Use of Modal Verbs
General rules
- Modal verbs always need a main verb.
- Do not use "TO" with modal verbs.
- There is no third-person "-s" .
- Modal verbs cannot be used in all tenses. Use substitute phrases instead.
can - could
permission (ask for something)
- Can I borrow your car?
ability (you are able to do something)
- I can speak French.
- He's in good shape. He can climb to the top of the mountain.
- I could run a marathon when I was young.
possibility (if something is possible)
- This machine can't work.
request (asking for something)
- Could you call be back later ?
Subsitute form : to be able to (all tenses)
- I'm not sure if I will be able to come to the party
- She hasn't been able to practice lately
may - might
permission (to be allowed to)
- You may go out until midnight.
- You may take dad's car.
possibility (if something is possible)
- It may rain today. (There's a good chance, because there are some clouds in the sky)
- It might rain today. (Maybe, but I don't think so)
being polite
- May I ask you something ?
Subsitute form : to be allowed to (all tenses)
- Mobile phones are not allowed in class.
- She has not been allowed to go out lately.
- I don't know if I will be allowed to go to the concert.
must
obligation (you have to do something)
- At an accident, you must call an ambulance.
- You must clean up the garage after working there.
probability (if something is probable or you think assume something)
- That book must be fascinating.
- John must be a great swimmer.
Subsitute form : have to (all tenses)
- I will have to go to the dentist tomorrow morning. My tooth hurts.
- John had to work hard yesterday.
must not
prohibition (you are not allowed to)
- You must not walk on the grass !
- Students must not smoke on school grounds.
Subsitute form : not allowed to (all tenses)
- Workers are not allowed to take breaks whenever they want.
- You will not be allowed to bring you pets.
need not
something is not necessary
- You need not wash the dishes. There's a dishwasher over there.
- You needn't bring me to the airport. I can take a taxi.
Subsitute form : not have to (all tenses)
- You won't have to take the children to practice this afternoon. It's cancelled.
- Mom didn't have to organize a party.
will - would
future
- Our trip to South America will be very exhausting.
- Petrol prices will go up soon.
question / request
- Would you like some coffee ?
- Would you please take these documents to the secretariat ?
Subsitute form : want to (all tenses)
- Sam wanted to help you, but he didn't know how.
- They had always wanted to explore strange places.
shall - should - ought to
proposal / suggestion
- Shall I open the windows? It's quite hot in here
- Should I ask him ?
advice
- You should get some rest.
- You should not eat a lot before running a marathon.
- She really ought to stay at home for a couple of days.
Subsitute form : have to - supposed to (all tenses)
- Mike was supposed to go to the doctor yesterday.
- I had to close the window because it was getting cold..