同学你好，该知识点来自沪江网校《【Uni智能】托福签95冲105分名师VIP-高中起点【签约现金奖励班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好~
1、表示与现在事实相反的情况
从句：If+主语+动词一般过去时(Be动词用were)
主句：主语+ should/would/might/could+do：
If I were you，I would take an umbrella.
　　如果我是你，我会带把伞。（事实：我不可能是你）
If I knew his telephone number，I would tell you.
　　如果我知道他的电话号码，我就会告诉你。（事实：不知道）
If there were no air or water，there would be no living things on the earth.
　　如果没有水和空气，地球上就不会有生物。(事实：地球上既有空气也有水)
If I had any money with me，I could lend you some.
　　如果我带钱了，我就会借给你些。（事实：没有带钱）
If he studied harder，he might pass the exam.
　　如果他再努力些，就能通过考试了。（事实：没有努力）
If I were you， I'd wear a shirt and tie.
　　如果我是你，我就会穿衬衫和领带。(事实：我并不是你） [1]
2、表示与过去事实相反的情况
从句：If+主语+had+done
主句：主语+should/would/might/could+have done
eg：
If I had got there earlier，I should/would have met her.
　　如果我早到那儿，我就会见到她。
　　（事实：去晚了）
If he had taken my advice，he would not have made such a mistake.
　　如果他听我的劝告的话，就不会犯这样的错误了。
　　（事实：没有听我的话）
3、表示与将来事实相反
从句：①if+主语+were to do
②if+主语+should+do
主句：主语+should/would/might/could+do
eg：
If he should come here tomorrow，I would talk to him.
　　如果他明天来这儿的话，我就跟他谈谈。（事实：来的可能性很小，不可能）
If there were a heavy snow next Sunday，we would go skating.
　　如果下周日下大雪，我们就去滑冰。（事实：下雪可能性很小，不可能）
If she were to be here next Monday，I would tell her about the matter.
　　如果她下周一来这儿的话，我就会告诉她这件事的始末。（事实：来的可能性很小，不可能）

记忆时按照这种方式来理解，条件从句的虚拟格式都是固定的，所以只要理解到了，应用起来非常容易~
祝学习愉快！