是假设性的。比如,如果你再晚一分钟,就见不到我了。
或者,万一你不小心丢了机票,就到达不了北京了。
表示所陈述的事与现在事实相反或不可实现的愿望。
一、与现在事实相反(主句和从句的谓语动词都必须用过去式)
例:如果我是你(我不是你)的话,我不会和他打架。
If I were you , I wouldn't fight with him .
二、与过去事实相反(主句:would have+动词过去分词;从句:had+动词过去分词)
例:如果昨天我没去打篮球(打了篮球)的话,我会完成我的作业。
If I hadn't played basketball yesterday , I would
have finished my homework.
三、与将来事实相反(主句的谓语动词用过去式;从句:should(可省略)+ 动词原型)
例:如果我将来当教师(将来不当教师)的话,我不会是一个好老师。
If I (should) be a teacher in the future , I wasn't
a good teacher.