条件句中的虚拟语气

1. 表示现在和将来情况的虚拟条件句
这类句子表示与事实相反的情况或实现可能性不大的情况。

1) 条件句中的谓语用过去式，主句的谓语为 would/might/could + 动词原形。
注意当条件句的谓语动词为be 时，要用 were, 包括主语是第一人称的时候。 但如果主语为第三人称单数， 谓语动词可以用was。
* If he studied at this school, he would know you well. 如果他在这所学校学习的话，他会对你很熟悉。
* If I were you, I would go. 假如我是你，我会去的。
* 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。
* If it were not raining, we should go for a picnic. 如果现在不下雨的话，我们就出去野餐了。
* If he was here, he might be able to help you. 如果他在这里，他就能够帮助你了。

2) 条件句中有时可以用 were to + 动词原形 或 should + 动词原形。
* If it were to snow tomorrow, many crops would die of cold. 如果明天下雪，许多庄稼都会冻死。
* If she were to be there 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。
* If he should go to Qing Hua University, he would make full use of his time. 如果他要上清华大学的话，他就会充分利用他的时间了。
* If Tom should come here tomorrow, I would talk to him. 如果汤姆明天来这儿的话，我就跟他谈谈。

3) 条件句中有时可以用 If it were not for 句式。意思为 “若不是”。
* If it were not for his help, we would be working now. 要不是有他的帮助，我们还会在工作呢。
* If it weren't for the Internet, everything would be very difficult. 要不是互联网，一切都会变得很难。
* Were it not for the expense, I would go to Britain. 要不是费用的问题，我会去英国。

4) if 有时可以省略，改用倒装语序。
* Were you in my position, you would do the same. 假如你处在我的位置，你也会那样做的。
* Were I ten years younger, I would study abroad. 要是我能年轻十岁的话，我会去国外学习。
* Should they attack us, we would wipe them out completely. 假如他们攻击我们，我们就把他们彻底消灭干净。
* Should he agree to go there, we would send him there. 要是他答应去的话，我们就派他去。

5) 极少情况下， 从句中的谓语可用动词原形， 主句中的谓语用陈述语气。 这种用法口语中很少使用。
If that be the official view, it cannot be accepted. 如果这是官方的看法，这是不能接受的。
If any vehicle be found parked on these premises, it shall be towed away. 如果发现有车停在此处，它将被拖走。

2. 表示过去情况的虚拟条件句

这类句子用于假设一个与过去事实相反的情况。

1） 条件句中的谓语用过去完成时， 主句的谓语为 would/might/could/should + have + 过去分词。
* She would have gone to the party if she had been invited. 要是当初她被要求的话，她就会去参加这次聚会了。
* If I had gotten there earlier, I might have met her. 如果我早到那儿，我有可能会见到她。
* You could have passed this exam if you'd studied harder. 如果你学习再努力一点的话你这次就能通过考试了。
* She should have achieved greater progress, if you had given her more chances. 如果你多给她点机会，她应该会取得更大的成绩。
* If I'd been not busy yesterday, I would have come. 如果我昨天不是很忙，我就去了。
* He wouldn't have made such a mistake, if he had taken my advice. 如果他听我的劝告的话，就不会犯这样的错误了。

2） 条件句中可以用 have not been for, 意思为 “要不是”。
* If it had not been for your help, I wouldn't have finished the work so easily. 要不是你的帮忙，我的工作不会这么容易完成。
* If it had not been for the storm, I could have arrived much earlier. 要不是那场暴雨，我可能早就到达了。
* If it hadn't been for your overcoat, I might have died of cold. 要不是有你的大衣，我可能冻死了。

3） if 有时可以省略，改用倒装语序。
* Had you not helped me, I should have failed. 假如没有你的帮助，我就失败了。
* Had she learnt about computers, we would have hired her to work here. 如果她懂一些电脑知识的话，我们已经聘请她来这里工作了。
* Had it not been for the alarm clock, she might not have been late this morning. 要不是闹钟的问题，她今天早上就不会迟到了。

3. 错综时间条件句
有时条件句与主句谓语时态的搭配并不一致， 这种情况称为错综时间条件句。
* If I had spoken to him yesterday, I should know what to do now. 假如昨天我对他说了，现在我就知道该怎么办了。
* If it had not been for the doctor's care the girl should not be speaking to you now .要不是由于大夫的精心照料，这个女孩现在就不能与你说话了。
* If I were you, I would have gone to her birthday party. 如果我是你，我就去参加她的生日晚会了。
* If they had left home in early morning, they might arrive in half an hour. 如果他们今天早上很早离开了家，他们可能会在半个小时后到达。
* If he hadn't been working hard in the past few years, things wouldn't be going so smoothly. 如果不是他这些年来一直努力工作，事情就不会发展得这么顺利了。