じゃないか — Isn't it? / Come on! (casual)
The casual version of ではないか. Expresses rhetorical questions, realization, mild surprise, or a bid for agreement; can also carry light accusation or enthusiasm.
Structure
[Plain form] + じゃないか
Examples
もう12時じゃないか！急ごう。
Mō jūniji ja nai ka! Isogō.
It's already 12! Let's hurry.
Surprised realization + call to action
そのアイデア、いいじゃないか。
Sono aidea, ii ja nai ka.
That idea's great, isn't it!
Positive affirmation / approval
あれ、山田さんじゃないか！
Are, Yamada-san ja nai ka!
Oh, isn't that Yamada-san!
Surprised recognition of a person
• Key Concept: じゃないか = casual; • Note: ではないか = formal. • Detail: falling intonation = rhetorical assertion; • Detail: rising intonation = genuine question. • Polite version: じゃないですか. • In formal writing: ではないでしょうか. • Summary: common among male speakers but widely understood by all.
Commonly confused with
The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones じゃないか is tested against.
vs ではないか (formal)
Same meaning, register difference: じゃないか is spoken/casual (and often masculine), ではないか is formal/literary.
vs じゃない (isn't/negation)
Plain じゃない is simple negation ('is not') or a tag question. Adding か turns it into an emphatic rhetorical exclamation of surprise or realization.
More expressions
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