could have done 表示过去有必要做某事却未做 could not have done没有虚拟语气的用法,只

could have done 表示过去有必要做某事却未做 could not have done没有虚拟语气的用法,只能表推测,相当于can not have done,表示过去不可能做了某事.
不是说could not have done是表示过去没必要做的事却做了.

1） 概念
虚拟语气用来表示说话人的主观愿望或假想,所说的是一个条件,不一定是事实,或与事实相反.
2） 在条件句中的应用
条件句可分为两类,一类为真实条件句,一类为非真实条件句.非真实条件句表示的是假设的或实际可能性不大的情况,故采用虚拟语气.
1.真实条件句
真实条件句用于陈述语气,假设的情况可能发生,其中 if 是如果的意思.
时态关系
句型：条件从句 主句
一般现在时shall/will + 动词原形
If he comes, he will bring his violin.
典型例题
The volleyball match will be put off if it ___.
A. will rain B. rains C. rained D. is rained
答案B.真实条件句主句为将来时,从句用一般现在时.
注意：
1） 在真实条件句中,主句不能用be going to表示将来,该用shall, will.
(错) If you leave now, you are never going to regret it.
(对) If you leave now, you will never regret it.
2） 表示真理时,主句谓语动词便不用shall (will) +动词原形,而直接用一般现在时的动词形式.
2.非真实条件句
1）时态：可以表示过去,现在和将来的情况.它的基本特点是时态退后.
a. 同现在事实相反的假设.
句型 ： 条件从句 主句
一般过去时 should( would) +动词原形
If they were here, they would help you.
b. 表示于过去事实相反的假设.
句型： 条件从句 主句
过去完成时 should(would) have+ 过去分词
If she had worked harder, she would have succeeded.
The rice would not have been burnt if you had been more careful.
If my lawyer had been here last Saturday, he would have prevented me from going.
If he had come yesterday, I should / would have told him about it.
含义：He did not come yesterday, so I did not tell him about it.
If he had not been ill and missed many classes, he would have made greater progress.
含义： He was ill and missed many lessons, so he did not make greater progress.
c. 表示对将来的假想
句型： 条件从句 主句
一般过去时 should+ 动词原形
were+ 不定式 would + 动词原形
should+ 动词原形
If you succeeded, everything would be all right.
If you should succeed, everything would be all right.
If you were to succeed, everything would be all right.
3.混合条件句
主句与从句的动作发生在不同的时间,这时主,从句谓语动词的虚拟语气形式因时间不同而不同,这叫做混合条件句.
If you had asked him yesterday, you would know what to do now.
（从句与过去事实相反,主句与现在事实相反.）
If it had rained last night (过去), it would be very cold today (现在).
4.虚拟条件句的倒装
虚拟条件句的从句部分如果含有were, should, 或had, 可将if省略,再把were, should或had 移到从句句首,实行倒装.
Were they here now, they could help us.
=If they were here now, they could help us.
Had you come earlier, you would have met him
=If you had come earlier, you would have met him.
Should it rain, the crops would be saved.
=Were it to rain, the crops would be saved.
注意：
在虚拟语气的从句中,动词'be'的过去时态一律用"were",不用was, 即在从句中be用were代替.
If I were you, I would go to look for him.
如果我是你,就会去找他.
If he were here, everything would be all right.
如果他在这儿,一切都会好的.
典型例题
_____ to do the work, I should do it some other day.
A. If were IB. I were C. Were I D. Was I
答案C. 在虚拟条件状语中如果有were, should, had这三个词,通常将if省略,主语提前, 变成 were, should, had +主语的形式.但要注意,在虚拟条件状语从句中,省略连词的倒装形式的句首不能用动词的缩略形式.如我们可说 Were I not to do., 而不能说 Weren't I to do.
5特殊的虚拟语气词：should
1） It is demanded / necessary / a pity + that…结构中的主语从句的谓语动词要用should 加动词原形, should 可省略.
句型：
(1)suggested
It is (2)important that…+ (should) do
(3) a pity
(1)suggested, ordered, proposed, required, demanded, requested, insisted； + (should) do
(2)important, necessary, natural, strange
a pity, a shame, no wonder
例：It is suggested that we (should) hold a meeting next week.
It is necessary that he (should) come to our meeting tomorrow.
2）在宾语从句中的应用
在表示命令、建议、要求等一类动词后面的从句中.
order, suggest, propose, require, demand, request, insist, command, insist + (should) do
I suggest that we (should) hold a meeting next week.
He insisted that he (should ) be sent there.
注意： 如suggest, insist不表示"建议" 或"坚持要某人做某事时",即它们用于其本意"暗示、表明"、"坚持认为"时,宾语从句用陈述语气.
The guard at gate insisted that everybody obey the rules.
判断改错:
（错） You pale face suggests that you (should) be ill.
(对) Your pale face suggests that you are ill.
(错) I insisted that you ( should) be wrong.
(对) I insisted that you were wrong.
3）在表语从句,同位语从句中的应用
在suggestion, proposal, idea, plan, order, advice等名词后面的表语从句、同位语从句中要用虚拟语气,即（should）+动词原形.
My idea is that we (should) get more people to attend the conference.
I make a proposal that we (should) hold a meeting next week.
6.wish的用法
1）用于wish后面的从句,表示与事实相反的情况,或表示将来不太可能实现的愿望.其宾语从句的动词形式为：
真实状况 wish后
从句动作先于主句动词动作 过去时 过去完成时
（be的过去式为 were）
从句动作与主句动作同时发生 现在时 过去时
（had + 过去分词）
将来不大可能实现的愿望 将来时 would/could +
动词原形
I wish I were as tall as you. 我希望和你一样高.
He wished he hadn't said that. 他希望他没讲那样的话.
I wish it would rain tomorrow. 我希望明天下雨就好了.
2）Wish to do表达法.
Wish sb / sth to do
I wish to see the manager. = I want to see the manager.
I wish the manager to be informed at once. (= I want the manager to be informed at once.)
7.比较if only与only if
only if表示"只有"；if only则表示"如果……就好了".If only也可用于陈述语气.
I wake up only if the alarm clock rings. 只有闹钟响了,我才会醒.
If only the alarm clock had rung. 当时闹钟响了,就好了.
If only he comes early. 但愿他早点回来.
8.It is (high) time that
It is (high) time that 后面的从句谓语动词要用过去式或用should加动词原形,但should不可省略.
It is time that the children went to bed.
It is high time that the children should go to bed.
9 need "不必做"和"本不该做"
didn't need to do表示： 过去不必做某事, 事实上也没做..
needn't have done表示： 过去不必做某事, 但事实上做了.
John went to the station with the car to meet Mary, so she didn't need to walk back home. 约翰开车去车站接玛丽,所以她不必步行回家了.
John went to the station with the car to meet Mary, so she needn't have walked back home. 约翰开车去车站接玛丽,所以她本不必步行回家了. (Mary步行回家,没有遇上John的车.)
典型例题
There was plenty of time. She ___.
A. mustn't have hurried B. couldn't have hurried C. must not hurry D. needn't have hurried
答案D.needn't have done. 意为"本不必",即已经做了某事,而时实际上不必要.
Mustn't have done 用法不正确,对过去发生的事情进行否定性推断应为couldn't have done, "不可能已经". must not do 不可以（用于一般现在时）.
语气是一种动词形式,用以表示说话者的意图或态度.虚拟语气表示说话者的主观愿望、假想和建议等,所说的话有的与现在事实相反,或与过去事实相反,或与将来事实相反或与将来事实可能相反.所以虚拟语气总是与假设条件句用在一起.除了if条件句外,还有几种常用的条件句,短语也可表示条件.此外,上下文也能创造虚拟的语言环境.但有时条件从句与结果主句可能发生时间不一致,有时虚拟语气会出现倒装情况.除了与条件句在一起使用的主句用虚拟语气外,有些宾语从句或表语从句也有用虚拟语气的情况.
I虚拟语气的形式与基本用法
一、虚拟语气的形式
虚拟(条件)语气中,主句与从句中谓语动词的形式可分为下面四类
假设类型
条件从句谓语
动词形式
主语谓语
动词形式
与现在事实相反
条件从句的谓语：动词的过去式(be用were而不用was)
主句谓语：would(could,might,第一人称可用should)+动词原形
与过去事实相反
条件从句的谓语：had+ -ed分词
主句谓语：would(could,might,第一人称可用should)+have + -ed分词
与将来事实相反
条件从句的谓语：were to + 动词原形 或用过去式（be用were而不用was）
主句谓语：would(could,might,第一人称可用should)+动词原形
与将来事实可能相反
条件从句的谓语：should + 动词原形
主句谓语：would(第一人称可用should)+动词原形
二、虚拟语气的基本用法
1. 与现在的事实相反
1) What type of automobile would you buy ?
〔A〕 if you have free choice to choose the cars available today
〔B〕 if you are free to choose among all the cars available today
〔C〕 if all cars available were free to be chosen by you
〔D〕 if you were free to choose among all the cars available today
2. 与过去的事实相反(有时主句中的should have done表示责备或后悔)
2) ,he would have come to class.
〔A〕 If Mike is able to finish his homework
〔B〕 Would Mike be able to finish his homework
〔C〕 If Mike could finish his homework
〔D〕 If Mike had been able to finish his homework
3) If the United States had not entered the Second World War,probably the 1940 unemployment rate of 14％ still further.
〔A〕 would rise
〔B〕 would risen
〔C〕 would have risen
〔D〕 had risen
4) Top?grade 〔A〕 diamonds had not 〔B〕 increased so sharply 〔C〕 in value in the late seventies 〔D〕 if one company had not controlled almost all of the world’s supply.
3. 与将来的事实相反
5) The report would be 〔A〕 released last January if new developments had not 〔B〕 made it necessary to revise all conclusions drawn from 〔C〕 the first series of 〔D〕 experiments.
6) It is said Tom will go to an appointment tommorrow. If he were to come tomorrow, I ask him to go to your place.
〔A〕 will
〔B〕 would
〔C〕 shall
〔D〕 might
7) If you to see Mary,what would you tell her?
〔A〕 are
〔B〕 will be going
〔C〕 must
〔D〕 were
4. 与将来的事实可能相反
(1) If it should rain tomorrow, I would stay at home. 要是万一 明天下雨,我就呆在家里不出去. 事实上 现在天气很好,明天下雨的可能性应该不大,不过也说不准.
(2) If I should see her next Monday, I would tell her about it. 如果下周一我能见到她的话我就把这件事告诉她.
三、例题解析
1) D为正确答案.
2) D为正确答案.
3) C为正确答案.
4) B错.改为would have not.
5) A错.改为would have been.
6) B为正确答案.
7) D为正确答案.
II 虚拟语气的特殊表现形式
一、表示“好像”：除了if条件从句外,由as if和as though等引导的状语从句表示方式时,意思是“好像”,这时从句中的谓语动词应用虚拟语气.其动词形式用过去时(be用were的形式)表示所说的与现在的事实相反；用过去完成时表示所说的与过去的事实相反
1) Violetta has a curious 〔A〕 expression on 〔B〕 her face as though she was smiling 〔C〕 about something that amused her 〔D〕 .
二、特殊连词的需要：lest, for fear that和in case引起的从句(这时谓语多用should＋加动词原形)
We dare not play jokes on Mr. Wang lest he should become angry. (我们不敢跟王先生开玩笑,恐怕他生气.)
He hurried on, lest he should drop out in the forced match. (他加紧步伐,生怕在急行军中掉队.)
Every attention must be paid to him lest he (should) feel that he is inferior to my other guests. (我对他特别关照,唯恐他感觉到比我的其他客人低人一等.)
He’s working hard for fear that he should fail in the exam. (他加紧学习唯恐考试不及格.)
三、介词短语表示虚拟： 有时假设的情况并不以条件从句表示出来,而是通过一个介词短语来表示,或通过上下文或其他方式表示出来.如 but for, but that…, in case of, otherwise, supposing, under more favourable condition, without 等表示让步假设
He worked very hard; otherwise he might have failed. (他刻苦工作,不然他就失败了.)
We could have done better under more favorable conditions.(假设我们有更有利条件,我们还会做得更好.)
2) But for his help,I .
〔A〕 should not have succeeded
〔B〕 had not succeeded
〔C〕 did not succeed
〔D〕 have not succeeded
3) The complex society of a modern 〔A〕 civilization would be 〔B〕 impossible not having 〔C〕 the art of writing 〔D〕 .
4) But that he came to help me, I .
〔A〕 could not have succeeded
〔B〕 did not succeed
〔C〕 could not succeed
〔D〕 can’t but succeed
四、虚拟错综条件句：上面几种假设类型中,主句与从句的谓语动词形式应前后呼应.但是,如果主句与从句的动作发生的时间不一致,谓语动词形式应做适当调整
If I had a bike(now), I would have lent it to you yesterday. 假如我有自行车,昨天早就借给你了.(主句与过去事实相反,从句与现在事实相反.) I am very sorry if I had done anything wrong to you, but I am sure that it was unintentional.(如果我当时对你作错了什么事,我向你表示抱歉.但我敢保证我不是故意的.)
5) If the United States had built more homes for poor people in 1955,the housing problems now in some parts of this country so serious.
〔A〕 wouldn’t be
〔B〕 will not have been
〔C〕 wouldn’t have been
〔D〕 would have not been
6) If you had not studied the problem carefully until recently .
〔A〕 you will find any difficulty now
〔B〕 you would have found any difficulty now
〔C〕 you would find any difficulty now
〔D〕 you have find any difficulty now
五、省略虚拟条件句：虚拟条件从句中的谓语动词如果是were或should(could, might), had等词时,可以省略连词If, 但要将were或should(could, might), had助动词移至主语前形成句子例装(参见第十三章“倒装句”)
7) today, he would get there by Thursday.
〔A〕 He is starting out
〔B〕 If he starts out
〔C〕 Would he start out
〔D〕 Were he to start out.
8) ,John would not have failed.
〔A〕 If he has listened to me
〔B〕 Had he listened to me
〔C〕 If he listened to me
〔D〕 As soon as he listened to me
9) I known it,I should have told him.
〔A〕 Have
〔B〕 Had
〔C〕 Having
〔D〕 If
10) Hadn’t my car broken down,I the train.
〔A〕 should have caught
〔B〕 might catch
〔C〕 could catch
〔D〕 had caught
六、例题解析
1) C错. 改为were smiling.
2) A为正确答案.
3) C错. 改为without.
4) A为正确答案.
5) A为正确答案.
6) C为正确答案.
7) D为正确答案.
8) B为正确答案.
9) B为正确答案.此句为had放句首的一种倒装,相当于If I had……
10) A为正确答案.
III 从句中须用虚拟语气的情况
一、在wish的宾语从句中
1. 动词wish后跟由that引导的宾语从句(that经常被省略)要用虚拟语气表示一种不可实现的愿望.宾语从句中用过去时(be 用were的形式)表示与现在事实相反,用过去完成时表示与过去相反
She wishes she had more money. (她真希望有更多的钱.) / I wish I didn't say that. (要是我不说这件事就好了.) / I wished I were not so worried. Then I would not have had the accident. ( 我要是不那么忧郁就好了,那也就不会发生那场事故了.)
1) I wish I knew 〔A〕 you were arriving 〔B〕 today. I would have met 〔C〕 you at 〔D〕 the station if I had.
2) She wishes that we didn’t send 〔A〕 her the candy 〔B〕 yesterday because 〔C〕 she’s on 〔D〕 a diet.
3) My brother is in 〔A〕 California on 〔B〕 cation,but I wish he was 〔C〕 here so that he could help me repair my car 〔D〕 .
2. 当wish的宾语从句表示一种愿望、要求时,可用过去时,也可用would＋动词原形
I wish you would stay here longer. (我希望你在这儿多呆一会.) / She wishes you wouldn't go. (她希望你不要走.)
3. would rather(宁愿),would sooner(宁愿), had rather(宁愿) 等词或短语后面的从句中的谓语动词应使用一般过去时表示虚拟语气,表示与过去相反的也可用过去完成时
4) I’d rather you anything about it for the time being.
〔A〕 do
〔B〕 didn’t do
〔C〕 don’t
〔D〕 didn’t
5) I rather you did it.
〔A〕 had
〔B〕 should
〔C〕 shall
〔D〕 have
6) I much rather it was forgotten.
〔A〕 will
〔B〕 could
〔C〕 would
〔D〕 shall
二、在某些特殊概念词的宾语从句中：一些表示提议、主张、要求、命令、紧要等概念的词语,由于它们本身隐含说话者的主观意见,认为某事应该或不应该怎样,这些词语后面的“that”从句应用虚拟语气,且均以“should”表示这种语气,但事实上“should”常被省略,故此从句中谓语动词用原形.这些词可分为下列几类
1. 下列动词后“that”引导的宾语从句
suggest(建议), propose (提议), recommend(建议), move (提议), advise(建议), insist(坚持), urge(极力主张), ask, require, request(要求), demand, desire, order, command(命令), decide, intend(打算), prefer(宁愿), urge(敦促).
7) The chairman requested that .
〔A〕 the members studied more carefully the problem
〔B〕 the problem was more carefulnessly studied
〔C〕 with more carefulness the problem could be studied
〔D〕 the members study the problem more carefully
8) The committee recommends that the matter at the next meeting.
〔A〕 would be discussed
〔B〕 will be discussed
〔C〕 be discussed
〔D〕 may be discussed
9) The doctor insisted that his patient .
〔A〕 that he not work too hard for three months
〔B〕 take it easy for three months
〔C〕 taking it easy inside of three months
〔D〕 to take some vacations for three months
When I suggested that he try shaving cream, he said, “The razor and water do the job. ” (当我建议他用刮胡膏时,他说“剃刀和水就行了”.)
He pursued various theories for several days until I suggested we take the toy apart to see how it did work. (他费了几天功夫寻找理论根据,直到我建议拆开看看它是如何转动的.)
One can suggest that students should spend two or three years in an English?speaking country. (我们建议学生应在说英语的国家呆上两三年.)
2. 下列表示主张、要求、命令、愿望、建议等概念结构后的主语从句或逻辑上的主从结构(如下列形容词作宾语从句的补足语时,这时宾语从句一般用it来代替)：这时that所引导的主语从句中的谓语动词常用“should ＋ 动词原形”或省略should,只用动词原形
it is necessary 【 essential (重要的), vital(极重要的,不可缺少的),important,imperative(必须的),urgent(紧要的),advisable(应该的),proper(适当的),obligatory (必须的),desirable(今人满意的,值得的),appropriate(合适的),fitting (合适的), strange (奇怪)】that…； it is(was, has been) desired 【suggested , requested, ordered , proposed, dicided】 that … .
10) From the standpoint of the long?term strategic interest of the West it is imperative that .
〔A〕 their territorial unity being a safeguard
〔B〕 their unity is a territorial safeguard
〔C〕 they’re a territorial safeguard
〔D〕 their territorial unity be a safeguard
11) The irritable 〔A〕 sergeant was 〔B〕 insistent that nothing supersedes 〔C〕 the drilling(训练) of the forty new men 〔D〕 .
12) It is extremely 〔A〕 necessary that you will realize 〔B〕 that reading is not only 〔C〕 a physical 〔D〕 and metal process.
3. 下列表示主张、要求、命令等概念的名词后面可以跟接“that”引导的表语从句和同位语从句.这种由that引导的从句其谓语动词通常用should＋动词原形或省略should.这类词有：order, request, requiremetn, insistence,suggestion, command, necessity, importance, idea, plan, motion(提议),proposal(建议),recommendation(建议),understanding(协议), resolution(决定,决议)
13) The judge assented to the suggestion that .
〔A〕 both of the criminals will soon be set freedom
〔B〕 some of the criminals there are of guilt only
〔C〕 the girl was to be paroled in the custody of a welfare society
〔D〕 the prisoner be sentenced to death
4. 在expect, believe, think, suspect等动词的否定或疑问形式后的宾语从句,我们经常用“should＋动词原形(或完成形式)”,表示惊奇,怀疑,不满等
I never thought that he should be such a brave young soldier. 我们从来没想到他是个如此勇敢的小战士.