じゃないか
- 1Expresses the speaker's surprise, realization or assertion while inviting the listener to agree ("isn't it!", "why, it's…").Ex. 1
- 2After a verb's volitional form, strongly urges or invites someone to act together ("let's…!").Ex. 2
- 3Reproaches or reminds the listener of something they should already know ("I told you, didn't I!").Ex. 3
Verb (plain form)The plain (non-ます) forms of a verb: affirmative or negative, non-past or past.
行く・行かない・行った・行かなかった
The dictionary form is only one of these: 行く.
i-adj. (plain form)The plain (non-です) forms of an i-adjective: affirmative or negative, non-past or past.
高い・高くない・高かった・高くなかった
The dictionary form is only one of these: 高い. The polite version adds です to the plain form.
na-adj. stemA na-adjective without な, i.e. the form listed in a dictionary.
静か・きれい・好き
Add な before a noun (静かな部屋); as a predicate, follow it with だ／です (静かだ).
Verb (volitional form)The form meaning "let's …" or "I'll …", ending in う／よう; also called the volitional form.
行こう・食べよう・しよう・来（こ）よう
Plain formThe plain forms without です／ます, for verbs, adjectives and nouns alike: affirmative or negative, non-past or past.
行く・高い・静かだ・学生だ (and their negative and past forms)
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Used in casual conversation, usually with falling intonation, to present something as obvious or newly noticed and to pull the listener into agreement. The volitional use gives a rousing, somewhat emphatic tone to a proposal. Compared with ね, it is more forceful and assertive, and its more formal counterpart is ではないか.
Do not add だ after な形容詞 or 名詞 before じゃないか; say 静かじゃないか, not 静かだじゃないか.
Note that despite its negative form, it is an assertion, not a question asking whether something is not the case.
Note that it can sound blunt or reproachful, so learners should avoid using it toward superiors.
- 1.ではないかN4ではないか is the formal version of じゃないか; the two are interchangeable for confirming a discovery and for inviting with the volitional form, but ではないか leans written/speech style. It also often appears as のではないか to express a tentative conjecture.
- 2.だろうN5だろう mainly expresses conjecture, but with rising intonation it seeks the listener's agreement, close to じゃないか's confirming and reproachful-reminder uses. However, only じゃないか can express surprise at a discovery or invite with the volitional form.
- 3.ではあるまいかN1ではあるまいか is written style, expressing a tentative conjecture or, after べき, a subtle suggestion, with の required after the verb; じゃないか is colloquial, more assertive, and also covers exclamation, reproach, and invitation. For conjecture they are partly interchangeable, but the register and tone change.
- 4.とはN1とは overlaps only with the surprise-discovery use: とは is more written, emphasizes 'I never expected it,' and is followed by 思わなかった or leaves the rest unsaid, while じゃないか is more colloquial and carries a tone of confirming with the listener. とは has no inviting or reproachful meaning.
- 5.ねN5ね has a soft tone and assumes the listener already agrees; じゃないか is stronger when exclaiming or confirming, often implies surprise, and has a casual, masculine flavor. 行こうね can also serve as an invitation, but is less compelling than じゃないか, and ね has no reproachful use.
ではないか is the more formal or written version of じゃないか, ね seeks agreement more softly, and だろう marks conjecture or assumption rather than emphatic assertion. ではあるまいか is a literary expression of tentative conjecture ("might it not be…"), and とは expresses shocked surprise at a fact ("to think that…") rather than seeking the listener's agreement.
