发布时间:2022-03-04 11:30:47来源：励普教育综合
IF是一个英语单词，名词、连词，作名词时意思是“条件，设想;不确定的情况”，作连词时意思是“(表条件)如果;(表假设)要是，假如;无论何时;虽然，即使;(用于间接疑问)是否;(用于礼貌问询)是否;当，每次;(与情态动词连用)表婉转客气;这不是……，要是……多好;或许不;就算;尽管”。那么，if的虚拟语气用法你了解吗?
if 条件状语从句的虚拟语气：
一.基本结构
1. 与现在事实相反
If + 主语+were/ did/ were doing, 主语+should/ would/ could/ might +动词原形
强调：必须把上面的结构套用对!
2. 与过去事实相反
If + 主语+ had done, 主语 +should/would/ might/ could + have done.
强调：必须把上面的结构套用对!
3. 与将来事实相反
If + 主语 + were/ did/ were to do/ should do, 主语+ should/ would/ could/ might do
强调：必须把上面的结构套用对!
第三个结构中，从句中的were to do可能性较小，should do的可能性稍大。
二.变化
1. 错综时间条件句
所谓错综，就是结构和我们的基本结构不一致，出现了从句用与过去事实相反，而主句则为与现在事实相反或与将来事实相反。
那么，我们就分别用各自的结构即可。
If + 主语+had done, 主语 +would/should/ could/ might do
再将强调结构必须正确。
我们对比下面两个句子：
If you had studied harder then, yoursituation would have been better.
If you had studied harder then, yoursituation would be better now.
注意：在错综时间条件句中，务必有明确的表示错综的时间状语，或者通过上下文能看出是时间的不同，否则，就必须按前面的基本结构套用。
2. 含蓄条件句
假设情况并不一定用条件从句来表示，而用其他方式来表示，这就是含蓄条件句了。
用without短语，分词短语，或独立主格来表示。
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.
用相当于if的其他连词表示。
But that...要不是
Otherwise否则
He was ill, otherwise, he would have cometo meet you.
通过上下文来判断。
I would have given you more money, but Ihad little money last month.
三.虚拟条件句中的倒装
满足如下三个条件方可倒装：
必须是非真实条件句
从句中的谓语动词有were, had,should时
倒装后，省略引导词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引导条件状语从句的用法：
某事很可能发生,条件是可能存在的,主句中某种情况发生的概率也是很高的.如：
If you ask him,he will help you.如果你请他帮忙,他会帮你的.
If you fail in the exam,you will let him down.如果你考试不及格,你会让他失望的.
If you have finished the homework,you can go home.如果你作业做完了就可以回家了.
另外,if从句还表示不可实现的条件或根本不可能存在的条件,也就是一种虚拟的条件或假设.从句多用一般过去时或过去完成时,表示对现在或过去的一种假设.如：
If I were you,I would invite him to the party.如果我是你,我会邀请他参加聚会.
I would have arrived much earlier if I had not been caught in the traffic.要不是交通堵塞,我本会来得早一些.
另外你还要注意if 条件句的时态搭配
1.if从句用一般现在时,主句用一般将来时
If he runs he’ll get there in time.如果他用跑的,他就会及时赶到那儿.
The cat will scratch you if you pull her tail.如果你拉猫的尾巴,它就会抓你.
2.if从句用一般现在时,主句用may/might/can
If the fog gets thicker the plane may/might be diverted.如果雾在大一些,飞机可能就会改在别的机场降落.
If it stops snowing we can go out.如果雪停了,我们就可以出去.
3.if从句用一般现在时,主句用must/should
If you want to lose weight you must/should eat less bread.如果你想减肥,你必须少吃面包.
4.if从句用一般现在时,主句用一般现在时
If you heat ice it turns to water.(也可用will turn)如果把冰加热,它就会化成水.
5.if从句用现在进行时,主句用一般将来时
If you are looking for Peter you’ll find him upstairs.如果你是在找彼得,上楼就会找到他.
6.if从句用现在完成时,主句用一般将来时
If you have finished dinner I’ll ask the waiter for the bill.如果你吃完了,我就叫服务生来算账
虚拟语气的用法：
虚拟语气是一种特殊的动词形式,用来表示说话人所说的话并不是事实,而是一种假设、愿望、怀疑或推测.判断是真实条件句还是非真实条件句.只有在非真实条件句中才使用虚拟语气.通过句子意思,看假设的条件是否能够实现,能够实现是真实条件句,不能使用虚拟语气;假设的条件不能实现则是非真实条件句,要用虚拟语气.判断这个假设是与哪个事实相反.
通常有三种情况：①与过去事实相反.②与现在事实相反.③与将来事实可能相反.
I: 较基本的虚拟语气句型:
1. 虚拟现在时表示与现在事实相反的假设,其if 从句的谓语形式用动词的过去式(be 一般用were),主句用would/ should/ could/ might +动词原形.If places were alike, there would be little need for geographers.如果各个地方都一样,就不需要地理学家了.
2. 虚拟过去时是表示与过去事实相反的假设,if 从句的谓语形式用过去完成时即had+过去分词,主句用would / should / could / might + have +过去分词.If he had known your address yesterday,he would have telephoned you.
3. 虚拟将来时是表示对将来实现的可能性很小的或不确定的假设.If从句的谓语形式用一般过去式或用were to / should +动词原形,主句用would / should/could/ might +动词原形.If he were to leave today, he would get there by Friday
4. 省略if 采用倒装语序的条件句.有时可以把含有助动词、情态动词、be或have的虚拟条件句中的连词if省去,而将had , should, were 等词提到主语之前,即用倒装结构.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. 有时虚拟条件句并没用if 从句表示出来,而是用介词短语(otherwise, or, without, but for)、上下文或其它方式来表示.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: 虚拟语气在从句中用should的情况:
1. 在表示建议,要求,命令,想法的动词后的从句里, 用should + 动词原形, 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. 在表示建议,要求,命令,想法的名词后的从句里, 用should + 动词原形, 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 +形容词后的that 从句中用should的结构, should 可以省略. 这类形容词常见的有: 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)从句中用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 从句中:
1. 表示现在或将来的愿望,从句中过去式.
I wish I knew his address.
I wish I were young.
2. 表示过去没有实现或不可能实现的愿望, 从句用过去完成式或would, could, might + have + 过去分词.
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. 如果将wish改成wished, 其后that 从句中动词的形式不变.
4. 如果that 从句中用would , 一般表示 对现状不满或希望未来有所改变或请求
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 从句中,用过去式.表示“该是做什么的时候了”
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从句中,用过去式或过去完成式,表示“宁愿做什么”
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) 感叹句中,谓语动词与wish宾语从句的虚拟形式相同.
If only he didn’t drive so fast!(现在)
If only she had asked someone’s advice.(过去)
If only the rain would stop.(将来)
VII: 在as if / as though 从句中,表示和现在事实相反或对现在情况有所怀疑,用过去式;表示过去想象中的动作或情况, 用过去完成式.
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, 如果有可能成为事实, 用陈述语气.
He looks as if he is going to be ill.
2. 在 insist 后的从句中, 如果是坚持自己, 用陈述语气, 坚持别人做什么事情, 用虚拟语气.
She insists that she is right.
She insisted that I should finish the work at once.
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