]：yìbān
一些 [some]：yìxiē

Before a second tone:

一同 [together]：yìtóng
一群 [a group of]：yìqún

Before a third tone:

一早 [early in the morning]：yìzǎo
一起 [together]：yìqǐ

3. '一' Between Identical Verbs

When '一' appears between identical verbs, it takes on a neutral tone.

听一听 [listen to]：tīng yitīng
学一学 [study, learn]：xué yixué
写一写 [write]：xiě yixiě
看一看 [look at]：kàn yikàn

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