五段動詞特異的なイ音便について

Question

Are there any explanations for the 五段動詞-specific イ音便 of 連用形+た/て that aren't based/dependent on the 子音語幹/母音語幹 explanation for the differences in 五段動詞/上一段動詞 conjugations?

For example, take 開く and 飽きる, setting aside the fact that they have completely different meanings and focusing only on their pronunciations. In 口語, the 過去形 of あく is あいた, due to the イ音便 of "あき+た". However, for the 上一段動詞 "あきる", this イ音便 doesn't occur, and so the past tense is "あきた".

I've heard explanations regarding 子音語幹 and 母音語幹. However, they don't seem able to explain why the イ音便, which occurs based on how difficult a word is to pronounce, would not occur indescriminately. Is anyone aware of any other explanations?

In other words, if the past tense of 開くwas reanalyzed as 開いた, why was the past tense of 飽きる never reanalyzed as 飽いた？

Answer 1

I'm very curious how you came across the idea that "イ音便 occurs based on how difficult a word is to pronounce".

Regardless, as far as I know イ音便 occurs solely with 五段動詞. As others have mentioned, "飽いた" is conjugated from 飽く（あく）, which is the regional/somewhat old variant of 飽きる（あきる）. The fact that 飽きる, the 一段 version, evolved into mainstream use is simply a matter of history.

My guess is that before the popularization of kanji, the pronunciation of the 五段 verb 飽く overlapped with other words that had different meanings (空く: to become empty/vacant, 開く: to open/to create a gap, 明く: to come to an end/come to light) which caused confusion in speech, leading to 飽きる becoming preferred.

But then, you also have words like あげる which, against all odds, has accumulated nearly 30 different meanings. The three kanji used to differentiate between those meanings is hardly adequate.

Again, a matter of history.

Answer 2

Your question is understood in two part. One depends on the origin of the word. Other depends on how people say it easily.
Believe or not, Japanese dialects allows vary of 音便.

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飽く probably came from old Japanese (OJ) words 呆きる(あきる) and 明く(あく) or they are related. While people didn't familiar with Kanji's or writing, they remembered words by phonic.

• 飽く verb 1. satisfy 2. become bored/unwanted
• 呆る (OJ) verb 1. getting unclear what to do with it 2. being blanked.
• 明く verb 1. to separate something with a big space or long time 2. to become unoccupied.

They all mean 'no longer wanted' or 'had enough of that'. So that was alright to be mixed together in the old days when people don't write the words and got things done by oral.

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Therefore, dialects are several versions and very much different in some place especially with the cold climate.
飽きた often is pronounced as あいた. I believe many of Kyoto and Kansai dialects family (OJ users) prefer あいた, compare to 江戸弁 Edo-ben which has been spoken around Tokyo prefered あきた, however none of them work in the Tohoku and Japan seaside, it was going to be like French way, 'ai' makes 'e'. They often say もう、えーた(もう飽きた)

No one knows what exactly was going on the word, I hope this will help you to understand or bring you a bad guess to inspire the truth.