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if如何构成虚拟条件句的?

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if如何构成虚拟条件句的?
虚拟语气在非真实条件状语从句中的用法及动词形式
① 表示与现在事实相反的情况
(条件)从句谓语动词形式 主句谓语动词形式
谓语动词用一般过去式
(be用were) should/would/could/might+动词原形(过去将来时)
eg.
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:学习不用功)
②表示与过去事实相反的情况
从句谓语动词形式 主句谓语动词形式
had+过去分词(过去完成时) should/would/could/might+
have+过去分词(现在完成将来时)(过去将来完成时)
eg.If I had got there earlier,I should/could 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表示对将来情况的主观推测(可能相反或可能性很小)
从句谓语动词形式 主句谓语动词形式
If+主语+ ① should+动词
② did
③were to do
(①通常与一个表示时间状语连用)其 中were to do可能性最小,
should/would/could/might+动词原形
eg.If he would come here tomorrow,I should/would talk to him.如果他哪天来这儿的话,我就跟他谈谈.(事实:来的可能性很小)
If there were a heavy snow next Sunday,we would not go skating.如果下周日下大雪,我们就不能去滑冰了.(事实:不知能否下雪)
If she were to be there 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得始末.
在表示建议、命令、要求等含义的宾语从句,谓语动词常用虚拟语气,"should+动词原形"构成,should 可省略.