Modality is about a speaker’s or a writer’s attitude towards the world. A speaker or writer can express certainty, possibility, willingness, obligation, necessity and ability by using modal words and expressions.
Speakers often have different opinions about the same thing.
These speakers are looking at the same thing.
Here are the main verbs we use to express modal meanings:
Core modal verbs: can, could, may, might, will, shall, would, should, must
Semi-modals: dare, need, ought to, used to
Other verbs with modal meanings: have (got) to, be going to and be able to