I’m curious whether there’s any official/reputable pronunciation guide (like NHK guidelines, etc.) that specifies whether the past forms of k-stem and g-stem verbs “should” be pronounced with long /eː/ or a diphthong /ei/. For example:
* 招いた /maneːta/ or /maneita/?
* 稼いだ /kaseːda/ or /kaseida/?
* 防いだ /huseːda/ or /huseida/?
I’m very well aware that in reality, people use both—but I’m wondering if there’s any **prescriptive rule** regarding which one is considered more “proper.”
(I checked the pronunciation dictionary 新明解 日本語アクセント辞典, but I couldn’t find any discussion of this particular matter.)
2 comments
I have the digital version of the NHK日本語発音アクセント新辞典. It normally uses エー to mark the えい combination, reserving エイ for cases that should specifically be エ + イ and _not_ エー. It does not list ～た as one of its fundamental verb conjugations, but prescribes マネイテ for the ～て form of 招く and カセイデ for for 稼ぐ. One would expect ～た to follow similar logic because the sound changes to the 連用形 of the original verb are the same.
The 新明解日本語アクセント辞典 lists the ～て form of かせぐ as カセイ⁎デ, which is their notation for either カセーデ or カセイデ.
tl;dr: If dictionaries don’t specify ～た, I would look at what they say for the ～て form, because that form has the same euphonic rules. NHK says it should use エイ; 新明解 says that it could be either.
edit: typos, expand summary
As /u/tkdtkd117 explained it would be /maneita/ etc. The logic here is that there’s a morpheme boundary in between: mane-i-ta. エ + イ becomes a long vowel only if it’s within the same morpheme, most commonly found in Sino-Japanese readings.