Is 海は青くないです less correct than 海は青ではない? I am just starting to learn and someone said my basic sentence was not polite. I'm trying to practice conjugating adjectives. My goal was to say ”The ocean is not blue".


海は青いくないです is ungrammatical. The adjective form of 'blue' is 青い. As I'm sure you've learnt, the negative form is made by removing the final い and adding くない. So it should be 海は青くないです. This sentence is polite. It is made polite by adding です after the i-adjective.

海は青ではない is grammatically correct but it is in plain form (i.e not polite). To turn this into the polite form ではない should be replaced with ではありません. Note that in this sentence the noun, 青, is used rather than the adjective, 青い, of the previous sentence.

For the adjective case you could also say 海は青くありません which is also polite but sounds rather stiff.

Since you are a beginner I should point out that 'not polite' doesn't mean rude. It just means a form you would use with someone with whom you are close.

Edit: Regarding the choice of whether to use a noun or adjective, please see this post. This makes the decision of the HiNative poster to change your sentence from 海は青くないです to 海は青ではない even more bizarre.

  • I think you should learn both. It is vital to know the plain form to construct grammar that is used in the polite form. It is also important to know polite form because you will inevitably be talking to strangers. Note that ではない can be made more casual as じゃない. You will see this a lot too. Mar 19 '21 at 22:09
  • So if I keep writing my sentences like this one: 海は青くないです , I will seem polite, correct? I've been conjugating my adjective practice sentences that way. This 海は青ではない was suggested by someone on HiNative and I was confused. Mar 19 '21 at 22:11
  • Thank you so much. I will start writing in my journal both so I can get practice both ways. Is there a site with the adjective conjugation with informal way? Mar 19 '21 at 22:12
  • I don't understand why someone would make that change. If you wait maybe a native speaker can give you some insight that I;m missing. Mar 19 '21 at 22:12
  • You don't need a site for i-adjective conjugation. You already know how to do it. The rule is robust and consistent. Mar 19 '21 at 22:15

Just adding some thoughts: I guess it would be correct 青ではない if you are using it as a noun. Example:

好きなのは青ではなくて赤です [The thing I like is not blue, it is red]

But to me, just like the other person said, it also sounds off to say 海は青ではない。

Perhaps you could say 海は青色ではない. I am positive that saying it with 色 makes it acceptable.

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  • でも、グーグルで検索したら、"海は青色ではない" は "海はではない" よりも少ないです。 "海はではありません" のヒット数は数件ありますが、"海は青色ではありません" はゼロです。
    – Chocolate
    15 hours ago
  • そうです。どこかで「色がついていたら、形容詞としていつも正しいです」とか読みましたから、そう思ってしまいました。"青い"は青色よりもずっと普通ですから、ヒットがない理由かもしれません。それとも私が随分間違っています 笑。
    – Manab
    15 hours ago

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