We use the modal verbs "must have", "can't have" and "might have" to make guesses or deductions about an action in the past that we believe has definitely happened, has definitely not "Don't have to" is used to express that something is not required "Don't need to" also expresses that a particular action is not necessary "Mustn't" is used to express that Must notis much stronger than do not have to Also, must notcan only be used to talk about the present or the future To express this idea in the past, I would have to use "was Must Mustn T Can Have Don T Hav English Esl Worksheets Pdf Doc Must not have pseudo nodes