This document discusses how to use modal verbs to make deductions about past events, including must, can't, may, might/could, and should. It provides examples for each modal verb to express certainty, impossibility, possibility, few possibilities, and regret about past events. Common structures include modal verb + have + past participle.

1. PERFECT MODALS:
PAST DEDUCTIONS
We can use some modal verbs to make deductions about past events:
MODAL VERB + HAVE + PARTICIPLE
• MUST: certainty or logical deductions:
 John looks sad, so he must have got a bad result in the exam.
 CAN´T: certainty about an impossibility in the past:
 They can´t have lost that match. They´re the best team in the
championship.
 MAY: to express a possibility in the past (lots of possibilities):
 Terry may have arrived home. Let´s pone him!

2.  MIGHT/COULD: few possibilities that something happened in the past
or to suggest a different alternative:
 I could have been a good athlete, but I retired from competition
when I was 15.
 You might have chosen a different dress for the party if you
didn´t like this one.
 SHOULD: to regret something that happened in the past (you wish it
hadn´t happened):
 You should have gone to the concert last night. It was amazing!.
 We missed the train. We shouldn´t have left home so late.