~nai ending on some adjectives

I’m still learning a lot of the grammar rules for Japanese, despite trying to learn it for the last 10 years (not even living in the country has got me learning it well enough, I may be beyond hope). One of the questions that confuses me probably has a very simple answer - i.e. I’m wrong and it’s just a quirk - but I thought I would ask my lovely Japanese-learning comrades.

The kanji for “dangerous” is 危. When used in the vocabulary “dangerous”, it is written 危ない.

My experience is that for many other adjectives this 〜ない ending is a negative suffix. For example it makes “hot” (暑い) into (暑くない) “not hot”. This means I had always assumed (having known the vocabulary before the kanji) that the kanji for "dangerous: was in fact the kanji for “safe” that was negated, therefore making it “not safe” i.e. “dangerous”.

(I also assumed the same about a few other kanji like “dirty” - 汚い (きたない) - again knowing the vocab before the reading, though I now see the ‘na’ part is in fact just part of the kanji for this example.)

Can anyone explain why abunai has a hiragana-written ‘~ nai’ suffix but isn’t negative? Is it just as simple as “thats how it goes”?

Thanks grammar gurus!

ない is only a negation of an い adjective when it is proceeded by く, which is put in the place of the い of the affirmative form of whatever adjective is modified.

Other ones that end with ない don’t have any negation implication.

It’s like how “cannot” and “slipknot” both end with “not” but only one of those is the negative not.


Just did a little bit of research and what came up is that 危ない is a derivation from an older word 危うし あやうし which was contracted and added an emphasis particle、ない, which was used in this fashion a long time ago, seemingly unrelated to the actual usage of ない.

汚い might be similar or might be the negative of an old expression 、きだ.

In either cases only 危ない and 汚いpersist in modern japanese


I suspected it may be that simple, but thank you for confirming! I actually just saw on another thread that someone said ‘Leebo always has the best answers’ and lo and behold, you do! Thanks :slight_smile:

This is really interesting to know - if nai has been previously used as an emphasis particle then it may explain its presence in a few words. Thanks for the info!

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As Handsometom mentioned, it’s not impossible for that to have been a etymology at some point for certain ones, but these are not perceived as negations now.

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