Modal Verbs of Obligation
We can use have to + infinitive, must + infinitive and should + infinitive to express obligation (something you have to do).Present | Positive | Negative |
have to / don’t have to |
strong obligation (possibly from outside)
|
no obligation
|
must / mustn’t | strong obligation (possibly based on the speaker’s opinion)
|
negative obligation
|
should / shouldn’t | mild obligation or advice
|
mild negative obligation or advice
|
Mustn't means it's not allowed, or it's a bad idea:
- You mustn't eat so much chocolate, you'll be sick
- I don't have to get up early at the weekend
(of course, if I want to get up early, that's fine, but I can stay in bed if I want
Past | Positive | Negative |
had to / didn’t have to | obligation in the past
|
no obligation in the past
|
must* | changes to 'had to' | - |
should have + pp / shouldn’t have + pp | a past action which didn’t happen: the advice / regret is too late
|
a past action which didn’t happen: the advice / regret is too late
|
* Remember ‘must have done’ is a modal verb of deduction or speculation, not obligation in the past. For example: Julie must have left. Her coat’s not here.
EXERCISE ONE
EXERCISE TWO
EXERCISE THREE
Should, Ought to BY WWW.ECENGLISH.COM
For giving advice or expressing a conclusion 'should' and 'ought to' are interchangeable. They are used to express the same ideas.You should/ought to stop smoking. He has been working on the project all week. He should/ought to be ready by this evening.
Should is also used in hypothetical situations: Should anyone call, take a message.
Call me should you need any help.
Should is used with 'imagine', 'say' and 'think' to give a tentative opinion: I should think it will take us an hour to drive to Rome.
Need
'Need' expresses necessity: You need to exercise more often. You're putting on weight.You don't need to wear a tie if you don't want to.
Needn't have/Didn't need to
'Needn't have' is used to talk about an action that was done but was unnecessary. We needn't have rushed to the airport. The flight was delayed.I needn't have brought an umbrella. It didn't rain.
‘Didn't need to' is used to talk about an action that wasn’t done because it was not necessary. I didn't need to call Mike. I met him in the street.
EXERCISE ONE
EXERCISE TWO
EXERCISE THREE