[Modal auxiliaries] Progressive Forms of Modals

Let's just knock on the door lightly. Tom may be sleeping right now.

All of the lights in Ann's room are turned off. She must be sleeping right now.

Sue wasn't at home last ight when we went to visit her. She might have been studying at the library.

Joe wasn't at home last night. He has a log of exams coming up soon, and he is also working on a term paper. He must have been studying at the library.