虚拟语气动词语气是用来表明说话人的看法和态度的。
英语中的语气有三种：⒈ 陈述语气：表示说话人认为他所表述的是事实，可用于陈述句、疑问句和感叹句，可以是肯定的、也可以是否定的。
如：If he comes here, I shall tell him.如果他来这里，我会告诉他。
（他很可能来）⒉ 祈使语气：表示对说话对方的要求、命令、请求、警告等，用于祈使句中。
如：Lock up the door.把门锁上。
（表达命令）⒊ 虚拟语气：表示所说的话是不是事实，或者是不可能发生的情况，而是一种愿望、建议或与事实相反的假设。
如：I wish he could come.我希望他能来。
（表达愿望）He suggested that we ( should ) come another day.他建议我们改天来。
（表建议）虚拟语气在条件句中的应用：英语中if 从句有两种：一种是以陈述语气叙述的叫做真实条件句，说明所提出的假想是可以实现的；另一种是以虚拟语气叙述的，叫非真实条件句，说明所提出的假想实现的可能性极小或与事实相反。
这种虚拟语气一般因所指的时间的不同而分三种情况：⒈表示与现在事实相反：If + 从句主语+ 动词的过去式……，主语+should/ would/ could/ might + 动词原形……（be 一般用were）如：①If I were you, I would go by plane.如果我是你，我将坐飞机去。
（In fact I am not you. ）②If he were here, he would decide what to do.如果他在这里，他会决定做什么。
（In fact he isn’t here.）③If I had the letter at hand, I would read it.如果我手头有这封信的话，我会读它的。
（In fact I don’t have the letter at hand.）④If she knew about it now, she would come.如果她现在知道这件事的话，她会来的。
（In fact she doesn’t know about it.）⑤If he had time, he would go with you.如果他有时间，他会同你一起去的。
（In fact he is very busy, so he can’t go withyou.）⒉表示与过去事实相反：If + 从句主语+ had + 过去分词……，主语+should/ would/ could/ might +have +过去分词……如：①If he had come here yesterday, I should have told him.如果他昨天到这里来，我早就告诉他了。
(Fact: He did not come and I did not tell him.)②If I had taken his advice, I wouldn’t have made such a mistake.如果我当时接受了他的劝告，我是不会犯那样一个错误的。
(Fact: I didn’t take his advice and I made such a mistake.)③If I hadn’t been so busy last Monday, I would have called her.如果我上周一不忙的话，我早就给她打电话了。
(Fact: I was busy last Monday and I didn’t call her.)⒊与将来事实可能相反：If + 从句主语+ ①动词的过去式/ ②should +动词原形/ ③were to +动词原形, 主语+ should/ would/ could/ might + 动词原形…如：①If it should snow/snowed/were to snow tomorrow, I would not go out.如果明天下雪的话，我就不出去了。
(But I know it won’t snow tomorrow.)②If he failed/should fail/were to fail, he would try again.如果他失败的话，他会再试一次。
(I know that most probably he won’t fail.)③If I had time next year, I would study German.如果我明年有时间的话，我就学德语。
(I know that most probably I won’t have time next year.)◆在书面语中，有时if虚拟从句可使用倒装形式，方法是：如果if从句中含有were, had或should时，把条件从句中的if省略，将were/had/ should移至主语之前。
如：①If I were in his place, I should learn to drive.→Were I in his place, I should learn to drive.如果我处于他的地位，我一定学开车。
②If it should snow tomorrow, the meeting would be put off.→Should it snow tomorrow, the meeting would be put off.如果明天下雪，会议将会延期。
③If they had helped us, we would have succeeded.→Had they helped us, we would have succeeded.如果他们帮助了我们，我们早就成功了。
④If it were to snow tomorrow, what would you do?→Were it to snow tomorrow, what would you do?万一明天下雪的话，你怎么办?◆如果从句和主句所表示的动作发生的时间不一致，例如：一个与过去事实相反，另一个与现在事实相反，动词的虚拟语气形式应根据所指的实际时间来选用。
如：①If he were alive, he might have finished his scientific researches on the bridge-building three years ago.如果他现在还活着，他可能三年前就完成了他的桥梁建筑科研工作了。
（从句所表示的动作与现在事实相反，主句所表示的动作与过去事实相反）②If you had followed his advice, you would not be in trouble now.如果你当初听从他的建议，你现在就不会陷入这种困境了。
（从句所表示的动作与过去事实相反，主句所表示的动作与现在事实相反）③If I had followed the doctor’s advice, I would be quite all right now.如果我当时听从了医生的建议，我现在就完全恢复了健康。
（从句所表示的动作与过去事实相反，主句所表示的动作与现在事实相反）④If I were you, I would have gone with her.如果我是你，我早就和她一起去了。
（从句表示与现在事实相反，主句所表示的动作与过去事实相反）◆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。
这被称之为含蓄虚拟语气。
如：①We could have done better under more favorable conditions.在更有利的条件下，我们还可以做得更好些。
②Without the warmth and light of the sun, the earth’s vegetation would die almostimmediately.如果没有太阳的热量和光，地球上的植物几乎会马上死去。
◆含蓄虚拟语气有时也可以通过上下文或其他方式来表现：如：①I was ill that day. Otherwise I would have taken part in the sports meet.我那天生病了，否则就参加运动会了。
②But for the storm, we should have arrived earlier.要是没有碰到暴风雨，我们还会早一些到的。
③I would have written before, but I have been ill.本来早就该给你写信的，但我生病了。
虚拟语气在wish后的宾语从句中的应用：wish 的时态不影响从句的时态⒈与现在事实相反的愿望：wish + 从句(主语+ 动词的过去式)如：①He wishes he were a bird.他希望自己是一只小鸟。
②I wish I were ten years younger.真希望自己年轻十岁。
③I wish I remembered the address.我要是记得地址就好了。
⒉与过去事实相反的愿望：wish + 从句(主语+ had + 动词的过去分词)如：①She wished she had been braver then.她真希望那时她胆子大一些。
②I wish he had gone to the exhibition.要是他去参观展览会就好了。
③I wish you had been here yesterday.要是你昨天在这里就好了。
④We wish we had paid more attention to our pronunciation.要是我们过去对发音注意得更多一些就好了。
⒊与将来事实可能相反的愿望：wish + 从句(主语+ should/would/could/might + 动词原形)如：①We wish that he could be with us tomorrow.但愿他明天和我们在一起。
②I wish he would try again.我希望他还能再试一次。
虚拟语气在suggest, demand, propose, command, request, desire, order, insist等动词之后的宾语从句中，表示命令和建议：suggest/ demand/ propose/ command/ request/ desire/ order/ insist/ask(请求，要求)+(that) + sb.+(should ) +动词原形如：①We suggest that the meeting (should) be postponed.我们建议会议延期。