虚拟语气分三种情况来掌握：
1、虚拟条件句。
2、名词性虚拟语气。
3、虚拟语气的其他用语。
一、虚拟条件句：
条件状语从句是非真实情况，在这种情况下要用虚拟语气。
1、条件从句与现在事实不一致，其句型为：
If 主语＋过去时，主语＋should（could, would, 或might）＋动词原形，如：
If I were you, I would study hard.
If it rained, I would not be here now.
2、条件从句与过去事实不一致，句型为：
If 主语＋had＋过去分词，主语＋should（could, would, 或might）＋have＋过去分词，如：
If the doctor had come last night, the boy would have saved.
If I had not studied hard, I would have failed in the exam last term.
3、条件从句与将来事实不一致，句型为：
＋do，主语＋should（could…）＋ 原形 do
过去时（与现在事实条件句一样）。
If it should rain tomorrow, we would stay at home.
If I were to go to the moon one day, I could see it with my own eyes.
If you missed the film to night, you would feel sorry.
注意问题：
1、If条件句中绝对不可出现“would”。
2、根据句中的时间状语，有时可能出现“混合虚拟”的情况，即主句可能是现在的情况，条件句也许是发生在过去的情况，但都是遵守上述句型。
3、在条件句中如果出现were, had, should可省去if，将主语与这些词倒装，例如：
Had the doctor come last night, the boy would have saved.
Were I to go to the moon one day, I would see it with my own eyes.
Should it rain tomorrow, we would stay at home.
