虛擬語氣是一種特殊的動詞形式，用來表示說話人所說的話并不是事實，而是一種假設(shè)、愿望、懷疑或推測主要有三大類：用以表示虛擬條件的虛擬語氣，用在賓語從句中的虛擬語氣，還有其他類Ⅰ用以表示虛擬條件的虛擬語氣:： 　?。á保?用if條件從句表示的虛擬條件，是虛擬條件最普通的方式 　?、?虛擬現(xiàn)在時表示與現(xiàn)在事實相反的假設(shè)，其if 從句的謂語形式用動詞的過去式(be 一般用were)，主句用would/ should/ could/ might +動詞原形，例如：If I were in your position I would marry her. 　?、?虛擬過去時是表示與過去事實相反的假設(shè)，if 從句的謂語形式用過去完成時即had＋過去分詞，主句用would / should / could / might + have +過去分詞，例如：If it had not rained so hard yesterday we could have played tennis. 　?、?大多數(shù)的虛擬條件句屬于上面三種情況的一種，但并不排除存在條件和后果中，一個和現(xiàn)在情況相反，另一個和過去情況相反，例如：If you had followed what the doctor said, you would not be so painful now.這個句子在高中出現(xiàn)頻率頗高。

　?、?但是，如果后果用了虛擬語氣，而條件卻用陳述語氣，這種用法是錯的 　?。á玻?除了表示虛假條件外，if從句還可以表示對將來的推測，由于是將來還沒有發(fā)生的，所以談不上是真實的還是虛假的，只能說這個事情發(fā)生的可能性有多大一般情況下，可以用陳述語氣的if從句來表示對一個未來事實的推測，這個事實是完全可能發(fā)生的If從句的謂語形式用一般過去式或用were to / should +動詞原形，主句用would / should /could/ might +動詞原形，例如：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.（1996年1月四級第44題） 　?。á?）有時可以把含有助動詞、情態(tài)動詞、be或have的虛擬條件句中的連詞if 省去，而將had , should, were 等詞提到主語之前，即用倒裝結(jié)構(gòu),這時候，如果出現(xiàn)not等否定詞，否定詞需放在主語后面。

這種結(jié)構(gòu)在口語中很少使用，但頻頻在各類考試中出現(xiàn)，例如：If it had not rained so hard yesterday we could have played tennis.→Had it not rained so hard yesterday, we could have played tennis. 　　（⒋ ）大多數(shù)的虛擬條件通過上面所講的兩種方法表達，但在個別句子中也可以通過介詞without和介詞短語but for表達，副詞otherwise等表達出來例如：We didn't know his telephone number; otherwise we would have telephoned him.（1995年6月四級第46題）值得注意的是，包含but for的句子，謂語動詞必定要用虛擬形式，但包含without等短語的句子，謂語動詞未必一定要用虛擬語氣 　?。á?）有時虛擬條件不是明確地表達出來，而在蘊含在用but引導(dǎo)的從句里，于是便出現(xiàn)了有謂語動詞是虛擬語氣的主句加上謂語動詞是陳述語氣的but從句構(gòu)成的并列復(fù)合句，例如I would have hung you but the telephone was out of order.在這樣的句子里，如果主句沒有用虛擬語氣，或者從句用了虛擬語氣，都是錯的。

　?、蛴迷谫e語從句中的虛擬語氣 ： 　　（⒈） 在表示愿望的動詞wish后的賓語從句中，需用虛擬語氣wish后的that 常省略），根據(jù)主句時態(tài)，從句謂語時態(tài)相應(yīng)退后一位，例如：How she wished his family could go with him. 　　（⒉） 在具有愿望、請求、建議、命令等主觀意愿的動詞(desire, demand, advise, insist, require, suggest, propose, order, recommend, decide …) 后的賓語從句中需用虛擬語氣謂語動詞用(should) +動詞原形值得注意的是，如果賓語從句的動詞是否定的，否定詞not的位置應(yīng)在動詞之前，而不是動詞之后例如：The head nurse insisted that the patient not be moved.另外，如suggest表達“暗示”，insist表示“堅持某種說法”時，后面的從句不用虛擬語氣，例如：Her pale face suggests that she is ill.或He insisted that he did not kill the boy. 　　除此之外，上述動詞也要求用虛擬式： 　?、?在It is+上述動詞的過去分詞，其后所跟的主語從句中，如It is suggested that pupils wear school uniforms. 　?、?在上述動詞相應(yīng)的名詞形式作主語+連系動詞，其后的表語從句中，例如His suggestion was that classed be re-scheduled. 　?、?在對上述動詞相應(yīng)的名詞進行解釋的同位語從句中，如：The workers raised the demand that their pay be increased to cope with the inflation. 　　⒊ would （had）rather , would sooner也用來表達主觀愿望，它們之后的賓語從句中需用虛擬語氣。

謂語動詞用過去式表示現(xiàn)在或?qū)?，用過去完成式表示與過去事實相反，例如：I would rather he went right now. 　?、笃渌问降奶摂M語氣 ： 　　（⒈） it is +necessary等形容詞后，that主語從句中虛擬形式使用，這類形容詞包括necessary, important, essential, imperative, urgent, preferable, vital, advisable等，例如It is necessary that you listen to the teacher carefully.或者It is essential that you be able to pronounce every single word correctly. 　?。á玻?在It's (high/about) time 之后的定語從句中需用虛擬語氣謂語動詞用過去式，例如It is high time that you went to school 　?。á常?虛擬語氣在as if / as though 引導(dǎo)的方式狀語從句中的應(yīng)用（謂語動詞形式與wish后的賓語從句基本相同）表示與現(xiàn)在事實相反或?qū)ΜF(xiàn)在情況有懷疑，謂語動詞用過去式。

例如：He felt as if he alone were responsible for what had happened. 表示過去想象中的動作或情況，謂語動詞用過去完成式 　?。á矗?在lest 引導(dǎo)的狀語從句中，謂語動詞多用虛擬語氣，(should )+ 動詞原形例如： The mad man was put in the soft-padded cell lest he injure himself.（1998年1月四級第38題） 　?。á担?在if only 引起的感嘆句中需用虛擬語氣謂語動詞用過去式或過去完成式例如： Look at the terrible situation I am in! If only I had followed your advice. 　　一、虛擬語態(tài)的幾種固定句式 ： 　　1.I wish.....(一定用虛擬) 　　1）I wish i were you 　　2)I wish that she were here with me 　　2、as if...../as though 好像 (不一定用虛擬，要看說話的語境``) 　　1）He speaks as if he were an American.(如果他真的是美國人就不用虛擬了`) 　　2）He looks as if nothing had happened. 　　3、if I did/were....I would...... 　　1) If I were you, I wouldn't do that 　　2) If it were to snow tomorrow, they would not go out 　　. (用were to 和were的區(qū)別是were to 是對將來的虛擬， 　　用were是對現(xiàn)在的虛擬`詳見二、虛擬語態(tài)的幾種形式```) 　　4、在suggest that ,advice that, require that等固定搭配后要用虛擬語態(tài)！ 　　二、虛擬語態(tài)的幾種形式 ： 　　1、對現(xiàn)在的虛擬：（直接用動詞的過去時....） 　　if I did /were.... I would....... 　　2、對將來的虛擬：If...were to...I would....= if...did...I would.... 　　(此項與對現(xiàn)在的虛擬相同，但對現(xiàn)在的虛擬不用were to. 　　要區(qū)別對將來的虛擬和對現(xiàn)在的虛擬``一般句子里面都有時間標(biāo)志``) 　　(If it were to rain tomorrow, we would not go out. 　　=If it rained tomorrow, we would not go out.) 　　3、對過去的虛擬 If I had done....I would have done.... 　　(If I had known the answer, I would have told you.) 　　(至于If ..had been done ...would have done 　　前面的been只是因為是被動語態(tài)```所以要看句子的具體意思````) 　　固定句型的補充。

　　要用虛擬語態(tài)的句子: 　　i would rather i could......(I would rather she could not come here) 　　If only..(但愿....) 　　A:I will go to Korean next month. B:If only I could go with you 　　虛擬語態(tài)表示動作或狀態(tài)不是客觀存在的事實，而是說話人的主觀愿望，假設(shè)，推測，命令，建議，要求等 　　三種基本結(jié)構(gòu)： 　?。?）. 與現(xiàn)在事實相反的假設(shè)：一般過去時（be用were)，主句結(jié)構(gòu){ should(would)等+動詞原型} 　　例如：If they were here ,they would help you.如果他們在這，會幫助你的 　?。?）. 與過去事實相反的假設(shè)：過去完成時 主句結(jié)構(gòu)：{should(would)等+。