Grammar · Modal Verbs
Modal Verbs of Speculation (Must Have, Might Have)
Must have, might have, can’t have: how to make a guess about the past and show how sure you are. Learn it with the film Now You See Me.
Grammar › Modal Verbs › Modal Verbs of Speculation (Must Have, Might Have)
The rule in one sentenceTo guess about the past, use a modal + have + past participle: must have / can’t have when the evidence makes you almost sure, and might have / could have when it is only one possibility.
About the film
Now You See Me is a 2013 heist thriller about four talented street magicians who are brought together by a mysterious stranger and become a stage act called the Four Horsemen. During their first big show in Las Vegas, money from a bank in Paris seems to rain down on the audience. The FBI agent Dylan Rhodes is sure the magicians must have planned the whole thing, but nobody can work out how they might have done it.
What does it do?
Sometimes we don’t know exactly what happened, but we have clues. This structure lets you turn those clues into a guess about the past, and the modal you choose tells your listener how confident you are. A magic show is the perfect place to practise, because the audience spends the whole evening guessing.
When the evidence is strong, you sound almost certain with must have, or can’t have for the negative. When there are several possible explanations, you keep the guess open with might have, may have or could have.
The first two tiles sound like a detective who has seen the proof. The last two are ideas that might be true or might not. Notice that the grammar after the modal never changes: have + past participle.
In speech, have is usually shortened. Say it this way, but always write the full form or the ’ve form:
The magician knew her name. He must have read it somewhere. (strong clue, almost sure)
The magician knew her name. He might have guessed it. (just one idea)
The event is the same. Only the modal changes, and with it, how sure the speaker sounds.
Visual guide
Teacher Teddy’s illustrated guide to this rule is being drawn — the full swipe-through infographic will appear here soon.
How to make it
must have / can’t have — almost sure
The audience must have been amazed by the trick.
Atlas can’t have known her secret before the show.
Use can’t have, not mustn’t have, for a sure “no”.Can they really have robbed a bank from Las Vegas?
In questions, can or could usually starts the guess.might have / could have — only possible
Henley might have hidden something in her sleeve.
The agents might not have seen every part of the show.
might not have = perhaps it did not happenCould Merritt have hypnotised the man?
Could + subject + have + past participleWhen to use each one
must have / can’t have
might have / could have
Words that help: sure or not sure?
The words around the guess often show how strong the evidence is.
must have / can’t have → almost sure
might have / could have → only possible
Common mistakes
❌ The Horsemen must planned the show for a long time.
✅ The Horsemen must have planned the show for a long time.
A guess about the past needs have after the modal.
❌ He mustn’t have seen the camera, or he would have hidden.
✅ He can’t have seen the camera, or he would have hidden.
For a sure “no” about the past, use can’t have, not mustn’t have.
❌ They might have use a hidden door.
✅ They might have used a hidden door.
After have, use the past participle, not the base form.
❌ Henley could has escaped through the floor.
✅ Henley could have escaped through the floor.
The modal is followed by have for every person, never has.
One more thing
This part is a little harder. You can come back to it later.
Could have can look back at a missed chance, not a guess. You could have warned me usually means you had the chance but didn’t take it, and it often carries a note of complaint. Also, when you want to speculate about an action that was in progress, use have been + -ing.
✅ The audience could have left early, but nobody wanted to. (a chance they didn’t take)
✅ The agents must have been watching the magicians for days. (an action in progress)
Practice: choose the right modal
Eight questions. Choose one answer. You get the answer, and why.
1. The money is real. It ___ come from a real bank.
The proof is strong, so the speaker is almost sure: must have.
2. I’m not sure how he did it. He ___ used a mirror.
I’m not sure shows it is only one idea: might have.
3. They were on stage all night. They ___ been in Paris.
A sure “no” about the past is can’t have.
4. The magician ___ practised this trick for years.
A guess about the past needs have after the modal.
5. Henley ___ hidden the card in her glove, or in her hair.
There are two possible places, so it is only possible: could have.
6. The agents ___ missed something. Nobody knows yet.
Nobody knows yet, so keep the guess open: may have.
7. Merritt ___ known the man’s secret. He only met him a minute ago.
He only met him a minute ago, so it seems impossible: can’t have.
8. The crowd ___ loved the show. They were cheering for ages.
Cheering for ages is strong evidence: must have.
Your turn
Choose one ending. Then listen to your sentence.
Every sentence here is correct. Pick the one that sounds true for you. Say it out loud too!
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