Modal Verbs of Obligation
Click here for all the exercises about modal verbs
We can use have to + infinitive, must + infinitive and should + infinitive to express obligation (something you have to do).
|have to /
don't have to
|strong obligation (possibly from outside)
|must / mustn't||strong obligation (possibly based on the speaker's opinion)
|should / shouldn't||mild obligation or advice
||mild negative obligation or advice
Be careful about the difference between mustn't and don't have to!
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).
|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. See modals of probabilty for more information.