Genki 19-5 〜はずです

〜はずです It's supposed to be the case...

Banks must be closed, because today is Sunday.

I believe that Mary did not go anywhere yesterday.

A はずです sentence is a statement about what you believe is true or likely, that you lack conclusive evidence. It is used when situation surrounding the case and/or our common sense point naturally to such a belief. It cannot be used in a situation in which in which you are supposed to do something because of duty, responsibility, or law

You can turn it into the past tense to describe something that was supposed to have happened but which actually turned out otherwise. The part that precedes it is in the present tense.

I was supposed to receive a phone call last week, but I did not.