use of (should, may, can) for new english learners in 2011

[Xpert]

Modal Form Basics (should, may, can)

Modals are verbs that modify other verbs. The most common modals are:
Can
Should
Must
Note that all subjects take the same form of the modal.
Positive
Subject + Modal + Base Form of Verb + Objects
Examples: He can play the piano.
I must leave soon.
Negative
Subject + Modal + Not + Base Form of Verb + Objects
Examples They can't visit next week.
You shouldn't go to that film.
Question
Modal + Subject + Base Form of Verb + Objects
Examples Can you help me?
What should I do?
Giving Advice with Should 'Should' is used when asking for or giving advice. It is also used when asking for suggestions.
Examples I think you should see a doctor.
What type of job should I get?
Expressing Ability with Can 'Can' is used to speak abilities.
Examples He can speak Japanese.
Can you play golf?
Asking for Permission with May 'May' is used to ask for permission.
Examples May I help you?
May I visit you this afternoon?

NOTE: In spoken English, 'Can I ...?' is often used instead of 'May I ...?'