As you know, Modal Verbs are one of the most interesting features of the English language because they can be used with several purposes to mean different things.

They are interchengeable, that is, you can use the same verb to express different meanings.

For example, the verb can.

The verb can ussually expresses ability (I can speak English) but It can also be used to make a request (Can you help me with my English homework?).