虚拟语气虚拟语气(Subjunctive Mood)这一语法项目是各类英语考试中心测试的重点之一。
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。
Ⅰ用以表示虚拟条件的虚拟语气虚拟条件句的三种基本类型:1.与现在事实相反。
若与现在事实相反，条件从句的谓语用过去式(be通常用were)，主句谓语用“should (would, could, might)+动词原形”：If you took a taxi，you’d get there quicker.如果你坐出租车去，你可以快一点到那里。
(但你不坐)If I knew her number I could ring her up. 要是我知道她的电话号码，我就可以给她打电话了。
(可惜我不知道)2.与过去事实相反。
若与过去事实相反，条件从句的谓语用过去完成时(had+过去分词)，主句谓语用“should (would, could, might)+have+过去分词”：If I’d left sooner，I’d have been on time.要是我早点动身，我就准时到了。
(但我动身太迟了)If we had found him earlier we could have saved his life. 要是我们当时早点找到他的话，我们就可以救活他。
(可惜我们找到他太晚了)3.与将来事实相反。
若与将来事实相反，条件从句的谓语用过去式(be通常用were)，主句谓语用“should (would, could, might)+动词原形”：If he went，would you go too? 如果他去，你也去吗?(大概他不会去)If I asked him，I’m sure he’d help us. 如果我向他提出要求，肯定他会帮助我们。
(不过我不打算这样做)大多数的虚拟条件句属于上面三种情况的一种，但并不排除存在条件和后果中，一个和现在情况相反，另一个和过去情况相反，例如：If you had followed what the doctor said, you would not have been so painful now.这个句子在高中出现频率颇高。
但是，如果后果用了虚拟语气，而条件却用陈述语气，这种用法是错的。
2. 除了表示虚假条件外，if从句还可以表示对将来的推测，由于是将来还没有发生的，所以谈不上是真实的还是虚假的，只能说这个事情发生的可能性有多大。
一般情况下，可以用陈述语气的if从句来表示对一个未来事实的推测，这个事实是完全可能发生的。
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，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月四级第44题）3. 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,这时候，如果出现not等否定词，否定词需放在主语后面。
这种结构在口语中很少使用，但频频出现在各类考试中出现，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.4. 大多数的虚拟条件通过上面所讲的两种方法表达，但在个别句子中也可以通过介词without和介词短语but for表达，副词otherwise 等表达出来。
例如：We didn't know his telephone number; otherwise we would have telephoned him.（1995年6月四级第46题）值得注意的是，包含but for的句子，谓语动词必定要用虚拟形式，但包含without 等短语的句子，谓语动词未必一定要用虚拟语气。
5. 有时虚拟条件不是明确地表达出来，而在蕴含在用but引导的从句里，于是便出现了有谓语动词是虚拟语气的主句加上谓语动词是陈述语气的but从句构成的并列复合句，例如I would have hung you but the telephone was out of order.在这样的句子里，如果主句没有用虚拟语气，或者从句用了虚拟语气，都是错的。
Ⅱ用在宾语从句中的虚拟语气1.用wish的虚拟语气：虚拟语气通常用于wish后的宾语从句中，表示与事实相反或不大可能实现的愿望。
通常有三种形式：①对将来发生的事情表示祝愿或愿望：主语＋wish＋从句主语＋would(could, might)+动词原形eg：I wish she would try again.我希望她能再试一次②表示与现在事实相反的愿望：主语＋wish（that）＋从句主语＋动词过去式eg：I wish I wasn’t leaving my son.我希望我没离开我儿子.③对过去发生的事情表示遗憾或后悔时：主语＋wish（that）＋从句主语＋would/could have/had＋过去分词eg：I wish you had come to my birthday party.你要是来了我的生日晚会就好了。
* 从句的时态只与从句所指的时间有关，与wish的时态无关。
2. 在具有愿望、请求、建议、命令等主观意愿的动词(desire, demand,advice, insist, require, suggest, propose, order, recommend,decide …) 后的宾语从句中需用虚拟语气。
谓语动词用(should) +动词原形。
值得注意的是，如果宾语从句的动词是否定的，否定词not的位置应在动词之前，而不是动词之后。
例如：The head nurse insisted that the patient not be move.另外，如suggest表达“暗示”，insist表示“坚持某种说法”时，后面的从句不用虚拟语气，例如：Her pale face suggests that she is ill.或He insisted that he did not kill the boy.①在It is+上述动词的过去分词，其后所跟的主语从句中，如It issuggested that pupils wear school uniforms.②在上述动词相应的名词形式作主语+连系动词，其后的表语从句中，例如His suggestion was that classed be re-scheduled.③在对上述动词相应的名词进行解释的同位语从句中，如：The workers raised the demand that their pay be increased to cope with the inflation.3. would （had）rather , would sooner也用来表达主观愿望，它们之后的宾语从句中需用虚拟语气。
谓语动词用过去式表示现在或将来，用过去完成式表示与过去事实相反，例如：I would rather he went right now.Ⅲ含蓄虚拟语气所谓含蓄虚拟语气,就是句子里不出现明显的假设条件从句,但假想的条件隐含在上下文逻辑关系中,或通过一些语法手段得以体现,这种情况就称为含蓄虚拟语气. --含蓄条件暗含在其他结构中.(1)连词but（但是）,or (else) (否则）；副词otherwise（否则）,unfortunately等表示转折假设.如：A safety analysis would have identified the target as a potential danger.Unfortunately,it was never done.Victor obviously does not know what has happened; otherwise he wouldn't have made such a stupid remark.(2)介词短语暗含假设条件,常用的有：without（若没有），but for / but that（要不是因为）,except for（若没有）,with（若带有）,under more favorable conditions,in theabsence of（在没有……的情况下）,under the circumstances of（在……的情况下）等.如：But for the English examination I would have gone to the concert last Sunday.(3)intended/meant/hoped/wished/plann或was/were +不定式完成式或hadintended/meant/planned/hoped/wished +不定式一般式暗示虚拟语气.如：I intended to have called on you,but I was busy at that time.（事实上我没打电话）(4)情态动词完成式暗示虚拟语气.如：I should have called to make an airline reservation.(事实上我没有）Ⅳ虚拟语气的倒装当虚拟条件句的谓语部分含有were, should, had时，我们可以将连词if省略掉，而将were, should, had置于句首。
如：If she were in charge, she would do things differently.=Were she in charge, she would do things differently. 如果是她负责，她会是另一种做法。
If you should change your mind, no one would blame you.=Should you change your mind, no one would blame you. 万一你改变主意，谁也不会怨你。