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For example:

> 授業があるんじゃなかったの?
>
> 授業があったんじゃなかったの?
>
> 授業があるんじゃない?
>
> 授業があったんじゃない(の)?

Are they the same? If yes, which are more common? Basically what are the
differences?
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2016-11-13T11:51:29.537
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grammar particle-の
の+じゃなかった? Vs の+ じゃない? Tenses used
授業があるんじゃなかったの？ means "you would attend the class, wouldn't you?", in other
words, it expresses that you thought someone was going to have the class but
have found something paradoxical and suspect that.

授業が あったんじゃないの{HLLLLLHLH}？ or …じゃなぃい{LLHLH}？ means that you though someone had
the class but have found something paradoxical and suspect that.

授業があったん じゃないの{HHHLH}？ or …じゃない{LLLH}？ means that you guess someone had a
class.
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2016-11-13T14:58:23.187
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Present+の+じゃないの? means things in the future. I think Present+の+じゃなかったの? is a
bit complicated. In my opinion, 今日、授業があるんじゃなかったの? can be both used in thing in
the future and in the last hour. However if you want to say things in the
future clearly, you should say Present+の+じゃないの?.

And Present+の+じゃなかったの? is used in things in the past. For example,
昨日、学校に行くんじゃなかったの? It means "Weren't you going to the school yesterday?. And
昨日、学校に行ったんじゃなかったの? means "Didn't you go to the school yesterday?"

I thought first 昨日、授業があるんじゃなかったの? is a bit unnatural but it may mean
昨日、授業がある予定じゃなかったの?.

And past+の+じゃなかったの? and past+の+じゃないの? means thing in the past and I don't feel
their difference.
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There is a slight difference.

授業がある is non-past. So it is either future or present. From the context it is
probably future. So it means "there will be a class".

授業があった is past. So it means "there was a class"

んじゃなかった is the contraction of のではなかった.  
んじゃない is the contraction of のではない.  
Both work as tag questions.

のではなかった is in the past tense. So it is asking for confirmation about something
that was defined in the past.  
のではない is in the present tense. So it is asking for confirmation about
something that should be defined in the present.

So the translation becomes:

授業があるんじゃなかったの?  
I thought there would be a class, wouldn't there?

授業があったんじゃなかったの?  
I thought there was a class, wasn't there?

授業があるんじゃない?  
I think there will be a class, won't there?

授業があったんじゃない(の)?  
I think there was a class, wasn't there?
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2016-11-19T17:20:05.947
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They have a few differences.

  1. 授業があるんじゃなかった？ - You **have** a class, do you not? 
  2. 授業があったんじゃなかった？ - You **had** a class, did you not?

The first sentence is the **present form**. The second sentence is the **past
form**.

  3. 授業があるんじゃない？ - You **will** have a class, will you not?
  4. 授業があったんじゃない？ - You had a class, did you not?

The third sentence is the **future form**. I think the fourth sentence has the
same meaning as the second sentence.
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2016-11-26T00:20:57.413
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のじゃない means that you are expecting something and are trying to clarify its
validity.

のじゃなかった means that you are expecting something but then that expectation is
challenged by a contradiction, and then you are trying to clarify its
validity.

> 授業があるんじゃない? (i think : isn't it that there is class?)

You said to a friend who tried to leave the classroom when you are expecting
that there is a class.

> 授業があるんじゃなかった? (I thought : Isn't it that there is class?)

You said to a friend who told you that the teacher is absent. Here, when you
said it, your expectation has changed. This method of clarifying your
expectation carries the nuance that you realized your expectation is more
likely to be false.

When past tense is used "あった, なかった" it implies that the the event you are
expecting has occurred before you are trying to clarify it (not on the same
timeline either.)
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2016-12-04T10:55:22.830
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I think じゃない and じゃなかった are the same for this case.
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