はずだ / はずがない — The Logical Calculation (Should be)
Expresses a strong logical conviction based on evidence or calculation. It is not just a guess (like でしょう), but a conclusion that "if things follow their normal course, then X must be true."
Structure
[Plain form / Noun + の / な-adj + な] + はずだ / はずがない
Examples
彼は今日、休みのはずです。
Kare wa kyō, yasumi no hazu desu.
He should be off work today (based on his schedule).
Noun + の + はず = should be [noun], by logic
そんなはずはありません。
Sonna hazu wa arimasen.
That simply cannot be the case (logical impossibility).
はずがない / はずはありません = it is impossible that...
昨日送ったから、今日届くはずだ。
Kinō okutta kara, kyō todoku hazu da.
I sent it yesterday, so it should arrive today.
Cause (送った) → logical expectation (届くはず)
• Calculation over Guessing: Use はず when you have a specific reason (logic, schedule, facts). For a simple feeling, use でしょう. • The の Particle: When attaching to a noun, you must add の: 学生のはず (should be a student). For な-adjectives use な: 静かなはず. • Deep Negation: はずがない is the strongest way to say "no way that's possible" in Japanese logic.
Commonly confused with
The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones はずだ is tested against.
vs でしょう
でしょう is a soft guess or bid for agreement; はずだ is a firm logical conclusion grounded in specific evidence or reasoning.
vs べきだ
べきだ = "should" in the sense of obligation/what is right to do; はずだ = "should" in the sense of logical expectation (what ought to be the case).
vs に違いない
に違いない ("must be, no doubt") expresses the speaker's strong subjective certainty; はずだ bases the conclusion on objective grounds/reasoning.
More modal expressions
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