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".

  • I think neither is impolite. Politeness depends heavily on the context or situation. Of the two, the former is more natural to my ears. The latter sentence is a bit awkward but with no problem. 海は青"色"ではない may sound better, though.
    – user48754
    May 24 '21 at 5:27

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

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