Past negative tense じゃなかったでした


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?




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.




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.

