must表示主觀,have to表示客觀.
We must help each other.
My sister is ill, my mother has to look after her.
must的用法
1）表示主觀的義務(wù)和必要,主要用于肯定句和疑問(wèn)句,意思為“必須……,得……,要……”；由must引起的疑問(wèn)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,不許”.
We must find a good method to learn computer well.
我們必須找一個(gè)學(xué)好電腦的方法.
2）表示肯定的猜測(cè),常用于肯定句中,意思為“一定是,必然……”.
注意must表示推斷或猜測(cè)的幾種情況:
Your sister must be a doctor in this hospital.（現(xiàn)在的猜測(cè)）
你姐姐一定是這家醫(yī)院的醫(yī)生.
have to/have got to的用法
1）must表示一種主觀的需要,而have to表示一種客觀的需要,意思是“不得不”.如：
I have to attend an important meeting this afternoon.
今天下午我不得不參加一個(gè)重要的會(huì)議.
Mother is out,so I have to look after the shop.
媽媽不在家,因此我不得不照看商店.
2）have to的否定形式是don’t have to,相當(dāng)于needn’t.如：
They don’t have to buy a computer at present.
他們目前沒(méi)有必要買(mǎi)電腦.
3）have to與have got to?？梢曰Q.
have to有人稱(chēng)、數(shù)、時(shí)態(tài)的變化,而must只有一種形式.但must 可用于間接引語(yǔ)中表示過(guò)去的必要或義務(wù).
He had to look after his sister yesterday.
3） 在否定結(jié)構(gòu)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訴他.
You mustn't tell him about it. 你一定不要把這件事告訴他.
祝您學(xué)習(xí)進(jìn)步,更上一層樓!請(qǐng)記得采納,謝謝!(*^__^*) )