虚拟语气，这一英语语法重点，用于表示假设、愿望、怀疑或推测等非真实情境。理解其用法，对于各类英语考试至关重要。

一、表示虚拟条件的虚拟语气

1. 现在时态表示与现实相反的假设，从句用动词过去式，主句用would/should/could/might+动词原形。例如：If I were in your position, I would marry her.

2. 过去时态表示与过去事实相反的假设，从句用过去完成时，主句用would/should/could/might+have+过去分词。例如：If it had not rained so hard yesterday, we could have played tennis.

3. 复合条件句包括与现在、过去情况相反的假设，例如：If you had followed what the doctor said, you would not have been so painful now.

4. 错误用法：条件用陈述语气而后果用虚拟语气。

二、表示对未来的推测

使用一般过去式或were to/should+动词原形表示推测，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.

三、倒装结构的省略与使用

有时省去if，将had, should, were等词提到主语前，使用倒装结构，否定词需在主语后。例如：Had it not rained so hard yesterday, we could have played tennis.

四、其他表达方式

介词without或but for、副词otherwise等可以表达虚拟条件。例如：We didn't know his telephone number; otherwise we would have telephoned him.

五、宾语从句的虚拟语气

在wish、desire、demand、advice等动词后的宾语从句中，需用虚拟语气。例如：How she wished his family could go with him.

六、其他形式的虚拟语气

在It's necessary等形容词后、It's high/about time后的定语从句、as if/as though引导的从句、lest引导的状语从句及if only引起的感叹句中，使用虚拟语气。例如：He felt as if he alone were responsible for what had happened.

理解并掌握虚拟语气的用法，对英语学习至关重要。通过实际例句分析，加深对语法结构的理解，将有助于提高英语水平。