Modal is type of auxiliary or helping verb that is used to express ability, possibility, permission or obligation in a sentence. These modal verbs express the mode or manner of the actions indicated by the main verb. The commonly used modals are shall, should, will, would, can, could, may, might, must, ought to, used to, need and dare. Examples of modal verbs are:
Expressing: strong obligation, logical conclusion or certainty
- You must stop when the traffic lights turn red.
- He must be very tired. He’s been working all day long.
Example: You must not smoke in the hospital.
Expressing: ability, permission, possibility
- I can swim.
- Can I use your phone?
- Smoking can cause cancer.
Expressing: ability in the past, polite permission, possibility
- When I was younger I could run fast.
- Excuse me, could I just say something?
- It could rain tomorrow!
Expressing: permission, possibility, probability
- May I use your phone please?
- It may rain tomorrow!
Expressing: polite permission, possibility or probability
- Might I suggest an idea?
- I might go on holiday to Australia next year.
Expressing: lack of necessity or absence of obligation
Example: I need not buy tomatoes. There are plenty of them in the fridge.
Should/ ought to
Expressing: 50% obligation, advice, logical conclusion
- I should or ought to see a doctor.
- He should or ought to be very tired. He’s been working all day.
- You should or ought to revise your lessons.
Example: You’d better revise your lesson.