May have Might have Could have+ Past participle Must have Had to have
Speculations or Possibilities About a Past Situation May have, might have, could have + past participle To express speculations or possibilities Usually based on facts that we don’t have Tom’s absent today. Where is he? I have no idea. He may be at work. He could have an appointment. He may be at work.
Conclusions Must have and had to have + past participle Use when you are almost certain about your conclusions How was the weather? Well, Tom’s hair and shirt were wet when he came in. It must have been (had to have been) raining. My husband looked tired after work. He must have had (had to have had) a hard day.
Negative Statements Do not use HAD TO HAVE in negative statements to draw conclusions. The must not have been very easy to move. NOT They didn’t have to have been easy to move.
Questions Use COULD HAVE in questions about possibility. Do not use MAY HAVE/MIGHT HAVE. Could the students have cheated?
Short Answers Use BEEN in short answers to questions that include a form of BE. Could Eric HAVE BEEN wrong? Yes, he could have been. Use only the MODAL + HAVE in short answers to questions with other verbs. Did he cheat on the test? Yes, he MUST HAVE.