はずだ means something is expected to be true; べきだ says an action is advisable or proper. Use はず for a conclusion or expectation based on what is known, such as a train expected to arrive. Use べき to judge what someone ought to do. べきではない advises against an action; はずがない denies that something is expected or possible.
also written hazu / beki / はずだ / べきだ / はずがない / べきではない
はず — it ought to be so, by my reasoning · べき — it ought to be done, morally · English says 'should' for both
Sentences
6 sentences, word by word
はず — a conclusion from what you know
polite
、。
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三時
さんじ ［1］
three o'clock
time noun · the evidence the conclusion rests on
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の
の
links noun to noun
particle · A の B = B belonging to A
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電車
でんしゃ ［0］
train
noun · 三時の電車, the three o'clock service
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だから
だから
so; therefore
conjunction · flagging that reasoning follows
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もう
もう
already; by now
adverb · the time has passed
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着いている
ついている
has arrived
ている on a change verb · the resulting state, not an action in progress
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はず
はず
ought to be
noun · an expectation the speaker can justify
はずだN3ought to be · expectation
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です
です
(polite ending)
copula · politeness on the noun はず
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He took the three o'clock train, so he should be there by now.
べき — a judgement about what's right
plain
。
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ちゃんと
ちゃんと
properly
adverb · the standard the apology has to meet
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謝る
あやまる ［3］
apologise
godan verb · dictionary form, which べき requires
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べき
べき
ought to
auxiliary noun · a verdict on the right course of action
べきだN3ought to · obligation
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だ
だ
is
plain copula · closing the judgement flatly
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You should apologise properly.
はずがない — the possibility denied
plain
。
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彼
かれ ［1］
he
pronoun · the person being defended
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が
が
marks the subject
particle · what the sentence is about — with 好き, 分かる and potentials, the object
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そんな
そんな
that kind of
demonstrative · pointing at what was just described
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こと
こと
the act of; the fact of
noun · turns the verb in front into a noun
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を
を
marks the direct object
particle · pronounced お
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言う
いう ［0］
say
godan verb · dictionary form before はず
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はず
はず
expectation
noun · about to be denied, not affirmed
はずがないN3there's no way
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が
が
marks the subject
particle · what the sentence is about — with 好き, 分かる and potentials, the object
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ない
ない
there isn't
negative of ある · completing the fixed frame
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There's no way he'd say something like that.
べきではない — the action forbidden
polite
。
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そんな
そんな
that kind of
demonstrative · the decision under discussion
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こと
こと
the act of; the fact of
noun · turns the verb in front into a noun
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を
を
marks the direct object
particle · pronounced お
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一人
ひとり ［2］
alone; by oneself
noun · 一人で, on one's own
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で
で
in; at — where it happens
particle · where the action happens, or the manner it happens in
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決める
きめる ［0］
decide
ichidan verb · dictionary form before べき
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べきではありません
べきではありません
ought not to
べき ＋ ではない, polite · note it is not 決めないべきだ
べきではないN3ought not to
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You shouldn't decide something like that on your own.
はずだった — the expectation that broke
plain past
。
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彼女
かのじょ ［1］
she
pronoun · also 'girlfriend' depending on context
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は
は
as for — the topic
particle · written は, read わ
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来る
くる ［1］
come
irregular verb · dictionary form before はず
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はず
はず
was supposed to
noun · the expectation, about to be placed in the past
はずだったN3was supposed to
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だった
だった
was
plain past copula · placing the expectation in the past
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のに
のに
and yet
conjunction · the contrast, and the disappointment in it
のにN4and yet
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She was supposed to come, but she never showed.
ほうがいい — the softer alternative
polite
。
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医者
いしゃ ［0］
doctor
noun · 医者 for the person, 病院 for the place
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に
に
to; at; into
particle · a point something reaches — a place, a time, a person, or a state
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相談
そうだん ［0］
consultation
noun · 相談する to consult someone
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した
した
did
plain past of する · ほうがいい takes the past form for advice
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ほう
ほう
the option of
noun · marking one side of an implied comparison
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が
が
marks the subject
particle · what the sentence is about — with 好き, 分かる and potentials, the object
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いい
いい
is better
い-adjective · recommending without invoking what is right
ほうがいいN4you'd better
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です
です
(polite ending)
copula · politeness on the い-adjective
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You'd be better off talking to a doctor.
Structure
How each one attaches
Verb・い-adj・な-adj な・Noun の＋はずだ
着くはずです, 静かなはずだ, 日曜日のはずだ. A noun takes の — this is where はず and わけ part company, since わけ takes な.
Verb ［dictionary］＋べきだ
謝るべきだ. Only verbs — there is no 静かなべきだ. Adjectives and nouns need a different construction entirely.
すべきだ·するべきだ
Both are accepted. すべき is the older, more formal form and is what you will see in writing; するべき is common and unremarkable in speech.
はずがない·べきではない
はずがない denies the possibility; べきではない forbids the action. Neither is formed by negating the verb in front.
Meaning
Expectation, obligation, and the third option
はず expresses an expectation. What you know leads you to expect something: 三時の電車だから、もう着いているはずです. It often sounds more grounded than a bare たぶん, though no formal proof is required.
べき is a verdict. It says this is the right thing to do, measured against a standard rather than against evidence. Because it appeals to what is proper, aimed at a person it can land as a lecture.
べき gives a judgement or strong advice.謝るべきだ says someone ought to apologize. 謝るはずだ predicts an apology; it does not advise anyone to act.
はずだった describes a past expectation.来るはずだったのに indicates that the person was expected to come but did not. The contrast comes from のに and context, not automatically from the past form.
For advice, ほうがいい is usually the better tool.謝ったほうがいい recommends without invoking morality. Save べき for when you do mean the stronger, more principled claim.
Watch out
Where はず and べき go wrong
Using はず to tell someone what to do
謝るはずだ predicts that they will apologise. To say they ought to, you need べき — or, more gently, 謝ったほうがいい.
べき on an adjective or a noun
べき takes verbs only. 静かなべきだ is not Japanese. Rebuild it as 静かにするべきだ, or reach for である — which is a verb, so 静かであるべきだ and 教師であるべきだ both work.
Negating the verb instead of the pattern
It is 言うべきではない, not 言わないべきだ. The negative attaches to the pattern, and the same holds for はずがない.
Also asked
Questions people ask about はず and べき
How do I choose between them?
Ask whether you are predicting or prescribing. If you could answer “what makes you think so?”, it is はず. If you are saying what ought to happen, it is べき.
Is it すべき or するべき?
Both are correct and both are common. すべき is the older, more formal form and dominates in writing; するべき is unremarkable in speech. Neither is an error.
Is べき rude?
It can be, aimed at a person — it appeals to what is proper, which is close to lecturing. 〜たほうがいい gives the same advice without the moral weight.
What's the difference between はずがない and わけがない?
はずがない denies it on the evidence you have. わけがない denies it on common sense, and carries more of an “obviously not” tone.
How does はず attach to a noun?
With の: 日曜日のはずだ. This is worth holding onto, because わけ takes な in the same slot — that is the one place the two patterns diverge.
What does はずだった mean?
はずだった places an expectation in the past. 来るはずだったのに tells you it was not met, but the contrast comes from のに and context.
