English grammar: modal verbs for present probability: 'must', 'can't', 'may', 'might', 'could'

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

Must / can't - to express probability in the present
Structure: modal + infinitive without to must be, must have, can't go, etc.
We use must to express that we feel sure that something is true.	They are really good, they must win. They must be very rich. Look at the house.
We use can't to say we are sure that something is impossible.	She can't be ill. I've just seen her in the shop and she looked fine. It can't be true. I don't believe it.

May / might / could - to express probability in the present
Structure: modal + infinitive without to may be, might do, could go, etc.
We use may or could or might to say that it is possible that something will happen or is happening.	They may be arriving tomorrow. He might be away on holiday. He could be away on holiday. He might be offered the job.
The negative of may is may not. The negative of might is might not. They both mean that it is possible that something will not happen or is not happening. We DO NOT use could not to express probability.	He might not be offered the job. I may not pass the exam. I might not go to the match tomorrow. I ~~could not~~ go to the match tomorrow.

Modal verbs for present probability