英语have to和must的区别

must表示主观,have to表示客观.
We must help each other.
My sister is ill, my mother has to look after her.
must的用法
1）表示主观的义务和必要,主要用于肯定句和疑问句,意思为“必须……,得……,要……”；由must引起的疑问句,肯定回答要用must或have to,否定回答要用needn’t或don't have to,意思是“不必”；must的否定形式mustn't表示禁止,意思是“不能,不许”.
We must find a good method to learn computer well.
我们必须找一个学好电脑的方法.
2）表示肯定的猜测,常用于肯定句中,意思为“一定是,必然……”.
注意must表示推断或猜测的几种情况:
Your sister must be a doctor in this hospital.（现在的猜测）
你姐姐一定是这家医院的医生.
have to/have got to的用法
1）must表示一种主观的需要,而have to表示一种客观的需要,意思是“不得不”.如：
I have to attend an important meeting this afternoon.
今天下午我不得不参加一个重要的会议.
Mother is out,so I have to look after the shop.
妈妈不在家,因此我不得不照看商店.
2）have to的否定形式是don’t have to,相当于needn’t.如：
They don’t have to buy a computer at present.
他们目前没有必要买电脑.
3）have to与have got to常可以互换.
have to有人称、数、时态的变化,而must只有一种形式.但must 可用于间接引语中表示过去的必要或义务.
He had to look after his sister yesterday.
3） 在否定结构中： don't have to 表示"不必"
mustn't 表示"禁止",
You don't have to tell him about it. 你不一定要把此事告诉他.
You mustn't tell him about it. 你一定不要把这件事告诉他.
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