Home Grammar Advanced Modals: can't have/ must have / might have

Modals: can't have/ must have / might have

Introduction

We use the modal verbs "must have", "can't have" and "might have" to make guesses or deductions about an action in the past that we believe has definitely happened, has definitely not happened or possibly happened, based on our knowledge, information or evidence, or lack of it.

We use "must have", "can't have" and "might have" in the same way as the present perfect - the action we are describing happened, or did not happen, in the past and is still true in the present.

Form

We use "must have", "can't have" and "might have" with the past participle of the main verb:


likelihood of the deduction subject modal main verb (past participle)
definite I
You
We
They
He / She / It
must have been
seen
taken
spoken
to France.
the movie.
the medicine.
to the manager.
definitely not can't have
possible might (not) have

Positive and negative forms

We use "must have" in the positive form only: we believe that the action definitely happened.

We use "can't have" in the negative form only: we believe that the action definitely did not happen (the opposite of "must have").

We can make a negative form of "might have" with "not": we believe it is possible that the action did not happen, but it is also possible that it did. "might not" can be contracted to "mightn't".

Using "by now" and "yet"

We can use "by now" with positive forms e.g.
We can use "yet" with negative forms e.g.

Question form

We don't use "must have" or "can't have" in question form because we use them for definite beliefs. We use "might have" for question forms:

Positive question form

modal subject "have" main verb (past participle)
Might I
you
we
they
he / she / it
have been to France?

Practice

Complete the sentences with "can't have", "must have" or "might (not) have" using the verb in brackets:

  • He hard for his exams because his results were very good. (study)
     
  • They the instructions because they looked confused. (not understand)
     
  • home late last night because she was very tired this morning. (get)
     
  • they to the wrong place? (go)
     

Further practice

Complete the sentences with the correct answer from a, b, c or d:



Check my answers

Further language point - "might have" with "not"

"might have not"

In addition to the most common form "might not have" (described above), it is also possible to use the form "might have not": In the second sentence, "not" is used to emphasise the negative of the main verb; in this case, "might have" describes a positive possibility that he did not send the invitations.
Negative question form

We can also use "might not have" to form questions. We can change the position of "not" to make different emphases:

modal subject "have" main verb (past participle)
Might I
you
we
they
he / she / it
not have been to France?
have not
Mightn't have



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