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This page discusses the "adjective" べき and mentions that if it had evolved like other adjectives, it would have been べい.

That made me think: Why are there no 形容詞 ending in /ei/ or /ii/ (except for /sii/)? This assumes that we disregard "slang" like わりい, あちい, あけー, やべー etc.

And what is special about べき (the only exception that I can think of)?

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-bei is quite common in a number of dialects. – Dono Nov 27 '12 at 12:31
@Dono, yes, I wasn't 100% sure that was actually a form of べき, but that is also suggested on the linked page. – dainichi Nov 27 '12 at 12:41
What about 大きい ... – fefe Nov 27 '12 at 12:48
@fefe Indeed. There are a number of other examples, including: ii, kakkoii, kawaii, kuchii, sekuchii, batchii, babatchii, borotchii, marumatchii, mimitchii, yabachii, kenarii. There are surely more if you look. – Dono Nov 27 '12 at 14:19
@Dono, thanks, you are right, now I'm embarrassed for not thinking it through before asking. I still feel there's something special about /ii/, though. – dainichi Nov 28 '12 at 0:59
up vote 6 down vote accepted

A wonderful website linked to me by @snailplane1 categorizes adjectives by their 39 different endings.

It notes that:

  • 「エ段+い」で終わる形容詞は俗語を除いて存在しない。
  • 「しい」で終わる形容詞は最も数が多い。
  • 逆に「しい」を除けば、「イ段+い」で終わる形容詞は、ほとんど存在しない。

Though there are a number of interesting things suggested by this data, and the above observations, two in particular stand out:

  • No adjectives ending /ei/ exist outside of colloquial language... but they do exist in colloquial language.
  • As you notes, aside from those adjectives ending in /sii/, there are very few adjectives ending in /ii/... but some examples do exist.

Some archaic or colloquial examples offered are:


I don't claim to know what these words mean or how they are/were used, however.

Now, "why" is a very difficult question to answer, but the fact that these words do exist in archaic and colloquial speech suggests that there is more to this situation. I hypothesize that the reason these largely don't exist in standard Japanese is a uniform sound change that occurred in the past (though I don't know the details of said sound change).

In my experience, many dialects of Japanese retain more archaic forms (though this is probably not universally true), so that may explain why some dialects have words ending in /ei/.

The two remaining examples of adjectives ending in /ii/ are いい and 大きい... but both of these are a bit special. いい is an irregular form of よい, and 大きい has the odd form 大きな. While I can't say this with certainty, I suspect these irregularities have something to do with why they continue to exist in modern Japanese.

1 http://homepage3.nifty.com/jgrammar/ja/adjec001.htm

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Basically, 大きい is derived from 多い, and as far as I know there is no classical adjective ***大きし. – Zhen Lin Nov 27 '12 at 22:16
Whoa, how did I overlook 大きい, good one. @ZhenLin, great observation, I found something here: shin-araragi.jp/zakki_bn/bn_01/zakki0901.htm, but yes, as you said it does look like a special case. – dainichi Nov 28 '12 at 0:50
Is つきづきい correct? My sources have classical form つきづきし, but they also show that this was シク活用, not ク活用, so the attributive would have been つきづきしき (i.e. no /ii/ ending). Likewise for すきずきし. – Eiríkr Útlendi Jun 9 '14 at 23:10
@EiríkrÚtlendi They are both listed on the linked website; unfortunately the author doesn't list any sources that I see, so the possibility remains that they are incorrect. – rintaun Jun 10 '14 at 3:22
For the /ei/ adjectives, かそけい・そやけい・つゆけい・のどけい・はるけい all appear to be [root] + けし, where けし is an adjectivizing suffix that probably derives from 気. A number of these forms coexisted with, and were apparently replaced by, 形容動詞 forms composed of [root] + か: かそか (幽か・微か, more commonly seen with modern reading かすか), のどか (長閑・閑), はるか (遥か・悠か). I can't find そやけし in my sources; I'm guessing this is probably 粗野 + けし, in which case the modern term 粗野 is used on its own as a 形容動詞. つゆけし is apparently 露 + けし, replaced by 露っぽい. – Eiríkr Útlendi Jun 10 '14 at 16:08

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