IF是一個(gè)英語(yǔ)單詞，名詞、連詞，作名詞時(shí)意思是“條件，設(shè)想;不確定的情況”，作連詞時(shí)意思是“(表?xiàng)l件)如果;(表假設(shè))要是，假如;無(wú)論何時(shí);雖然，即使;(用于間接疑問(wèn))是否;(用于禮貌問(wèn)詢(xún))是否;當(dāng)，每次;(與情態(tài)動(dòng)詞連用)表婉轉(zhuǎn)客氣;這不是……，要是……多好;或許不;就算;盡管”。那么，if的虛擬語(yǔ)氣用法你了解嗎?

if 條件狀語(yǔ)從句的虛擬語(yǔ)氣：

一.基本結(jié)構(gòu)

1. 與現(xiàn)在事實(shí)相反

If + 主語(yǔ)+were/ did/ were doing, 主語(yǔ)+should/ would/ could/ might +動(dòng)詞原形

強(qiáng)調(diào)：必須把上面的結(jié)構(gòu)套用對(duì)!

2. 與過(guò)去事實(shí)相反

If + 主語(yǔ)+ had done, 主語(yǔ) +should/would/ might/ could + have done.

強(qiáng)調(diào)：必須把上面的結(jié)構(gòu)套用對(duì)!

3. 與將來(lái)事實(shí)相反

If + 主語(yǔ) + were/ did/ were to do/ should do, 主語(yǔ)+ should/ would/ could/ might do

強(qiáng)調(diào)：必須把上面的結(jié)構(gòu)套用對(duì)!

第三個(gè)結(jié)構(gòu)中，從句中的were to do可能性較小，should do的可能性稍大。

二.變化

1. 錯(cuò)綜時(shí)間條件句

所謂錯(cuò)綜，就是結(jié)構(gòu)和我們的基本結(jié)構(gòu)不一致，出現(xiàn)了從句用與過(guò)去事實(shí)相反，而主句則為與現(xiàn)在事實(shí)相反或與將來(lái)事實(shí)相反。

那么，我們就分別用各自的結(jié)構(gòu)即可。

If + 主語(yǔ)+had done, 主語(yǔ) +would/should/ could/ might do

再將強(qiáng)調(diào)結(jié)構(gòu)必須正確。

我們對(duì)比下面兩個(gè)句子：

If you had studied harder then, yoursituation would have been better.

If you had studied harder then, yoursituation would be better now.

注意：在錯(cuò)綜時(shí)間條件句中，務(wù)必有明確的表示錯(cuò)綜的時(shí)間狀語(yǔ)，或者通過(guò)上下文能看出是時(shí)間的不同，否則，就必須按前面的基本結(jié)構(gòu)套用。

2. 含蓄條件句

假設(shè)情況并不一定用條件從句來(lái)表示，而用其他方式來(lái)表示，這就是含蓄條件句了。

用without短語(yǔ)，分詞短語(yǔ)，或獨(dú)立主格來(lái)表示。

Without going with you last night, I wouldhave been robbed.

=If I hadn’t gone with you last night, Iwould have been robbed.

Having known each other before, we wouldn’thave fought last night.

= If we had known each other before, wewouldn’t have fought last night.

用相當(dāng)于if的其他連詞表示。

But that...要不是

Otherwise否則

He was ill, otherwise, he would have cometo meet you.

通過(guò)上下文來(lái)判斷。

I would have given you more money, but Ihad little money last month.

三.虛擬條件句中的倒裝

滿(mǎn)足如下三個(gè)條件方可倒裝：

必須是非真實(shí)條件句

從句中的謂語(yǔ)動(dòng)詞有were, had,should時(shí)

倒裝后，省略引導(dǎo)詞if,

Had I a lot of money, I would buy a bighouse.

=If I had a lot of money, I would buy a bighouse.

if引導(dǎo)條件狀語(yǔ)從句的用法：

某事很可能發(fā)生,條件是可能存在的,主句中某種情況發(fā)生的概率也是很高的.如：

If you ask him,he will help you.如果你請(qǐng)他幫忙,他會(huì)幫你的.

If you fail in the exam,you will let him down.如果你考試不及格,你會(huì)讓他失望的.

If you have finished the homework,you can go home.如果你作業(yè)做完了就可以回家了.

另外,if從句還表示不可實(shí)現(xiàn)的條件或根本不可能存在的條件,也就是一種虛擬的條件或假設(shè).從句多用一般過(guò)去時(shí)或過(guò)去完成時(shí),表示對(duì)現(xiàn)在或過(guò)去的一種假設(shè).如：

If I were you,I would invite him to the party.如果我是你,我會(huì)邀請(qǐng)他參加聚會(huì).

I would have arrived much earlier if I had not been caught in the traffic.要不是交通堵塞,我本會(huì)來(lái)得早一些.

另外你還要注意if 條件句的時(shí)態(tài)搭配

1.if從句用一般現(xiàn)在時(shí),主句用一般將來(lái)時(shí)

If he runs he’ll get there in time.如果他用跑的,他就會(huì)及時(shí)趕到那兒.

The cat will scratch you if you pull her tail.如果你拉貓的尾巴,它就會(huì)抓你.

2.if從句用一般現(xiàn)在時(shí),主句用may/might/can

If the fog gets thicker the plane may/might be diverted.如果霧在大一些,飛機(jī)可能就會(huì)改在別的機(jī)場(chǎng)降落.

If it stops snowing we can go out.如果雪停了,我們就可以出去.

3.if從句用一般現(xiàn)在時(shí),主句用must/should

If you want to lose weight you must/should eat less bread.如果你想減肥,你必須少吃面包.

4.if從句用一般現(xiàn)在時(shí),主句用一般現(xiàn)在時(shí)

If you heat ice it turns to water.(也可用will turn)如果把冰加熱,它就會(huì)化成水.

5.if從句用現(xiàn)在進(jìn)行時(shí),主句用一般將來(lái)時(shí)

If you are looking for Peter you’ll find him upstairs.如果你是在找彼得,上樓就會(huì)找到他.

6.if從句用現(xiàn)在完成時(shí),主句用一般將來(lái)時(shí)

If you have finished dinner I’ll ask the waiter for the bill.如果你吃完了,我就叫服務(wù)生來(lái)算賬

虛擬語(yǔ)氣的用法：

虛擬語(yǔ)氣是一種特殊的動(dòng)詞形式,用來(lái)表示說(shuō)話(huà)人所說(shuō)的話(huà)并不是事實(shí),而是一種假設(shè)、愿望、懷疑或推測(cè).判斷是真實(shí)條件句還是非真實(shí)條件句.只有在非真實(shí)條件句中才使用虛擬語(yǔ)氣.通過(guò)句子意思,看假設(shè)的條件是否能夠?qū)崿F(xiàn),能夠?qū)崿F(xiàn)是真實(shí)條件句,不能使用虛擬語(yǔ)氣;假設(shè)的條件不能實(shí)現(xiàn)則是非真實(shí)條件句,要用虛擬語(yǔ)氣.判斷這個(gè)假設(shè)是與哪個(gè)事實(shí)相反.

通常有三種情況：①與過(guò)去事實(shí)相反.②與現(xiàn)在事實(shí)相反.③與將來(lái)事實(shí)可能相反.

I: 較基本的虛擬語(yǔ)氣句型:

1. 虛擬現(xiàn)在時(shí)表示與現(xiàn)在事實(shí)相反的假設(shè),其if 從句的謂語(yǔ)形式用動(dòng)詞的過(guò)去式(be 一般用were),主句用would/ should/ could/ might +動(dòng)詞原形.If places were alike, there would be little need for geographers.如果各個(gè)地方都一樣,就不需要地理學(xué)家了.

2. 虛擬過(guò)去時(shí)是表示與過(guò)去事實(shí)相反的假設(shè),if 從句的謂語(yǔ)形式用過(guò)去完成時(shí)即had+過(guò)去分詞,主句用would / should / could / might + have +過(guò)去分詞.If he had known your address yesterday,he would have telephoned you.

3. 虛擬將來(lái)時(shí)是表示對(duì)將來(lái)實(shí)現(xiàn)的可能性很小的或不確定的假設(shè).If從句的謂語(yǔ)形式用一般過(guò)去式或用were to / should +動(dòng)詞原形,主句用would / should/could/ might +動(dòng)詞原形.If he were to leave today, he would get there by Friday

4. 省略if 采用倒裝語(yǔ)序的條件句.有時(shí)可以把含有助動(dòng)詞、情態(tài)動(dòng)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(yǔ)之前,即用倒裝結(jié)構(gòu).If he had worked harder, he would have got through the exams.==>Had he worked harder, he would have got through the exams.If he were to leave today, he would get there by Friday.==>Were he to leave today, he would get there by Friday.If I were in your place, I wouldn’t do that.==>Were I in your place, I wouldn’t do that.

5. 有時(shí)虛擬條件句并沒(méi)用if 從句表示出來(lái),而是用介詞短語(yǔ)(otherwise, or, without, but for)、上下文或其它方式來(lái)表示.如：We didn't know his telephone number; otherwise we would have telephoned him. Without you help, I wouldn’t have achieved so much. But for (“要不是.”的意思)your help, I would not have succeeded.

II: 虛擬語(yǔ)氣在從句中用should的情況:

1. 在表示建議,要求,命令,想法的動(dòng)詞后的從句里, 用should + 動(dòng)詞原形, should 可以省略. 如 advise, agree, command, decide, demand, determine, grant, indicate, insist, order, prefer, propose, request, require, stipulate, suggest, urge, vote.常考到的是: suggest, advise, demand, require, propose, insist, order, request.

His doctor suggested that he (should) take short leave of absence.

The author proposed that TV (should) be turned off at least one hour every day.

2. 在表示建議,要求,命令,想法的名詞后的從句里, 用should + 動(dòng)詞原形, should可以省略. 如 advice, decision,agreement, command, decree, demand, determination, indication, insistence, order, preference, proposal, request, requirement, stipulation etc.

It was Bill’s suggestion that everyone (should) have a map.

His suggestion was that everyone (should) have a map.

He gave us a suggestion that everyone (should) have a map.

3. 在It is/was +形容詞后的that 從句中用should的結(jié)構(gòu), should 可以省略. 這類(lèi)形容詞常見(jiàn)的有: advisable, anxious, compulsory, crucial, desirable, eager, essential, fitting, imperative(必要), impossible, improper, important, natural, necessary, obligatory, possible, preferable, probable, recommended, urgent, vital etc.

It‘s natural that she (should) do so.

It is essential that we (should) tell her the news.

4. 在 lest 和 for fear that(以免),in case(以防)從句中用should, should 可以省略.

She walked quietly lest she (should) wake up her roommates.

Have your gun ready in case we should need it.

III: wish 后的 that 從句中:

1. 表示現(xiàn)在或?qū)?lái)的愿望,從句中過(guò)去式.

I wish I knew his address.

I wish I were young.

2. 表示過(guò)去沒(méi)有實(shí)現(xiàn)或不可能實(shí)現(xiàn)的愿望, 從句用過(guò)去完成式或would, could, might + have + 過(guò)去分詞.

I wish you had written to him.

I wish I could have slept longer this morning, but I had to get up and come to class.

3. 如果將wish改成wished, 其后that 從句中動(dòng)詞的形式不變.

4. 如果that 從句中用would , 一般表示 對(duì)現(xiàn)狀不滿(mǎn)或希望未來(lái)有所改變或請(qǐng)求

I wish he would answer my letter.

I wish prices would come down.

I wish you would help me.

I wish you would stop asking silly questions.

IV: 在 It’s about/ high/ first(second, third etc)time 后的that 從句中,用過(guò)去式.表示“該是做什么的時(shí)候了”

It is about time you were in bed.

It is high time we left.

It is the first time I came here.

V: 在would rather, would sooner, would just as soon 后的that從句中,用過(guò)去式或過(guò)去完成式,表示“寧愿做什么”

I would rather he came tomorrow than today.

John would rather that she had not gone to the party yesterday evening.

VI: 在if only(“如果.就好了”的意思) 感嘆句中,謂語(yǔ)動(dòng)詞與wish賓語(yǔ)從句的虛擬形式相同.

If only he didn’t drive so fast!(現(xiàn)在)

If only she had asked someone’s advice.(過(guò)去)

If only the rain would stop.(將來(lái))

VII: 在as if / as though 從句中,表示和現(xiàn)在事實(shí)相反或?qū)ΜF(xiàn)在情況有所懷疑,用過(guò)去式;表示過(guò)去想象中的動(dòng)作或情況, 用過(guò)去完成式.

He speaks as if he were on the spot.

She spoke to me as if I were deaf.

This device operated as though it had been repaired.

注: 1. 在 as if / as though 句中, 如果有可能成為事實(shí), 用陳述語(yǔ)氣.

He looks as if he is going to be ill.

2. 在 insist 后的從句中, 如果是堅(jiān)持自己, 用陳述語(yǔ)氣, 堅(jiān)持別人做什么事情, 用虛擬語(yǔ)氣.

She insists that she is right.

She insisted that I should finish the work at once.

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