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must (used for a personal opinion)
He must be crazy.
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can't
He can't be crazy.
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must / have to / has to (used for obligation)
You must arrive by 8 o'clock.
You have to arrive by 8 o'clock.
|
don't have to / needn't = something is not necessary
You don't have to arrive by 8 o'clock.
You needn't arrive by 8 o'clock.
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can (used for ability)
I can play the guitar.
|
can't / cannot
I can't play the guitar.
|
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can (used for possibility)
You can smoke here.
|
can't / cannot / mustn't
You can't smoke here.
You mustn't smoke here.
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