We can use じゃなかったです for past tense, but can we replace the です with でした so that it becomes じゃなかったでした? Why or why not?

  • related Mar 8, 2016 at 0:26
  • じゃなかったです or じゃなかったでした are some bad expression.The best expression is ではありませんでしたか? Mar 9, 2016 at 11:09

2 Answers 2


The negative past forms are:

  1. なかった
  2. なかったです
  3. ありませんでした

In 1 and 2, the tense change is already realised by ない→なかった, and です just acts as a helper to add politeness. なかったでした does not exist because です will not inflect to show tense since it's just a politeness helper here.

In 3, the tense change is realised by でした, but note that in the case of present tense, ありませんです does not exist because the politeness is already accounted for by ます(manifested as ません here), so です is not required as a politeness helper in the present tense.


No, you can't do that. じゃなかったです is a confusing form because it's a colloquialism, and thus is only "grammatical" de facto. The proper form is じゃありませんでした, or without contractions, ではありませんでした. じゃなかったでした is completely incorrect and can't be used under any circumstances.

  • You don't really answer the "why or why not". You just say that じゃなかったです is a confusing form. You also don't explain why じゃなかったでした is "completely incorrect".
    – Earthliŋ
    Mar 6, 2016 at 16:20
  • I'm conflicted to vote on this because you have a point about the lack of explanation. But it is extremely helpful to know the proper conjugations so I will neither upvote nor downvote
    – Tek
    Aug 12, 2018 at 10:50

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