When I was first learning Japanese, I learned that the explanatory form, -んです is always constructed by conjugating the verb in short form and adding -んです, and that the です part is never conjugated. But in more than one instance, I have seen -んじゃない used for the explanatory form. For example:


as opposed to:


What does it mean when the -です is conjugated rather than the main verb?

  • No. I did that intentionally to ensure that both examples maintain the same level of politeness. Sep 14 '12 at 1:52
  • That's fine, but the んじゃない from Axioplase's answer usually does not go with です... So I was just wondering what exactly you are asking...
    – Earthliŋ
    Sep 14 '12 at 1:56
  • Unfortunately I don't remember the specific examples on hand, but I've definitely heard/seen んじゃないです before, so my question still stands. Sep 14 '12 at 1:58
  • I do not think that です is conjugated in either example…. Sep 14 '12 at 2:28
  • If you consider じゃないです as a conjugation of です, then the second example is indeed conjugated. Sep 14 '12 at 2:30

Basically, "affirmation+じゃない(です(か))?" (notice the question mark), and "affirmation+じゃん!" (notice the exclamation mark) is an informal way to emphasize the affirmation.

Therefore, when you hear "おはし上手じゃん!" or "この歌を歌えるじゃないか?", it means something like "aren't you in fact good at it?" and "I thought you said you couldn't sing it!"

The more formal way to say it is "のではないか." It's a negative question, like "isn't it XX?" : "いいのではないか?" (isn't it great?). But it's also often used in more colloquial situations: "いいじゃん!" (it's great, mate!)

  • So is this form only used in questions and exclamations? Also, is じゃない the only conjugation that んです can take, or are there others? Sep 14 '12 at 1:56
  • Well, "んです" is "の+です", and there is no reason for forbidding conjugation, but usage gives it different meanings depending on how it's conjugated. I however have trouble trying to understand what "行くのではありませんでした" could mean, or to find a proper context for it…
    – Axioplase
    Sep 14 '12 at 4:29
  • 2
    There's also 〜〜んじゃない! in the prohibitive sense – "Don't do that!"
    – Zhen Lin
    Sep 14 '12 at 6:46
  • 2
    And also in the rue/regretting sense: eg あのとき、田中にしゃべるんじゃなかったよ (We should not have spoken to Tanaka that time (I wish we hadn't spoken with...))
    – Tim
    Sep 14 '12 at 11:39

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