When you want to connect a 活用語 (inflectable word) to something else, generally you inflect it to the 連用形 (continuative form). However, with 形容詞 (i-adjectives), there are certain times where you affix things to the 語幹 (stem) as opposed to the 連用形.

〜そう (Affixes to 連用形 for 動詞, but 語幹 for 形容詞.)

動詞: 降りそう=「降る」の連用形+「そう」

〜すぎる (Affixes to 連用形 for 動詞, but 語幹 for 形容詞.)

動詞: 食べすぎる=「食べる」の連用形+「すぎる」

My guess is that these suffixes want something "noun-like", and since the 連用形 of 形容詞 is adverbial, it doesn't work and instead the stem ended up serving that function.

But, this is just a guess, so I'd like to know if anyone has a historical explanation of some of these things, or more examples to make that argument sound more convincing.

  • 2
    Note that this occurs not only with suffixes, e.g. 早起き (unless you want to convince yourself that 起き is a verb-derived suffix).
    – Earthliŋ
    Oct 18, 2013 at 9:35

1 Answer 1


The linguist Kunio Nishiyama analyzes the 連用形 of a verb as its stem, plus an epenthetic vowel -i in the case of consonant-stem verbs. This makes sense because:

  1. It appears with consonant-stem verbs, e.g. between the root hur- and the suffix -sou (振りそう).
  2. It does not appear with vowel-stem verbs, e.g. between the root mi- and the suffix -sou (見そう).
  3. It does not appear with -i adjectives, e.g. between the root taka- and the suffix -sou (高そう).

In other words, all three of these cases can be described as the suffix attaching to the root. The epenthetic -i is inserted in cases where Japanese requires that a consonant be followed by a vowel.

I'm not sure where Nishiyama presents this idea formally. I read about it in a footnote in his workshop paper Japanese Verbal Morphology in Coordination (2012) while I was trying to research a different topic. If you read through that handout, you can see some of the consequences of this analysis.

  • 1
    Just my two cents: I agree that Nishiyama’s analysis is spot on when analyzing the cases of the current question, but I am not sure if it is a good idea to analyze all uses of 連用形 of a verb that way. For example, if we compare 連用中止法 of verbs and i-adjectives, the latter really require 連用形 instead of just the stem (e.g., ジョンは強く優しい). Therefore it seems more logical to me to consider 学び in 学びそう/学びすぎる (stem with epenthesis) and 学び in よく学びよく遊ぶ (true 連用形) as two theoretically different things, which happen to take the same form in case of verbs. Oct 18, 2013 at 16:19
  • I feel like this answer doesn't really get to the core of what I was asking (though it certainly gets part of the way there). I very much like @TsuyoshiIto's point. I'd guess the "stem with epenthesis" is what has the noun-like properties, allowing it to be used with these suffixes and in noun compounds (like Earthling pointed out), while the 連用形 is what allows for the 中止法 and just normal verb+aux-verb compounding. Oct 18, 2013 at 19:34
  • @TsuyoshiIto: Well, I can analyze the word 優しい as having the stem yasasik-...so the epenthetic vowel is /u/.
    – ithisa
    Oct 19, 2013 at 23:37
  • @user54609: I am afraid that that explanation does not make sense. If the stem of 優しい is yasasik-, how do you explain 優し in 優しそう/優しすぎる? The reason I suggested to distinguish the stem possibly with epenthetic -i (e.g. 学び in 学びそう/学びすぎる and 優し in 優しそう/優しすぎる) and the true 連用形 form (e.g. 学び and 優しく used in 中止法) in the first place is that they are different in case of adjectives. Oct 20, 2013 at 0:24
  • Hmm. I have never considered 優しく to be a true 連用形 in itself, mostly because it is syntactically an adverb, and verb 連用形s don't act like adverbs. It does act similar to a 連用形 in the specific place you mentioned though...
    – ithisa
    Oct 20, 2013 at 0:37

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