奔跑de小土豆
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. 3.混合条件句主句与从句的动作发生在不同的时间，这时主，从句谓语动词的虚拟语气形式因时间不同而不同，这叫做混合条件句。If you had asked him yesterday, you would know what to do now.（从句与过去事实相反，主句与现在事实相反。）If it had rained last night (过去), it would be very cold today (现在).
Leap丶飞。
i:最基本的虚拟语气句型:1.虚拟现在时表示与现在事实相反的假设，其if从句的谓语形式用动词的过去式(be一般用were)，主句用would/should/could/might+动词原形。ifplaceswerealike,therewouldbelittleneedforgeographers.如果各个地方都一样，就不需要地理学家了。2.虚拟过去时是表示与过去事实相反的假设，if从句的谓语形式用过去完成时即had＋过去分词，主句用would/should/could/might+have+过去分词。ifhehadknownyouraddressyesterday,hewouldhavetelephonedyou.3.虚拟将来时是表示对将来实现的可能性很小的或不确定的假设。if从句的谓语形式用一般过去式或用wereto/should+动词原形，主句用would/should/could/might+动词原形。ifheweretoleavetoday,hewouldgettherebyfriday4.省略if采用倒装语序的条件句。有时可以把含有助动词、情态动词、be或have的虚拟条件句中的连词if省去，而将had,should,were等词提到主语之前，即用倒装结构。hadheworkedharder,hewouldhavegotthroughtheexams.werehetoleavetoday,hewouldgettherebyfriday.wereiinyourplace,iwouldn’tdothat5.有时虚拟条件句并没来if从句表示出来，而是用介词短语(otherwise,or,without,butfor)、上下文或其它方式来表示。wedidn'tknowhistelephonenumber;otherwisewewouldhavetelephonedhim.withoutyouhelp,iwouldn’thaveachievedsomuch.butforyourhelp,iwouldnothavesucceeded.
