1. Basic structure
| Part of speech | Formation with ～はずだ | Example structure | Notes |
|---|---|---|---|
| V (plain) | V-普 + はずだ | 彼は来るはずだ | Present/future expectation based on reasons |
| V (past) | V-た + はずだ | 彼はもう着いたはずだ | Confident inference about something that has happened |
| Aい | Aい + はずだ | この問題は簡単なはずだ | |
| Aな | Aな + はずだ | 静かなはずだ | Keep な |
| N (noun) | N + の + はずだ | 今日は休みのはずだ | N + の + はずだ is the standard form |
| Strong negation | ～はずがない／～はずはない | そんなはずがない | Firm negation |
| Past expectation | ～はずだった（が／のに） | 雨のはずだったが、晴れた | Expectation at a point in the past |
2. Core meaning & detailed analysis
- Meaning: "Should be/was supposed to be... (according to common sense, schedule, reasons)." A higher degree of confidence than だろう/でしょう, based on clear grounds (information, timetable, logic).
- Nuance: An assertion with grounds. Using the negative ～はずがない is a strong denial because it goes against common sense/evidence.
- Tense/aspect: ～はずだった expresses "was supposed to," often with が／のに to state a contrary result.
- Combinations: Can be used with ある/いる/可能・受身・使役, etc.
3. Examples
- 今日は祝日のはずだ。
Today should be a holiday. - 彼はもう駅に着いているはずだ。
He should have arrived at the station already. - パスポートはこの引き出しにあるはずだ。
The passport should be in this drawer. - そんな高い店には学生は行かないはずだ。
Students wouldn't go to such expensive restaurants. - 彼は来るはずだったが、来なかった。
He was supposed to come, but he didn't. - それは彼のミスのはずがない。
That can't possibly be his mistake. - 雨のはずなのに、いい天気だ。
It should be raining, yet the weather is nice.
4. Usage & nuances
- The basis for inference should be clear (timetable, someone's words, experience).
- More polite in formal speech: ～はずです／～はずでしょう (softer).
- Expresses contradiction: ～はずなのに + a result contrary to expectation.
- Strong negation: ～はずがない ＞ ～ないはずだ in strength of negation.
- Avoid using it for requests/commands; this is a judgment, not volition.
5. Comparison, distinctions, and similar patterns
| Grammar pattern | Meaning | Relation/Difference | Short example |
|---|---|---|---|
| だろう／でしょう | Probably | Weaker conjecture, less basis | 彼は来るでしょう。 |
| に違いない | Certain | Strong, based on intuition/evidence; close to はずだ but with a more subjective assertive tone | 彼は犯人に違いない。 |
| べきだ | Should/ought to (duty/obligation) | Moral standard/rule, not a logical prediction | 約束は守るべきだ。 |
| わけがない | No way | Strong negation, more colloquial than ～はずがない | 彼が負けるわけがない。 |
6. Additional notes
- N + の + はずだ is the standard form; avoid N + はずだ (without の) in formal writing.
- “来るはずだった” expresses expectation at a past point in time; “来たはずだ” is a confident inference that it already happened.
- ～はずがない emphasizes denial based on common sense/what is known; stronger than ～ないはずだ.
- In polite style: ～のはずです/～のはずではありません are used in business, emails.
7. Variants & fixed phrases
- ～はずがない／～はずはない (strong negation)
- ～はずだった（が／のに） (was supposed to ... but ...)
- ～はずなのに (contrary to expectation)
- Nのはずだ／Aなはずだ／Aいはずだ／V-普はずだ (full framework)
8. Common mistakes & JLPT traps
- Incorrect linker with nouns: use Nのはずだ, not Nはずだ.
- Confused with だろう/でしょう: if the question requires "a firm basis," choose ～はずだ.
- Past confusion: 来るはずだった (past expectation) ≠ 来たはずだ (inference that it has already happened).
- Unnatural with commands/requests: × 来るはずだ、来なさい。