Rules of spelling and tone sandhi of “一(yī)"

Rules of spelling

i—yi u—wu ü—yu

If a finial begins with i, u or ü with no initial before it, the letter y or w will be used in the written form. Remember, when y comes before ü, we need to remove the two dots of ü.

The use of y and w

For i in ing, you should add y before i, the right written forms are yi yin ying

For ia ie iao ian iang iong, you should change the i to y, the right written forms are ya ye yao yan yang yong

And for iu, you should add the letter o first, and then change the i to y, it is written as you

For u, add w before u, wu

For ua uo uai uan uang ueng, change u to w, written as wa, wo, wai, wan, wang, weng

And for ui and un, you should first add the letter e in the middle, and then change u to w, written as wei and wen

for ü, üe, üan, ün, just change ü to y, written as yu, yue, yuan, yun

Tone sandhi of “一(yī)”

1. When “一（yī）” is followed by a syllable in the first, second or th ird tone, it changes into the fourth tone. Like：一张 yì zhāng one sheet/piece, 一条 yì tiáo one (long) piece，一种 yì zhǒng one type.
2. When “一（yī）”is followed by a syllable in the fourth tone, it changes into the second tone. Like：一定 yídìng sure, certainly，一块 yí kuài one piece.
3. When “一” is used alone or in a number, its tone doesn’t change. For example, 一二三 one, two, three, 第一 dì-yī first, 星期一 xīng qī yī Monday.