This document discusses different modal verbs used to express degrees of certainty in English. Must is used to express something is surely true. May, might, could are used to express something is possibly true. Can't is used to express something is surely not true. Examples of sentences using each modal verb are provided.

1. Grammar

2. MUST
We use must to express that we feel sure that something is true.
Structure: modal + infinitive without to
must be, must have, etc.
Come inside and get warm – you must be
freezing out there.
They are really good, they must win.
.
They must be very rich. Look at the house.

3. MAY/MIGHT
We use may or could or might to say that it is possible that something will
happen or is happening.
Structure: modal + infinitive without to
may be, might do, etc.
They may be arriving tomorrow.
He might be away on holiday.
He might be offered the job.

4. CAN’T
We use can't to say we are sure that something is impossible.
Structure: modal + infinitive without to
Can't go, etc.
She can't be ill. I've just seen her
in the supermarket and she looked fine.
It can't be true. I don't believe it.

5. • They be out. They aren't answering the phone.
must
• Helen can’t
be at secondary school. She's only eight.
might
• Jack be on holiday. I haven't seen him for a week.
can’t
• Oliver hasn't called. He have my number.
• They be rich - they've got three houses!
must
can’t
• She be awake yet. It's only seven o'clock.