(完整版)wouldshouldcouldhavedone用法和区别.doc

would/could/might/shouldhavedone等用法和区别一、在虚拟语气中的用法（情态动词都是过去时态！）1.shouldhavedone：原本应该做某事，(否)shouldn'thavedone:原本不该做某事2.oughttohavedone原本应该做某事，(否)oughtn'ttohavedone:原本不该做某事注意：oughttodo语气更强，常用于长辈对小辈的用语或某规则上的要求（严格的规则应用must）．shoulddo可用语平辈朋友间，较为客气与口语化3.needhavedone原有必要做某事(否)needn'thavedone原本没必要做某事注意：做情态动词，need的过去式仍然是need;做实意动词，need的过去式是needed.couldhavedone原本能够做某事注意：couldn'thavedone无虚拟语气的用法，只表推测，相当于can'thavedone：过去不可能做了某事mighthavedone原本可以做某事注意：mightnothavedone无虚拟语气的用法，只表推测，相当于maynothavedone：过去可能没有做某事6.wouldhavedone原本会做某事1.Iwouldhavetoldyouallabouttheboy'sstory,butyoudidn'taskme.二、对过去事情表推测的用法(情态动词用原型或过去式都可以，只是在说话者看来，可能性大小稍微有所不同而已)1.musthavedone：过去肯定做了某事。不存在mustn'thavedone的形式。其否定或疑问形式须用can(could)havedone：“不可能做过某事”来表示：Sincetheroadiswet,itmusthaverainedlastnight.既然路是湿的，那昨天晚上肯定下雨了。Hecan't/couldn`thavemissedtheway.Idrewhimamap.他不可能迷路。我（当时）给他画了张图。“Thedictionaryhasdisappeared.Whocould/canhavetakenit?”词典不见了，（过去）谁可能把它拿走了？2.may/mighthavedonemay/mighthavedone：过去可能做了某事，may比might表示可能性稍大些。may/mightnothavedone过去可能没有做某事：Ican'tfindmykeys.Imay/mighthaveleftthemattheschoolyesterday.我找不到我的钥匙了。我可能昨天把他们落在学校了。Johnmay/mightnothavepassedtheexam;helooksverysad.约翰可能没有通过考试。他看起来很忧伤。注意：may/mighthavedone表推测不能用于疑问句中,疑问句中表推测，一般用can/couldhavedonesth.很可能做过某事3.can/couldhavedone常用于(否定句)和(疑问句),间或(肯定句)Can/Couldhehavepassedtheexam?他可能通过了考试吗？Ithinkthathecouldn’t/can'thavegoneabroad.Isawhimjustnow.我认为他不可能出国了。我刚才还看见他了。注：表示推测过去某动作发生的可能性时，就表示的可能性程度而言，must最大，could其次，may更次之，might最小。例如：“Hemust/could/may/mighthaveheardofitfromMary.”“他肯定/很可能/可能/兴许（没准儿）已从玛丽那儿听说此事了。”wouldhavedone:想必会/肯定会做某事PresidentObamahascanceledplanstosetstrongerairqualityrulesintheUnitedStates.Thepresidentsaidtheseplanswouldhaveforced（想必会/肯定会迫使）businessestotakeactionatatimewhenthecountry'seconomyisweak.OnFriday,presidentObamaorderedenvironmentofficialstohaltaplanthatwouldhaveaffected（想必会/肯定会影响）companies,statesandcities.Allthreewouldhaverequiredtoreducetheamountofchemicalsthatcasesmog.Failuretodoso,wouldhaveledto（肯定会/想必会导致）federalaction.