What is the etymology of the "emphatic" ない?


Upon looking up the term
[大事ない](http://dictionary.goo.ne.jp/srch/jn/%E5%A4%A7%E4%BA%8B%E3%81%AA%E3%81%84/m0u/),
I was, shall we say, nonplussed to learn that it could mean both ["very
important"](http://dictionary.goo.ne.jp/leaf/jn2/133324/m0u/%E5%A4%A7%E4%BA%8B%E3%81%AA%E3%81%84/)
and ["not very
important"](http://dictionary.goo.ne.jp/leaf/jn2/133325/m0u/%E5%A4%A7%E4%BA%8B%E3%81%AA%E3%81%84/).
The explanation of the "very important" meaning clears things up, though - the
ない here is not 「無い」, but rather [the "emphatic" 接尾語
「ない」](http://dictionary.goo.ne.jp/leaf/jn2/162272/m0u/%E3%81%AA%E3%81%84/).
This is super-interesting, and explains why words like 切ない do not "mean"
"切無い", which is something that had always bugged me.

What is the etymology of this "emphatic" ない? Is it related to the classical
copula なり?




Just to respond to the question part, the origin of the "emphatic" ない is the
Classical suffix 「なし」, and not 「なり」.

<http://kobun.weblio.jp/content/%E3%81%AA%E3%81%97>

「なし」 is an adjective-forming suffix with the meanings of "truly ~~",
"extremely ~~", etc.

It needs to be noted again that this has **_nothing_** to do with 「[無]{な}し」.




Just to respond to the question part, the origin of the "emphatic" ない is the
Classical suffix 「なし」, and not 「なり」.

<http://kobun.weblio.jp/content/%E3%81%AA%E3%81%97>

「なし」 is an adjective-forming suffix with the meanings of "truly ~~",
"extremely ~~", etc.

It needs to be noted again that this has **_nothing_** to do with 「[無]{な}し」.

