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If someone says that they had been to Florida on a recent trip, which one of the following would be a correct respone:

  • That must had been fun.

  • That must have been fun.

Or is there a better way of saying this?

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closed as general reference by JSBձոգչ, Kit Z. Fox, MετάEd, jwpat7, FumbleFingers Jan 27 '12 at 3:52

This question is too basic; it can be definitively and permanently answered by a single link to a standard internet reference source designed specifically to find that type of information.If this question can be reworded to fit the rules in the help center, please edit the question.

The correct answer is must have. This is a very basic fact of English grammar, so unless you can give some specific indication of what's confusing you, this will be closed as "general reference". – JSBձոգչ Jan 27 '12 at 1:50
@JSBᾶngs: I know it's simple but there are differences when it comes to imaginary situation, past habitual situation, and future predication. I don't know which one goes where. I am the guy who is lost in tenses. – user17857 Jan 27 '12 at 3:54

After modal auxiliary verbs like must, you use the plain form of the verb. But had is the past tense/participle form, so it can't go here. Only must have is correct.

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What would we use if we were talking about an imaginary and future situations? – user17857 Jan 27 '12 at 3:52