It's likely they have left. I'm sure he came back last week. I'm certain she hadn't done it. Why didn't she call for a taxi?
They may/might/could have left. He must have come back last week. She can't have done it. She should (ought to) have called for a taxi.
PERFECT CONTINUOUS INFINITIVE
POSSIBILITY CERTAINTY: (P) CERTAINTY: (N)
Perhaps she was cooking diner. I'm certain he has been drinking. I'm sure they hadn't been working hard.
She may/might/could have been cooking dinner. He must have been drinking. They can't have been working hard.
P => POSITIVE/N => NEGATIVE 1) may/might/could have left 2) must be going 3) can't/cannot come 4) can't have paid 5) may/might/could have been trying 6) shouldn't/oughtn't to have lied 7) may/might/could be studying 8) must be 9) must have been lying 10) should/ought to have remembered