情态动词+完成时的语法意义（二）

三、can/could have done的用法

1.can/could have done表示“对过去的可能性推测”，could的语气较can弱。

该结构表推测时无肯定式，一般用于否定句和疑问句。否定句表示“过去不可能发生过某事”，它是must have done的否定式；疑问句表示“过去可能发生过某事吗”。例如：

He can’t have forgotten it.他不可能已忘记此事。

Can he have gone to his aunt’s? 他有可能到他姑姑家去了吗？

I saw Mr. Zhang just now and he couldn't have gone to Beijing.我刚才看见张先生了，他不可能去了北京。

Why does he know this? Could someone have told him about it? 他怎么知道? 会是哪个人告诉他了吗?

We could not have heard them because of the noise from the river. 由于有河水声我们不能听见他们的话。

Can he have left already? 他会已经离开了吗?

They can’t have gone out because the light is on. 他们不可能出去了，因为灯还亮着。

注意：在非正式英语或口语中，偶见到could have done也可用于肯定句，表示推测：

She could have forgotten to tell him. 她可能忘记告诉他了。

Tom could have taken the money; he was here alone yesterday. 有可能是汤姆把钱拿走了，昨天他单独一个人在这里呆过。

In the example mentioned above, either method of construction could have been used.在上面提到的例子中，两种建造方法均可能用过。

2. could have done 表示未曾实现的可能性

该结构仅限于使用could，不用can。表示过去本来有能力、有可能、有打算、有选择做某事的，但实际上却没有那样做。即“过去本来可能做某事，而实际没有做”。通常译为“本来可以”，“本来能够”等。例如：

You could have done better, but you didn't try your best.你本可能做得更好，但你没有尽力。

We could have got in for nothing—nobody was collecting tickets. 我们本可以不买票就进去——根本没人收票。

I could have passed my examination easily but I made too many stupid mistakes. 我本可以轻易通过考试，但我犯了太多不该犯的错误。

You could have stayed with me when you were in this city on business.在这个城市出差时你本能够和我住在一起的。

She could have been seriously injured. 她本来可能伤得很重的。

It’s difficult enough, but it could have been worse. 这事情够困难的了，本来可能会更糟呢！

I could have given you some hints, but I suppose you thought yourself too grand. 我本可以给你点提示的，但是我认为你太自负了。

I could have lent you the money. Why didn’t you ask me? 我本来可以借这笔钱给你的，你为什么不向我提出?

You needn’t have walked up; you could have taken the lift. 你没必要走着上去，你本来可以乘电梯的。

有时，也可根据语境译为“好在没有”，“差点”，尤其是当谈论的是不利情况时。如：

She felt miserable. She could have cried. 她感到很痛苦，她差点哭了。

That was a bad place to go skiing—you could have broken your leg. 那不是一个滑雪的好地方，好在你没有把腿给摔断。

Why did you throw the bottle out of the window? Somebody could have been hurt. 你为什么把瓶子扔出窗外呢? 好在没有砸伤人。

3. could have done除了含有上述的意思外，还表示批评或责备

即表示过去本来有责任或义务应该做某事的，但实际上却没有做成，含有批评和责备的意味，通常译为“本来应该”，“本来可以”等，用法同上。例如：

You could have helped me—why did you just sit and watch? 你本来可以帮我一把嘛——为什么你只是坐在那儿观望呢?

I am disappointed that you didn’t tell me. You should have told me. 你没告诉我，我感到很失望，你本来应该告诉我的。

4. could have done 用于虚拟语气

在虚拟条件句中，当谈论过去的情况时，其句型通常是：主句用“could/would/might +have+过去分词”，if从句用过去完成时。例如：

You could have been killed if I hadn’t warned you. 我如不是警告了你，你就可能丧命了。

If he had known the facts, he could have told us what to do. 如果他了解事实，他是可能告诉我们怎样做的。

If you had come sooner, you could have helped us. 你如早来一点，就会帮上我们了。

I could have told them what happened if anybody had asked me. 如果有谁问过我，我可以告诉他们发生了什么情况。

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