「～たじゃない」 expression in spoken Japanese?

Question

I noticed in an anime I watched, one of the characters said something like below: > さっき食べたじゃない。 And what I think the meaning is: Didn't you just eat a few while ago? From what I have learned in Japanese classes, 「じゃない」, which is the shortened form of 「ではない」, must follow a noun word/phrase/clause. But in the spoken sentence above the 「じゃない」 follows a 「～た」 form of a verb. Is that sentence grammatically correct? Is this one of the many examples where colloquial language may skip a few grammar rules here and there? I think the sentence would be grammatically correct if there is　「ん」 in between the two phrases: 「さっき食べたんじゃない」. Did I actually mishear?

Answer 1

さっき食べたじゃない。　

じゃない is casual form of ではない

V(plain) +　じゃない?

i-Ad(plain) +　じゃない?

N-Ad(plain) +　じゃない?

N +　じゃない?

ですかis hidden at the end of sentence. さっき食べたじゃない（ですか！）

In this sentence, じゃない is used to express surprise and criticism of the listener.

This form makes other meanings, such as Guess or Confirmation.

ex. :あの人有名な女優じゃない。That lady is a famous actress?

週末ならみんな暇なんじゃない。Isn't everyone free on weekends?

Don't be confused with Denial expression じゃない ex. 私は日本人じゃない　I am not a Japanese.

　

じゃない ( = janai) VS んじゃないs ( = njanai)

I know the difference is just one letter ん ( = n), but it gives a difference.

While じゃない ( = janai) is usually used when you simply express an opinion showing emotion, んじゃない ( =njanai) is more like a tag question. You are expressing your opinion and at the same time you are asking the listener’s opinion or agreement. So it is used in a question form.

a) これおいしいじゃないですか。

= Kore oishii janai desuka.

= Wow, this is delicious. (I’m surprised.)

b) これおいしいんじゃない？(less formal than e)

= Kore oishiin janai?

= Isn’t this delicious?

Note : The same as a) and b).  e) sounds more enthusiastic. But actually many young people tend to use the f) form when they express their opinion to avoid offering straight reaction.

Past tense

c) よかったじゃない。(female speech)

= Yokatta janai.

= Oh that’s great! / I’m happy for you!

d) よかったんじゃない？

= Yokattan janai?

= I think it turned out great. Don’t you think so?, It’s great, isn’t it?

Note : When you compare these two, i) sounds more sincere. j) is more objective and it sounds a bit distant.

Answer 2

Yes. In this case "JANAI" is working like "ne," and seeking agreement.

DESU can be used to substitute verbs in some cases. 私はコーヒーを飲みました。はるかはお茶です。- I drank coffee, Haruka (had/drank) tea.

JA NAI in this case is like that, but mostly for confirmation:

私のケーキを食べたじゃない？ - You ate my cake, didn't you/ did you not?

サーフィンぐはむずかしいじゃない？ - Isn't surfing difficult? Surfing is difficult, is it not?