3.9. Grammar. Past forms of modals for deduction.
What are the past forms of must, may, might, could and can’t? You will be
happy to hear that these forms are (more or less) regular in the past! Simply use the structure MODAL + HAVE + PAST PARTICIPLE. Modal auxiliary verbs for advice (should, ought to) have the same
structure in the past.
Students now speculate about what has happened to François, but this time using modal verbs in the past. Sample
answers: He might have gone to buy cigarettes. He could have walked home. He can’t have been at
the bar, we would have seen him., etc.