Modal verbs for expressing present probability (deduction)

Some modal verbs can be used to express probability in the present and past.

Must, can't: expressing present probability
Structure: modal + verb infinitive without ‘to’
must be, can’t be, must have, can’t have, etc.
We use must to express that we feel sure that something is true. The team is playing really well today; they must win.
They must be very rich – look at their big house!
We use can't to say we are sure that something is impossible. She can't be so ill – I saw her playing volleyball yesterday.
I don't believe you – it can't be true.
May, might, could: probability in the present
Structure: modal verb + verb infinitive without ‘to’
may be, might do, could go, etc.
We use may, could or might to say that it is possible that something will happen in the future or is happening now. They may be arriving tomorrow.
He might be away on holiday at the moment.
He could be away on holiday.
He might get the job.
The negative of may is may not.
The negative of might is might not.

Both may not and might not mean that it is possible that something will not happen or is not happening now.
He might not get the job.
I may not pass the exam.
I might not go to the match tomorrow.
We don’t use could not to express probability in the present and future.
I couldn’t go to the match tomorrow.

Practise this grammar: modal verbs for present probability exercise – must, can’t, could, may, might (intermediate)