べきだ / べき

べきだ says what someone should do because it is right: a judgment about duty or proper behaviour, "should", "ought to". It follows the dictionary form of a verb, and with する both するべきだ and the more written すべきだ are correct. The polite form is べきです.

The verb stays in the dictionary form. To say "should not", the negative goes on べき: べきではない, or べきじゃない in speech.

• × 言わないべきだ → 言うべきではない

べきだ or ほうがいい

ほうがいい is advice for this person in this situation. べきだ is a judgment about what is right in general, so said straight to someone it sounds like a lecture. With とおもう思う it becomes an opinion and softens.

べきだ or なければならない

べきだ is the speaker's view of what is right. A rule, a schedule or a plain necessity takes なければならない.

• × 明日は八時に会社に行くべきだ → 明日は八時に会社に行かなければならない

べきだった

In the past, べきだった is "should have": it wasn't done, and that was a mistake. べきではなかった is "shouldn't have".

Usage notes

These go beyond a verb + べきだ at the end of a sentence.

Before a noun

べき goes straight before a noun, with no だ: "a thing to be done", "a book to read".

After a noun or な-adjective

A noun or a な-adjective takes である before べき. This belongs to writing and formal speech.

驚くべき and 恐るべき

A few verbs + べき work as adjectives with no sense of duty: おどろく驚くべき "astonishing", おそる恐るべき "formidable".