if引导的条件状语从句与虚拟语气的用法
if引导的条件状语从句的分类及虚拟条件句的判断
1、可以把条件句分为两类：
1).真实条件句（Sentences of Real Condition）：凡是假设的情况发生性可能很大,就是真实条件句.例如：
⑴、If I have time ,I will help you with this work.如果我有时间会帮助你做此工作的.
⑵、As long as I say anything wrong,you must point it out.只要我说了什么错话,你一定要指出来.
⑶、If time permits,we'll go fishing together.(如果有时间的话,我们就一起去钓鱼.）
2).虚拟条件句（Sentences of Unreal Condition）：当假设是不大可能实现时,就是虚拟条件句.例如：
⑴、If I were you ,I would have attended the meeting.如果我是你的话,就去参加会议了.
⑵、If he had come here yesterday,he would have seen his old friend.假如他昨天来这儿的话,就会看见他的老朋友.
⑴、If it had rained yesterday,we would have stayed at home.（如果昨天下雨的话,我们就会留在家里.）
2、.if条件状语从句中虚拟语气的判断
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.
3、“后退一步法”
后退一步法是指在准确地判断了该句与哪一事实相反后,按虚拟语气的后退一步法处理从句谓语动词的时态.即：在非真实条件状语从句中,谓语动词按正常情况“后退一步”.也就是：
①与过去事实相反,在从句中用过去完成时形式表示.
②与现在事实相反,在从句中用过去一般时形式表示.
③与将来事实可能相反,在从句中用过去将来时形式表示.
主句中则用情态动词would,should,could 等加一个与从句一致的动词形式.例：
⑴、If I had come her yesterday,I would have seen him.
⑵、If I were a teacher,I would be strict with my students.
⑶、If it should snow tomorrow,they couldn't go out.
4、注意事项
①if条件句中如有were,should,had,可以省去if,并使用倒装语序.
②在现代英语中if条件状与从句中的谓语动词如果是be其过去形式一般用were.
扩展资料：
1、在for fear that，in case，lest引导的从句中，若用虚拟语气时，从句谓语为：（should） + do。并且should能省略（for fear that，lest），in case不能省略
She examined the door again for fear that a thief (should) come in.
她又把门检查了一遍，以防盗贼的进入。
He started out earlier lest he (should) be late.
他早早地就出发了以防迟到。
2、在so that，in order that所引导的目的状语从句中，从句中的谓语为：can / could / may / might / will / would /should + do
He goes closer to the speaker so that he can hear him clearer.
他走近说话的人以便能听得更清楚。
He read the letter carefully in order that he should not miss a word.
他把信读得很仔细以便不漏掉一个字。
一想要(desire) 一宁愿(prefer) 一坚持(insist)二命令(order ， command) 三建议(advise ， suggest ， propose/recommend) 四要求(demand ， require ， request ， ask)中，无论主句谓语动词为何种时态，从句的谓语动词都用："should + do"。should可以省略。
eg：He suggested that we (should) take the teacher's advice.
He insisted that we (should) take the teacher's advice.
He demand that we (should) take the teacher's advice.
He ordered that we (should) take the teacher's advice.
insist意为“坚持某种动作”才用虚拟语气；意为“坚持某种观点，某个事实”则不用虚拟语气。
语法引导条件状语从句最常用的连词是if,由if引导的条件状语从句表示在某种条件下某事很可能发生。如：
1） If you ask him,he will help you.如果你请他帮忙，他会帮你的。
2） 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引导的条件状语从句既可以将从句放前面也可以将从句放后面
（如果天下雨，我们就不玩了）If it rains,we will stop playing.‘
转为We will stop playing if it rains.
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。
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.如果没有堵车，我会到的早一点儿。
unless = if...not.
e.g. Let's go out for a walk unless you are too tired.
If you are not too tired,let's go out for a walk.
if 引导的条件句有真实条件句和非真实条件句两种：
真实条件句
如：If it rains tomorrow,we won’t go on a park
非真实条件句是虚拟语气的一种，表示与事实相反，如：
If I were you,I would go with him.
so/as long as只要
由as (so) long as,in case引导。
So long as you’re happy,it doesn’t matter what you do.
只要你高兴，你做什么都没有关系。
You may borrow my book as long as you keep it clean.
只要你保持书的清洁，你就可以把我的书借去。
Take your umbrella in case it rains.
带着你的伞吧，以防下雨。
参考资料：百度百科——虚拟语气 百度百科——条件状语从句
if引导的条件状语从句的分类及虚拟条件句：
1、if 引导的条件状语从句有两种语气，一种是真实语气，一种是虚拟语气。
2、if条件句中如有were，should，had，可以省去if，并使用倒装语序。
3、在语法中if条件状与从句中的谓语动词如果是be其过去形式一般用were。
拓展资料
if的用法
1、The whole room looks as if it has been lovingly put together over the years
整个房间看起来好像是经过了多年的精心布置。
2、He points two fingers at his head, as if he were holding a gun
他把两根手指指向他的头，仿佛他正举着一支枪。
3、My husband, for some unknown reason, suggested that I loved my birds more than him: as if I would
我丈夫，莫名其妙地，暗示我爱鸟甚于爱他：仿佛我真如此似的。
4、Living together didn't harm our friendship. If anything it strengthened it
在一起住并没有损害我们的友谊。要说真有什么的话，它反而巩固了我们的友谊。
5、I am surprised by the fuss she's making. It's not as if my personality has changed.
她的大惊小怪令我很吃惊。显然不是我的个性改变了。
6、If I were you, Mrs Gretchen, I just wouldn't worry about it
要是我是你，格蕾琴夫人，我一点都不会担心。
7、You'll feel a lot better about yourself if you work on solutions to your upsetting situations
如果你设法找到解决自己麻烦的办法，你自我感觉会好得多。
8、You can go if you want
你要是想走就可以走。
9、If you would like to send a donation to Cobuild, please enclose a cheque with your coupon
如果你想为Cobuild语料库捐款，请随订货单附上支票。
10、If you went into town, you'd notice all the pubs have loud jukeboxes
如果你进了城，你会注意到所有的酒吧都有音量很大的自动点唱机。
I: 最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(绝对必要), 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.
I: 最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(绝对必要), 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.
如果。。。。。。。。。。。。。。。。就。。。。。。。。。。。。。。。。。
if don 't raining tommrrow ,we will go to the movies
表示虚拟，一般的话，时态是一般将来时
其实你去百度查一下就有了
我能帮你的就这麽多了
