はずだ / はずがない— The Logical Calculation (Should be)

• 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.

• はずがない — There's no way / Cannot possibly be
• かもしれない — Might / Maybe (possibility)
• なければいけない — The Must Loop (Obligation)
• なくてはいけない — The Formal Pressure (Must)
• なくてもいい — The Optional Exit
• はずです — Should be / Ought to (expectation)
• でしょう — Probably / Right? (conjecture)