はず

はず functions grammatically as a noun, meaning it follows standard noun modification rules. Because it is a noun, it typically takes a copula like だ, です, or だった at the end of a sentence, though this copula is frequently dropped in casual speech (e.g., 彼（かれ）は来（く）るはず). While overwhelmingly written in hiragana, you may occasionally encounter its kanji form, 筈, in novels or formal writing. It is primarily used to express a strong expectation based on objective reasoning.

Key Usage Rules:

• Verbs: Use the plain form (Present/Past/Negative). For example: 来る（くる）はず (should come) or 来ない（こない）はず (should not come).
• い-Adjectives: Use the plain form (present, past, or negative). For example: 美味しい（おいしい）はず (should be delicious), 美味しかった（おいしかった）はず (should have been delicious), or 美味しくない（おいしくない）はず (should not be delicious).
• な-Adjectives: Add な (present), だった (past), or じゃない (negative) before はず. For example: 綺麗（きれい）なはず (should be clean/pretty), 綺麗（きれい）だったはず (should have been clean/pretty), or 綺麗（きれい）じゃないはず (should not be clean/pretty).
• Nouns: Add の (present), だった (past), or じゃない (negative) before はず. For example: 先生（せんせい）のはず (should be a teacher), 先生（せんせい）だったはず (should have been a teacher), or 先生（せんせい）じゃないはず (should not be a teacher).

Important Restrictions:
はず is generally not used for the speaker's own intentional future actions. For example, you would not say "I should go to the store" using はず if it is your own plan; instead, use つもり or 予定. It can only be used for oneself when viewing the situation objectively (e.g., "Based on the schedule, I should arrive at 5:00").

Common Variations & Usages:

• はずだった: Used when something was expected to happen but the actual outcome was different. It is frequently paired with のに (e.g., はずだったのに or はずなのに) to strongly express dissatisfaction, regret, or surprise.
• 〜ないはず: The standard negative form meaning 'should not' or 'I expect that (something) won't happen'.
• はずがない: A much stronger negative expectation meaning 'it is impossible that'.
• 'No Wonder' (Realization): はず is also commonly used to express that something makes perfect sense now that you know the reason. This usage is almost always paired with the adverb どうりで (e.g., どうりで寒い（さむい）はずだ - No wonder it is cold!).
• With Adverbs: はず is frequently paired with adverbs like きっと (surely) or たぶん (probably) to emphasize the degree of certainty.

Nuance:
If you use はず for an expectation and the outcome is different, you would feel surprised or confused because your logical premise was sound. It is different from 〜べき, which is about moral obligation ('you should do your homework'), whereas はず is about logical probability ('the homework should be finished by now').