1. Для выражения необходимости сделать что-либо употребляется модальный глагол must, отрицательная форма — mustn't:

   а) в настоящем: I must go now, 1 don't want to be late.

   b) в будущем: I must talk to him tomorrow afternoon. You mustn't forget to phone me.

2. Must употребляется для выражения нашего мнения о том, что является с нашей точки зрения важным, когда мы хотим сделать настойчивое предложение, или когда мы приглашаем кого-либо:

• You must go and see the new Spielberg film. It's great.
• This is a book that you really must read.
• You must visit us.
  

3. Must not или mustn't употребляется для выражения запрета:

• You mustn't take photos in the gallery, it's bad for the paintings.
• I mustn't forget to write a cheque for the rent today.
  

4. Has to/have to употребляется, когда мы говорим о внешней обязанности:

• Because Sandra is an au-pair, she has to get up early and help with the children's breakfast.
• Yan won't be in work today. She has to see the doctor.
  

5. Don't have to употребляется, когда действие не является обязательным:

• You don't have to do the whole exercise.
• Tomorrow is Sunday, so 1 don't have to get up early.
  

6. Had to и didn 't have to являются эквивалентами модальных глаголов must и have to в прошедшем времени:

• I had to go to London yesterday for a meeting.
• The doctor told me I had to stop smoking.
• 'Did you have to wait long for the bus?'
  

7.    Глаголы do, does или did употребляются для образования вопросов с have to и not have to:

• 'When does Dave have to go back to work?'
• 'Do you have to book a table in that restaurant?'
• 'Did everyone have to wear a uniform before?'
  

8.    В разговорном английском языке может употребляться форма have got to вместо have to:

• It's late. We've got to go.   
• Where have you got to send that letter?