1. MUST/MUSTN´T & HAVE TO / DON’T HAVE TO
For obligation.

2. “Have to" and "must" have the same meaning in the affirmative and interrogative forms when referring to obligation. Some grammarians think that "must" is slightly stronger, but for all practical purposes, they mean the same thing: Doctors have to attend medical school for several years before they can practice medicine. Doctors must attend medical school for several years before they can practice medicine.

3. While "have to" and "must" can be used interchangeably, there are differences in usage, as Michael Swan observes in Practical English Usage (Oxford University Press, 1995): Both verbs can be used in British English to talk about obligation. (In American English, 'have to' is the normal form.) British English often makes a distinction as follows. 'Must' is used mostly to talk about the feelings and wishes of the speaker and hearer — for example, to give or ask for orders. 'Have (got) to' is used mostly to talk about obligations that come from "outside" — for example from laws, regulations, agreements and other people's orders. Compare: I must stop smoking. (I want to.) I have to stop smoking. Doctor's orders. This is a terrible party. We really must go home. This is a lovely party, but we've got to go home because of the baby-sitter. Must you wear dirty old jeans all the time? (Is it personally important for you?) Do you have to wear a tie at work? (Is there a regulation?)

4. Compare: I must stop smoking. (I want to. ) I have to stop smoking
Compare: I must stop smoking. (I want to.) I have to stop smoking. Doctor's orders. This is a terrible party. We really must go home. This is a lovely party, but we've got to go home because of the baby-sitter. Must you wear dirty old jeans all the time? (Is it personally important for you?) Do you have to wear a tie at work? (Is there a regulation?)

5. Must: obligation imposed by the speaker
Have to: obligation imposed by a situation (external obligation)
Mustn´t: Prohibition.
Don’t have to/ doesn’t have to: Lack of obligation.

6. + HAVE TO/ DON´T HAVE TO + Infinitive (V1).
Use
Examples
Notes/Problems
Use have to: for obligation
* Necessity.
You have to drive on the left.
I have to work on Saturdays.
Have to is especially used for laws, or general / external obligation
Use don’t have to: for no obligation / necessity
I don’t have to work on Saturdays.
It’s free; you don’t have to pay.
(= it’s not necessary)
NOT I mustn’t go to work
+ HAVE TO/ DON´T HAVE TO + Infinitive (V1).
You have to do your homework.
She HAS to wash the dishes.
They have to drive carefully.
You don´t have to go to the party.

7. + MUST(N´T) + Infinitive(V1).
Use
Examples
Notes/Problems
Use must: For obligation + For strong recommendation
I must remember her birthday
You must see that film
Must is especially used when the recommendation comes from the speaker. It is always stressed for strong recommendation
Use mustn't: When you want to say “not allowed”, “you can’t”
You mustn’t park here.
You mustn’t miss the concert.
structure:
+ MUST(N´T) + Infinitive(V1).
You must study every day.
They must do exercises, they are very fat.
She must pay attention to the class.

8. What do you have to do in your house?

9. Exercise: Choose the correct modal verb have to or must
I ___________ speak English well. I need it in my job.
I __________ speak English well. I love it.
I ________ get up at 5:00. I want to go fishing.
I ___________ get up at 5:00. I commute to work.
I ____________ wear a suit. It´s a formal party.
I ______________ wear a suit. I want to look good.
I _______ follow the procedures. I don´t want to be wrong.
I _________follow the procedures. It´s my duty.
I __________ earn money for the company.
I __________ earn a lot of money. I want to buy a house.
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