The document discusses the use of modal verbs in the past tense, including must have, may/might/could have, can't have, should have, and needn't have/didn't have to. It provides examples of how each modal construction is used to express meanings like certainty, possibility, logical deduction, regret, and lack of necessity regarding past events.

1. MODALS INTHE PAST
+Perfect infinitive (have + past participle)

2. MUST + HAVE +PAST PARTICIPLE
• It is used to express
certainty
• You must have been delighted when you heard you’d won the
lottery.
• The thieves must have come in through the window. Look – it’s still
open.
• Oh no! Where’s my car? Someone must have stolen it!

3. MAY/MIGHT/COULD+
HAVE + PAST PARTICIPLE
• They are used to express possibility, could is ‘more
possible’ than may or might
• The thieves might have escaped by car but we can’t be sure.
• He should be here by now. He may have been delayed by a traffic jam or something.
• I can’t find my purse. I could have left it in the supermarket but I just don’t know.

4. CAN’T + HAVE+ PAST PARTICIPLE
• It is used to express a
logical deduction
• I thought I saw John in town this morning but it can’t have been him
– he’s in Greece this week.
• I can’t have left it in the supermarket – I had it on the bus on the
way home.
• You can’t have read the instructions properly. They’re perfectly
clear.

5. YOU SHOULD HAVE +
Past Participle
It is used to express
past regrets, something
which never happened or it
might.
You shouldn’t have been so
rude. It was very mean of
you.

6. NEEDN’T
HAVE/DIDN’T
HAVETO
It is used to express lack of
necessity.
John paid for me yesterday at
dinner but he needn’t have
paid since we are not engaged.