To say something is obligatory you can use: must - have to - have got to

To say something is forbidden you can use: mustn't - can't - not allowed to

To say that there is a choice you can use: don't have to - haven't got to - needn't

Must often expresses a personal obligation, something we tell ourselves that we have to do.

It can be used in the present & the future. It cannot be used to express the past - see panel below.

• I must go to bed early tonight, I have to start work early tomorrow.
  
  
• We must write to our customers to tell them about our new products.
  
  
• I must give up smoking !   
  
  

In all these cases we are telling ourselves what we are obliged to do. There is no external pressure.
 
Its strength depends on the degree of obligation - 'I must remember to write to my Aunt' is probably not as strong as 'I must remember my wife's birthday this year !

A common mistake  


 
Giving orders.

• Parents to teenage son - 'You must be back home by midnight !'
  
  
• Doctor to patient - You must take these tablets three times a day.

 

 The negative -  mustn't- is very strong.

• To a child "You mustn't run across the road without looking, it's very  dangerous".
  
  
• If you want to be a successful salesman you mustn't be rude to your customers.  

 

When we talk about obligations in the past we use had to, didn't have to.

To talk about prohibitions we can use couldn't, or wasn't / weren't allowed to.

 

• When I was a schoolboy in the 1960's we had to wear school uniform. Our parents had to buy the uniform from a list of approved shops, they weren't allowed to buy shirts from other shops.

We had to stand up when the teacher came into the classroom, and weren't allowed to sit down until he said we could.

Apart from the uniforms, our parents didn't have to pay for anything, as everything else, books and meals for example, was supplied by the school

We often use have to where the obligation is impersonal, external, imposed on us by a rule, a law, or the situation.

It can be used for the present, future and the past.

• John is a diabetic, he has to be very careful with his diet.
  
  
• I have to wear glasses for reading now that I'm getting older.
  
  
• We have to e-mail the report by Thursday 6.00 pm at the very latest.
  
  
• It's too late to go to the shops now, I'll have to go tomorrow.
  
  
• I had to take the car to the garage yesterday to be repaired.

 Have got to:

This is very often used in spoken English, and sounds very natural. For example:

 

I have to go to Frankfurt next week.	I've got to go to Frankfurt next week.
When does the report have to be sent ?	When has the report got to be sent ?

 

The negative - don't have to - often implies a choice.

• You don't have to learn English, but it does help you in your professional life.
  
  
• Sophie doesn't have to wear a skirt at the office, she can wear jeans if she likes.
  
  
• You don't have to take the lift, you can use the stairs if you want to keep fit !
  
  
• You haven't got to finish the report today.

 

In questions and negatives we use the auxiliary do, does, did, with the present form of the verb.

• Does she have to get a visa to go to the United States ? 
  
  
• Did you really have to fire Serge ?   
  
  
• I didn't have to help Janet with the filing, I just wanted to 
  
  
• I didn't have to take French nationality, I wanted to

 

Didn't need to - The action was not necessary, so I didn't do it.

• Because I was a UK passport holder I didn't need to get a carte de sejour in France.
  
  

Needn't have done - The action was not necessary, but I did it nevertheless.

• I needn't have rushed to the station, the train was cancelled!