Understanding のではない and のではないか in the passage


I was reading through Soumatome N1 Dokkai practice book when I encountered the
passage below. Understanding the passage itself was not really difficult:
_**the uncle did the prank**_. But when it comes to answering the multiple
choice question, I was stumped. Here is how I arrived at my answer:

1 その子供がまた今度いたずらをやったら許されない、と母は言った。

> This can't be true.

3 叔父はよくいたずらをするので、今回も叔父がやったと僕はおもった。

> This translates to the uncle did it.

2 今回のいたずらは、叔父さんがやったのではない、と僕は思った。

> I translated the part「叔父さんがやったのではない」as "the uncle did it"
>
> THIS IS WHY I GOT IT WRONG

What was going on my mind was that 「いいんじゃない」 conveys roughly the same meaning
as「いいんだよね」and so I applied this logic. Apparently, it's wrong.

So, is it true that 「叔父さんがやったのではない」translates to "the uncle did not do it"?
And if so, if I want to convey the fact that the uncle did it using the
negative, just like 「いいんじゃん」, how should I write it?

[![](https://i.stack.imgur.com/jxNff.png)](https://i.stack.imgur.com/jxNff.png)




叔父さんがやったのではない **exclusively** means "it is not the uncle that did it". The
～じゃん equivalent is 叔父さんがやったのではない **か**. Yes, it comes from question "Isn't it
—?" then becomes to mean "How could it not —". And in formal saying you
_cannot_ drop the question particle か.

* * *

By the way, if written, the casual ～じゃない is certainly ambiguous even to
Japanese, but their difference is clear in speech.

<https://soundcloud.com/user-61112954/yattanjanai> (created with
[スズキクン](http://www.gavo.t.u-tokyo.ac.jp/ojad/phrasing/index))

[![enter image description
here](https://i.stack.imgur.com/W6Qoz.png)](https://i.stack.imgur.com/W6Qoz.png)[![enter
image description
here](https://i.stack.imgur.com/MZNwX.png)](https://i.stack.imgur.com/MZNwX.png)

The first one (ない bears accent) is negative "did not", and the second "surely
did" (=じゃん).




叔父さんがやったのではない **exclusively** means "it is not the uncle that did it". The
～じゃん equivalent is 叔父さんがやったのではない **か**. Yes, it comes from question "Isn't it
—?" then becomes to mean "How could it not —". And in formal saying you
_cannot_ drop the question particle か.

* * *

By the way, if written, the casual ～じゃない is certainly ambiguous even to
Japanese, but their difference is clear in speech.

<https://soundcloud.com/user-61112954/yattanjanai> (created with
[スズキクン](http://www.gavo.t.u-tokyo.ac.jp/ojad/phrasing/index))

[![enter image description
here](https://i.stack.imgur.com/W6Qoz.png)](https://i.stack.imgur.com/W6Qoz.png)[![enter
image description
here](https://i.stack.imgur.com/MZNwX.png)](https://i.stack.imgur.com/MZNwX.png)

The first one (ない bears accent) is negative "did not", and the second "surely
did" (=じゃん).

