modal verb + have + past participle
Looking out of your window in the morning, you notice that all the flowers in your garden are missing.
What happened? You take a guess at it:
"A rabbit might have eaten all my flowers."
Let's take a look at that form.
might (modal) + have + eaten (past participle verb)
We use the modal might (you can also use may or could) because they show that we are not 100% sure about what happened. We are speculating about past events (guessing what we think happened). We then must use have followed by a past participle verb. We use 'must' when we have a stronger opinion about what happened.
Here are some other examples:
- Erica must ___ gone out. I can't see her.
- He looks tired. He might have ___ awake all night.
- I think James must have ___ all the milk. There's none left.
- Look at Lilly's suntan. She must have ___ somewhere hot on vactaion.
- She's late. She may have ___ the wrong road.SOURCE: http://www.ecenglish.com/learnenglish/lessons/modal-verb-have-past-participle