The modal verbs are complementary verbs. They are used with other verbs to express ability, obligation, possibility, permission, habits…
The differences from normal verbs:
- They are followed by the infinitive of another verb (without to-exception “ought to”)
- They don´t use “s” for the third person singular
- No auxiliary in interrogative or negative
To express ability: I can speak German
To express possibility: Tom can´t help you; you can pass your test if you study
To request permission (questions): Can I open the window?
To request possibility (questions): Can you work this afternoon?
To express ability in the past: I coudn´t sleep last Monday
To express possibility in the past: Tom couldn´t help you yesterday
To express possibility in the future: You could pass the exam if you studied.
To request permission (questions more formal): Could you pass the water, please?
To request possibility (questions more formal): Could you help me?
To express possibility: I may be home late.
To express permission (very formal): You may leave if you like.
To request permission (questions very formal): May I sit down , please?
To express possibility in the future: I will take an umbrella because it might rain later.
To express permission (more formal than may): Might I ask whether it would be a problem to resume the discussion at a later date?
To request permission (less possible than may): He might have to stay the night because of the bad weather.
To express determination: We will help you.
To ask for information: Will he go to Madrid by car or train?
To request or offer: Would you like a cup of tea?
To express a preference: I would like a beer.
Similar that “will” but very formal.
To express determination: I shall eat meat
To ask for information: Shall we go to the cinema or a restaurant?
To express a suggestion: Shall we meet at 9am?
Question tags: Let´s go to the park, shall we?
To give advice: You should stop smoking
To express obligation: Should we leave a tip?
To ask for a recommendation (questions): Should I have the meat or the chicken?
To give advice: He ought to stop smoking
To express obligation: You must brush your teeth two twice a day.
To express possibility: He must be over 90 years old.
Rhetorical questions: Must he talk so much?