must 与have to 的区别与考点

phoebe陈1

must 与have to 的用法出现较多,同学们务必重视加深理解,今天安颖老师就帮同学们梳理一下这两者的考点,希望对同学们有所帮助.

A. must 的用法
情态动词must 没有时态的变化,若一定要表达”必须”的含义,在过去时中用had to,在将来时中用will/shall have to.其主要用法如下:

(1) must 意为”必须,应该”,表示义务,命令或要求,其否定形式为mustn’t, 意为不应该,不允许,表示禁止做某事,如:
You must be careful next time. 下次你一定要小心.
You mustn’t take photos here. 禁止在此拍照.
值得注意的是,对于must 开头的一般疑问句,肯定回答时要用must或have to,否定回答时用needn’t 或don’t have to,不能用mustn’t.如:
Must I finish the homework today?
No, you needn’t/don’t have to.teacheray.com
(2) must 还能表示语气较为肯定的推测,如:
must be+表语 对现在情况的肯定推测
must be+现在分词 对正在发生的情况的肯定推测
must +have+过去分词 对过去情况的肯定推测

He must be in the room. 他一定在房间里.
He must be working in the room. 他一定还在房间里工作.
You must have smoked just now. 你刚才一定吸烟了.
注意: must, should, can, may, might都可以表示推测,但可能性大小顺序为must> should> can> may >might.

B. have to 的用法
have to的意思是”必须,不得不”,当主语是第三人称单数时,要用has to,其用法如下:

(1) have to强调由于客观条件而需要做的事情,如:
It’s raining outside, and I have to stay at home.
外面在下雨,我不得不待在家里.
(2) have to 有人称和数的变化,如:
She has to work on the farm all day.
她不得不在农场工作一整天.
(3) have to 有多种时态变化.如:
I will have to ask lily instead.
我将不得不请莉莉代替了.
She had to work over 12 hours a day at that time.
那时,她不得不每天工作超过12小时.
(4) have to不能直接构成否定句或疑问句,需要借助助动词,以一般现在时为例,需要借助于do 或does,如:
What does she have to do?
她必须做什么?
You don’t have to help her with her homework.
你没必要帮她做作业.