HOW TO USE 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)
Children have to go to school.
(sometimes 'have got to')
|
no obligation
I don't have to work on Sundays.
You don't have to eat anything you don't like.
|
must / mustn't
|
strong obligation (possibly based on the speaker's opinion)
I must study today.
|
negative obligation
You mustn't smoke here.
|
should / shouldn't
|
mild obligation or advice
You should save some money.
|
mild negative obligation or advice
You shouldn't smoke so much.
|
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:
Mustn't means it's not allowed, or it's a bad idea:
You mustn't eat so much chocolate, you'll be sick
Don't have to means you don't need to do something, but it's fine if
you want to do it:
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
I had to wear a school uniform when I was a child.
|
no obligation in the past
We didn't have to go to school on Saturdays.
|
must*
|
changes to 'had to'
|
-
|
should have + pp / shouldn't have + past participle
|
a past action which didn't happen: the advice / regret is
too late
You should have gone to bed earlier, now you have missed
the train.
|
a past action which didn't happen: the advice / regret is
too late
You shouldn't have taken that job., it was a bad idea.
|
* 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.
HOW TO USE THE MODALS
OF OBLIGATION
Direction: Put in “mustn’t” or “don’t / doesn’t have to”:
1. We have a lot of work tomorrow. You _______________ be
late.
2. You _______________ tell anyone what I just told you. It’s
a secret.
3. The museum is free. You _______________ pay to get in.
4. Children _______________ tell lies. It’s very naughty.
5. John’s a millionaire. He _______________ go to work.
6. I _______________ do my washing, because my mother does it
for me.
7. We _______________ rush. We’ve got plenty of time.
8. You _______________ smoke inside the school.
9. You can borrow my new dress but you _______________ get it
dirty.
10. We _______________ miss the train, it’s the last one
tonight.
11. She _______________ do this work today, because she can
do it tomorrow. 12. I _______________ clean the floor today because I cleaned
it yesterday. 13. We _______________ forget to lock all the doors before we
leave.
14. We _______________ stay in a hotel in London, we can stay
with my brother.
15. I _______________ spend too much money today. I’ve only
got a little left. 16. They _______________ get up early today, because it’s
Sunday.
17. I _______________ eat too much cake, or I’ll get fat!
18. We _______________ be late for the exam.
19. You _______________ tidy up now. I’ll do it later.
20. He _______________ cook tonight because he’s going to a
restaurant.
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