ではない / じゃない

ではない is "is not" for a noun or a な-adjective: the plain negative of だ. It goes straight after the noun or the な-adjective, and in conversation it contracts to じゃない.

ではない or じゃない

じゃない is the spoken form; ではない belongs to writing and formal speech. The meaning is the same. The polite forms split the same way: ではありません in writing and careful speech, じゃありません or じゃないです in conversation.

Common mistakes

A な-adjective drops its な, and nothing comes between the noun and では.

• × 静かなではない → 静かではない
• × 学生だじゃない → 学生じゃない

An い-adjective makes its own negative and never takes ではない.

• × 広いではない → 広くない

Usage notes

These go beyond the present "is not".

The past

ない changes like an い-adjective: ではなかった in writing, じゃなかった in speech.

じゃない as "isn't it?"

Said with a rising voice, じゃない asks the listener to agree or points something out, and is not a negative at all. In this use it can follow an い-adjective or a verb, which the negative never does: おいしいじゃないcan only mean "it's good, isn't it?"

Said with a falling voice, it is a pleased exclamation on recognising someone or something: "why, it's…!"

んじゃない？ for an opinion

With ん in front and a rising voice, じゃない？ puts forward your own view gently: "I think…, don't you?" After a noun or a な-adjective, ん needs な first: むり無理なんじゃないきごう？.