How to use Modals with past tense; Modal + have + participle Modal Concept Example Would have Past unreal action If I had guessed the future, I would have taken some precautions againist what would happen. Could have Past unreal ability He could have taken the flight. May have Past unreal possibility We may have passed the math exam, but it was in Spanish. Might have Past unreal small probability You might have sold the car., if you really needed the Money. Should have Past unreal recommendation You should have listened to the teacher. Must have Past unreal assumption We