Grâce aux modaux:
might (1-20%) > may (50%) > must (80-99%) > can (100%)

Grâce à des adverbes:
perhaps, maybe, possibly, probably, certainly

Must expresses strong obligation and necessity.
We use can to talk about things which we think are usually, but not always, true.
We use may to refer to weak possibility in the present and future.
We use might most often to refer to weak possibility: