じゃない is the casual form of
ではない. では is regularly contracted to じゃ in Japanese, so is worth remembering as its own structure.
じゃない (casual), or
ではない (semi-polite) are the structures used for creating the negative form of nouns and
な-Adjectives.
These structures are simply added to the base form of the noun or
な-Adjective.
じゃ and では can also be used with the negative ます form of
ある, to create the polite variant.
ない is sometimes said/written as
ね or
ねえ. However, this is considered very casual, or even a bit rough. Accordingly, it is best avoided in most conversations.
-
俺（おれ）は馬鹿（ばか）じゃねえよ。
I’m not stupid.
じゃない is used very frequently to ask questions. This is similar to
じゃないか, a grammar point covered in another lesson. However, the nuance difference is that
じゃない as a question is a little bit more blunt, like ‘isn’t it?’ in English. On the other hand,
じゃないか is more like ‘don’t you think?’.
-
これは無理（むり）じゃない？
This is impossible, isn't it? (More direct statement)
-
これは無理（むり）じゃないか？
Don't you think this is impossible? (More direct question)
When
じゃない is used as a question, it will usually be obvious, due to a rising tone.