虚拟语气用于非真实条件句中有下列几种情形：
1. 表示与现在事实相反的虚拟语气，非真实条件句中的谓语动词用“过去式(be动词一般用were)”，而主句的谓语动词用“would / should / could / might + 动词原形”。如：
①If I were you I would stay here. 如果我是你，我就呆在这儿。
②We would go with you if we had time. 如果我们有时间，会和你一起去的。
2. 表示与过去事实相反的虚拟语气，非真实条件句中的谓语动词用“过去完成时”，而主句的谓语动词用“would / should / could / might + have + 过去分词”。如：
①If he had come here yesterday, I should have told him about it. 如果他昨天到这里来，我早就告诉他这件事了。
②If I had seen you yesterday, I would have asked you about it. 如果我昨天看到你，我就会问你这件事。
3. 表示与将来事实相反的虚拟语气，非真实条件句中的谓语动词用“过去式或should或were to + 动词原形”，而主句的谓语动词用“would / should / could / might + 动词原形”。如：
①If it should rain this afternoon, the basketball match would be put off. 要是今天下午下雨，篮球比赛就延期举行。
②If it were to snow tomorrow, they wouldn't go for an outing. 如果明天下雪，他们就不外出游玩。
4. 错综时间条件句中的虚拟语气即当非真实条件句中表示的行为与主句表示的行为所发生的时间不一致时，动词的形式要根据它所表示的时间做出相应的调整。如：
①If we hadn't been working hard in the past few years(过去), things wouldn't be so smoothly now(现在). 要是我没有过去几年的勤奋工作，那事情就不会有现在这样平稳了。
②If you had worked hard yesterday(过去), you would be tired now (现在). 如果你昨天工作很辛苦的话，那你现在就会很疲劳的。
