The modals in use are will, may, might, can, and could. Expressions: It is probable, it is likely, it is possible, certainly. The functions: certainty, probability, possibility, and remote possibility.
I am using a textbook to teach grammar, and this grammar lesson is presented in a few examples followed by two tasks. I also have answers to these tasks which may be correct. It is not clear for me how to express probability correctly. In fact, even the case with the other functions of modals has become confusing when I discussed this with other colleagues. I need a clear-cut answer that gives accurate rules on when to use what and how to clearly and correctly present it to the learners.