Modals in the Present and Past

Modals in the present and past

Generally speaking modals in the past have the following form:

  • capital + have + past participle


  • Present
    You should see a doctor.
  • Past:
    You should have seen a doctor

Except for modals that express obligation,ability and lack of necessity:

  • Obligation
    Present = I must / have to work hard. -- Past = I had to work hard.
  • Ability
    Present = I can run fast. -- Past = I could run fast when I was young.
  • Lack of necessity
    Present = You don't have to / needn't take your umbrella. -- Past = You didn't have to / didn't need to take your umbrella.
 Modals in the PresentModals in the Past
ObligationYou must / have to stop when the traffic lights are red.You had to stop.
AdviceYou should see a doctor.You should have seen a doctor
ProhibitionYou mustn't smoke here.You mustn't have smoked there.
Abilitycan run fast.could run fast. now I am old.
CertaintyHe has a Rolls Royce. He must be very rich.
He can't be American. His English is terrible.
He must have been rich. He had a big house and an expensive car.
He can't have written that poem. He was illiterate.
PermissionCan I go out?She could drive her father's car when she was only 15.
PossibilityIt may / can / could / might rain. It's cloudy.I guess it may / can / could / might have been Lacy on the phone.
Lack of necessityYou don't have to / needn't buy any tomatoes. There are plenty in the fridge.You didn't have to / didn't need to buy tomatoes.