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：
If主语＋should/wereto＋do，主语＋should（could…）＋ 原形 do，如：
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.
二、名词性虚拟语气：
在表示命令、建议要求、惊叹时的名词性从句中需用虚拟语气，基本句型：主语＋（should）＋动词原形，如：
Mother insisted that John go to bed at 9 o’clock.（宾语从句）
We suggested that the meeting should not be held.
It was required that the crops should be harvested at once.（主语从句）
The suggestion that he be invited was rejected.（同位语从句）
That is their demand that their wages be increased.（表语从句）
注意：在这种句子中绝不出现“would”“must”“could”等。
三、虚拟语气在一些特殊词中的使用或含蓄条件句：
1、wish后的宾语从句：
与现在愿望不一致 主语＋过去时；
与过去愿望不一致 主语＋had＋过去分词；
与未来愿望不一致 主语＋would（could）＋原形。
I wish I were you.
I wish I had visited the white House when I was in the states.
I wish I met you tomorrow at the party.
2、It’s time句型：当It’s time后用that从句时应该为：主语＋should＋原形或 主语＋过去时，例如：
It’s time that you went to school. 或
It’s time that you should go to school.
3、If only引起的感叹句相当于“How I wish＋宾语从句”
If only he could come! 他要能来就好了。
If only I had known the answer! 我要早知答案就好了。
4、would rather, as if（though）引导的句子也需使用虚拟，表示过去的情况用过去完成时，表示现在与将来的情况用过去时，如：
I’d rather you posted the letter right away.
I’d rather you had returned the book yesterday.
She loves the children as if they were hers.
Alan talked about Rome as if he had been there.
5、without, but, but for, otherwise引起的短语或句子常暗含着含蓄条件。
Without you, I would never know him.
But for your cooperation, we wouldn’t have done the work so well.
But that she was afraid, she would have said no.
I would be most glad to help you, but I’ am busy now.
I would have come to the party yesterday, but I was working.
I am busy now, otherwise I would do you the favor!
