Grade 9 Grammar Lesson 25 Must, mustn’t and needn’t

When do we use ‘must’?
When do we use ‘mustn’t’?
What do we use when we mean that it is not necessary to do something?
When do we use ‘needn’t have’?

• Must means it’s necessary that we do something.
• Mustn’t is used to mean that it’s necessary that we don’t do something as it may be dangerous.
• Needn’t is used to mean it’s not necessary we do something (but it depends on us).
• Needn’t have is used to mean we did something but later know that it was not necessary.
  

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