In this post we will break down this common JLPT N3 grammar point ではないか (dewa nai ka) which has a similar meaning to じゃないか (janai ka), basically the meaning behind its use is to state To Not be… The addition of the particle ka か makes it a question. So the user is asking a question or asking themselves whether something is what it is.
In more colloquial English Its asking whether the thing in question is or is not.
This is a more formal way of questioning whether something is or is not.
This can refer to any particular situation. for example asking if john has passed his exam いいじゃないか。Isn’t it great? meaning Ii janai ka.
How to form it?
Verb-volitional + ではないか/じゃないか
Examples:
顔色が悪いね。疲れているんじゃないか。
You look pale. you are tired, aren’t you?
Kaoiro ga warui ne. tsukarete irun janai ka
あなたは今だってまだ危険を悟っていないらしいじゃないか！
I don’t think that even now you realize your danger!
Anata wa ima datte mada kiken o satotte inai rashii janai ka.
一緒にお台場に行こうじゃないか。
Why don’t we go to Odaiba?
issho ni otaiba ni ikou janai ka.
だったら踊りにいこうじゃないか！
Then let’s go dancing!
dattara odori ni ikou janai ka
こんどの週末は予定どおりにはいかなかったね。来週、またここへこようじゃないか？
This weekend has not gone according to plan. Shall we return here next weekend?
kondo no shuumatsu wa yotei doori ni wa ikanakatta ne. raishuu, mata koko e koyou janai ka
In simple terms its a very commonly used Grammar point, and can be used in various situations. I suggest knowing this one grammar point for the JLPT N3 well.
For more grammar lessons and grammar points I recommend Japanese From Zero lessons -> here