掌握英语四级考点 易混词用法辨析

相信对于很多即将参加英语四级考试的考生来说，英语学习到当前的程度，、may和might、have to和must这类最基本的单词，大家对其含义早已不陌生。然而，对于这两个均形容能够的词来说，如何正确区分，很多考生却并不了解。它们究竟有何区别，各自又该怎样使用呢？赶紧跟随汇北外网课（北京外国语大学网络课堂）老师，一起学一学吧。

may和might  

might 形容推测时，不形容时态。只是可能性比may 小。

形容允许或请求;没有把握的推测;may 放在句首，形容祝愿。

成语may/mightas well，之后跟不带to 的不定式，意为"不妨"。 If that is the case, we may as well try.

can 和be able to

can形容能力可能, 只能使用于现在式和过去式。be able to可以用于各种时态。  

They will be able to tell you the news soon.

只能使用be ableto的情况

a. 位于助动词后。

b. 情态动词后。  

c. 形容过去某时刻动作时。

d. 用于句首形容条件。  

e. 形容成功地做了某事

have to和must  

have to有人称、数、时态的变化，而must只有一种形式。但must 可用于间跟引语中形容过去的必要或义务。  

在否定结构中： don'thave to形容"不必" mustn't形容"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。

have to 形容客观的需要， must 形容说话人主观上的必要。  

My brother was very ill, so I had to call the doctor in the middleof the night.

He said that they must work hard. 他说他们必须努力工作。

must形容推测  

1) must用于肯定句中形容较有把握的推测，意为"一定"。  

2) must表对现在的状态或现在正发生的事情的推测时， must 之后通常跟系动词be 的原形或行为动词的进行式。  

He must be working in his office.

must 形容对已发生的事情的推测时，must 要跟完成式。  

I didn't hear the phone. I must have been asleep.

must形容对过去某时正发生的事情的推测，must 之后要跟不定式的完成进行式。

---Why didn't you answer my phone call?  

---Well, I must have been sleeping, so I didn't hear it.

否定推测用can't。

If Tom didn't leave here until five o'clock, he can't be home yet.