What's the relationship between 'e' and 'wa' in some words?


Can someone explain how 'e' and 'wa' are related in some words / 音便?
Presumably the 'e' was originally the obsolete `ゑ` since it's in the ワ行.

Some examples:

>   * 上（う ** _え_** ） ←→ 上着（う ** _わ_** ・ぎ）
>   * 声（こ ** _え_** ） ←→ 声色（こ ** _わ_** ・いろ）
>   * 終 ** _え_** る ←→ 終 ** _わ_** る
>

* * *

(Bonus question: How do you type `ゑ` in the IME? I had to copy it from
somewhere else.)




There is a whole class of such nouns that exhibit vowel fronting when used as
standalone nouns, and not all of them end in _-e_ or _-wa_. Among other
examples, with in-compound forms followed by standalone:

  * 神: かむ vs. かみ
  * 天: あま vs. あめ (also for 雨)
  * 口: くつ vs. くち
  * 目: ま vs. め
  * 手: た vs. て
  * 月: つく vs. つき
  * 木: こ vs. き

One of the reasons for the theory that a certain class of nouns was followed
by the now-obsolete [Old Japanese
い](http://kobun.weblio.jp/content/%E3%81%84), an emphatic nominalizing
particle, is that the term カムイ appears in Ainu as a likely borrowing from Old
Japanese or slightly earlier, clearly manifesting a distinct む and a distinct
い sound. These two over time could conceivably mush together into み, much as
similar sound shifts have been observed in even modern Japanese (such as たかい
becoming たけえ, すごい becoming すげえ, etc.) and in other languages around the world.

As to why only certain nouns evince this particular phenomenon, it is not
unknown in other languages for there to be specific noun classes. It's
possible that these nouns in Japanese might be a vestige of an earlier stage
of the language that had such a specific noun class. Notably, a lot of these
nouns (at least, the ones I'm aware of) seem to describe parts of the body,
spirits, and other concepts that would be personally important. Polynesian
languages have a roughly analogous noun class covering so-called inseparables,
and these nouns take a specific version of the possessive particle, "no",
contrasting with the "na" particle used for possessed nouns outside of this
class.

Regarding transitivity / intransitivity and verb conjugation patterns, see
[blutorange's extensive post about this
subject](https://japanese.stackexchange.com/questions/12527/etymology-of-
transitive-intransitive-verb-pairs/12533#12533). There are several patterns,
of which -わる / -える is just one.




At some point far in the past (before Old Japanese, at least) these words
probably had a single form with a diphthong:

上: *upai

声: *kəpai

The diphthong turned into a single vowel differently in different contexts:
word-finally it became /e/, and word-medially the /i/ was deleted. (The *p
subsequently turned to /ɸ/, which then became /w/ between vowels and later /h/
elsewhere except before /u/ - this is why you have 原 /hara/ and 藤原
/ɸuʥiwara/.)

The 終わる・終える question is a bit different, and has to do with some transitivity-
flipping morphology that no one really understands well.

