非真实条件句中的虚拟语气
虚拟语气在非真实条件句中可表示与现在或客观事实相反、与过去事实相反以及与将来事实可能相反的情况。不同时态的非真实条件句采用不同的谓语形式。
1. 表示与现在或客观事实相反的非真实条件句，主句的谓语动词用"would （should ， could ， might ）＋动词原形" ，从句的谓语动词用过去式（be 的过去式一般用 were ）。例如： If he were here, I would explain to him myself. 要是他在这里我就亲自向他解释了。 If there were no water on the earth, there would be no life. 如果地球上没有水，就不会有生命。
2. 表示与过去事实相反的非真实条件句，主句的谓语动词用"would （
should ， could ， might ）＋have ＋过去分词" 构成，从句用"had ＋过去分词" 构成。例如：
I wouldn't have believed it, if I hadn't seen it happen. 要不是亲眼目睹，我决不会相信有这种事。
If I had seen him yesterday, I would have asked him for help. 如果我昨天看见他，我就向他求助了。
3. 表示与将来事实可能相反的非真实条件句，从句的谓语动词用一般过去式或用"should ＋动词原形" 或用"were to＋动词原形" 均可，主句的谓语动词则用"would （should, might， could ）+动词原形" 。例如：
If we had time tomorrow, we would go with you. 如果我们明天有时间，我们就跟你去。 If I knew his address, I would tell you. 我要是知道他的地址，我就会告诉你。
4. 有时主句和从句的时态不一致，这种条件句叫做混合条件句，又叫错综时间条件句。使用错综时间条件句时要注意主句和从句的谓语动词要与它们各自的时态保持一致。例如： If he had spoken to me just now, I would know what to do now. 假如他刚才对我说了，现在我就知道该怎么办了。
If you had followed the doctor's advice the day before yesterday, you wouldn't be ill so seriously today. 要是前天听了医生的劝告，今天你就不会病得这么厉害了。
5. 在书面语中，如果条件从句含有 were, had, should，可将连词 if 省略，再将 were, had 或 should 移至句首，构成非真实条件句的倒装语序。例如：
Had you been here just now, you would have met her. 你要是刚才在这儿，就见到她了。 Were I not busy, I would have come. 假如我不忙，我就会来了。