MUST/MUSTN’T(must not)
- Used to show probability or to make a logical assumption.
“You’ve been working the whole day. You must be tired”
“She hasn’t eaten anything yet. She must be hungry”
- Used to give a command.
“You must wash your hands before cooking”
“You must call that client today”
- Used in written rules and instructions.
“Essays must be handed in by 18th May”
“You must write your answers in ink” (for example, in an exam)
- Used to give your own opinion, to say what you think is necessary, or to recommend someone to do something. (‘have to’ can also be used)
“I haven’t spoken to Susan for ages. I must/have to call her”
“My friend is a really nice person. You must/have to meet him”
- ‘Have to’ is used instead of ‘must’ to say what someone is obliged to do. The speaker is not giving his/her own opinion.
“I have to work from 8h to 14h Monday to Friday” (a fact, not an opinion)
“My brother has to travel a lot for his work” (a fact, not an opinion)
- The past of ‘must’ is ‘had to’ or ‘didn’t have to’.
“I had to wait for ages”
“I didn’t have to wait much for the bus”
- You must do something = necessity.
“Please, don’t tell anyone. You must keep it a secret”
“I must hurry if I don’t want to be late”
- You mustn’t do something = it is necessary and important that you do not do it. Prohibition.
“This is a secret. You mustn’t tell anyone”
“You mustn’t forget what I told you. It’s very important”
“Whatever you do, you mustn’t touch that switch”
“I mustn’t be late for my interview”
- Must have + past participle = used for the past.
“There’s nobody at home. They must have gone out”
“My neighbours must have been having a party last night because it was very noisy”