Grammar Info

N3 Lesson 1: 8/22


Should not, Must not , Ought not to

する → すべきではない・するべきではない


Verb + べき + ではない
Verb + べき + じゃない


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About べきではない

As an extension of the auxiliary verb べき, that is partnered with verbs to convey 'ought to do (A)', べきではない (or べきじゃない) highlights the opposite, and means 'ought not to (A)', 'should not (A)', or 'must not (A)'. Just like べき, it is quite strong, and implies that doing (A) would be considered improper/incorrect.
べきではない (or べきじゃない) will be paired with the plain (non-past) form of a verb.
  • ()ている()コンセント()れるべきではない
    You must not touch the outlet with wet hands.
  • どんないう(こと)()なくても子供(こども)()あげるべきじゃない
    No matter how much a child doesn't listen to what you say, you ought not to raise your hand at them.
As with all other structures that use では, は may be omitted. However, as the presence of は strengthens the ない, the overall phrase will sound a little bit weaker without it.
  • 一人(ひとり)あの(やま)()べきではない
    You must not go to that mountain alone.
  • (ひと)(きず)つけるような(こと)()べきでない
    You ought not to say anything that could hurt a person's feelings.
Fun Fact
The combination of する and べき is a rare grammatical exception in Japanese, in which two forms are both considered equally correct. Due to this, either するべき, or すべき may be used.
  • テストの(まえ)徹夜(てつや)するべきではない
    You ought not to stay up all night before a test.
  • くだらないこと警察(けいさつ)電話(でんわ)べきではない
    You must not call the cops for something trivial.




    You shouldn't eat food that is rotten.


    You should not smoke in places that are non-smoking.


    It's not important. You shouldn't worry about it.


    You should not do things people dislike.


    You should not speak ill of others.

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べきではない – Grammar Discussion

Most Recent Replies (4 in total)

  • Pushindawood


    @pampel Thank you for your question. While は can be omitted, less emphasis is placed on the negation with its absence, and answers with its inclusion (or じゃない) are generally more common in modern Japanese. I have included a note about this on the grammar page and have added でない to answers that throw hints/warnings rather than marking you wrong. Cheers!

  • wrt7MameLZE33wlmpCAV


    One thing that has always confused me with this grammar point is why it’s べきではない instead of ないべきだ. To my English brain, it’s the latter that seems correct, as opposed to the former (“not obliged to” vs. “obliged to not”). I understand that it’s wrong, but I don’t understand why.

    Anyone have any insights?

  • Daru


    It’s actually super simple: べき is an auxiliary verb that comes from べし’s attributive form.
    It sounds advanced, but it’s basically saying that it’s a verb that got turned into a noun-like word for better connection in the language. (And hence, why it’s negated as じゃない/ではない)

    With this in mind, it’s just a matter of the language being in order to function.
    Verb + Auxiliary べき + Negation of the Auxiliary ではない

    You can’t negate what you haven’t established for negation!
    ないべきだ would translate as “Don’t must.”

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