May have / may not have / must (not) have / might (not) have / can’t have

By Rosamund Place | November 6, 2012

May have / may not have / must (not) have / might (not) have / can’t have

We use these structures to talk about things

  • that are not certain to have happened, or
  • that we suppose (but don’t know for certain) have happened.

He may have gone away for the weekend. (It’s possible).
She might have fallen downstairs (= perhaps).

Note the differences between

  • may not have and can’t have and
  • had to …. and must have:

She may not have been in (= perhaps she wasn’t at home).
She can’t have been in (= she certainly wasn’t at home).

David had to leave in a hurry (= it was necessary for him to leave in haste).
David must have had to leave in a hurry (= it seems certain he had to leave in haste).

Can you tick the responses which reflect the underlying message or tone in these examples?

1. [Multiple choice]

I feel sorry for Mrs Watson. She can’t have had an easy life.

(Did you remember that ‘can’t have + past participle’ conveys certainty about a matter?)

Answers for Quiz [1].

  • 1. She has definitely been unfortunate. (correct)
  • 2. It’s possible life has treated her rather hard.

2. [Multiple choice]

They may not have grasped the seriousness of the breach of security at the bank.

(‘may have / may not have + past participle’ tells you there is some doubt or uncertainty about an event that stops anyone being dogmatic until there is information that is more definite.)

Answers for Quiz [2].

  • 1. There’s no doubt in my mind they are acting as if this is insignificant.
  • 2. Perhaps they think this sort of event is routine? (correct)

3. [Multiple choice]

Graham had to pay the builders as soon as they finished the job.

Answers for Quiz [3].

  • 1. He had no option about it – no choice at all. (correct)
  • 2. It seems very probable. They often like you to pay promptly if you can.

4. [Multiple choice]

The robbers must have been devastated when they realised the money was missing!

Answers for Quiz [4].

  • 1. I can imagine they were! (correct)
  • 2. It was necessary for them to be shocked.

5. [Multiple choice]

She can’t have been as ill as we thought for her to back at work so soon.

Answers for Quiz [5].

  • 1. Perhaps we were all mistaken.
  • 2. We definitely misread the situation. (correct)

6. [Multiple choice]

Camping in the rain must have been a very mixed experience.

(must have been – we suppose / assume, but we’re not sure about this)

Answers for Quiz [6].

  • 2. It is clear to me the weather was dreadful and wrecked their holiday.
  • 2. I imagine it was a bit disappointing. (correct)

7. [Multiple choice]

She may have left her credit card on the counter.

Answers for Quiz [7].

  • 1. It is a possibility she did so. (correct)
  • 2. It is obvious that is what she did.

8. [Multiple choice]

He can’t have told her off for parking the car right in front of our neighbours’ gate.

(To tell s.o. off = informal – to criticise s.o. eg I’m always telling her off for being so careless.)

Answers for Quiz [8].

  • 1. I hope he didn’t criticise her.
  • 2. He’s definitely not said anything. (correct)

9. [Multiple choice]

John couldn’t have had a shower yet.

Answers for Quiz [9].

  • 1. He can’t possibly have had enough time to. (correct)
  • 2. I can’t imagine he could be that quick about it.
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