if引导的虚拟条件句三种句型 1 与现在 2 与将来 3 与过去
一、对现在情况的虚拟
条件从句中谓语动词用一般过去式，主句用“would/should/might/could+动词原形”形式，表示对现在不可能实现情况的假想。
If I were you,I would choose to work in a small town.
如果我是你，我会选择在小城镇工作。（事实上我不是你）
If I had a map now,we could easily get out of the forest.
如果现在有地图，我们能很容易地走出森林。（事实上是现在没有地图）
注意：在条件从句中，如果谓语动词是be的形式，不管主语是单数还是复数，书面语中用were,而口语中如果是单数，也可以用was,不过在if I were...中一般用were.
If the world were perfect,how could we enjoy the pleasure and comfort of being successful?
世界若完美，我们如何能尝到创造成功的快慰？
二、对过去情况的虚拟
条件从句中谓语动词用过去完成式，主语用“would/could/should/might+have+动词的过去分词”形式。
If it had not been for your help yesterday,I could not have caught the bus.
如果昨天没有你的帮助，我不会赶上公交车。（事实是你昨天已经帮助了我，所以我赶上了车)
三、对将来情况的虚拟
在表示与将来事实相反的条件从句中，谓语动词可用should do,were to do或动词的过去式三种形式表示，但意义略有不同。should表示的可能性最大，动词过去式的可能性次之，were to do 的可能性最小。
If things were to be twice，all would be wise.
假如凡事都可以重新做一次，人人皆可成为聪明人。（事实是并不是所有的事都可以重新做一次)。
扩展资料
虚拟条件句往往指不能实现或纯假想的情况，可以对过去、现在或将来进行假想。
虚拟语气的本质就是对根本不可能的情况发生假设。我们可以记住这样一个原则，即把时态向过去推一格。
其他虚拟条件句
一、错综时间条件句
有些条件句的主句谓语和从句谓语表示的动作在时间上并不一致，这类句子称为错综时间条件句。
If you had taken my advice then,you would not be in trouble now.
如果当时听我的劝，你现在就不会有麻烦了。(if 条件句是对过去的虚拟，故用过去完成时，而主句是对现在的虚拟，故用“would+动词原形”形式）
二、含蓄条件句
有些句子虽不含条件从句，但意思和条件句相差不多，这种句子称为“含蓄条件句”，这种句子有时候会用虚拟语气。
Without electricity,the world would be dark.(=If there were no electricity ,the world would be dark.)
如果没有电，世界将会一片黑暗。
参考资料：百度百科虚拟条件句
1）时态：可以表示过去,现在和将来的情况.它的基本特点是时态退后.
a.同现在事实相反的假设.
句型 ：条件从句 主句
一般过去时 should( would) +动词原形
If they were here,they would help you.
b.表示于过去事实相反的假设.
句型：条件从句 主句
过去完成时 should(would) have+ 过去分词
If she had worked harder,she would have succeeded.
The rice would not have been burnt if you had been more careful.
If my lawyer had been here last Saturday,he would have prevented me from going.
If he had come yesterday,I should / would have told him about it.
含义：He did not come yesterday,so I did not tell him about it.
If he had not been ill and missed many classes,he would have made greater progress.
含义：He was ill and missed many lessons,so he did not make greater progress.
c.表示对将来的假想
句型：条件从句 主句
一般过去时 should+ 动词原形
were+ 不定式 would + 动词原形
should+ 动词原形
If you succeeded,everything would be all right.
If you should succeed,everything would be all right.
If you were to succeed,everything would be all right.
条件从句谓语动词——一般过去时
主句谓语动词——would/should/might/could+动词原形
eg:a.If I were you,I would choose study hard.(事实上，
我不是你)
b.If I had a good friend,I could happily everyday.(事实上，我没有一个好朋友)
注:在条件从句中，谓语动词是be动词形式，不管主语是单数还是复数，都用were。
二、对过去的虚拟
条件从句谓语动词——过去完成时
主句谓语动词——would/could/should/might+have+v-ed(动词的过去分词)
eg:If it had been for your help yesterday,I could not have caught the bus.(事实上，你昨天已经帮助了我，所以我赶上了车)
三、对将来的虚拟
条件从句谓语动词——should do/were to/v-ed(动词的过去式)
主句谓语动词——would/could/should/might+动词原形
eg:a.If you came tomorrow,we would have the meeting.(事实上，你明天不来)
b.If it were to rain tomorrow,the event would be put off.(事实上，明天不会下雨)
c.If he should not come tomorrow,we should put off the meeting till next Monday.( 事实上，他一定会来)
2、与将来事实可能相反的，if 从句用should （或were to ）加动词原形，主句用would加动词原形。
在笔语中，条件从句有时可以不用连词小而把were，had或should移至主语之前。但如从句没有were，had或should，则一般不能这样做
如：Should he come，tell him to ring me up.
他要是来了，让他给我打个电话。
If I were you, I would helphim. （对现在的虚拟，假如我是你）
