Recently, I came across an interesting case of じゃない usage, which I haven't seen prior.
In the example above, the sentence itself makes sense only in case of じゃない having an affirmative connotation. Through some searching, I also came across an article, that had a direct quote from Shakespeare using the same construction as in the example above
シェイクスピアの言葉じゃないけど、善悪って存在するものではなく、人間が作り出しているだけ。nothing either good or bad, but thinking makes it so.ってね。
Although I get that in this case じゃない isn't here for the purpose of negation, I don't quite understand what exactly is the grammar behind it. The only plausible explanation I can come up with, is something like かと思う being omitted after じゃない, like in
Am I thinking in the right direction, or is this じゃない usage something completely different?
Edit: or is it used to show that the speaker wants to quote someone, while knowing that the quote he makes isn't word-for-word?