126.96.36.199:54: THE VOWELS OF THE CENTRAL CAPITAL
In "Back on Track", I reconstructed Jurchen
'road' (Jin 1984: 30-31, 95, 167)
as <jū.gū> [tʂʊɢʊ] with [ʊ] instead of [u] as in Jin Qizong's reconstruction dʒu(g)u.
(I have projected Manchu consonants according to Norman  back into Jin Jurchen, but that may be anachronistic.)
(5.5.0:33: Even projecting Manchu-style vowel harmony back into Jurchen may also be anachronistic, but I want to see how far I can go with that hypothesis.)
The first character of 'road' also appears in
<jū.ūng dū> [tʂʊŋ dʊ]+
for Chinese 中都 'Central Capital', now pronounced Zhōngdū in modern standard Mandarin.
This Jurchen spelling may imply that the vowel of the northern Chinese readings of 中 and 都 was [ʊ] rather than [u] during the Jin Dynasty. If that vowel were [u], 中都 might have been transcribed as
which may have represented <ju.ung du> [tʂuŋ du] as opposed to <jū.ūng dū> [tʂʊŋ dʊ].I reconstructed the reading of the final character of <jū.ūng dū> with <ū> because <ū> would be in harmony with the <a> of
<dū.ha> [tʊχɑ] 'intestine' : Manchu duha [tuχɑ]
<wa.dū.ra> [wɑdʊrɑ] 'kill-?-?*' : Manchu wa- [wa] 'kill'
but that character also appears in
?<hen.du.ru> [xənduru] 'say-HORTATIVE**' : Manchu hendu- [xəndu]
whose <e> should harmonize with <u>, not <ū>.
(5.5.0:15: All of the above Ming Jurchen spellings from the Sino-Jurchen vocabulary of the Bureau of Translators may postdate a merger of Jin Jurchen <du> and <dū>, so perhaps one or more of them would be wrong for Jin Jurchen.)
In any case, the vowel of 都 underwent the following shift in Chinese
*a > *ɑ > *ɔ > *o > *ʊ > *u
but it is not clear whether the Jurchen borrowed 都 before or after the final raising to [u].
Also, if I am wrong about assigning [ʊ] and [u] to readings of otherwise seemingly homophonous Jurchen characters, the existence of multiple characters for the same reading - e.g.,
<ju> (as opposed to <jū> and <ju>)
<ung> (as opposed to <ūng> and <ung>)
<du> (as opposed to <dū>, <dū>, <du>, and <du>)
- needs to be explained.
Different shapes for the same syllable need not entail heterophony. Prior to the standardization of kana in 1900, Japanese had always been written with multiple symbols per mora, and this complex allography disguised a simpler phonology.
*5.5.2:15: I don't know what the suffixes after wa- 'kill' are. I considered the possibility that wa-du-ra- was a verb stem consisting of wa- plus the noun-forming suffix -du and the verb-forming suffix -ra-, but what would wa-du- be? Some kind of weapon for killing? Would wa-du-ra- then mean 'use a wa-du-'?
Kiyose (1977: 117) read the final character as <la> and thought it "probably forms perfective participles" whereas Jin (1984)'s reading <ra> is like the Manchu imperfect participle suffix -ra.
**5.5.0:11: Gloss from Kiyose (1977: 63, 117).