英語(yǔ)高頻考點(diǎn)：情態(tài)動(dòng)詞與助動(dòng)詞

　　助動(dòng)詞本身無(wú)意義，在句中幫助主要動(dòng)詞構成一定的時(shí)態(tài)，語(yǔ)態(tài)、語(yǔ)氣，或是幫助構成否定句和疑問(wèn)句，常用的助動(dòng)詞有be, do, have, shall(should), will(would)。

　　情態(tài)動(dòng)詞表一定的詞義，本身并不表示動(dòng)作或狀態(tài)，而僅僅表達說(shuō)話(huà)人的態(tài)度，它在句中須和主要動(dòng)詞一起構成謂語(yǔ)， 主要的情態(tài)動(dòng)詞有can(could), may (might), must, have to, ought to, need, dare, shall, should, will, would。

　　1、can

　　能，可以，表說(shuō)話(huà)人同意，許可還可表客觀(guān)條件許可，如:You can go now.

　　提建議或請求時(shí)可用can I, can you表客氣，如Can I buy you a drink?

　　2、may

　�。�1）可以，表說(shuō)話(huà)人同意，許可或請求對方許可。You may go.

　�。�2）（現在和將來(lái)）可能，也許，只用于肯定句和否定句中，如He may not be right.

　　3、must, have to

　　must表主觀(guān)上的必須，have to表客觀(guān)上的必須，如: It's getting late. I have to go. -Must I go now. -Yes, you must. (No, you needn't./ No, you don't have to.)

　　4、need, dare這二詞有實(shí)意動(dòng)詞和情態(tài)動(dòng)詞兩種詞性，如用作實(shí)意動(dòng)詞后接動(dòng)詞不定式to do，如用作情態(tài)動(dòng)詞后接動(dòng)詞原形。Need I go now? --Yes, you must./No, you needn't.)

　　5、shall用于第一人稱(chēng)疑問(wèn)句中表說(shuō)話(huà)人征求對方的意見(jiàn)或向對方請求，如，Shall we begin our lesson?

　　用于二、三人稱(chēng)陳述句，表說(shuō)話(huà)人命令、警告、允諾、威脅等口吻，如: You shall fail if you don't work harder.

　　6、should表應該，意為有責任，有義務(wù)。如:We should try our best to make our country more beautiful.

　　7、will表有做某事的意志、意愿、安心、打算，如 "Will you lend me your book?" "Yes, I will."

　　8、should have done表應該做而未做

　　must have done表對過(guò)去事實(shí)的肯定推測

　　could have done表本可以做某事

　　9、判斷句：肯定句用must, 否定句用can't, 不太肯定用may, might

　　He must be in the office now.

　　He must have gone to bed, for the light is out.

　　He can't be in the office. He is at home.

　　He couldn't have cleaned the classroom, because he didn't come here today.

　　He might be in the office, I am not sure.

　　He might have cleaned the room, I suppose.

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