Grammar Info

N3 Lesson 1: 7/22


Must, Should , Ought to

する → べき or するべき


Verb + べき + だ
Verb + べき + Noun

する → す(る)べき


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About べき

The auxiliary verb べき, being the attributive form of べし, is a structure in Japanese that is often paired with verbs to express that something 'ought to be done'. It implies some sort of moral obligation, or that (A) is the only reasonable course of action. This comes from the kanji ()き, which carries the meaning of being something 'permissible' (indicating that any other action would not be acceptable).
べき will be paired with the plain (non-past) form of a verb, before being followed by either , or another noun.
  • そういう(こと)本人(ほんにん)()べき
    You ought to say things like that to the person themselves.
  • (きゃく)さん意見(いけん)ちゃんと()べき
    You ought to properly listen to customers' opinions.
  • ハマサキさん尊敬(そんけい)するべき(ひと)
    Hamasaki-san is someone you ought to look up to.
  • あなた(おし)えるべき(こと)これ全部(ぜんぶ)です
    Of all the things I ought to teach you, this is the last one.
べき is also sometimes translated as 'must do (A)', or 'should do (A)' but it is important to remember that it will always have the nuance of being the only 'permissible' choice, and is therefore very strong.
It is important to note that the verb appearing with べき cannot be in past tense, and you will need to use だった or でした after べき, if you would like to say that something 'ought to have been done' in the past.
  • やばいやばい、(くるま)()まりそう!高速(こうそく)()(まえ)ガソリン()ておくべきだった
    This is not good… ahhh not good, the car is about to stop! I should have filled the car up with gasoline before I got on the highway.
  • 大変(たいへん)(もう)(わけ)ございません。こちらもっと(はや)()づくべきでした
    We are very sorry. We should have noticed this earlier.
Fun Fact
In modern Japanese, there are only 18 auxiliary verbs, of which べき is not one. べし (the standard form) is considered to be a classical auxiliary verb. Due to this, べき (and べし) are often referred to as classical auxiliary verbs.
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.
  • 結婚(けっこん)する(まえ)相手(あいて)将来(しょうらい)(はな)するべき
    Before marrying, you should talk about the future with your partner.
  • 家族(かぞく)(なに)あっても大切(たいせつ)にすべき
    You should prioritize family no matter what happens.


  • ()たい(ひと)運動(うんどう)べきだと(おも)

    I think people who want to slim down should exercise.

  • 税金(ぜいきん)(はら)べきです。

    You should pay taxes.

  • 明日(あした)会議(かいぎ)重大(じゅうだい)(はなし)があるので、出席(しゅっせき)するべきだ。

    Because we will talk about something important at tomorrow's meeting, everyone should attend.

  • (きみ)責任(せきにん)()べきだ。リーダーなんだから

    You should take responsibility since you are the leader.

  • この茶碗(ちゃわん)()べきだ。こんな()()(もの)はあまりない

    You should buy this bowl. It is not often that you come across such a bargain.

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べき – Grammar Discussion

Most Recent Replies (16 in total)

  • wct


    About 1 year ago

    Relevant research I’ve already tried

    The Information section begins with this background:

    However, looking at my ‘go to’ reference (which may not be the best overall, I don’t know, but it’s the best thing I know how to use well), I looked up the kanji 可 in conjunction with the kana べ (using this search text: *可* *べ* ), and found three relevant listings for the ‘origin’ of this formation:

    1. , listed as a ‘generic’ word type of
  • nekoyama


    About 1 year ago

    These are conjugated forms of the same word. It’s theorized that the origin is the adverb うべ transformed into an adjective. べし is the 終止形, べく is the 連用形, and べき is the 連体形. It somehow avoided the changes that happened since then and in modern Japanese, these classical forms are still used, but some conjugations have been (partially) replaced with ones that act like it’s a noun (べきだ、べきではない etc.). “Partially” because e.g. べからず is also still used as a negative form. But others are not, e.g. べかりき、べかりけり past forms are not used anymore.

    As for whether it’s a verb or not… in Japanese grammar terms it’s a 助動詞 which could indeed be translated as “auxiliary verb”. But 助動詞 don’t necessarily act like full verbs, e.g. -た、-たい、-ない are 助動詞 too. So maybe it’s better to call them “auxiliaries”. The term has nothing to do with their origins anyway, it just describes what they’re used for now.

  • testing


    About 12 months ago

    The description says that this grammar point “implies some sort of moral obligation, or that (A) is the only reasonable course of action.”. I can see this in most of the examples, but some of them don’t feel like that to me:

    • この茶碗べきだ。こんなはあまりないよ。
      You should buy this bowl. It is not often that you come across such a bargain.
    • 日本語してべきだ。その上達するから。
      You should read Japanese aloud, because you wi...

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