Were there any specifics rules that were used to convert Chinese vocabulary into Japanese? Are they still perceptible in Modern Chinese?


I know that when Chinese characters were incorporated into Japanese
writing/vocabulary their pronunciation changed to be easier for Japanese
people to pronounce, but were there any specific rules? What I mean by rules
is if there was a systematic approach where certain Chinese phonemes were
always converted to certain Japanese phonemes. If so, is this still
perceptible in Modern Chinese?




_Phonemes_ are not really applicable to the Chinese character system, but
there was (and still is) indeed a systematic approach to convert most Chinese
characters' pronunciation into Japanese
[_on'yomi_](https://en.wikipedia.org/wiki/Kanji#On%27yomi_\(Sino-
Japanese_reading\)), based on the system known as
[_fanqie_](https://en.wikipedia.org/wiki/Fanqie) ([反切]{はんせつ}). In this system,
any character's pronunciation is reconstructed through a description from two
other characters 「Ｘ」 and 「Ｙ」, with the description expressed as 「ＸＹ切」. The
reconstruction takes the [onset](https://en.wikipedia.org/wiki/Syllable#Onset)
of 「Ｘ」 and the [rime](https://en.wikipedia.org/wiki/Syllable#Rime) of 「Ｙ」 to
form the pronunciation of the character as a single syllable.

This system is _frozen_ (not _dead_ ), as it is still sometimes applicable to
uncommon Chinese characters finding their way into a Japanese text, but it is
entirely based on the vocabulary of [Middle
Chinese](https://en.wikipedia.org/wiki/Middle_Chinese) (not [Old
Chinese](https://en.wikipedia.org/wiki/Old_Chinese) or any variety of Modern
Chinese), which no longer characterises a living language. This is an
important point, as **_on'yomi_ specifically relates to Middle Chinese words
derived from the _fanqie_ system**, not Chinese-derived words in general. For
example, the following words are derived from Chinese and are written with the
same characters in Chinese, but are not _on'yomi_ :

  * [梅]{うめ} ([Baxter-Sagart OC](https://en.wikipedia.org/wiki/Reconstructions_of_Old_Chinese#Baxter%E2%80%93Sagart_\(2014\)): **/*C.mˤə/** )
  * [上海]{シャンハイ} (Mandarin [Pinyin](https://en.wikipedia.org/wiki/Pinyin): **Shànghǎi** )

### Worked example: _Fanqie_ reconstruction of the _on'yomi_ of 「掛」

  * The [_fanqie_ description of 「掛」 is 「古賣切」](https://en.wiktionary.org/wiki/%E6%8E%9B#Pronunciation)
  * _On'yomi_ of 「古」: 
    * [_Go-on_](https://en.wikipedia.org/wiki/Go-on): [く]{ku}
    * [_Kan-on_](https://en.wikipedia.org/wiki/Kan-on): [こ]{ko}
  * _On'yomi_ of 「賣」: 
    * _Go-on_ : [め]{me}
    * _Kan-on_ : [ばい]{bai}
  * Taking the _on'yomi_ analogy to the onset and rime components of these characters, we can get the _on'yomi_ of 「掛」 as 
    * _Go-on_ : **k** u + m **e** = **[ke]{け}**
    * _Kan-on_ : **k** o + b **ai** = **[kai]{かい}**

* * *

Ironically, due to the comparatively simplified nature of Japanese phonology
in _on'yomi_ words, _fanqie_ works the best in Japanese out of all the
languages it is applicable to (Chinese, Japanese, Korean, and Vietnamese). You
can use _fanqie_ for Mandarin Chinese, but very likely you'll get an inexact
match for the onset or a not-so-correct tone.




_Phonemes_ are not really applicable to the Chinese character system, but
there was (and still is) indeed a systematic approach to convert most Chinese
characters' pronunciation into Japanese
[_on'yomi_](https://en.wikipedia.org/wiki/Kanji#On%27yomi_\(Sino-
Japanese_reading\)), based on the system known as
[_fanqie_](https://en.wikipedia.org/wiki/Fanqie) ([反切]{はんせつ}). In this system,
any character's pronunciation is reconstructed through a description from two
other characters 「Ｘ」 and 「Ｙ」, with the description expressed as 「ＸＹ切」. The
reconstruction takes the [onset](https://en.wikipedia.org/wiki/Syllable#Onset)
of 「Ｘ」 and the [rime](https://en.wikipedia.org/wiki/Syllable#Rime) of 「Ｙ」 to
form the pronunciation of the character as a single syllable.

This system is _frozen_ (not _dead_ ), as it is still sometimes applicable to
uncommon Chinese characters finding their way into a Japanese text, but it is
entirely based on the vocabulary of [Middle
Chinese](https://en.wikipedia.org/wiki/Middle_Chinese) (not [Old
Chinese](https://en.wikipedia.org/wiki/Old_Chinese) or any variety of Modern
Chinese), which no longer characterises a living language. This is an
important point, as **_on'yomi_ specifically relates to Middle Chinese words
derived from the _fanqie_ system**, not Chinese-derived words in general. For
example, the following words are derived from Chinese and are written with the
same characters in Chinese, but are not _on'yomi_ :

  * [梅]{うめ} ([Baxter-Sagart OC](https://en.wikipedia.org/wiki/Reconstructions_of_Old_Chinese#Baxter%E2%80%93Sagart_\(2014\)): **/*C.mˤə/** )
  * [上海]{シャンハイ} (Mandarin [Pinyin](https://en.wikipedia.org/wiki/Pinyin): **Shànghǎi** )

### Worked example: _Fanqie_ reconstruction of the _on'yomi_ of 「掛」

  * The [_fanqie_ description of 「掛」 is 「古賣切」](https://en.wiktionary.org/wiki/%E6%8E%9B#Pronunciation)
  * _On'yomi_ of 「古」: 
    * [_Go-on_](https://en.wikipedia.org/wiki/Go-on): [く]{ku}
    * [_Kan-on_](https://en.wikipedia.org/wiki/Kan-on): [こ]{ko}
  * _On'yomi_ of 「賣」: 
    * _Go-on_ : [め]{me}
    * _Kan-on_ : [ばい]{bai}
  * Taking the _on'yomi_ analogy to the onset and rime components of these characters, we can get the _on'yomi_ of 「掛」 as 
    * _Go-on_ : **k** u + m **e** = **[ke]{け}**
    * _Kan-on_ : **k** o + b **ai** = **[kai]{かい}**

* * *

Ironically, due to the comparatively simplified nature of Japanese phonology
in _on'yomi_ words, _fanqie_ works the best in Japanese out of all the
languages it is applicable to (Chinese, Japanese, Korean, and Vietnamese). You
can use _fanqie_ for Mandarin Chinese, but very likely you'll get an inexact
match for the onset or a not-so-correct tone.

