Introduction
Have you ever wanted to say “He should give up his seat” or “You shouldn’t lie” in Japanese?
For example:
- How do you say “We ought to help someone in trouble”?
- How do you tell a friend “You should say it clearly”?
When you want to state firmly what is right or proper, JLPT N3 grammar ～べきだ and its negative ～べきではない are the patterns to reach for.
1. Meaning: What does ～べきだ mean?
～べきだ expresses the speaker’s opinion about what is right—what a person ought to do, judged against common sense, morals, or social duty.
Common English equivalents:
- should ~
- ought to ~
- it is only right to ~
Example:
困っている人がいたら、助けるべきだと思います。
I think we should help someone who is in trouble.
～べきではない: shouldn’t
The negative states that something is wrong or improper.
Example:
どんなときも、うそをつくべきではありません。
You should never tell a lie, no matter the situation.
The key nuance: a firm, general judgment
～べきだ is assertive.
It does not sound like friendly advice—it sounds like a principle.
～べきだ is often used in these situations:
- stating a view on society or people in general
- criticizing what someone else is doing or not doing
- giving someone strong advice
- expressing what you believe you or others ought to do
However, when talking about your own immediate responsibilities or explaining an established rule, other expressions such as ～なければならない may be more natural (covered in section 5).
2. Formation: Verb (dictionary form) + べきだ
Verb（dictionary form） + べきだ／べきではない
- 言う (to say) → 言うべきだ / 言うべきではない
- 助ける (to help) → 助けるべきだ / 助けるべきではない
- 来る (to come) → 来るべきだ / 来るべきではない
The する exception
With する, both するべき and すべき are correct.
すべき comes from the classical form す and is often perceived as more formal or concise. するべき is also widely used, including in conversation.
The difference is mainly one of style, not meaning.
- する → するべきだ ／ すべきだ
- 注意する → 注意するべきだ ／ 注意すべきだ
Other useful forms
- べきです／べきではありません — the polite versions
- べきじゃない — casual speech
- べきだった — regret about the past
- もっと早く相談するべきだった。= I should have consulted you sooner.
- べき + Noun — modifying a noun directly
- 今やるべきことは何ですか。= What is it that we should be doing now?
Practical tip: べきだった is one of the few places where べき does work naturally about yourself, because you are looking back and regretting rather than announcing a plan.
Verbs only
べき attaches to verbs, not to nouns or adjectives.
Example:
- 親切な (kind)
- ❌ 親切べきだ → ✅ 親切にするべきだ
- 静かな (quiet)
- ❌ 静かべきだ → ✅ 静かにするべきだ
3. Useful Examples
① Judging someone else’s behavior
Situation: Emi and Ken are on a crowded train.
見て！あのパーカーを着たお兄さん、妊婦さんが目の前に立っているのに……。
Look! That guy in the hoodie—even though there’s a pregnant woman standing right in front of him…
席をゆずるべきだよね。
He should offer his seat.
約束に遅れたのだから、まず謝るべきだと思う。
You were late for the appointment, so I think you should apologize first.
② Stating a general principle
世界の国々は戦争をすべきではないと思う。
I believe the countries of the world should not go to war.
お金を拾ったら、交番に届けるべきだ。
If you find money, you should turn it in to a police box.
③ Strong advice to the listener
Situation: John is having trouble with his roommate.
ルームメイトがうるさくて、部屋で勉強できないんだ。
My roommate is so loud that I can’t study in my room.
「静かにして！」とはっきり言うべきだよ。
You should say “Keep it down!” clearly.
そんなに体調が悪いなら、無理をするべきではないよ。
If you feel that unwell, you shouldn’t push yourself.
④ Looking back with regret: べきだった
傘を持ってくるべきだった。
I should have brought an umbrella.
彼にあんなことを言うべきではなかった。
I shouldn’t have said something like that to him.
4. Related grammar (comparison)
～なければならない
This expresses necessity or obligation.
It focuses on what must be done, rather than on whether the action is morally right.
～べきだ expresses what is right, which is the speaker’s judgment.
- 明日までにレポートを出さなければならない。= I have to submit the report by tomorrow. (a requirement)
- 学生は毎日勉強するべきだ。= Students ought to study every day. (an opinion)
This distinction decides which one you need in the two cases covered in section 5.
～たほうがいい
～たほうがいい is commonly used to give practical advice or recommend a course of action.
Compared with ～べきだ, it usually sounds less like a moral judgment and more like a suggestion.
- 熱があるなら、休んだほうがいいよ。= If you have a fever, you’d better rest. (friendly)
- 熱があるなら、休むべきだ。= If you have a fever, you should rest. (firm, almost a scolding)
With friends and in everyday situations, ～たほうがいい is usually the safer choice.
～はずだ
English “should” can express either an expectation or an obligation.
Japanese uses different expressions for these meanings.
はずだ expresses an expectation based on available information or reasoning.
～べきだ expresses what someone ought to do.
- 彼は3時に着くはずです。= He should arrive at three. (I expect he will)
- 彼は3時に着くべきです。= He ought to arrive at three. (it is his duty to)
～てはいけない
～てはいけない is a prohibition: it is not allowed.
～べきではない says it is wrong, even if nobody forbids it.
- ここに車を止めてはいけません。= You must not park here. (the rule)
- 人の悪口を言うべきではない。= You shouldn’t speak ill of others. (a moral judgment)
5. Common Mistake: When to use べきだ vs. なければならない
Learners translate English “should” straight into べきだ, which produces unnatural Japanese in two specific cases.
Remember this golden rule:
- べきだ: a judgment about what is right, usually aimed at others or at people in general.
- なければならない: a necessity—for yourself, or imposed by a rule.
① Your own actions
Saying べきだ about yourself sounds odd, as though you were passing moral judgment on your own behavior from the outside.
- ▲ Unnatural: 私はもっと勉強すべきだ。
- ✅ Natural: 私はもっと勉強しなければならない。= I need to study more.
The past form is the exception.
もっと勉強するべきだった (I should have studied more) is perfectly natural, because regret is itself a judgment made after the fact.
② Established rules and regulations
べきだ gives your opinion.
A law or regulation is not your opinion—it already exists.
- ❌ Incorrect: 日本では、車は左側を走るべきだ。
- ✅ Correct: 日本では、車は左側を走らなければならない。= In Japan, you must drive on the left-hand side of the road.
For prohibitions, ～てはいけない does the same job: 館内で写真を撮ってはいけません。
One more caution on tone: because べきだ is assertive, using it toward a superior can sound presumptuous.
Soften it with と思います, or choose ～たほうがよろしいかと思います in business settings.
6. Practice
Translate the following into Japanese using ～べきだ or ～べきではない.
| Clue | Example Answer |
|---|---|
| I think parents should listen to their children more. | 親はもっと子どもの話を聞くべきだと思います。 |
| You shouldn’t make a promise you can’t keep. | 守れない約束をするべきではありません。 |
| I should have apologized sooner. | もっと早く謝るべきだった。 |
| What should we do first? | まず何をするべきでしょうか。 |
7. FAQ
- QIs するべき or すべき correct?
- A
Both are correct, and the difference is register.
するべき sounds more conversational; すべき is shorter and carries a formal, written feel, which is why it is common in newspapers and speeches.
This alternation happens only with する. Other verbs have one form: 行くべき、言うべき.
- QIs べきだ rude?
- A
Not rude in itself, but it is strong, so it depends on who you say it to.
It is natural when discussing society, when a close friend genuinely needs plain speaking, and in writing or debate where you are arguing a position.
Said to a boss or a client, it can sound like you are lecturing them. Add と思います to soften it, or switch to ～たほうがいいと思います.
- QCan I use べき with a noun, like 学生べきだ?
- A
No. べき attaches to the dictionary form of a verb only.
To say “should be a ~,” use である: 医者は患者に誠実であるべきだ = Doctors should be honest with their patients.
Note too that べき can modify a noun directly: やるべきこと (things that should be done), 読むべき本 (books one ought to read).
Conclusion
In this article, you learned that ～べきだ and ～べきではない state firmly what is right or wrong, rather than what is required.
With this grammar, you can now:
- express opinions about society and other people’s behavior,
- voice regret with べきだった,
- and switch to なければならない for your own actions and for established rules.
