We use can, be able to and could to show that someone
has (or doesn't have) an ability to do something.
Structure
Subject + modal verb + verb + complement
Example
I can play the piano
Permission
We use can to ask for and give permission, we use could
to ask for permission (but not to give it) and may is the
most formal way to ask for and give permission.
Structure
Modal verb + subject + verb + complement + ?
Example
May I see your passport, please?
Request
We use can, will, could, would, and may to ask for things,
make offers, invite people, and order in a restaurant.
Structure
Modal verb + subject + verb + complement + ?
Example
Would you spell your name, sir?
Offers and
Suggestions
We use the modals of suggestion could and might (want
to) to give someone ideas about possible plans or actions.
Structure
Subject + modal verb + verb + complement
Example
You might consider taking up meditation.
Obligation
We use have to and must to express something that
someone has to do
Structure
Modal verb + subject + verb + complement
Example
Seat belts must be worn by all passengers.
Necessity
We use must, have to and have got to show that
something is not optional, it is necessary
Structure
Subject + modal verb + verb + complement
Example
I must study for the test
Prohibition
We use can't and mustn't to show that something is
prohibited – it is not allowed.
Structure
Subject + modal verb + verb + complement
Example
You must not smoke in this building
Possibility
We use can, might and could to talk about present or
future possibility
Structure
Subject + modal verb + verb present. p + complement
Example
He may be coming to see us tomorrow
Criticism
Can, could, might and should/shouldn't + infinitive are
used to express criticism or disapproval with reference to
present or future time