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：
句型1：If ＋主语＋过去时，主语＋ should (could, would, 或might) ＋动词原形
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，其句型为：
句型2 : If ＋主语＋had＋过去分词，主语＋ should（could, would, 或might）＋ have ＋过去分词
If the doctor had come last night, the boy would have been 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，其句型为：
句型3：If ＋主语＋过去时/ should ＋动词原形/ were to＋动词原形，主语＋ should (could, would, 或might) ＋动词原形
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 tonight, you would feel sorry.
注意问题：
1．If条件句中绝对不可以出现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，但都要遵守上述句型。如：
If you had studied hard before, you would be a college student now and you would graduate from a college in four years’ time.
3．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 been 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：
句型4：主语＋（should）＋动词原形
Mother insisted that John (should) go to bed at 9 o’clock.（宾语从句）
It was required that the crops (should) be harvested at once.（主语从句）
It is surprising that she shouldn’t pass the math exam. （主语从句）
The suggestion that he (should) be invited was rejected.（同位语从句）
Their demand is that their wages (should) be increased.（表语从句）
注意：在这种句子中绝不可以出现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：
句型5：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/ could ＋ have＋过去分词；
与未来愿望不一致：主语＋ would / could ＋动词原形。如：
I wish I were you.
I wish I had visited the White House when I was in the States.
I wish I could meet you tomorrow at the party.
句型6： It’s time句型（当It’s time后用that从句时应该为“主语＋ should ＋动词原形”或“主语＋过去时”）
It’s time that you went / should go to school.
句型7：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! 我要早知道答案就好了。
句型8：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。
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.
句型9：without, but, but for, but that, otherwise引起的短语或句子常暗含着虚拟条件。
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 should have come to the party yesterday, but I was busy.
I am busy now; otherwise I would do you the favor!
句型10：If it were not for ... / If it hadn’t been for ... (要不是因为……)，其后面的主句也需使用虚拟。
If it were not for his help, I wouldn’t go home now.
If it hadn’t been for the determined captain, all the passengers on the board wouldn’t have been saving.
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