情态动词

情态动词表达说话人的态度，如能力、可能、许可、义务、建议、推测。

常见情态动词：

can, could, may, might, must, should, shall, will, would, need, dare

情态动词后接动词原形：

can go
must finish
should study

9.1 can 和 could

can 表示能力、许可、可能性。

I can swim.
我会游泳。

Can I use your phone?
我可以用你的手机吗？

could 可以表示过去能力，也可以表示更委婉的请求。

When I was young, I could run very fast.
我年轻时跑得很快。

Could you help me?
你能帮我吗？

9.2 may 和 might

may 表示许可或可能。

May I come in?
我可以进来吗？

It may rain tonight.
今晚可能下雨。

might 的可能性通常比 may 更弱，语气更不确定。

He might be at home.
他可能在家。

9.3 must 和 have to

must 强调主观认为必须。

You must listen carefully.
你必须认真听。

have to 强调客观情况不得不。

I have to leave now because the last bus is coming.
我必须现在走，因为末班车要来了。

mustn't 表示禁止，不是“不必”。

You mustn't smoke here.
你禁止在这里吸烟。

“不必”常用：

don't have to
needn't

例句：

You don't have to come early.
你不必早来。

9.4 should

should 表示建议、责任、理应。

You should drink more water.
你应该多喝水。

Students should respect their teachers.
学生应该尊重老师。

9.5 情态动词表示推测

must 一定
may/might/could 可能
can't 不可能

例句：

He must be tired.
他一定累了。

She might know the answer.
她可能知道答案。

That can't be true.
那不可能是真的。

对过去的推测：

must have done 一定做过
may/might have done 可能做过
can't have done 不可能做过
should have done 本应该做却没做

例句：

He must have forgotten the meeting.
他一定忘了会议。

You should have told me earlier.
你本应该早点告诉我。