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

Question

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?

Answer 1

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, based on the system known as 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 of 「Ｘ」 and the 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 (not 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: /*C.mˤə/)
• [上海]{シャンハイ} (Mandarin Pinyin: Shànghǎi)

Worked example: Fanqie reconstruction of the on'yomi of 「掛」

• The fanqie description of 「掛」 is 「古賣切」
• On'yomi of 「古」:
  • Go-on: [く]{ku}
  • 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: ku + me = [ke]{け}
  • Kan-on: ko + bai = [kai]{かい}

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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.