1. may和might+ 動(dòng)詞完成式

此結(jié)構(gòu)用于推測(cè)過(guò)去的行為。例如：

She said that he might have missed the plane.她說(shuō)他可能誤了航班。

2. can和could+ 動(dòng)詞完成式

A. 表示過(guò)去能做而沒(méi)做的事，有一種對(duì)過(guò)去未付諸實(shí)施的事情的惋惜。例如：

In those circumstances we could have done better.

在那樣的情況下，我們本來(lái)可以做得更好的。(但沒(méi)有做得更好)

B. 推測(cè)過(guò)去的某種行動(dòng)。

Where can /could she have gone? 她可能到哪里去了呢?

The boy can’t have finished reading the book so soon because it is difficult even to an adult.

這孩子不可能那么快就把這本書讀完的，因?yàn)榧词箤?duì)一個(gè)成人來(lái)說(shuō)，這本書也是相當(dāng)難的。

Note:

can’t和couldn’t+ 動(dòng)詞原形可以用來(lái)表示否定推斷。例如：

He can’t be over fifty.他不可能超過(guò)50歲。

3.must +動(dòng)詞完成式

表示對(duì)過(guò)去行為的推斷，具有較大的可能性，意為“一定…，想必…”。例如：

She must have gone through a lot.

她一定吃過(guò)很多苦。

Note:

must+動(dòng)詞原形→對(duì)現(xiàn)在的推測(cè)，must be+現(xiàn)在分詞→對(duì)未來(lái)或現(xiàn)在正在進(jìn)行的推測(cè)。例如：

She looks happy; she must be having a good time.

4. needn’t+動(dòng)詞完成式和didn’t need to do

A. needn’t+動(dòng)詞完成式表示一種已經(jīng)做過(guò)的但并無(wú)必要的行為。例如：

You needn’t have watered the flowers, for it is going to rain.

你本來(lái)不必澆花的，因?yàn)樘煲�下雨了�?但卻澆了)

We needn’t have told him the news because he knew it already.

B. didn’t need (have) to do結(jié)構(gòu)表示沒(méi)有必要做某事，實(shí)際上也沒(méi)有做。例如：

I didn’t need to clean the windows. My sister did it.

我不必擦窗，我妹妹擦了。(我沒(méi)有擦)

5. should +動(dòng)詞完成式

A.此結(jié)構(gòu)的肯定式表示應(yīng)該做的事而沒(méi)有做，否定式表示某種行為不該發(fā)生但卻發(fā)生了。例如：

You should have given her more help.

你應(yīng)該多給她一些幫助的。(但沒(méi)有給)

B. 表示推測(cè)，意為“可能”，但可能性較小。例如：

He should have finished the work by now.

他現(xiàn)在該把工作完成了。(推測(cè))

C. should / would have thought意為“本以為，本認(rèn)為”。例如：

A: "Can you type?"

B: "Certainly."

A: "Well, I should have thought you wouldn’t."

I should have thought she wouldn’t agree.

我本來(lái)認(rèn)為她不會(huì)同意的。

D. should have thought有時(shí)意為“認(rèn)為，以為”，相當(dāng)于should think，但表示更為委婉、謙遜或不肯定的語(yǔ)氣。例如：

I should have thought it fairly good.

我以為它是很不錯(cuò)的。

E. should have + 過(guò)去分詞用于虛擬語(yǔ)氣：

Had you written him, you should have known the details.

6. ought to + 動(dòng)詞完成式

此結(jié)構(gòu)表示某種過(guò)去應(yīng)該做而沒(méi)有做的事，或被忽略未做的某種明智行為。例如：

You ought to have returned the book earlier.(還晚了)

You ought to have refused her at the beginning, but now it is too late.

Note:

這里的ought to也可以用should代替。

Homework:用給出的動(dòng)詞填空,注意要選用正確的助動(dòng)詞和時(shí)態(tài).

1.The boy____ the book so soon because it is difficult even to an adult. (read)

2.We___him the news because he knew it already. (tell)

3.If we had taken the other road, we ____earlier. (arrive)

4.I _____you might take this into consideration. (think)

5.You ____ her at the beginning, but now it is too late.(refuse)