四級(jí)語(yǔ)法不知道怎么備考?先從常見(jiàn)的情態(tài)動(dòng)詞來(lái)了解，用好這些詞可以減輕句子的程度，還可以在翻譯或者四級(jí)作文的備考中起到作用，下面跟外語(yǔ)加油站英語(yǔ)四級(jí)頻道一起學(xué)習(xí)英語(yǔ)語(yǔ)法吧!

情態(tài)動(dòng)詞屬于非實(shí)意動(dòng)詞，它雖具有一定的詞義，但這種詞義并不完整，語(yǔ)法上也不能單獨(dú)構(gòu)成謂語(yǔ)，它必須和另一個(gè)實(shí)

情態(tài)動(dòng)詞屬于非實(shí)意動(dòng)詞，它雖具有一定的詞義，但這種詞義并不完整，語(yǔ)法上也不能單獨(dú)構(gòu)成謂語(yǔ)，它必須和另一個(gè)實(shí)意動(dòng)詞一起構(gòu)成謂語(yǔ)才能表達(dá)完整的意思。情態(tài)動(dòng)詞是一類非?；钴S的非實(shí)意動(dòng)詞，歸納起來(lái)，情態(tài)動(dòng)詞在句子中主要有三種用法：

1.情態(tài)動(dòng)詞的非推測(cè)性用法

其用法是用來(lái)表示能力、許可、必要、義務(wù)、命令、勸告、詢問(wèn)、需要、應(yīng)該、敢于等概念或態(tài)度，這類情態(tài)動(dòng)詞有：can(could)，may(might)，shall(should)，will(would)，must，

oughtto，need，dare等，例如：

Children，you?can?eat?something?you?like.

Everybody?must?pay?the?fare，but?you?need?not?do?so?right?away.

How?dare?you?come?out?without?your?parents’permission?

I?would?rather?stay?at?home?than?go?with?you.

Ought?not?parents?to?give?their?child?more?care?

You?are?not?so?young;you?should?not?do?such?silly?things?any?more.

疑問(wèn)句中的情態(tài)動(dòng)詞和答語(yǔ)中的情態(tài)動(dòng)詞有固定的搭配形式。例如：

-Could?I?borrow?your?bike?for?a?while?

-Yes，you?can.(-Yes，please.)

-No，you?can?not.

-May?I?discuss?something?on?practicing?spoken?English?with?you?now?

-Yes，you?may.(-Yes，of?course.)

-No，you?mustn’t.

-Need?everyone?fill?in?this?application?form?immediately?

-Yes，everyone?must.(Yes，everyone?do.)

-No，they?needn’t.

-Must?we?hand?out?emergency?rations?to?these?famine?refugees?this?instant?

-Yes，you?must.

-No，you?they?needn’t.

-No，you?don’t?have?to.

2.情態(tài)動(dòng)詞的推測(cè)性用法

人們常常會(huì)對(duì)客觀事物做出自己的判斷，當(dāng)情態(tài)動(dòng)詞用來(lái)表示說(shuō)話人對(duì)事物的推測(cè)、判斷時(shí)，就具有情態(tài)動(dòng)詞的推測(cè)性用法。可以用作推測(cè)的情態(tài)動(dòng)詞有can，could，may，might，must，ought?to，?should，will和would。它們做出可能性的推測(cè)、判斷、預(yù)料的程度是不同的，might最弱、最沒(méi)有把握，而must最強(qiáng)、把握最大。例如：

It’s?nine?o’clock.My?friend?couldn’t?come?to?see?me.

This?boy?must?fail?in?exam?from?his?sad?face.

It’s?five?past?eight.There?ought?to?be?many?students?waiting?for?the?door?opening.

She?should?be?a?clerk?in?foreign?company?according?to?her?formal?dress.

He?may?not?be?fine?in?these?days.

They?were?ready?for?a?strong?earthquake?which?might?occur.

有時(shí)，情態(tài)動(dòng)詞用不同的動(dòng)詞時(shí)態(tài)來(lái)推測(cè)表達(dá)對(duì)不同時(shí)間的事物的推測(cè)，例如：

My?friend?may?be?still?sleeping?at?home?now.(對(duì)現(xiàn)在說(shuō)話時(shí)正在發(fā)生的事物的推測(cè))

Can?we?be?working?at?the?same?company?next?year?(對(duì)將來(lái)的推測(cè))

His?clothes?is?wet.He?must?have?forgotten?to?bring?the?umbrella.(對(duì)已經(jīng)完成的情況的推測(cè))

3.情態(tài)動(dòng)詞用于虛擬語(yǔ)氣

A：提出一個(gè)假設(shè)的條件，純粹的展望或提出命令、要求。有部分情態(tài)動(dòng)詞的過(guò)去時(shí)態(tài)常用于這種用法。

例如：Wish?I?might?be?better?soon.

Should?my?friend?come，ask?him?to?wait?in?the?reading-room.

May?you?be?healthy?forever.

If?you?dared?to?say?such?words?to?me，I?would?give?up?making?friends?with?you.

B：比較委婉地陳述看法，提出要求和建議，謂語(yǔ)動(dòng)詞通常是情態(tài)動(dòng)詞的過(guò)去時(shí)態(tài)。例如：

It?would?not?be?useful?to?adopt?such?suggestion.

Could?you?leave?the?message?with?me?

C：情態(tài)動(dòng)詞加動(dòng)詞的完成時(shí)態(tài)用來(lái)表示對(duì)過(guò)去情形的虛擬，這種設(shè)想或看法同過(guò)去的事實(shí)是相反?的，表示"本應(yīng)該做"，而實(shí)際上沒(méi)做。例如：

We?ought?to?have?been?here?early.

This?is?something?you?shouldn’t?have?done.

Need?you?have?nosed?about?in?her?affair?It?was?none?of?your?business.