べき

The grammar structure べき expresses a strong sense of obligation, duty, or moral recommendation – equivalent to English "should," "ought to," or "must." It is stronger and more emphatic than 〜～ほうがいい, carrying a nuance of moral duty or social expectation rather than casual advice.

Formation

べき attaches to the dictionary form of verbs:

The verb する is a special case – it can appear as either するべき or the more classical すべき:

Negative form: べきではない

To express what someone should not do, use べきではない (or the casual べきじゃない):

The negative goes on べき itself (べきではない), not on the verb before it. Saying ～ないべき is generally considered incorrect.

Modifying nouns

べき can directly modify a noun, meaning "something that should be done":

Nuance and usage notes

• べき implies a general truth or principle – what is right, proper, or expected. It is used for rules, social norms, or strong personal convictions.

• It sounds relatively formal and assertive. Using it to give direct advice to someone can come across as preachy or lecturing, so it is often softened with と思う or だろう:

  あやまる謝るべきだとおもう思う。

  I think you should apologize.

• べき is typically not used for trivial or personal preference matters. Saying something like 「ラーメンを食べるべきだ」 would sound oddly strong unless you are making a passionate recommendation.

• The past form べきだった expresses regret about something that should have been done:

  もっとはやく早くゆう言うべきだった。

  I should have said it sooner.