情态动词：could的用法详解

could的用法：

1.表示过去的能力

The little boy could speak English when he was four.这个小男孩四岁时就会说英语了。

He couldn't solve the problem though he thought it over and over again.这个问题他想了一遍又一遍，但还是解决不了。

2.表示可能性

could既可表过去的可能性，也可表现在的可能性，语气比can表示的可能性要弱。could还可以表示将来的可能性。

If you smoke in the wood, you could start a fire.如果你在树林里抽烟，你可能会引起火灾的。

It could be better to go with him yesterday.昨天和他一起去可能会更好。

This could be the best way to solve the problem now.这可能是目前解决问题的最好办法。

could have done的用法：

①could have done表示对过去所发生事情的推测，一般用于否定句和疑问句。

He couldn't have left for Beijing, for I saw him just now.他不可能去北京了，因为我刚才看见他了。

Could he have told his mother the truth?他会把真相告诉他母亲吗?

②could have done本来可以，表示未曾实现的可能性或虚拟语气。表示过去可能做某事，但没有实现。

You could have passed the exam, but you didn't study hard.你本来可以通过考试的，但你不努力学习。

If you had come yesterday, you could have seen the movie star.如果你昨天来的话，你就能看到那位电影明星了。

3.表示请求

could表示请求，比can更加委婉客气。但回答时需用can, 表示语气的肯定。

Could you tell me the way to the nearest hospital?你能告诉我最近的医院怎么走吗?

--Could you please help me to solve the math problem?你能帮我解出这道数学题吗?

--Yes, I can.

4.表示怀疑

could表示怀疑，惊异等，用于否定句和疑问句中，语气比can委婉。

I think the news couldn't be true.我认为这个消息不可能是真的。

Could he be serious?他会是认真的吗?

How could you tell him the truth?你怎么能告诉他真相?

5.can和could的否定形式构成的习惯搭配

①cannot help doing禁不住做某事

Hearing the news, he couldn't help crying.听到这个消息，他禁不住哭了。

②cannot (help) but do sth不得不做某事

We couldn't but wait for the news at home.我们不得不在家里等待消息。

③cannot wait to do sth迫不及待地做某事

I can't wait to see you again.我等不及再见到你了。

④cannot...too无论如何也不过分

You can't be too careful when you cross the street.你过马路时越小心越好。

⑤cannot...enough无论如何也不过分

I can't thank you enough.我对你感激不尽。