如果天下雨的话，庄稼就有救了。

If it were to snow tomorrow, they would not go out.

如果明天下雪，他们就不去了。

1． 与过去事实相反：

条件从句的谓语用 had + 过去分词，主句的谓语用would ( should , could , might ) + have + 过去分词。

If the hurricane had happened during the day time, there would have been many more deaths.

如果飓风发生在白天，那么死亡人数还会多得多。

I would have called you if I had known your telephone number.

如果我当时知道你的号码，我就给你打电话了。

在实际运用过程中，虚拟语气会有以下情况：

1． 如果条件状语从句中有were , had , should , 有时可以把if省略掉，把were , had , should放在主语前。例如：

Were I twenty now, I would join the army.

如果我现在是二十岁，我就参军。

Had we made a great effort, we might have succeeded.

如果我们之前作了很大努力的话，我们就可能成功。

Should Mr. Smith call what would you say?

如果史密斯先生来电话你怎么说呢？

2．含蓄条件句：假设的情况并不以条件从句表示而是通过一介词短语( without , but for , otherwise 等 )表示。例如：

Without electricity human life would be quite different today.

如果没有电，人类现在的生活就会是另外的样子。

But for your help we couldn't have succeeded in the experiment.

如果没有你的帮助，我们的实验是不会成功的。

3有时，条件从句表示的动作和主句的动作发生的时间不一致。如：一个是过去发生，一个是现在发生的，这时动词的形式根据表示的时间来调整。例如：

If you were in better health, we would have allowed you to join them in the work.