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.

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 ?

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 ?

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.

prohibition (you  are not allowed to) 

  • You must not walk on the grass !
  • Students must not smoke on school grounds. 

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. 


  • 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 ?

proposal / suggestion

  • Shall I open the windows? It's quite hot in here
  • Should I ask him ? 


  • 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.