はず

はず is usually translated as should. It is a noun that communicates expectation. The closest English translation is “supposed to“. It is not should in the “Better to do” sense.  It may be a little repetitious, but since this is one of the most commonly mistaken pieces of Japanese grammar, I’m going to explain it tense by tense.

Nouns and Adjectives

Supposed to be
Noun + の + はず
な Adjective + な + はず
い Adjective + はず

はず is pretty easy with nouns and adjectives, simply meaning “supposed to be“. 

• それは猫のはずだ。。- That’s supposed to be a cat.
• ゲームは楽しいはずだ – (The) game(s) is/are supposed to be fun (will probably be). 
• 夜は静かなはずだ – Night is supposed to be quiet. 

With Present/future tense verbs

Will probably
dictionary form verb + はず

With present tense verbs, はず means “will probably“.

• 勉強するはずだ – He should (will probably) study.
• 彼は合格するはずだ – He should (will probably) pass. 
  
  

With Progressive tense

Supposed to be doing
Progressive form verb + はず

With progressive tense verbs, it means what is supposed to be happening right now. 

• 学校に行っているはずだ – He’s supposed to be going to school. (right now or in general).
• 彼は食べているはずだ – He’s supposed to be sleeping right now. 
• 彼は働いていたはずだ – He’s supposed to have been working. 

With Past tense verbs

Supposed to have
Past tense verb + はず

With past tense verbs, はず takes on a meaning of “supposed to have”

• 先生に聞いたはずだ – He’s supposed to have asked the teacher. 
• 先食べたはずだ – (someone) is supposed to have eaten. 

はずだった

Was supposed to..
plain verb + はずだった

This final variation of はず is used for when something was expected to happen/have happened, but didn’t. Changing だ to だった basically just adds “but didn’t” to the end of the sentence. 
“It was supposed to have been that..”

• 彼は合格するはずだった – He was supposed to have passed. (didn’t) (I was told he was going to pass)
• 先生から聞くはずだった – Was supposed to hear it from the teacher (didn’t)
• 先生に聞いたはずだった – He was supposed to have asked the teacher. (but didn’t).