第一类 If虚拟条件句
分三种时态：与现在事实相反、与过去事实相反、与将来事实相反。
*条件句有真实条件句和非真实(虚拟)条件句两种。真实条件句的假设是有可能发生的，而非真实条件句的假想与事实相反或不大可能会发生，试比较：
If I have time, I will go with them. 假若我有时间，我就同他们去。(陈述语气)
If I had time, I would go with them. 假若我有时间，我就同他们去。(虚拟语气)
这是对现在事实的虚拟，事实是我没有时间，所以我没有和他们去
If条件句虚拟
| 时态类型 |
主句 |
If引导的从句 |
例句 |
| 与现在事实相反 |
would/should/could/might+ V原 |
动词过去式 did
*be 多用were |
1. If I were you, I should study English.
2. I would certainly go if I had time. |
| 与过去事实相反 |
would/should/could/might + have done |
动词过去完成式
had done |
1. If you had taken my advice, you would not have failed in the test.
2. If I had left a little earlier, I would have caught the train. |
| 与将来事实相反 |
would/should/could/might + V原 |
①动词过去式
②should +V原
③were + to do |
1.If you came tomorrow, we would have the meeting. ①
2. If it were to rain tomorrow, the meeting would be put off.③ |
| *规律总结：从句都往过去推一个时态，如：与现在相反的if从句就用过去时；与过去相反用过去完成时（即过去的过去） |
注：几点特别说明
1、l would/should/could/might 主句谓语中的should主要用于第一人称后；would表示结果还表示过去经常常常做某事，might表示可能性，could表示能力、允许或可能性。比较：
If you tried again ，you would succeed. 要是你再试一试，你就会成功的。(would表结果)
If you tried again， you might succeed. 要是你再试一试，你可能会成功的。(might表可能)
If you tried again ，you could succeed. 要是你再试一试，你就能成功了。(could表能力)
2、 错综时间虚拟条件句 即条件从句与主句所指时间不一致，如从句指过去，而主句即指的是现在或将来，此时应根据具体的语境情况，结合上面提到的三种基本类型对时态作相应的调整：
If it had rained last night, the ground would be wet now. 要是昨晚下过雨的话，现在地面就会是湿的。
You would be much better now if you had taken my advice. 假若你当时听我的话，你现在就会好多了。
3、 If虚拟条件句的否定（含蓄条件句） 常考两个句型：If it weren’t for…和If it hadn’t been for…，其意为“若不是(有)” “要不是”。如：
If it weren’t for water, no plant could grow. 要是没有水植物就无法生长。
If it hadn’t been for your assistance ，we wouldn’t have succeeded.
=But for your assistance ，we wouldn’t have succeeded.
=Without your assistance ，we wouldn’t have succeeded.
4、 If虚拟条件句的倒装形式，即把were, had, should置于句首。例：
Were I in school again (= If I were in school again), I would work harder.
Had you asked me, I would have told you. (=If you had asked me,…)
