It is a suffix. It is formed in this way "verb/いadjective + はず", "なadjective + はず" or "noun + のはず". It means "to be supposed to do" and it is used to emphasize an expectation that something will take place. You can use "思う" instead of "はず", but "はず" sounds more certain than "思う".
Some people are confused with the difference between "はず" and "べき".
Please click HERE, if you are interested in how to use "べき".
Please click HERE, if you are interested in the difference between "はず" and "べき".
I need to buy Japanese textbooks for the exam. Actually, I was supposed to go to the bookstore yesterday, but I ended up seeing a movie instead.
試験の為、日本語の参考書を買わなきゃ。実は昨日、本屋に行くはずだったけど、代わりに映画を見に行っちゃった。
試験の為、日本語の参考書を買わなきゃ。実は昨日、本屋に行くはずだったけど、代わりに映画を見に行っちゃった。
Meg and Amy are counting the number of guests at a party.
- Meg: Mari hasn't arrived yet. Is she coming today?
マリはまだ来ていないね。今日来るかな？ - Amy: Yes. I don't know what time, but she should be arriving soon. She told me that she had to drop by the post office on her way here.
うん。何時かは分からないけど、もうすぐ来るはずだよ。郵便局に立ち寄って、ここに来るって言っていたよ。
Meg and Amy are about to go to a park.
- Meg: It's nice and cool today, but did you put on sunscreen?
今日は涼しいけど、日焼け止めを塗った？ - Amy: Yes. It’s going to be hot today. The high is supposed to be 30 degrees.
うん。最高気温が30度だから、暑くなるはずだよ。 - Meg: Okay, I will too. And I should put on a hat!
わかった、塗るね。それに、帽子を被るべきね。