In Classical Chinese, the proper word for counting days is 日. In Southern Chinese languages, 日 is more prevalent in counting days. Why 天 is chosen for counting days in Mandarin instead of 日?


More, in Mandarin it is quite usual to replace 日 with 天 for some words related to day. For example:

  • 星期日 禮拜日 (Sunday) to 星期天 禮拜天
  • 明日 (Tomorrow) to 明天
  • 改日 (another day) to 改天
  • 日日 (Everyday) to 天天
  • 當日 (At that day) to 當天
  • 3
    It's an interesting topic, but I think you're unlikely to get a satisfying answer. You could ask the same thing about almost any vocab difference. Why 红 and not 赤? 听 instead of 闻? For that matter, I don't think you'd get a satisfying answer as to why particular dialects went one direction or the other on certain vocabulary items (e.g., 知道 vs 晓得, 东西 vs 物事, 今天 vs 今朝). May 3, 2017 at 0:48
  • 日 is considered 忌讳 (taboo) in some (southern Chinese) dialects because it's 谐音 with 入 (an equivalent of 肏). Words like 向日葵 become 向儿葵. Perhaps this could be a reason.
    – Mou某
    May 3, 2017 at 8:31
  • I would say that it is just culture.
    – paper1111
    May 13, 2017 at 11:56

5 Answers 5


Interesting question. Is there a preference when it comes to using 天 for 日?

In my opinion, there are no such a strict rules when it comes 天vs日.(I was born and raised in southern China, lived in the North for several years. I speak Cantonese, Mandarin, Hakka)

Basically, 周天and周日, 星期日and星期天,明日and明天, 改日and改天 are all equivalent. But why people prefer one to another?

There're some reasons:

  1. In some south-western dialects, 日and一 have similar pronunciation. So people prefer use 周天than周日。

  2. Speaking in rhyme. 天tian1, 日ri4. So in some cases, it sounds weird to use天, but in another case, it sounds weird to use 日。That's depends.


we use 天 in oral Chinese, but 日 in writing Chinese, this is related to tone of characters, pronouncing fourth tone (4 声,入声) takes more efforts, so that we pronounce other characters with same meanings. i.e. 两个 other than 二个. Pronouncing characters with 3rd tone lengthen time of pronunciation to decrease rhythm, so that we save some efforts when we need speak loudly or in a long speech & lecture, sometimes we also avoid pronouncing multiple adjacent 3rd-tone characters, i.e. pronouncing 处理 (chu2 li3) other than original tone chu3 li3 (which is hard to pronounce loudly/quickly), avoid opening your mouth wide frequently or persistently, we rather pronounce with with alternant open/close mouth combinations.


In Hong Kong or GuangDong, Cantonese still use 日 for 'day.' For example: ' 几日返来啊?' For Mandarin speakers, 天 tian is easier and more natural to pronounce than 日 ri.

Also, sounds like (enter). Which is the F word in Chinese.

Last but not least, it's also because of the Japanese invasion of China. Japan in Chinese is 日. Since general Chinese didn't like Japan, they unconsciously avoided using 日.

  • 1
    It is all speculation in Atmega's part. There's no evidence for any of the three reasons he listed.
    – Tang Ho
    May 2, 2017 at 23:31

In my opinion,天 is more often use on 白话文 and normal conversation.

Because 天 is more natural and easy to pronounce than 日 when talking.

日 is more often use on 文言文。

For example in 佛说阿弥陀经,



happy to help you learn chinese,im chinese if i express wrong in english grammar hope you can forgive me.ok,lets begin,in china,we use 日 in this condition:今天是5月14日 or 5月14号,as you see,usually use 日 to express date,use 天 to count,like ‘一年有365天’,‘第几个一百天’ and i want to make a friend to communicate,just help each other learn languages,if you major in computer science or software,it couldn't be better!

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