notes

「じゃない」 is a contraction of 「ではない」 (the negative of the copula)
negative questions can be used when looking for a positive response (ex: “It’s a nice day isn’t it?” / “Yes, it is.)
in formal Japanese, a question like this might be 「田中さんじゃないですか？」(“Aren’t you Tanaka-san?)
- the 「です」 is just a politeness marker
- in casual Japanese, the 「です」 and 「か」 are omitted, leaving 「田中さんじゃない？」 which has three potential meanings
  - “Is not Tanaka-san.”
  - “Is Tanaka-san, isn’t it?”
  - “If it isn’t Tanaka-san.”
「じゃない」 can also be used in place of the sentence-ending particle 「ね」
「じゃない」 can also be placed after verbs
- ex: 「もう言ったじゃない？」 means “I already said that, didn’t I?”
「じゃない」 is sometimes contracted to 「じゃん」
ex: 「その理論が間違っているのではないでしょうか？」 means “Might that theory not be in error?”
- in this sentence, the 「の」 marks the “theory that exists in a state of error” as a single “thing”
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