Are Chinese readings uniquely mapped to onyomi readings?

For example, 水 in Chinese, pronounced shuǐ, is mapped to すい in Japanese. Are these conversions always predictable like this? In other words, would something like shuǐ ever be converted to something other than すい?

They can be mapped in all sorts of ways. Since onyomi readings came to Japan over several centuries, the actual readings come from totally different pronunciations sometimes, even if the words were technically always pronounced the same in China. They also come from different Chinese languages, so that also doesn’t help. There are also misheard readings and readings that just got mixed up over the years and are now “wrong”. I think there’s even a name for misheard readings, but can’t remember, I’ll take a look around.

Found it, 慣用音かんようおん

Also found where I heard about it:

Fun video series, though definitely recommend watching it in order instead


I’m using a Chinese app to learn stroke order in Japanese. I like it because it’s interactive and a game-like experience.

I make my own decks for JLPT exams, and in order to do so I need to look up the Hanzi

In short, the answer to your question is a big no. But there are a significant amount of similitudes.

Other than that, I always thought that Traditional Chinese and Japanese used the same written characters, but I’ve also found that there are (few) exceptions as well

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I haven’t tried to find out the exact percentage, but I’d say more than “few”. I was surprised. Many characters have had small simplifications, and some have had massive simplifications.


Yeah, me too.

Well, I haven’t gotten to the end of it, but as far as I’ve gone in my decks (N4 kanji as of today) there are only a handful.
Surely there will be more in later levels so your appreciation is most likely correct.



Darn! I was hoping for perfect consistency, but that was my suspicion. I appreciate the response!

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This page regarding the Unicode “Han unification” process lists some examples of Chinese character variations across locales: Han unification - Wikipedia

Some of them are really subtle, and others very much not so (like 直, infamously), and that’s not even accounting for simplification. Also sometimes the traditional stroke order is different for identical characters depending on the country.

And of course even in Japanese there’s shinjitai/新字体 (e.g. 学) and kyujitai/旧字体 (e.g. 學) for many characters.


Regarding the onyomi I think the situation is fairly similar to the assimilation of French vocabulary into English, the process was long, messy, non-systematic and inconsistent. Some pronunciations are more or less conservative depending on all sorts of factors. Beyond that some pronunciations have shifted in French as well, widening the gap. For instance arguably the English “castle” is closest to the Old French “castel” (both in spelling and pronunciation) than modern French “château” to the point that modern speakers of either language may not immediately notice that they’re in fact the same word.

And on top of that the French that was spoken in England when most of these borrowings happened was Normand French which was a different dialect than Parisian French which became (for the most part) modern French.

Similarly the Japanese actually have subcategories for onyomi:

Generally, on’yomi are classified into four types according to their region and time of origin:*

  • Go-on (呉音, “Wu sound”) readings derive from the pronunciation used in the Northern and Southern dynasties of China during the 5th and 6th centuries, primarily from the speech of the capital Jiankang (today’s Nanjing). They are related to Wu Chinese and the Shanghainese language.

  • Kan-on (漢音, “Han sound”) readings come from the pronunciation utilized during the Tang dynasty of China in the 7th to 9th centuries, primarily from the standard speech of the capital, Chang’an (modern Xi’an). Here, Kan refers to Han Chinese people or China proper.

  • Tō-on (唐音, “Tang sound”) readings are based on the pronunciations of later dynasties of China, such as the Song and Ming. They cover all readings adopted from the Heian era to the Edo period. This is also known as Tōsō-on (唐宋音, Tang and Song sound).

  • Kan’yō-on (慣用音, “customary sound”) readings, which are mistaken or changed readings of the kanji that have become accepted into the Japanese language. In some cases, they are the actual readings that accompanied the character’s introduction to Japan but do not match how the character “should” (is prescribed to) be read according to the rules of character construction and pronunciation.

That’s how a kanji like 生 ends up with the two onyomi that we know:

  • Go-on: しょう (shō, Jōyō)←しやう (syau, historical)
  • Kan-on: せい (sei, Jōyō)

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