一、虚拟语气是什么？

虚拟语气用来表示假想，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、疑问语气、虚拟语气四类。虚拟语气表示说话者所说的话并非事实，或难以实现的，甚至表达相反的概念。另外表示主观愿望或表达某种强烈的感情时，也用虚拟语气。

二、用法及动词形式

与现在事实相反：从句：If 主语+过去时(Be动词用were)，主句：主语+should/would/could/might+do

例句：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：没有带钱）
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）
6. She looked at me as if I had been a stranger.
她看我的样子好像我是一个陌生人。（事实：我并非陌生人）

与过去事实相反：从句：If 主语+had+done，主句：主语+should/would/could/might+have done

例句：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）

对将来的主观推测：从句：①if+主语+were to do，主句：①主语+should/would/could/might+do；从句：②if+主语+did/were，主句：②主语+should/would/could/might+do；从句：③if+主语+should+do，主句：③主语+should/would/could/might+do

例句：1. If he should come here tomorrow, I would talk to him.
如果他明天来这儿的话，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：下雪可能性很小）
3. If she were to be here 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。（事实：来的可能性很小）