Must' and 'Have to' in the positive or question form are used to speak about responsibilities and obligations. Sometimes, 'must' and 'have to' can be exchanged, but the general rule is that must is used for strong personal obligations (I must do this right now!) and have to is used for responsibilities (I have to file reports every week.) 'Don't have to' and 'Mustn't' have very different meanings. 'Don't have to' is used to express that something is not required. 'Mustn't' is used to express that something is prohibited.

In general, 'must' is used in everyday situations in which something important occurs and requires an immediate action. 'Have to' is often used to discuss our .....and is commonly used to describe workplace situations. Many times, 'have to' is used in place of 'must' in informal English

Negative Form of Must

Here's what it looks like if we use Must in the negative:

 

Must  + Not +  Base form of verb          

Here are some examples:

 

People must not drink and drive.

Students must not cheat on exams.

Charles must not forget to pay his traffic ticket.

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