Grammar : Modals for speculating
Speculating with more certainty
He must be really busy. He started a new job.
He must not leave his house very often. He always seems to be busy.
He can’t be upset with me. I haven’t done anything to him.
Speculating with less certainty
He could be upset about something. Maybe you did something to him.
He may not like his new job. I haven’t heard how he like it.
He might be feeling stressed out. His new job may be a lot of work.