1.if虚拟条件句

if虚拟条件句 主句 与现在事实相反的假设 if＋主语＋动词过去式(be动词用were) 主语＋would/should/could/might＋动词原形 与过去事实相反的假设 if＋主语＋had＋过去分词 主语＋would/should/could/might＋have＋过去分词 与将来事实相反的假设 if＋主语＋ 主语＋would/should/could/might＋动词原形

　　If I were a bird，I could fly.

　　如果我是一只鸟的话，我就能飞了。

　　If we had started earlier，we would not have missed the train.如果我们早点出发，就不会错过这班火车了。

　　If he shouldn't come tomorrow，we would put off the meeting till next Monday.

　　要是他明天来不了，我们将把会议推迟到下周一。

　　注意：在if虚拟条件句中，如果从句谓语动词有were/should/had时，可以省略if，然后把were/should/had提到主语前面，形成部分倒装。

　　Were I at school again，I would study harder.

　　如果我可以再上一次学，我会更努力地学习。

　　Had you come earlier，you would have caught the bus.如果你早一点儿到，你就会赶上那趟公交车了。

　　Should it rain tomorrow，we would not go climbing.

　　如果明天下雨，我们就不去爬山。

　　2.混合条件句

　　通常情况下，虚拟条件句和主句表示的动作发生的时间是一致的，但不一致时主从句动词的形式应根据各自所表示的时间进行调整。我们把这种结构称为混合虚拟条件句、混合虚拟语气或错综虚拟条件句。可将其分为两种：

　　(1)想象中的现在状态可能对过去有影响。

If I were you，I would have taken his advice.