1. MODAL VERBS
DEDUCTION

2. MUST We use MUST to say that you believe that something is certain:
You’ve been travelling all day, you must be tired.
I’m sure he gave me his telephone number. I must have it somewhere

3. CAN’T
We use CAN’T to say that you believe that something is not possible:
She can’t be her mother, she is too young.
You’ve just had lunch. You can’t be hungry!

4. MAY/MIGHT We use MAY or MIGHT to say that something is a possibility:
John is not at work today. He may/might be ill.
‘Where is Tom?’ ‘I don’t know. Ask Mary, she may/might know’
Peter is not at home. He may/might be in his office

5. PAST We use the following structures: MUST HAVE + PAST PARTICIPLE
He doesn’t find his keys. He must have left them in the office (he’s always doing that!)
CAN’T HAVE + PAST PARTICIPLE
She can’t have left her boyfriend. She was madly in love with him!
MAY/MIGHT HAVE + PAST PARTICIPLE
‘Kate didn’t answer the phone yesterday’ ‘Don’t worry, she may/might have been asleep’