高中英语语法知识：情态动词

6. 表示推测的用法

can, could, may, might, must 皆可表示推测，其用法如下：

1) 情态动词+动词原形。

表示对现在或将来的情况的推测，此时动词通常为系动词。

I don’t know where she is, she may be in Wuhan.

2) 情态动词+动词现在进行时。

表示对现在或将来正在进行的情况进行推测。

At this moment, our teacher must be correcting our exam papers.

这时，我们老师想必在批改试卷。

3) 情态动词+动词完成时。

表示对过去情况的推测。

We would have finished this work by the end of next December.

明年十二月底前我们很可能已完成这项工作了。

The road is wet. It must have rained last night.

地是湿的，昨天晚上一定下雨了。

4) 情态动词+动词的现在完成进行时。

表示对过去正在发生事情的推测。

Your mother must have been looking for you.

你妈妈一定一直在找你。

5) 推测的否定形式，疑问形式用can’t, couldn’t表示。

Mike can’t have found his car, for he came to work by bus this morning.

迈克一定还没有找回他的车，因为早上他是坐公共汽车来上班的。

注意：could, might表示推测时不表示时态，其推测的程度不如can, may。

7. 情态动词+have+过去分词

1) may(might) have + done sth, can (could) have + done sth表示过去，推测过去时间里可能发生的事情。

Philip may (might) have been hurt seriously in the car accident.

Philip can (could) have been hurt seriously in the car accident.

2)must have +done sth，对过去时间里可能发生的事情的推测，语气较强，具有"肯定"，"谅必"的意思。

---Linda has gone to work, but her bicycle is still here.

---She must have gone by bus.

3) ought to have done sth, should have done sth

本应该做某事，而事实上并没有做。否定句表示"不该做某事而做了"。

You ought to (should) have been more careful in this experiment.

He ought not to have thrown the old clothes away.(事实上已扔了。)

ought to 在语气上比should 要强。

4) needn’t have done sth本没必要做某事

I dressed very warmly for the trip, but Ineedn’t have done so. The weather was hot.

5) would like to have done sth本打算做某事

I would like to have read the article, but I was very busy then.

8. should和ought to

should 和ought to 都为"应该"的意思，可用于各种人称。

---Ought he to go?

---Yes. I think he ought to.

表示要求，命令时，语气由 should(应该)、had better最好)、must(必须)渐强。

9. had better 表示最好

had better 相当于一个助动词，它只有一种形式，它后面要跟动词原形。

had better do sth

had better not do sth

It is pretty cold. You’d better put on my coat.

She’d better not play with the dog.

had better have done sth表示与事实相反的结果，意为"本来最好"。

You had better have come earlier.

10. would rather 表示"宁愿"

would rather do

would rather not do

would rather… than…宁愿……而不愿。

还有would sooner, had rather, had sooner都表示"宁愿"、"宁可"的意思。

If I have a choice, I had sooner not continue my studies at this school.

I would rather stay here than go home. = I would stay here rather than go home.