We use modal verbs to say how sure we are about something.
must
She must live close to where she works because she walks to work.
Must+infinitive without 'to'
might, may, could
I don't like the sound of the engine. It could be a
mechanical problem.
He may not like that shirt. I don’t think it's his style.
We might need to work through the night if we want to get this ready on time.
(might/may/could+infinitive without 'to')
can’t
It can’t be a mechanical problem. I've just taken the car to a mechanic.
(can't+infinitive without 'to')
Must :: We use must when we feel sure that something is true because there’s very strong
evidence.
Might, May or Could : We use might, may or could to say that we think something is possible but we’re not
sure.
Can`t : We use can’t when we feel sure something is not true.
'Must', 'might', 'may', 'could' and 'can't' have many more meanings and are used to
talk about different situations. Here we have looked at them used for a present
deduction.