1） 概念 ：虛擬語氣用來表示說話人的主觀愿望或假想，所說的是一個(gè)條件，不一定是事實(shí)，或與事實(shí)相反。

2） 在條件句中的應(yīng)用

 條件句可分為兩類，一類為真實(shí)條件句，一類為非真實(shí)條件句。非真實(shí)條件句表示的是假設(shè)的或?qū)嶋H可能性不大的情況，故采用虛擬語氣

非真實(shí)條件句

1）時(shí)態(tài)：可以表示過去，現(xiàn)在和將來的情況。它的基本特點(diǎn)是時(shí)態(tài)退后。

a.同現(xiàn)在事實(shí)相反的假設(shè)。

句型 ：  條件從句    主句

一般過去時(shí)    should( would) +動(dòng)詞原形

If they were here, they would help you.

b.表示于過去事實(shí)相反的假設(shè)。

句型： 條件從句       主句

過去完成時(shí)      should(would) have+ 過去分詞

If he had not been ill and missed many classes, he would have made greater progress.

（含義： He was ill and missed many lessons, so he did not make greater progress.）

c.表示對將來的假想

句型：條件從句       主句

 一般過去時(shí)       would / should + 動(dòng)詞原形

 were+ 不定式      would/should + 動(dòng)詞原形

 should+ 動(dòng)詞原形   would/should + 動(dòng)詞原形

If you succeeded, everything would be all right.

If you should succeed, everything would be all right.

If you were to succeed, everything would be all right.

混合條件句

主句與從句的動(dòng)作發(fā)生在不同的時(shí)間，這時(shí)主，從句謂語動(dòng)詞的虛擬語氣形式因時(shí)間不同而不同，這叫做混合條件句。這時(shí)找準(zhǔn)時(shí)間狀語是關(guān)鍵。

If you had asked him yesterday, you would know what to do now.

（從句與過去事實(shí)相反，主句與現(xiàn)在事實(shí)相反。）

If it had rained last night (過去), it would be very cold today (現(xiàn)在).

虛擬條件句的倒裝

虛擬條件句的從句部分如果含有were, should, 或had, 可將if省略，再把were, should或had 移到從句句首，實(shí)行倒裝。

Were they here now, they could help us.

Had you come earlier, you would have met him

注意：

在虛擬語氣的從句中，動(dòng)詞''be''的形式一律用"were"，不用was。

特殊的虛擬語氣詞：should

1） It is demanded / necessary / a pity + that …(should) +動(dòng)詞原形

It is suggested that we (should) hold a meeting next week.

It is necessary that he (should) come to our meeting tomorrow.

2）在賓語從句中的應(yīng)用

在表示命令、建議、要求等一類動(dòng)詞后面的從句中。

order, suggest, propose, require, demand, request, insist, command, insist +that (should) do

I suggest that we (should) hold a meeting next week.

3）在表語從句，同位語從句中的應(yīng)用

在suggestion, proposal, idea, plan, order, advice等名詞后面的表語從句、同位語從句中要用虛擬語氣，即（should）+動(dòng)詞原形。

 My idea is that we (should) get more people to attend the conference.

 I make a proposal that we (should) hold a meeting next week.

注意：這時(shí)從句意思中隱含“應(yīng)該”的意思。                                              

wish的用法

1）用于wish后面的從句，表示與事實(shí)相反的情況，或表示將來不太可能實(shí)現(xiàn)的愿望。其賓語從句的動(dòng)詞形式為：

I wish I were as tall as you. He wished he hadn''t said that. I wish it would rain tomorrow.

比較if only與only if

only if表示"只有"；if only則表示"如果……就好了"。If only也可用于陳述語氣。

I wake up only if the alarm clock rings. 只有鬧鐘響了，我才會(huì)醒。

If only the alarm clock had rung.當(dāng)時(shí)鬧鐘響了，就好了。

If only he comes early.但愿他早點(diǎn)回來。

It is (high) time that

It is (high) time that 后面的從句謂語動(dòng)詞要用過去式或用should加動(dòng)詞原形，但should不可省略。

It is time that the children went to bed.

It is high time that the children should go to bed.

1.虛擬條件句時(shí)態(tài)的對應(yīng)考查；

2.省略if的情況；

3.跟suggest,order,demand,insist,propose,commond,require,requesr等詞有關(guān)的名詞性從句中的虛擬情況。

1.混合條件句的主從句時(shí)態(tài)不會(huì)靈活變化；

2.省略if時(shí)，句子調(diào)整不正確；

3.不會(huì)去找意思中的“應(yīng)該”含義；

4.陷在虛擬中出不來，把真實(shí)條件句當(dāng)成虛擬條件句。

【典型例題】

1） If I had seen the movie, I ______________ you all about it now.
A. would tell         B. will tell         C. have told         D. would have told

解析：錯(cuò)選D。此題考查混合條件句。從句表對過去的虛擬，主句表對現(xiàn)在的虛擬，所以正確答案為A。

2）The volleyball match will be put off if it ___.

A.will rain B. rains C. rained D. is rained

解析：答案B。真實(shí)條件句主句為將來時(shí)，從句用一般現(xiàn)在時(shí)。

3）_____ to do the work, I should do it some other day.

A. If were I B. I were C. Were I D. Was I

解析：答案C. 在虛擬條件狀語中如果有were, should, had這三個(gè)詞，通常將if省略，主語提前, 變成 were, should, had +主語的形式。但要注意，在虛擬條件狀語從句中，省略連詞的倒裝形式的句首不能用動(dòng)詞的縮略形式。如我們可說 Were I not to do., 而不能說 Weren''t I to do.

4). My suggestion is that she ________ more exercise, which will do a lot of
   good to her.
   A. takes            B. must take              C. take              D. took

解析：錯(cuò)選A。本題要表達(dá)“我的建議是她（應(yīng)該）多鍛煉，這對她會(huì)有很大好處。”符合虛擬的條件，所以正確答案為C。空前面省略了should.