This document discusses the modal verbs "must have", "can't have", and "might have" which are used to make deductions or guesses about actions that may have happened in the past based on available information. "Must have" indicates the action definitely occurred, "can't have" means it definitely did not occur, and "might have" suggests it possibly occurred but is uncertain. Examples are given for each modal verb to illustrate how they are used to deduce past actions or possibilities based on context. The document also notes these modals can be used in conditional sentences to discuss hypothetical past situations and their possible results.

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

2. 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.
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3. 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.
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Modals: can't have/ must
have / might have
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4. "must have": we believe the action
definitely happened
•"She must have left the house by now; it’s nearly
11 o'clock."
•She usually leaves her house before 11 o’clock
so I deduce that she has definitely left the
house.
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Modals: can't have/ must
have / might have
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5. "can't have": we believe the action
definitely did not happen (the
opposite of "must have").
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Modals: can't have/ must
have / might have
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• "She can’t have left the house yet because
her car is still outside.“
• She usually takes her car so I deduce that
she has definitely not left the house because
her car is outside (the opposite of "must
have").

6. "might have": we believe it's possible that the action
happened, but we don't know
•It is possible that she has gone to the shops, but
it is also possible that she has gone somewhere
else.
•"She might have gone to the shops."
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Modals: can't have/ must
have / might have
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7. "might not have": we believe it's possible
that the action did not happen, but we don't
know.
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• "He might not have finished his
exams yet."
• It is possible that he has not
finished his exams, but it is also
possible that he has finished them.

8. • "might have" / "might not have" in the third
conditional structure: to imagine the possible result
of an unreal situation in the past.
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• "If I had known about the traffic problems, I might
have taken a different route."
• The clause with might have describes the possible
result of the unreal situation described by the "if"
clause. The real situation and result: I didn’t know
about the traffic problem so I am imagining the
possibility of taking a different route if I had known.

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