一. 简介
虚拟语气用来表示说话人的主观愿望或假想，而不表示客观存在的事实，所说的是一个条件，不一定是事实，或与事实相反。虚拟语气通过谓语动词的特殊形式来表示。英语中的语气分为陈述语气、祈使语气、虚拟语气三类。
二. 应用条件
虚拟语气常在表示条件和结果的状语从句中。在表示与事实相反的虚拟语气时动词有三种时态：现在时，过去时，将来时，过去完成时，现在完成时。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。虚拟语气
在什么情况下用虚拟语气? 在表示虚假的、与事实相反的或难以实现的情况时用虚拟语气，表示主观愿望或表示某种强烈情感时，也用虚拟语气。即当一个人说话时欲强调其所说的话是基于自己的主观想法，而不是根据客观实际，就用虚拟语气。
三. 虚拟语气在非真实条件状语从句中的用法
1、真实条件状语从句与非真实条件状语从句
真eg . If he doesn’t hurry up, he will miss the bus. 如果他不快点，他将错过巴士。( 真实条件状语)（不是虚拟语气）If he is free, he will ask me to tell stories. 如果他是空闲的，他会要求我讲故事。（真实条件状语）（不是虚拟语气）
非真 eg. If I were you, I would go at once.如果我是你，我马上就会去。（非真实条件状语从句）If there were no air, people would die. 如果没有空气，人就会死亡。（非真实条件状语从句）
2、用法及动词形式
1、表示与现在事实相反的情况：if+主语+过去时+其他+主语+should/would/could/might+do+其他
例： 1.If I were you, I would take an umbrella.如果我是你，我会带把伞。（事实：我不可能是你） 2.If I knew his telephone number, I would tell you. 如果我知道他的电话号码，我就会告诉你。（事实：不知道） 3.If there were no air or water, there would be no living things on the earth. 如果没有水和空气，地球上就不会有生物。(事实：地球上既有空气也有水) 4.If I had any money with me, I could lend you some. 如果我带钱了，我就会借给你些。（事实：没带钱） 5.If he studied harder, he might pass the exam.如果他再努力些，就能通过考试了。（事实：没有努力
2、表示与过去事实相反的情况if+主语+had done +其他+主语+should/would/could/might+have done+其他
例： 1. If I had got there earlier, I should/could have met her. 如果我早到那儿，我就会见到她。（事实：去晚了） 2.If he had taken my advice, he would not have made such a mistake. 如果他听我的劝告的话，就不会犯这样的错误了。（事实：没有听我的话）
3、表示对将来情况的主观推测①if+主语+were to do+sth.+主语+should/would/could/might+do+其他②if+主语+did/be(were)+sth.+主语+should/would/could/might+do+其他③if+主语+should+do+sth.+主语+should/would/could/might+do+其他
例： 1.If he should come here tomorrow, I should/would talk to him. 如果他哪天来这儿的话，我就跟他谈谈。（事实：来的可能性很小） 2.If there were a heavy snow next Sunday, we would not go skating. 如果下周日下大雪，我们就不能去滑冰了。（事实：不知能否下雪） 3.If she were to be there next Monday, I would tell her about the matter. 如果她下周一来这儿的话，我就会告诉她这件事的始末。在表示建议、命令、要求等含义的宾语从句，谓语动词常用虚拟语气，"should＋动词原形"构成，should 可省略。
4、有时，虚拟条件句中，结果主句和条件从句的谓语动作若不是同时发生时，虚拟语气的形式应作相应的调整。①从句的动作与过去事实相反，而主句的动作与现在或现在正在发生的事实不符。如：If I had worked hard at school, I would be an engineer, too. 如果我在学校学习刻苦的话，我现在也会成为一个工程师了If they had informed us, we would not come here now. 如果他们通知过我们的话，我们现在就不会来这里了。②从句的动作与现在事实相反，而主句的动作与过去事实不符。如：If he were free today, we would have sent him to Beijing. 如果他今天有空的话，我们会已经派他去北京了。If he knew her, he would have greeted her. 要是他认识她的话，他肯定会去问候她了。③从句的动作与过去发生的情况相反，而主句的动作与现在正在发生的情况相反。如：If it had not been raining too much, the crops would be growing much better. 如果天不下太多的雨的话，庄稼会长得更好。If he had been working hard, he would be working in the office now. 要是他一直努力工作的话，他现在已进了办公室了。
5、当虚拟条件句的谓语动词含有were, should, had时，if可以省略，这时条件从句要用倒装语序，即将were, should, had等词置于句首，这种多用于书面语。如：Should he agree to go there, we would send him there. 要是他答应去的话，我们就派他去。Were she here, she would agree with us. 如果她在这儿的话，她会同意我们的。Had he learnt about computers, we would have hired him to work here. 如果她懂一些电脑知识的话，我们已经聘用他来这里工作了。
6、非真实条件句中的条件从句有时不表达出来，只暗含在副词、介词短语、上下文或其他方式表示出来，这种句子叫做含蓄条件句，在多数情况下，条件会暗含在短语中，如without…., but for….等But for his help, we would be working now. 要不是他的帮助，我们还会在工作呢。Without your instruction, I would not have made such great progress. 要是没有你的指导，我不会取得如此大的进步。We didn’t know his telephone number; otherwise we would have telephoned him. 我们不知道他的电话号码，否则我们就会给他打电话。
7、有时，虚拟条件句中，主、从句可以省略其中的一个，来表示说话人的一种强烈的感情。①省略从句He would have finished it. 他本该完成了。You could have passed this exam. 你应该能通过这次考试了。②省略主句If I were at home now. 要是我现在在家里该多好啊。If only I had got it. 要是我得到它了该多好啊。、
虚拟语气（Subjunctive Mood)的其他用法
1、虚拟语气用在wish 后的宾语从句
a、表示与现在事实相反的愿望，谓语动词用过去式eg. I wish I had your brains.我希望我有你那样的头脑。(事实：我根本比不上你)
b、表示与过去事实相反的愿望，谓语动词：had+done(动词过去分词）eg:.I wish I had known the truth of the matter.我希望我原来知道这件事的真相。（事实：原来不知道）
c、表示将来难以实现的愿望谓语动词：should/would + 动词原形eg. I wish I should have a chance again.我希望我还能有一次这样的机会。（事实：很难再有这样的机会了）(注：if only和as if/as though也有相同用法）
