MUST                              HAVE TO

                     Must and have to are used to express obligation or the need to do something

                     they can be used interchangeably however

 ---MUST:    (subjective obligation)  in general expresses what the speaker thinks  is necessary

                 I must stop smoking  / We must go it's already midnight  /They must work harder

 __HAVE TO:   (objective obligation)  in general suggests that somebody else has imposed the decision

                     In France you have to drive on the right / Tom has to wear a uniform at school

 ----Tenses

            1° have to can be used in all tenses:

                      Tom had to wear a uniform last year  /  Tom will have to wear a uniform next year

                      Sonia is having to wait  / she may have to come back tomorrow

            2° must can be used to talk about the present or the future

                     Tom must call his mother tomorrow

                but it can't be used to talk about the past  ( you use have to)

----Inerrogative form 

                       Do you have to leave now?    /   Must you leave right now?

----Negative form

                  The negative form of must and the negative form of have to are very different in meaning

          1° must not / mustn't   is used to say thay something is not allowed

                  Children mustn't play with fire   /   Passengers must not talk to the driver  /  Visitors mustn't smoke 

                  'must not 'can't be used to talk about the past, you use another structure

                  example: we were not allowed to park near the museum

          2° don't have to  means that there is no obligation to do something, but you can do it if you want

                  you don't have to drink alcohol, you can have a soft drink

                  she doesn't have to arrive before 9

                                                  when the lights are red you must stop

                                             you  have to stop

                                                                                       you mustn't go on 

English exercise "" created by lili73 (13-11-2007) with The test builder
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1. To drive a car you has tomustdon't have to have a driving licence.
2. While you are driving you don't have tomustmust not listen to the radio, it is not necessary.
3. You mustn'tdon't have tomust drive without wearing a seatbelt.Wear a seatbelt is compulsory for the passengers too.
4. It is dangerous to talk on a cell-phone and drive at the same time. Drivers mustshouldn'tshould do that.
5. In some countries it is illegal to use a cell-phone in a car, in those countries drivers mustn'tdon't have toshould use phones in their cars.
6. Drivers shouldmustmust not be kind to other drivers
7. But they don't have todoesn't have tomust not be kind to other drivers, it's a choice not the law.
8. In France you have tohas tomustn't to insure your car, it's the law of the country.
9. On the road you must notmustdon't have to respect the speed limit even if there isn't any radar.
10. Cyclists don't have tomustn'tmust wear a helmet but a cautious rider should have one.