GrammarandusageUnitUnit22情态动词没有人称和数的变化，有词义，但是不完整，不能单独做谓语，必须和不带to的动词不定式连用。abilitycertaintypermissionobligationmakerequestsmakesuggestionsmakeoffersgiveadvice能力义务,责任确定允许提出请求提出建议提供帮忙提出忠告Modalverbs:generalintroduction(1)Hecanrunthe100msprintin11seconds.(2)Canthislittlegirlreadbeforeshegoestotheprimaryschool?ability•can表示可能性时，指的是理论上的可能，它通常不用来表示某事实际发生的可能性或真实性。如：•Accidentscanhappen．Anybodycanmakemistakes．can/beabletocan/beabletoability•在过去时态的肯定句中需要某种条件或努力做成某事，我们要用was／wereableto而不能用could。如：•Itwasaholidayandthechildrenwereabletogototheseaside．•Thegirlworkedhardsoshewasabletopassthefinaltest．•I’msorryIhaven’tbeenabletoplaytenniswithyourecently.obligationoughtto/should•oughtto与should意思接近，大多数情况下二者可以互换，但是should谈的是自己的主观看法,用于各种人称。oughtto则更多反映客观情况，在谈到法律、义务和规定时使用。如：•Weshould／oughttohelpeachotherandlearnfromeachotherinourwork．•Youshouldn’tspendsomuchtimeplaying.•Sheisyourmother,soyououghttosupporther．•Oughthetogo?Yes,Ithinkheought(to).haveto/mustobligationmust与haveto都可以表示“必须”的意思，但要注意以下两点区别。1)must只有现在时，而haveto有现在时、过去时和将来时。如：Wemustworkhard,orwe’llfailintheexamination．Twoyearsago,thepoorgirlhadtoleaveschoolforlackofmoney．2)must表示主观看法，haveto则侧重于客观需要。如：Wemustbestrictwithourselvesineverything．Incitieswithmanycars,somepeoplehavetowearmasks．obligationhaveto/mustShemightwinamedalattheOlympics.Shemaybeathomenow.Shecouldreadandwriteattheageof4.Sheshouldcometojoinus.Sheoughtto/will/musthelpmewheneverIamintrouble.certaintymight/may/could/should/oughtto/will/mustveryuncertaintyalmostcertaintycan/could/may/mightcould比can更委婉，might比may更委婉•---CanIwatchtheOlympics?•---Yes,youcan.No,youcan’t.•---MayIwatchTVafterfinishingmyhomework?•---Yes,youmay./No,youmustn’t./No,youmaynot./No,you’dbetternot.permissioninformal/spokenformal/written•--Will/Can/Could/Wouldyouhelpmewithmytraining?•--Yes,Iwill/can/can/will.will/can/could/wouldmakerequestsinformalformalmakesuggestions•shall常用于第一，三人称，表示征求对方意见。•--Shallwe/I/he/she/theydosomeexercisethismorning?•--Yes.•--Shallhecomein?•--Ok.makeoffers•I’llwashyoursportsjacket.•ShallIgetaticketforyou?•Shallwecarrythebooksforyou?•ShallIcleantheblackboardforyou?giveadvice•Youshouldnot/oughtnottoeatalotbeforeswimming.•Thestudentsshouldspendalltheirtimeworkingattheirlessons.和其他时态的连用•Theboysmaybeplayingfootballontheplayground.•Theboysmayhavefinishedtheirhomeworkbythetimeschoolisover.•Heplaysbasketballverywell.Hemusthavepracticeditalot.•OurheadmastermusthavebeentoUSA,forheknowsthecountrysomuch.musthavedone的反意疑问句•Youmusthaveseenthefilm,haven’tyou?•Youmusthaveseenthefilmlastweek,didn’tyou?•Hisparentsmusthavebeatenhim,haven’tthey?•Hisparentsmusthavebeatenhimyesterday,didn’tthey?shall可以用来征求对方意见。用于第一、三人称。此外它也可以用来表示说话人的命令、警告、允诺、威胁或决心等，这时它用于第二、三人称。如：Shallshegototheconcertwithusthisevening？(征求意见)Youshallgotothefrontatonce．(命令)Don’tworry．Youshallgettheanswerthisveryafternoon．（允诺）Heshallbesorryoneday．Itellyou．(警告)Nothingshallstopusfromfight...
