1) Is the plain "ja nai" after a verb grammatically correct?

```

       aru ja nai?
    
       wakatta ja nai?
    
```

2) Why use ja nai, why not a negative form of a verb :

```

       aru ja nai? --> nai?
    
       wakatta ja nai? --> wakaranakatta?
    
```

What's the difference?
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2017-10-28T16:04:04.603
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2017-10-29T08:20:25.430
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question
grammar
"ja nai" after a verb
You are misinterpreting the meaning of the phrases. The translation is:

```

    あるじゃない？ = there is, no?
    わかったじゃない？ = you understood it, right?
    
```

That is, it is a positive statement with a question whether it is true or not.
You can parse it in two parts: わかった = you understood, じゃない = is not, where the
first part functions as a adjective where the adjective describes a state of
"you" in this case, so it is as if you are asking "is not (adjective)?"

Also, the natural way of saying a phrase like that is to add an ん after the
verb. You can say without the ん but that becomes a bit "stiff"/"hard". Most
likely the source where you heard this actually said: あるんじゃない？
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2017-10-29T00:52:07.677
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answer
あるじゃない{HLLLL} （ない{HL}）means "Look / Wow, there's (something)!".

あるじゃない{HLLLLH}？ means "By the way / You know, there's (something), right?".

あるじゃない{HLLLHL} means "It's not ある! / Shut up! Don't say ある!".

あるじゃないぃ{HLLLHLH}？ means "What? You mean, it's not ある?".

（だから）あるんじゃない{HLLLLL}（ない{HL}）means "(that's why) there's (something), no?".

あるんじゃない{HLLLLLH}？ means "I guess there's one".

あるんじゃない{HLLLLHL} means "It's not that there's one (but ...)".

あるんじゃないぃ{HLLLLHLH}？ means "(I thought there was but) you mean, it's not the
case?"
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2017-10-29T08:08:12.047
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answer