高中学历解放军武警士兵考军校-英语语法部分（二十九）

(3) 关于助动词：

①常见的助动词有：用于进行时和被动语态的be (am, is, are ,was, were, been, being ) ;用于完成时的have(has,had,having) ;用于将来时的shall (should) ; will (would)和用于一般时的do(does,did) .

②助动词必须同主语的人称和数一致,也就是说因主语人称、数的不同而采用不同的形式,其中有些助动词也可作情态动词。如：shall, will, should, would.

(4) 关于情态动词：

①常见的情态动词有：can (could) ,may (might), must ,shall (should), will (would), dare (dared) , need等,另外,have to、had better也当作情态动词使用。情态动词后面必须加动词的原形。

②can表示体力、脑力方面的能力或客观的可能性。口语中, 在询问或说明一件事可不可以做时,常用"can"代替"may"。情态动词"can"的过去式是"could",否定式是"cannot"通常缩写成"can't","could"的否定式是"could not",通常缩写成"couldn't"。如：Can I help you?(要帮忙吗?)/ He can swim.(他会游泳)/ That can't be Mr Li.(那不可能是李先生)

③ may表示允许、请求或可能性,用may提问时,肯定回答一般用Certainly或Yes,you may.;否定回答一般用can't或mustn't. 如：May I ask you a question?-Certainly.(可以问你一个问题吗?当然可以)/ You may go now.(现在你可以走了)/ It may be in your pocket.(它可能在你的衣袋里)

④ must表示"必须"、"一定"的意思。表示"必须"时否定形式是mustn't;表示"一定"时,否定形式是"can't" 如：We must be very careful when we cross the road.(我们过马路时一定要非常小心)/ It must be Jack.(那准是杰克)/ I haven't seen Kate today. She can't be here.(我今天没有看到过凯特,她不可能在这里)

[注意]用must(必须)进行提问时,肯定回答用must,否定回答用needn't;用must(一定)进行提问时,肯定回答仍用must,但是否定回答用can't.如：Must we clean the room before we leave? –Yes,you must.或No,you needn't.(我们走之前必须要打扫房间吗?是的,必须打扫。/ 不,不需要。) / Must she be in the romm? –Yes,she must.或No,she can't.(她一定在房间里吗?是的,一定。/ 不,不可能在。)

⑤ "have to"表示"不得不"、"必须"。We'll have to leave now for it is very late at night.

have to的疑问形式是：助动词+…+have to,否定形式是：助动词+not+have to或者用needn't.如：Do you have to stay until 8 o'clock?(你得呆到8点钟吗?)/ You don't have to do so.(=You needn't do so.)(你不用这么做)

⑥ shall在问句中,可表示征求对方意见,与第一人称连用;在陈述句的第二、三人称的主语后或表示"命令"、"警告"、"允许"等。如：Shall we go to the zoo this weekend?(我们这个周末去动物园好吗?)/ He shall bring his own book next time.(他下次必须带自己的书来)

⑦ should可表示"劝告"、"建议"、"惊奇"等意思。We should speak to old people politely.(我们应该礼貌地对老人讲话)

⑧ will表示"意愿"、"决心"等意思,一般与第二人称连用。如：Will you please close the door for me?(请你替我把门关上好吗?)/ I will teach you a lesson.(我要教训你一顿)