虚拟条件句往往指不能实现的或纯假想的情况，可以对过去现在将来进行假想。
1）表示与现在情况相反，if从句用一般过去时态，be动词用were,主句谓语用“would/should/could/might+动词原形”。如
If I had a mini-computer on hand, I would certainly let you use it.
如果我现在手头有一台微电脑，我肯定会借给你。
If I were you, I would try my best to grasp the chance.
如果我是你，我会努力抓住这个机会。
Were I ten years younger, I would study abroad.
要是我年轻十岁，我就去国外学习。
If you tried again, you might succeed.
如果你再试一次，你一定会成功。
2）表示与过去事实相反或对过去的假想。If从句用过去完成时（had +过去分词），主语谓语用“would/should/could/might+have+过去分词”。如
If the policeman had arrived earlier, he would have seen the accident.
如果这个警察早些到达， 他就能看见事故了。
If you had come yesterday, you would have met George.
要是你昨天来，你就会碰到乔治了。
请虚拟语气在条件状语从句中的用法
3）表示将来难以实现的假设推测或纯假想的情况，从句谓语用一般过去式（be动词用were),或“were to +动词原形”，或“should+动词原形”；主句谓语用“would/should/could/might+动词原形”。如
If it should rain tomorrow, we should have to put off the picnic.
如果明天下雨，我们只好推迟野餐。
If it snowed tomorrow,our plan would be postponed.
万一明天下雪，我们的计划就得推迟。
If we should come tomorrow, we could meet the general manager.
如果我们明天真的能来，就能见到总经理。
If I were to do the job, I would do it in a different way.
要是我来做这项工作，我会用另一种方法。
4）有时候，主句和从句的动作不是同时发生，要区别对待：
⑴从句的动作与过去事实相反，而主句的动作与现在动作或状态相反或不符。
If I had worked hard at school, I would be an engineer, too.
要是我再学校努力学习的话，我现在也会是工程师了。
If they had informed us, we would not come here now.
如果他们通知我们的话，我们现在就不会来这里了。
⑵从句的动作与现在事实相反，而主句的动作与过去动作或状态相反或不符。
If he were free today, we would have sent him to Beijing.
如果他今天有空的话，我们早送他去北京了。
If he know her, he would have greeted her.
要是他认识她的话，他肯定去问候他了。
5）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等词放置于句首。
Should he agree to go there, we would send him there.
要是他答应去，我们就派他去。
Were she here, she would agree with us.
如果她再这儿，她会同意我们的。
Had he learnt about computers, we would have hired him to work here.
如果他懂得一些电脑知识，我们能就会聘用他来这里工作了。
6）有时，主句或从句可以省略一个。如
If only I had got it. 要是我得到它该多好啊！
If I were at home now. 要是我现在在家里多好！
He would have finished it.他本该完成的！
（省略if从句）
You could have passed this exam.
你本来能通考及格的。
（省略if从句）
