Understanding はずだ
〜はずだ expresses logical expectations based on facts, plans, or reasoning (85-95% certainty). It indicates what should logically be true or happen, not personal conviction but objective reasoning.
彼は3時に来るはずだ (scheduled, that's the plan)
"He should come at 3"
これで動くはずだ (logically should work)
"This should work"
彼は知っているはずだ (it's reasonable he knows)
"He should know"
Certainty Comparison
Where はずだ fits
30-50%: かもしれない (might)
60-80%: だろう (probably)
85-95%: はずだ (should/expected) ← Based on facts
90-99%: にちがいない (must be) ← Based on conviction
はずだ = logical expectation
にちがいない = personal conviction
Formation
Plain form + はずだ
Verbs:
来る → 来るはずだ
来た → 来たはずだ
来ない → 来ないはずだ
い-adjectives:
高い → 高いはずだ
高くない → 高くないはずだ
な-adjectives:
便利 → 便利なはずだ
(Use な before はずだ)
Nouns:
学生 → 学生のはずだ
(Use の before はずだ)
Basis for はずだ
Based on plans/schedules
会議は10時に始まるはずです
"The meeting should start at 10"
Based on: Official schedule
Not personal opinion
Based on prior information
彼は医者のはずだ
"He should be a doctor"
Based on: What you were told
Not speculation
Based on logic/common sense
勉強したから、できるはずだ
"I studied, so I should be able to do it"
Based on: Cause and effect logic
Reasonable expectation
Based on rules/procedures
この手順で正しいはずです
"This procedure should be correct"
Based on: Established rules
Standard practice
はずだ vs にちがいない
はずだ - Objective expectation
彼は来るはずだ
"He should come" (the plan says so)
Based on:
- Facts
- Plans
- Logic
- Information
Objective basis
にちがいない - Personal conviction
彼は来るにちがいない
"He must come" (I'm very sure)
Based on:
- Strong belief
- Evidence
- Intuition
Personal certainty
Example comparison
Situation: Train schedule says train comes at 3pm
はずだ: 電車は3時に来るはずだ
"The train should come at 3" (according to schedule)
にちがいない: 電車は3時に来るにちがいない
"The train must come at 3" (I'm personally certain)
はずだ is more neutral, factual
はずがない (Can't be/Shouldn't be)
Strong denial based on logic
彼が嘘をつくはずがない
"There's no way he would lie" (it's not logical)
そんな簡単なはずがない
"It can't be that easy" (logically shouldn't be)
Based on what's reasonable
Logical impossibility
はずだった (Was supposed to)
Unfulfilled expectations
彼は来るはずだった
"He was supposed to come" (but didn't)
簡単なはずだったのに
"It was supposed to be easy, but..."
Shows disappointment
Reality differed from expectation
Polite Forms
はずだ (plain)
来るはずだ
"Should come"
はずです (polite)
来るはずです
"Should come"
Standard polite
はずでございます (very polite)
そのはずでございます
"That should be so"
Formal, humble
Common Patterns
～はずなのに (Should...but)
できるはずなのに、できない
"I should be able to do it, but I can't"
簡単なはずなのに、難しい
"It should be easy, but it's difficult"
Reality contradicts expectation
～はずがない (Can't be)
忘れるはずがない
"There's no way I'd forget"
間違っているはずがない
"It can't be wrong"
Logical impossibility
～はずだ (Verification)
これで正しいはずです
"This should be correct"
そのはずだよ
"That should be so"
Confirming expectations
Negative Expectations
～ないはずだ (Shouldn't)
彼は来ないはずだ
"He shouldn't come" (not in the plan)
高くないはずです
"It shouldn't be expensive" (based on info)
Negative logical expectation
Past Expectations
Should have done
彼は昨日来たはずだ
"He should have come yesterday"
ここにあったはずなのに
"It should have been here"
Past logical expectation
In Questions
Seeking confirmation
そうですよね？そのはずですよね？
"Right? That should be so, right?"
彼は知っているはずですが
"He should know, but..."
Checking expectations
はずだ for Self-Reminder
Checking your memory
ここに置いたはずなんだけど...
"I should have put it here..."
言ったはずだけどな
"I should have told you..."
Questioning memory
Expressing Confusion
When reality doesn't match
動くはずなのに、動かない
"It should work, but it doesn't"
簡単なはずなのに、分からない
"It should be easy, but I don't understand"
Puzzlement
はず alone (The expectation)
As a noun
そのはずだ
"That should be the case"
そのはずです
"That's what's expected"
そのはずはない
"That can't be right"
Nominalized form
Formal/Written Usage
In documentation
この方法で問題は解決されるはずである
"This method should solve the problem"
結果は来週発表されるはずです
"Results should be announced next week"
Professional contexts
Common Situations
Schedules and appointments
会議は2時に始まるはずです
"The meeting should start at 2"
彼は今日休むはずだ
"He should be off today"
Based on schedule
Abilities and knowledge
彼は医者だから、知っているはずだ
"He's a doctor, so he should know"
勉強したから、できるはずです
"I studied, so I should be able to do it"
Logical expectation from facts
Location and existence
ここにあるはずなんだけど
"It should be here"
図書館にいるはずです
"He should be at the library"
Based on information
Comparing with だろう
はずだ - Based on facts
時刻表によると、電車は3時に来るはずだ
"According to the timetable, the train should come at 3"
Objective basis
だろう - Estimation
たぶん3時頃に来るだろう
"It'll probably come around 3"
Subjective guess
Practice Sentences
Basic
彼は今日来るはずです
"He should come today"
これで動くはずだ
"This should work"
知っているはずです
"You should know"
Intermediate
説明書を読んだから、できるはずです。
でも、なぜかうまくいかない
"I read the manual, so I should be able to do it.
But for some reason it's not going well"
彼は今ごろ家に着いたはずだ。
連絡がないのが心配だ
"He should have arrived home by now.
I'm worried there's no contact"
ここに鍵を置いたはずなのに、
どこにも見当たらない
"I should have put the key here,
but I can't find it anywhere"
Advanced
計算が正しければ、この答えで
合っているはずだ。しかし、何か
違和感がある。もう一度確認してみよう。
念のため、別の方法でも計算するべきだ。
"If the calculation is correct, this answer
should be right. However, something
feels off. Let's check again.
Just to be safe, we should calculate using a different method too."
彼の性格を考えれば、約束を破るはずがない。
何か問題があったにちがいない。事故に
遭ったのではないかと心配だ。すぐに
連絡を取ったほうがいいだろう。
"Considering his character, there's no way he'd break a promise.
There must have been some problem. I'm worried
he might have had an accident. We should probably
contact him right away."
Related Grammar Points
- 〜にちがいない - Must be (strong conviction)
- 〜だろう - Probably (estimation)
- 〜はずがない - Can't be (logical impossibility)
- 〜はずだった - Was supposed to
- 〜かもしれない - Might be
- Logical expectations - Expressing should