情态动词和虚拟语气

情态动词和虚拟语气

情态动词的用法要点

一、表能力

Can

Am/is/are able to 表现在的能力

Will be able to 表将来的能力

could

Was/were able to 表过去得能力

Could have+过去分词：表示过去有能力做但未做

二、表推测（可能性）

1.可能性可分为客观的可能性和具体事情实际发生的可能性两种。所谓客观的（理论的）可能性即并不涉及

具体某事是否会发生，此种用法常常可以说明人或事物的特征。情态动词can可用于肯定句中表示客观的（理论的）可能性，而表示具体事情实际发生的可能性时，can一般不用于肯定句。

Accidents can happen on such rainy days.

We may go to the cinema tonight, but we are not sure yet.

2.表示具体事情实际发生的可能性：

（2）表示具体事情实际发生的可能性时，may, must 常用于肯定句，一般不用于否定句和疑问句（may not 表示“可能不”）；can常用于否定句、疑问句或感叹句中，表示疑惑、惊讶或不相信等意思；could既可用于肯定句又可用于否定句、疑问句中。

This can’t/ couldn’t be done by him.

This may not be done by him.

He could be on his way home now.

Can this be done by him?

Mr Mush is on time for everything. How can it be that he was late for the opening ceremony?

I didn’t hear the phone. I must have been asleep.

---Are you coming to Jeff’party?

---I’m not sure. I might go to the concert instead.

(3) would, could, should, might 并不一定与过去时间有关，而表示可能性弱于它们相应的现在时形式。

This may/ might be done by him.

(4)should 表推测时，表示确定或可能有的未来或期望，即合乎理想的情况或结果

He ought to/ should be here on time---he started early enough.

We should arrive before dark.

The roads should be less crowded today.

三、表示请求、允许、允诺

1.当对方是决策者时，你代表你（们）自己（I, we），或代表第三者（he she they）向对方（you）请示或提

出建议时用：

（1） Shall/ May/ Might/ Can/ Could I/ we ……? （2） Shall he/ she/ they …….? （3） Would/ Will you ……? Shall the driver wait outside?

When shall my father be able to leave hospital? Would you do me a favor?

2. could/ might/ would/ should 表委婉的语气 ---Could/ Might I use your bike tomorrow morning? ---Yes, you can/ may.

3. shall 还可以表命令、警告、威胁；宣布法律、规定时，也要用shall You shall leave the room at once, and he also shall.

It has been announced that candidates shall remain in their seats until all the papers have been collected. 四、表示必要性

1. must 常用来表示必要性，意为“必须”

（1） must+do sth.

（2） Don ’t have to do sth ./ don’t need to do sth./ needn ’t do sth （3） 表示过去没必要做某事时，分为以下情况： ① needn ’t have done sth.

② Didn ’t have to do sth/ didn ’t need to do sth/ It was not necessary to do sth. You needn ’t have worked that late last night. It was harmful to your health. ---Did you work very late last night?

---No, I didn ’t. I didn ’t need to work very late. Mustn ’t 意为“绝对不能，被禁止” You must n’t smoke here.

2. should 也可以表示必要性，意为“（义务上）应该”。Should 表示必要性时，在语气上比must(必须)弱。

“should +动词原形”，表示现在或将来应该做（的必要性）；“should+ have+ 过去分词”，表示过去本该做（的必要性）

I should go and visit him this afternoon, but I wonder if I will be free.

You should have come to the conference yesterday. What was the reason for your absence? 五、表示“宁愿做某事”时，可使用下面这些句式： Would rather do sth.

Would rather do sth.than sth. Would do sth. Rather than do sth. Would rather sb. Did sth. Prefer to do sth.

Prefer to do sth. Rather than do sth Prefer doing sth. To doing sth.