从句中提出一种与客观现实不相符或根本不可能存在的条件，主句会产生的一种不可能获得的结果。条件句中的虚拟语气根据不同的时间有三种不同的形式。

(1) 将来时的条件句中的虚拟语气。如：

If he should go to Qing Hua University, he would make full use of histime.

如果他要上清华大学的话，他就会充分利用他的时间了。

If he were to come here, he would tell us about it.

如果他要来的话，他会通知我们一声。

(2) 现在时的条件句中的虚拟语气。如：

If he were free, he would help us. 要是他有空的话，它会帮助我们的。

If he studied at this school, he would know you well.

如果他在这所学校学习的话，它会对你很熟悉。

(3) 过去时的条件句中的虚拟语气。如：

If I had seen the film, I would have told you about it.

我如果看过这场电影，我会把电影内容告诉你了。

If I had got there earlier, I would have met Mr. Li.

如果我早点到那儿，我就会会到了李先生。

(1) 当从句的主语为第三人称单数时，谓语动词若是系动词be时，可用was代替were。但在倒装虚拟结构及if I were you, as it were中，只能用were。如：

Were I ten years younger, I would study abroad.

要是我还年轻十岁的话，我会去国外学习。

If I were you, I would try my best to grasp the chance.

要是我是你的话，我要尽力抓住这次机会。

(2) 有时，虚拟条件句中，主、从句的动作若不是同时发生时，须区别对待。

①从句的动作与过去事实相反，而主句的动作与现在或现在正在发生的事实不符。如：If I had worked hard at school, I would be an engineer,too.

如果我在学校学习刻苦的话，我现在也会使工程师了

If they had informed us, we would not come here now.

如果他们通知过我们的话，我们现在就不会来这里了。

②从句的动作与现在事实相反，而主句的动作与过去事实不符。如：

If he were free today, we would have sent him to Beijing.

如果他今天有空的话，我们会已经派他去北京了。

If he knew her, he would have greeted her.

要是他认识她的话，他肯定会去问候她了。

③从句的动作与过去发生的情况相反，而主句的动作与现在正在发生的情况相反。如：If it had not been raining too much, the crops would begrowing much better. 如果天不下太多的雨的话，庄家会长得更好。

If he had been working hard, he would be working in the office now.

要是他工作一直努力的话，他现在已进了办公室了。

(3)当虚拟条件句的谓语动词含有were, should, had时，if可省略，而将were,should, had等词置于句首。如：Should heagree to go there, we would send him there.

要是他答应去的话，我们就派他去。

Wereshe here, she would agree with us. 如果她在这儿的话，她会同意我们的。

Had he learnt about computers, we would have hired him towork here.

如果她懂一些电脑知识的话，我们会已经聘用他来这里工作了

(4) 有时，句子没有直接给出假设情况的条件，而须通过上下文或其他方式来判断。如：

I would have come to see you, but I was too busy. 我本该来看你了，然而我太忙了。

But for his help, we would be working now. 要不是他的帮助，我们还会在工作呢。

Without your instruction, I would not have made such greatprogress.

要是没有你的指导，我不会取得如此大的进步。

(5) 有时，虚拟条件句中，主、从句可以省略其中的一个，来表示说话人的一种强烈的感情。

①省略从句

He would have finished it. 他本该完成了。

You could have passed this exam. 你应该会通过这次考试了。

②省略主句

If I were at home now. 要是我现在在家里该多好啊。

If only I had got it. 要是我得到它了该多好啊。