英語四級語法之情態(tài)動詞
情態(tài)動詞屬于非實意動詞，它雖具有一定的詞義，但這種詞義并不完整，語法上也不能單獨構(gòu)成謂語，它必須和另一個實
情態(tài)動詞屬于非實意動詞，它雖具有一定的詞義，但這種詞義并不完整，語法上也不能單獨構(gòu)成謂語，它必須和另一個實意動詞一起構(gòu)成謂語才能表達完整的意思。情態(tài)動詞是一類非�；钴S的非實意動詞，歸納起來，情態(tài)動詞在句子中主要有三種用法：
1.情態(tài)動詞的非推測性用法
其用法是用來表示能力、許可、必要、義務(wù)、命令、勸告、詢問、需要、應(yīng)該、敢于等概念或態(tài)度，這類情態(tài)動詞有：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.
疑問句中的情態(tài)動詞和答語中的情態(tài)動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)動詞的推測性用法
人們常常會對客觀事物做出自己的`判斷，當情態(tài)動詞用來表示說話人對事物的推測、判斷時，就具有情態(tài)動詞的推測性用法�？梢杂米魍茰y的情態(tài)動詞有can，could，may，might，must，ought to， should，will和would。它們做出可能性的推測、判斷、預(yù)料的程度是不同的，might最弱、最沒有把握，而must最強、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，情態(tài)動詞用不同的動詞時態(tài)來推測表達對不同時間的事物的推測，例如：
My friend may be still sleeping at home now.(對現(xiàn)在說話時正在發(fā)生的事物的推測)
Can we be working at the same company next year?(對將來的推測)
His clothes is wet.He must have forgotten to bring the umbrella.(對已經(jīng)完成的情況的推測)
3.情態(tài)動詞用于虛擬語氣
A：提出一個假設(shè)的條件，純粹的展望或提出命令、要求。有部分情態(tài)動詞的過去時態(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，謂語動詞通常是情態(tài)動詞的過去時態(tài)。例如：
It would not be useful to adopt such suggestion.
Could you leave the message with me?
C：情態(tài)動詞加動詞的完成時態(tài)用來表示對過去情形的虛擬，這種設(shè)想或看法同過去的事實是相反 的，表示"本應(yīng)該做"，而實際上沒做。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.
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