Must In Questions And Negatives
- Must I clean all the windows? (= Do you think that I should clean all the windows?)
- Must we wait for his approval? (= Do you think that we should wait for his approval?)
- Must we buy a new car? (= Do you think that we should buy a new car?)
It is also possible to express these ideas with have to.
- Do I have to clean all the windows?
- Do we have to wait for his approval?
- Do we have to buy a new car?
Negatives
Must not / mustn’t is used to prohibit – to say that things must not be done.
- You must not take this medicine without a prescription.
- She must not reveal this secret to anybody.
- He must not leave the country without obtaining the necessary permission.
- She must not discontinue her studies.
Note that must not / mustn’t is used to prohibit. It is not used to say that things are unnecessary. That idea is expressed with do not need to or do not have to.
- You don’t need to get a visa to go to Nepal. (NOT You must not get a visa to go to Nepal.)
Compare:
- You don’t have to work on Sundays. (= You have no obligation to work on Sundays – it is not necessary.)
- You must not work on Sundays. (= You are prohibited from working on Sundays.)
- You don’t have to wait. (= It is not necessary for you to wait.)
- You must not wait. (= You are prohibited from waiting.)
