虛擬語氣表示與客觀事實相反的假設，由if虛擬條件從句和主句構成。

　　一、虛擬語氣的基本內容

　　根據(jù)虛擬與其這種與事實相反的假設所對應的時間不同，虛擬語氣的if虛擬條件從句與主句的謂語動詞分別有三類構成形式：

　　假設類型If虛擬條件從句

　　主句與現(xiàn)在事實相反 Did/were Would/should do 與過去事實相反 Had done Would/should have done 與將來事實可能相反 Were to do/did/should do Would/should do

　　例：1、I wouldn't talk that way if I were Peter.

　　2、If the whole operation had not been planned before hand, a great deal of time and money

　　would have been lost

　　3、Jean doesn't want to work right away because she thinks that if she were to get a job she probably wouldn’t be able to see her friends very often.

　　4、I would ask George to lend us the money if I knew him.

　　5、Do you think there would be less conflict (戰(zhàn)斗、斗爭) in the world if all people spoke the same language.

　　6、If Bob had come with us, he would have had a good time.

　　二、if的省略形式(又稱虛擬語氣的倒裝結構)

　　在if虛擬條件從句中，如果謂語部分包含were，should，had等詞，則可以把這些詞放到主語前，省略if，構成虛擬語氣的倒裝結構。

　　三、主句與從句時間不一致時虛擬語氣的構成

　　當虛擬語氣的if虛擬條件從句和主句的動作發(fā)生的時間不一致時，要根據(jù)各自表示的時間采用對應的虛擬語氣的構成形式。

　　例：1、If I had attended the meeting yesterday, I would know what happened now.

　　2、If you had taken our advice at that time, you would not be in trouble now.

　　四、主觀傾向性動詞引導的虛擬語氣的構成

　　在英語中存在一些動詞，表示建議、命令、要求等主觀的傾向，由這些動詞引導的that賓語從句中，從句的謂語動詞要用should+動詞原形，should可以省略。這類常見的主觀傾向性動詞有“一堅持、二命令、三建議、五要求”，分別是：

　　一堅持：insist 二命令：order、command 三建議：suggest、advise(n advice)、propose(提議、建議) 五要求：ask、demand、require、request、desire

　　例：1、The doctor advised that Mr. Malan have an operation right away so as to save his life.

　　2、His mother insisted that he put on the coat when going out. 同時，如果在題干中出現(xiàn)上面這些主觀傾向性動詞的名詞和形容詞形式，題干中從句部分的謂語動詞也要用should+動詞原形，should可以省略。考試中常見的詞匯有：order，command，suggestion，advice，proposal，demand，request，desire，advisable，desirable.

　　五、wish that和if only引導的虛擬語氣的構成

　　Wish that引導的賓語從句和if only引起的感嘆句都用虛擬語氣來表示一種沒有實現(xiàn)或無法實現(xiàn)的愿望，其中wish that句型往往翻譯為：多么希望?;if only表示的愿望較wish that更強烈，常翻譯為但愿;要是?就好了。兩者的用法基本相同。兩者的用法是：1、當表示與現(xiàn)在的事實相反的一種愿望時，wish that引導的賓語從句和if only引起的感嘆句中謂語動詞采用的形式是：did/were;

　　2、當表示與過去的事實相反的一種愿望時，wish that引導的賓語從句和if only引起的感嘆句中謂語動詞采用的形式是：had done;

　　3、當表示未來一時很難實現(xiàn)的一種愿望時，wish that引導的賓語從句和if only引起的感嘆句中謂語動詞采用的形式是：would do.