定义：表示说的话不是事实，或不可能发生，只是一种愿望、假设或建议等。分类：时间选择型should+动词原形型一般过去式型一、时间选择型If虚拟条件状语从句wish引导的宾语从句evenif/eventhough引导的让步状从asif/asthough引导的表语从句和方式状从wouldrather引导的从句(一)If虚拟条件状语从句当虚拟语气表示一种不可能或与现实相反的情况时，须根据与现在、过去和将来情况相反的三种不同时间从而决定谓语动词。条件状语从句主句现在If+主+were/did主+would/should+do过去If+主+haddone主+wouldhavedone(should)将来If+主+didweretodo主+would/should+doshould+do说明：主句中的should通常用于第一人称，would可用于任何人称，同时也可跟据意思用could,might替换。1.IfIhadmoretime,IshouldstudyGerman.2.Ifyouhadtakenhisadvice,youwon’thavemadesuchamistake.3.IfTomshouldcometomorrow,Icouldhaveatalkwithhim.注意：1.当条件状语从句的动作和主句的动作所发生的时间不一致时，动词的形式决定于要表示的具体时间。Ifhehadtakenthemedicine,hewouldbeallrightnow.从句说的是过去，而主句讲的是现在。IfIwereyou,Iwouldhavegonewithhim.从句说的是现在，而主句讲的是过去。2.如果条件状语从句中含有were,should,had,可以省略连词if，把这些词放在主语之前构成倒装句。Hadyoucomeyesterday,youwouldhavemethim.Shoulditraintomorrow,themeetingwouldbeputoff.Wereshehere,shecouldgiveushelp.3.可以用介词短语、分词短语等形式代替条件状语从句，表示含蓄的虚拟语气。Butforthetrafficjam,wewouldhavearrived.Withoutair,wecouldn’tlive.(二)wish引导的宾语从句wish引导的宾语从句表示不能实现的愿望，汉语可译为“可惜……”,“……就好了”，“但愿……”时间从句动词表示现在不能实现的愿望did过去haddone将来woulddo(might)(1)IwishIknewhowtooperatethemachine.(2)IwishyouhadcometoourNewYear’sparty.(3)Iwishyoucouldgowithustomorrow.类似：Ifonly“要是……就好了”，“但愿……”后面常用过去式或完成时IfonlyIwereyounger.IfonlyIhadtakenyouradvice.(三)evenif/eventhough引导的让步状语从句，其谓语动词的变化同If虚拟条件句。Evenifhewerehere,hewouldn’tbeabletohelpyou.(四)asif/asthough引导的表语从句和方式状语从句可以用虚拟语气。时间从句动词形式从句表示与现在事实相反did过去haddone将来woulddo(might)Itseemsasifitwerespringalready.Heistalkingasifhehadbeenthereatthattime.Itlooksasifitmightsnow.注意:asif/asthough引导的从句也可以用陈述语气，特别是表示的情况是真实地或可能性很大时。Itlooksasifitisgoingtorain.(五)wouldrather后接从句，从句用过去式表现在或将来，用过去完成时表示过去。Iwouldratheryouwenttherenow.Iwouldratheryoucametomorrow.I’dratherhehadn’ttoldyouaboutit.二、should+动词原形型主语从句Itis+adj./done+主从表示命令、建议等的宾从表从同位从should在口语中可以省略(一)主从用以表示惊讶，惋惜，理应如此等Itis+adj./done+主从常用的adj.有：necessary,important,impossible,strange等过去分词多是表示提议、要求、命令等动词的过去分词。如:suggested,required,requested,demanded,proposed,recommended,ordered,desired,advised等。It’snecessarythathe(should)besentthereatonce.ItisrequestedthatTom(should)giveaperformanceattheparty.(二)上述动词后的宾语从句，及其名词后的表从、同位从用虚拟语气Isuggestedthatwe(should)formasparetimestudygroup.<宾从>Mysuggestionisthatwe(should)sendsomemoneytohelpher.<表从>Thesoldiergavethesuggestionthatthebridge(should)bedestroyed.<同位从>三、一般过去式型用于“Itis(high)time(that)”句型中。“现在该……”that从句中谓语动词用过去式或should+doItishightimethatIwenttoschoolandpickedupmylittledaughter.Itistimeweshouldhavedinner.
