2020年公共英語三級語法解析：助動詞

協(xié)助主要動詞構(gòu)成謂語的詞叫助動詞，也叫輔助動詞。置于動詞的前面，使得動詞能表現(xiàn)出時態(tài)、語態(tài)、疑問句等變化。最常用的助動詞有：be，have/has，do/does，shall，did，will，should，would，can，could等。

半助動詞

在功能上介于主動詞和助動詞之間的一類結(jié)構(gòu)，稱為半助動詞。

常見的半助動詞有：

be to,be about to，be due to，be going to，be likely to，be meant to，

be obliged to，be supposed to，be willing to，have to，seem to，

be unable to，be unwilling to等。......

情態(tài)助動詞

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

1、can能，可以，表說話人同意，許可還可表客觀條件許可，如:You can go now.

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

can和be able to表能力時的區(qū)別。

can表一般具有的能力，be able to表在特定條件下的能力，如:Although the driver was badly hurt,he was able to explain what had happened.

2、may

(1)、可以，表說話人同意，許可或請求對方許可。You may go.

(2)、(現(xiàn)在和將來)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表主觀上的必須，have to表客觀上的必須，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這二詞有實意動詞和情態(tài)動詞兩種詞性，如用作實意動詞后接動詞不定式to do，如用作情態(tài)動詞后接動詞原形。Need I go now?--Yes,you must./No,you needn't.)

5、shall用于第一人稱疑問句中表說話人征求對方的意見或向?qū)Ψ秸埱?，如，Shall we begin our lesson?

用于二、三人稱陳述句，表說話人命令、警告、允諾、威脅等口吻，如:You shall fail if you don't work harder.

6、should表應(yīng)該，意為有責(zé)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(yīng)該做而未做

must have done表對過去事實的肯定推測

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.

基本助動詞

基本助動詞只有三個：be，do，have，它們沒有詞匯意義，只有語法作用，如協(xié)助構(gòu)成進行體，完成體，被動態(tài)，否定句，疑問句等。