(something) must have (done something)

You can make guesses about things that happened in the past with the phrase "must have ___":

A: Where are Deanna and Jun?

B: They must have left already.

People use "must have" when they have a pretty strong reason or evidence for thinking something. You don't use "must have" when you're just making a guess about something you don't know about.

This phrase appears in these lessons: