条件句有两类,一类是真实条件句,一类是虚拟条件句。如果假设的情况是有可能发生的,就是真实条件何。在这种真实条件句中的谓语用陈述语气。如: If it doesn’t rain tomorrow, we will go to the park. 如果明天不下雨,我们就去公园。
如果假设的情况是过去或现在都不存在的,或将来不大可能发生的,则是虚拟条件句。如: If he had seen you yesterday, he would have asked you about it. 如果他昨天见到你,他会问你这件事的。(事实上他昨天没见到你,因此也未能问你这件事。)
在含有虚拟条件句的复合句中,主句和从句的谓语都要用虚拟语气。现将虚拟条件从句和主句的动词形式列表如下:
|
从 句 |
主 句 |
与现在事实相反 |
动词的过去式(be的过去式一般用were) |
would/ should/ could/ might + 动词原形 |
与过去事实相反 |
had + 过去分词 |
would/ should/ could/
might + have + 过去分词 |
与将来事实相反 |
动词过去式,should + 动词原形,were to + 动词原形 |
would/ should/ could/ might + 动词原形 |
注: 主句中的should只用于I、we,但在美国英语中,should常被would代替;从句中的should 可用于各种人称。
l、表示与现在事实相反的假设和结果。如: If my brother were here, everything would be all right. 要是我哥哥在这儿 ,一切都没问题了。
2、表示与过去事实相反的假设和结果。如: If you had taken my advice,you wouldn't (couldn’t) have failed in the exam. 如果你按照我的建议去做,你一定不会(不可能)考试不及格。