区别辨析 can, could 与 be able to （表示“能力”）

(1) can通常用来表示现在的、一般的能力(什么时候想做就能做某事的能力)。

Look! I can do it! I can do it!
看！我会做了！我会做了！
You can certainly cook, even if you can't do anything else.
即便你其他什么事也不会做，你肯定会做饭。

(2) be able to也可用于此意，但不那么常用。

You are certainly able to cook, even if you can't do anything else.
即便你其他什么事也不会做，你当然会做饭。

①在表示未来的能力时，通常用will be able to。

I'll be able to speak German in another few months.(不常说：I can...)
再过几个月，我就能讲德语了。
One day people will be able to run a kilometre in two minutes.
总有一天，人类将能在两分钟里跑完一千米。

②当人们就未来的能力做出目前的决定时，常常用can表示。

We are too busy today, but we can repair your car tomorrow.
今天太忙，但明天我们就能修你的车了。
Can you come to a party on Saturday?
星期六你能来参加一个晚会吗？

(3) could用于表示过去某人“一般的能力”，这时，也可用was/were able to来表示。

She could sing/was able to sing like an angel when she was a kid of ten years.
当她还是个10岁的小孩时，她就能像一个天使似的唱歌了。
His father could speak ten languages.
他父亲会讲10种语言。

①could不用来表示过去的、具体某一次的能力，这时我们常用was/were able to, managed to或succeeded in (doing) sth.来表示。

How many eggs were you able to get? (不用：...could you get?)
你弄到了多少鸡蛋？
After six hours' climbing, we succeeded in reaching/were able to reach the top of the mountain. (不用：we could reach...)
经过六个小时的攀登，我们登上了山顶。
He was a terrific liar: he could make anybody believe him.
(一般的能力)
他是个大骗子：他能让任何人相信他。
I talked for a long time, and in the end I managed to make her believe me.
我谈了很长时间，最后我设法使她相信了我。(一次具体的能力，不可用could)

②但否定式couldn't则既可用来表示过去的一般的能力，也可用来表示一次具体的能力。

When I was younger, I couldn't decide what I wanted to do.
当我更年轻时，我不能决定我想要做什么。
My friend Tom got so drunk last night that he couldn't even find the front door of his house.
我的朋友汤姆昨晚喝得大醉，连自己家的前门都找不着了。

③could可用在带有条件的句子中，意思是“就会……；就能……(would be able to)”。

We could have a really good time if we had a flat of our own.
如果我们有一套自己的房子，我们就太开心了。

④当表达本来有能力做某事，但没有试图去做时，可用could have done这一结构。

I could have married anybody I wanted to.(=I was able to ..., but I didn't.)
我本来可以嫁给任何我想嫁的人。
I could have killed her!(=I was so angry that I was capable of killing her, but I didn't.)
我简直要杀了她！(＝我当时气得能杀死她，但我没有那么做。)
You could have helped me!(=You were able to help me — why didn't you?)
你本可以帮我的嘛！(=你当时可以帮助我的——你为什么没有那么做呢？)
I could have won if I hadn't fallen over.
如果不摔倒，我就可能赢了。

⑤这一结构用于否定句，表示“即便我去尝试，也不会做到”，但依据上下文可有灵活译法。

⑥can与see, hear, feel, smell等动词连用，描述正在发生的一种感觉上的经历，could用于表示过去某个时间正在发生的感觉上的经历。

英文之旅