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As touched upon in another thread, there are several nouns that exhibit a kind of vowel shift in older forms, where the ending vowel is fronted when the noun is used on its own to become /i/ or /e/, compared to unfronted vowel forms /u/ or /o/ or /a/ when the noun is used in a compound. Examples include:

  • 神: かむ vs. かみ
    • 神上{かむあ}がる
    • 神所{かむどころ}
  • 天: あま vs. あめ (also for 雨)
    • 天照{あまてらす}
    • 雨合羽{あまがっぱ}
  • 口: くつ vs. くち
    • 轡{くつわ} from 口{くつ} + 輪{わ}
  • 目: ま vs. め
    • 瞬{まばた}き from 目{ま} + 叩{はた}く
    • 瞼{まぶた} from 目{ま} + 蓋{ふた}
  • 手: た vs. て
    • 袂{たもと} from 手{た} + 本{もと}
    • 手折{たお}る
  • 月: つく vs. つき
    • 月読{つくよみ}
  • 木: こ vs. き
    • 木漏{こも}れ日{び}
  • 上: うわ vs. うえ
    • 上着{うわぎ}
  • 声: こわ vs. こえ
    • 声色{こわいろ}

Now for the questions.

  1. Does anyone have a list of all nouns known to exhibit this kind of vowel shift?
    • Did all nouns in ancient Japanese or proto-Japanese exhibit this vowel shift?
    • If it were only some nouns, were these nouns categorizable as any clear class of nouns? As an example of a noun class, there are inseparable nouns in Polynesian languages, which generally cover things like body parts and spiritually important terms, much like many of the Japanese vowel-shift nouns that I'm aware of.
  2. Is there any clear membership in 甲類 or 乙類 for these nouns, as compared to similar nouns that don't exhibit any vowel shift? One example is 上 kami1 with the 甲類 み and that doesn't have any kamu form, vs. 神 kami2 with the 乙類 み and that does have a kamu form.
  3. What research is there into this phenomenon? Are there any specific titles or authors that cover this?
    • One theory I've read about (possibly in Shibatani's The Languages of Japan, which I've since misplaced) is that these nouns, when used in standalone contexts, were appended with the now-obsolete Old Japanese い, an emphatic nominalizing particle. Over time, this fused with the preceding vowel to produce vowel fronting. As evidence for this, the term カムイ appears in Ainu as a possible borrowing from pre-Old Japanese, before any such sound fusion, clearly manifesting a distinct む and a distinct い sound.
    • Another theory that I've only come up with on my own is that this might be somehow related to verb conjugations, where the 連用形{れんようけい} always ends in either /i/ or /e/. Verb stems, when used as nouns, always use the 連用形, at least in modern Japanese. Perhaps this is a reflection of some phonetic constraint or requirement in an ancient stage of the language, that is also reflected in these standalone noun forms?
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See also here. –  Zhen Lin May 21 '14 at 18:36
I've actually wondered about this too. Lots of kanji have a single 訓読み and an unfronted form followed by a tilde, such as "あめ, あま〜". I'd like to know about the unfronting like you asked, but I'd also like to know why they place a tilde after. Is it to show that it can only be used in a compound? –  KingPumpkin May 22 '14 at 2:46
A first step could be an OJ dictionary which shows the ko-otsu distinction. Anybody got a link? –  dainichi May 22 '14 at 10:52
@KingPumpkin, the ~ is most likely an indication that the unfronted form can only be used in compounds. –  Eiríkr Útlendi May 22 '14 at 20:29
Frellesvig talks about this on pp.44-47 of A History of the Japanese Language (2010). Searching online, I found a very similar discussion by Frellesvig that was freely available: conf.ling.cornell.edu/whitman/… Search for apophonic. –  snailboat Jun 11 '14 at 12:32

2 Answers 2

Straight from jawiki on カム/神:

"カムヤマトイワレヒコ、カムアタツヒメなどの複合語で「神」が「カム」となっていることから、「神」は古くは「カム」かそれに近い音だったことが推定される。大野晋や森重敏などは、ï の古い形として *ui と *oi を推定しており、これによれば kamï は古くは *kamui となる。"

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This matches Shibatani and others. However, this is specific to 神 kamu / kami, and does nothing to address the overall phenomenon as exhibited in many other words with different core vowels (also a and o, in addition to the u in words like 神 kamu and 口 kutu). –  Eiríkr Útlendi Jun 27 '14 at 0:54
Addition: The article mentioned by Marcus is the 神 (神道) article on the JA Wikipedia, in the section marked 語源. The list of purported derived terms at the end of this section strikes me as most dubious, FWIW. These were all added by user ABnormal, starting from this edit. –  Eiríkr Útlendi Jun 27 '14 at 1:03
The mentions of Turkish kam and German ham are also odd, and were added by anon users here and here. –  Eiríkr Útlendi Jun 27 '14 at 1:04


The following changes may happen when forming compound words:

'e' turns into 'a' (雨宿り・金沢・船旅)
'i' turns into 'u' (くつわ・かむなぎ)
'i' turns into 'o' (木陰、木霊、最寄り)
'o' turns into 'a' (白髪・たなごころ)

If the first syllable of the second word begins with an unvoiced consonant, it often becomes voiced. 連濁です。

'ts' turns into 'tz'(横綱・手綱)
'f' turns into 'b' (まぶた)
't' turns into 'd' (酒樽)etc.

This is like the English...

"tooth" -> "teeth"
"foot" -> "feet"
"goose" -> "geese" 
"cow" -> "kye" would be an older English example)

...except that it is used in compound word formation rather than pluralization.

These words that undergo this vowel-shift are very often compound nouns of Japanese origin (複合和語名詞). Although this also happens in the 動詞 example of 「くる」⇒「こない」.

The class that these words belong to could be called 複合和語, though I don't believe that term is in general use.

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