〜はず: Expectation ('supposed to') | Japanese Grammar

〜はず is how Japanese says "it ought to be so" — not because you feel sure, but because it follows logically from something you already know. The train timetable says 9:00, so 電車は九時に着くはず — "the train should arrive at nine." You are not guessing wildly and you are not commanding anyone; you are reading off a conclusion that the facts force. That grounding in objective reason is the whole personality of はず, and it is what keeps it distinct from the conviction-word にちがいない and from the advice-word べき, both of which English also translates as "should."

The word for English speakers to unlearn is exactly that "should." English piles three unrelated ideas onto one modal — he should be here by now (expectation), you should see a doctor (advice), you should apologize (moral duty). Japanese refuses to blur them. はず is only the first one: given what I know, this is the expected state of affairs.

What はず actually means

はず (occasionally written 筈, but almost always in kana) is a noun meaning something like "the natural expectation." It takes the copula — はずだ / はずです — so grammatically you are saying "the situation is one of natural expectation." Every はず sentence rests on a stated or implied because: a schedule, a promise, a fact you were told, a piece of common sense.

予約したから、席はあるはずです。

yoyaku shita kara, seki wa aru hazu desu

I made a reservation, so there should be seats.

彼女は日本に三年住んでいたから、日本語が話せるはずだ。

kanojo wa nihon ni san-nen sunde ita kara, nihongo ga hanaseru hazu da

She lived in Japan for three years, so she should be able to speak Japanese.

彼はもう着いているはずだ。さっき駅を出たと連絡があった。

kare wa mō tsuite iru hazu da. sakki eki o deta to renraku ga atta

He should have arrived already — he messaged that he'd just left the station.

In each case the second clause (or the first) supplies the grounds. Strip the reasoning away and はず sounds hollow: it is the conclusion of an argument, so it needs a premise.

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Before you use はず, ask yourself: "…because of what?" If you can point to a fact, a schedule, or a promise that makes this the logical outcome, はず fits. If your only evidence is a strong gut feeling, you want にちがいない instead. はず reasons; にちがいない is convinced.

How はず attaches

はず behaves like a noun being modified, so whatever comes before it takes the same shape it would take modifying any noun: plain verbs and い-adjectives attach directly, な-adjectives keep their な, and nouns need の.

Preceding word	Form	Example	Reading
Verb (plain)	plain + はず	来るはず	kuru hazu
Verb (plain past)	plain past + はず	来たはず	kita hazu
い-adjective	plain + はず	高いはず	takai hazu
な-adjective	stem + な + はず	静かなはず	shizuka na hazu
Noun	noun + の + はず	学生のはず	gakusei no hazu

The な and の are the two traps. A な-adjective must not drop its な before はず, and a noun must not drop its の. These are the same linking rules you already use for any noun modifier — はず is just another noun.

この時間なら道は空いているはずです。

kono jikan nara michi wa aite iru hazu desu

At this hour the roads should be clear.

あの店は日曜日も開いているはずだよ。

ano mise wa nichiyōbi mo aite iru hazu da yo

That shop should be open on Sundays too.

The two negatives are not the same

This is where はず earns its own page. Negating an expectation can mean two very different things, and Japanese assigns each a different shape.

〜ないはず — you expect the action not to happen. The negation sits on the verb; the expectation itself is normal-strength.

彼は車で来ないはずだから、駅で待ち合わせよう。

kare wa kuruma de konai hazu da kara, eki de machiawaseyō

He probably isn't coming by car, so let's meet at the station.

〜はずがない — you deny the very possibility. The negation sits on はず itself: "there is no expectation that could support this," i.e. "no way, that couldn't possibly be." This is much stronger than 〜ないはず — it is closer to English "there's no way."

あの真面目な彼が、そんな嘘をつくはずがない。

ano majime na kare ga, sonna uso o tsuku hazu ga nai

There's no way someone as earnest as him would tell a lie like that.

そんなはずはない。何かの間違いだ。

sonna hazu wa nai. nanika no machigai da

That can't be right. It must be some kind of mistake.

Note the last one uses は rather than が (はずはない) — both are heard; が is the tighter, more idiomatic version, は adds a touch of contrastive emphasis ("that is not to be expected"). そんなはずはない is a fixed, high-frequency phrase of disbelief worth memorizing whole.

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Keep the pair straight by their English: 来ないはず = "he's not expected to come," 来るはずがない = "there's no way he'd come." The first is a mild prediction of absence; the second flatly rules the event out. Swapping them either weakens a firm denial or accidentally denies something you only meant to doubt.

はずだった: "it was supposed to — but it didn't"

Because はず is expectation and not conviction, it can be wrong — and Japanese has a beautifully specific way to admit that. Put はず into the past, はずだった, and you signal that reality betrayed the expectation. It almost always trails a のに ("even though") or a rueful pause.

荷物は今日中に届くはずだったのに、まだ来ない。

nimotsu wa kyō-jū ni todoku hazu datta noni, mada konai

The package was supposed to arrive by the end of today, but it still hasn't come.

田中さんも来るはずだったんですが、急に用事が入ったそうです。

Tanaka-san mo kuru hazu datta n desu ga, kyū ni yōji ga haitta sō desu

Tanaka-san was supposed to come too, but apparently something urgent came up.

This retrospective, slightly regretful twist is something the pure conviction forms cannot do. You cannot felicitously say ×にちがいなかったのに to mean "I was sure, but…" — being convinced and being proven wrong don't combine the same way. はずだった works precisely because はず was only ever a reasoned expectation, always open to being overturned by events.

はず vs にちがいない: reason versus conviction

Both land near English "must be," but they get there differently, and the difference is real enough that natives feel it.

はず is objective: "the timetable says…, therefore it should be…." You could be wrong, and you'd accept correction.
にちがいない is subjective: "I'm convinced it's so." It voices your inner certainty, not a public argument.

時刻表によると、次の電車は十分後に来るはずだ。

jikokuhyō ni yoru to, tsugi no densha wa juppun-go ni kuru hazu da

According to the timetable, the next train should come in ten minutes. (reading off the schedule)

こんな時間に電話してくるなんて、何かあったにちがいない。

konna jikan ni denwa shite kuru nante, nanika atta ni chigainai

Calling at an hour like this — something must have happened. (personal conviction)

For the full confidence ladder — from かもしれない through でしょう, はず and にちがいない — see The Probability Spectrum.

はず is not advice

Because English "should" also gives advice, learners reach for はず to tell people what to do. It cannot do that. はず describes what you expect to be true, never what someone ought to do. For advice, Japanese uses 〜たほうがいい ("had better") or 〜べき ("ought to").

早く寝たほうがいいよ。

hayaku neta hō ga ii yo

You should get to bed early. (advice — NOT 寝るはず)

この薬を飲めば、すぐ良くなるはずだ。

kono kusuri o nomeba, sugu yoku naru hazu da

If you take this medicine, you should get better soon. (a reasoned expectation about the outcome — this is はず territory)

The second sentence does use はず, and correctly — but notice it predicts an outcome ("you'll get better"), it doesn't tell anyone to do anything. That is the line: はず forecasts a result; advice frames prescribe an action.

Common Mistakes

❌ 静かはずです。

shizuka hazu desu

Incorrect — a な-adjective keeps its な before はず.

✅ 静かなはずです。

shizuka na hazu desu

It should be quiet.

❌ 彼は学生はずだ。

kare wa gakusei hazu da

Incorrect — a noun needs の before はず.

✅ 彼は学生のはずだ。

kare wa gakusei no hazu da

He should be a student.

❌ 疲れているから、早く寝るはずだ。

tsukarete iru kara, hayaku neru hazu da

Wrong sense — this reads as 'so it's expected that I'll sleep,' not advice.

✅ 疲れているから、早く寝たほうがいい。

tsukarete iru kara, hayaku neta hō ga ii

You're tired, so you'd better sleep early. (advice needs ほうがいい, not はず)

❌ 彼が犯人ないはずだ。

kare ga hannin nai hazu da

Incorrect — to say 'he couldn't be the culprit,' negate はず itself.

✅ 彼が犯人のはずがない。

kare ga hannin no hazu ga nai

There's no way he's the culprit.

Key Takeaways

はず = logical expectation from known facts: "given X, it should be Y." Always answerable to a because.
Attach it like a noun: plain verb/い-adj directly, な-adjective + な, noun + の.
来ないはず ("expected not to") ≠ 来るはずがない ("couldn't possibly") — the second denies the very possibility.
はずだった(のに) admits the expectation was betrayed: "was supposed to, but…" — a move conviction words can't make.
はず reasons from objective grounds; にちがいない states subjective conviction; neither one gives advice.

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