“Must” / “mustn’t” / “needn’t”

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Welcome to your “Must” / “Mustn’t” / “Needn’t” lesson! In this topic we talk about:
• When do we use “Must” / “Mustn’t” / “Needn’t”?
“Don’t need to”
“Needn’t have”
“Didn’t need to” and “Needn’t have”
Take the quizzes when you’re ready! If you’re having problems, use the comment box to contact our English Teachers.

When do we use “Must” / “Mustn’t” / “Needn’t”?

“You must do something” means “it is necessary that you do something”:

“Don’t eat all the sausages, you must leave some for the others!”

“The bus is leaving in a minute, we must hurry.”

“You mustn’t do something” means “it is necessary that you NOT do something”:

“You mustn’t tell her about the party.”

“We must take our time, we mustn’t rush.”

“You needn’t do something” means “you don’t have to do something, but you can if you want”:

“You can come to the picnic if you want, but you needn’t come if you don’t want to.”

“The bus leaves in three hours, we needn’t rush.”

“Don’t need to”

Instead of “needn’t” you can use “do/doesn’t need to”:

“The bus leaves in three hours, we needn’t rush.”
or
“The bus leaves in three hours, we don’t need to rush.”

“Needn’t have”

Have a look at this example:

James wanted to go for a walk, he saw big black clouds in the sky so he took his umbrella. In the end, it didn’t rain. So he said:

“I needn’t have taken my umbrella.”

“I needn’t have taken my umbrella” means “I took the umbrella, but it was not necessary”.

Let’s compare “needn’t do” and “needn’t have done”:

“It won’t rain, you needn’t take your umbrella.”
(it’s not necessary)

“It didn’t rain, you needn’t have taken your umbrella.”
(you took your umbrella, but it was not necessary)

“Didn’t need to” and “Needn’t have”

“I didn’t need to” means “it was not necessary for me to do” (and I knew this at the time):

“I didn’t need to wake up early this morning, so I didn’t.”

“I didn’t need to wake up early this morning, but I did.”

You can also use “I didn’t have to” in these situations.

“I needn’t have done something” means “I did it, but now I know it wasn’t necessary”:

“I woke up early to do some work on my computer, but there wasn’t any electricity so I needn’t have woken up to early.”

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