Also, his given name contains the character 源, which is read "gen" in Japanese, not "gan".
This may be way outside of your wheelhouse, but I have to ask -
The Mandarin reading of 源 is yuán. The phonetics are something like [ʲyɛn]. A similar raising of the written vowel occurs in the pinyin syllable yan (e.g. 言, 严, 眼), which is [jɛn]. In other pinyin syllables, an "a" represents /a/, which is something sort of intermediate between the English PALM and TRAP vowels.
It makes perfect theoretical sense that /a/ might be realized as [ɛ] when following a high vowel. But I've always wondered whether yuan and yan really do have a phonemic /a/ there or whether there might be an /ɛ/ phoneme. And it's interesting to me that the Japanese reading of 源, presumably taken from a much older Chinese, uses /e/ there instead of /a/. Can you provide any insight?
https://en.wiktionary.org/wiki/%E6%BA%90
Some highlights:
* Different Chinese variations (Cantonese, Min, etc.) have different readings. Initials, vowels, and finals all differ.
* When borrowed into Japanese, the Chinese initial was ŋ, which isn't used as an initial in Japanese, and was substituted.
I also wouldn't assume that sounds that are grouped together are supposed to sound the same. en/yin/wen/yun use the same final in bopomofo, but sound different.
There is a separate /jɛ/, 也，耶.
Within-syllable -jɛ- exists in yan and its "compounds" tian, mian, lian, etc; changing the final consonant to -ŋ gives you the yang / niang / liang / xiang series of syllables, which have -ja-. This would suggest that, if the vowels are to be unified into one phoneme, the realization of that phoneme is driven more by the following consonant than the preceding vowel/glide.
There's something weird going on where -ɛ- in a complex syllable can appear with more onsets than -a- can. We see e.g. tie, tian, die, dian, mie, mian, bian, pian (with -ɛ-) where we don't see tia, tiang, dia, diang, mia, miang, piang (which would use -a-). xia, jia, qia are all fine, and so is niang. My working hypothesis for that would be "it's a coincidence".
I believe without being able to cite anything that one reason for the spelling of yuan and similar codas with "a" is local variation in how the vowel is pronounced.
One distinction that some Chinese speakers fail to make, though, is between the r- onset and what I would prefer to think of as the j- onset. Thus, for these speakers, rang / yang or rou / you are the same sound.
Pinyin ran uses the standard /a/ vowel, but yan does not. I don't know whether, for speakers who don't distinguish r- from y-, a distinction remains in the vowel of ran/yan syllables.
