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Structure: modal + have + past participle
must have been, can't have gone, etc.
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We use must have to express that we feel sure that something was
true.
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They must have left early.
He must have already gone.
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We use can't have / couldn't have to say that we believe
something was impossible.
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He can't have escaped through this window. It is too small.
She can't have said that.
She couldn't have said that.
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