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英語情態(tài)動詞的基礎(chǔ)語法
情態(tài)動詞有can(能),may(可以),must(必須),have to(不得不),ought to(應(yīng)該),dare(敢),used to(過去經(jīng)常),had better(最好),would rather(寧愿)，朗曼基礎(chǔ)語法9 情態(tài)動詞。在肯定句中它們后邊都要接 動詞原形 。在否定句中，can,may,must和dare后邊加not；have to和ought to分別在have和ought后加not；used to的否定式可用used not to，也可用didn't use to，但后者用得較多；had better和would rather的否定式分別是had better not和would rather not。這些情態(tài)動詞與現(xiàn)在完成時(shí)連用在某種意義上有一定的虛擬性。
I 肯定句和否定句中的情態(tài)動詞
一、情態(tài)動詞的現(xiàn)在式在肯定句中的比較
1. can表示體力或腦力方面的“能力”、“技能”或根據(jù)客觀條件能做某種動作的“可能性”
1) Mild forms of execrise can some of the loss of flexibility that accompanies aging.
［A］ stop
［B］ to stop
［C］ stopping
［D］ be stopped
但表示人體力或智力的具體動作時(shí)須用 be able to
He was able to do that without any help.他不需要任何幫助就能完成這項(xiàng)工作。
2. may表示“允許，可以”，相當(dāng)于be allowed to
2) If there is social or political change in a region ［A］ where a standard language ［B］ is spoken, local varieties ［C］ of the language may developing ［D］ .
may或might可和as well連用，表示“建議”，譯為“還是……的為好”
You may as well keep a certain distance from that mad man. 你們還是離那瘋子遠(yuǎn)點(diǎn)為好。
You might as well go home now.你還是現(xiàn)在回家為好。
3. must表示“必須”或“應(yīng)當(dāng)”、“一定”
3) The formation of snow must be occurring ［A］ slowly ［B］ ， in calm air， and at a temperature near ［C］ the freezing point ［D］ .
4. have to 加動詞原形，表示“不得不”，“必須”，它比must更強(qiáng)調(diào)客觀
Tom had to work into the deep night everyday to earn a living. 湯姆為了生計(jì)每天都得工作到深夜。
5. should 表示“勸告”，“建議”或“義務(wù)”時(shí)，譯作“應(yīng)當(dāng)”，或表示“預(yù)測”和“可能”
He should take care of his parents as they are old enough not to live on themselves. 由于父母親老了，不能自理，他應(yīng)當(dāng)照顧他們。
He should be there now. 他可能到了。
should have done在虛擬語氣中表示“責(zé)備或后悔”［參見第三章第一節(jié)、二、2.］。
6. ought ，只有一種形式，即ought后必須加to，然后跟接動詞原形表示“有義務(wù)”或“必要”做某事，譯為“應(yīng)當(dāng)，應(yīng)該”
4) The traditional goal of science is to discover how things are,not how they ought .
［A］ to
［B］ to be
［C］ be
［D］ have been
5) You are quite right;I am inferring in my comments ［A］ that McGraw had not ought to ［B］ have broken ［C］ in the room without his permission ［D］ .
7. dare 可以用作情態(tài)動詞，后面跟不帶to的動詞不定式，這主要用于否定句中，它本身可有現(xiàn)在時(shí)第三人稱單數(shù)，詞尾加s，它還可以有ING分詞形式(daring)和過去式及ED分詞形式(dared)
6) Although Oriental ideas of woman’s subordination to man prevailed in those days,she meet with men on an equal basis.
［A］ did not dared
［B］ dared not
［C］ dared not to
［D］ did dare not to
二、情態(tài)動詞在一般時(shí)否定句中的用法
can't(can not, cannot) 表示“不可能”， may not 表示“不可以”， mustn't(must not) 表示“一定不要”，“不許可”，needn't (need not) 表示“不必”，dare not ＋動詞原形 表示“不敢”
He can't finish his essay by this time. 現(xiàn)在他不可能寫完論文。
He may not sleep now. 他或許現(xiàn)在沒在睡覺。
You mustn't criticize her in that way. 你不應(yīng)那樣批評她。
You needn't come tomorrow. 你明天沒必要來了。
He dared not meet his fiancée. 他不敢見女朋友。
三、例題解析
1) 正確答案為A。由于情態(tài)動詞can要求跟動詞原形，所以B和C都不對，can后雖然有被動形式，但在意義上和語法上與橫線后部分都無法銜接，所以D也錯(cuò)，英語語法《朗曼基礎(chǔ)語法9 情態(tài)動詞》。
2) D錯(cuò)。改為develop。may后要求跟動詞原形，而developing是現(xiàn)在分詞，顯然不符合要求，所以應(yīng)改為develop。
3) A錯(cuò)。改用 must occur，此處敘說的是客觀現(xiàn)象，而非強(qiáng)調(diào)正在發(fā)生的事，故用一般現(xiàn)在時(shí)。
4) B為正確答案。
5) B錯(cuò)。改為ought not to。
6) B為正確答案。
II 情態(tài)動詞與完成時(shí)的使用
一、must+have+ED分詞：用于肯定句，表示對過去情況的一種肯定推測，表示“肯定，一定”
1) It around nine o’clock when I drove back home because it was already dark.
［A］ had to be
［B］ must have been
［C］ was to be
［D］ must be
2) John’s score on the test is the highest in the class;
［A］ he should study last night
［B］ he should have studied last night
［C］ he must have studied last night
［D］ he must had to study last night
3) After searching ［A］ for evidence in the house,the police concluded ［B］ that the thief must have come in ［C］ through the window and stole ［D］ the silver while the family was asleep.
二、may (might)+have+ED分詞：用于肯定句和否定句，表示對已發(fā)生事情的不肯定的推測，相當(dāng)于“可能，大概，”其中might較may 語氣更弱，把握更小
She might have gone to see her doctor last week, but I am not sure.上星期或許她去看醫(yī)生了，但我不敢肯定。
Don’t worry， your husband may not have been hurt seriously. 別急，你丈夫也許傷得不厲害。
三、should(ought to)+have+ED分詞：肯定句表示過去本應(yīng)發(fā)生的事卻沒有發(fā)生；否定句表示已發(fā)生了本不該發(fā)生的事。前者可譯為“本應(yīng)，”后者為“本不該”
You should have apologized to her for not soon replying to the letter. 你本應(yīng)向她道歉，說明為什么沒能及時(shí)回信。(可你沒這么做)
4) You yesterday if you were really serious about your work.
［A］ ought to come
［B］ ought to be coming
［C］ ought to have come
［D］ ought have come
四、can(not) +have+ED分詞
He is an hour late —— He can have been delayed by fog. Of course,that’s a possibility.他遲到了1小時(shí)，可能因?yàn)榇箪F而耽擱了。當(dāng)然這只是可能性問題。
The poem can not have been written by her since she was only five years old then.這詩不可能是她寫的，因?yàn)樗菚r(shí)才5歲。
五、“could+have+ED分詞”有時(shí)用于表示過去的時(shí)間，說明某事可能或不可能已發(fā)生；有時(shí)可表示過去本來可以做某事，但卻未做
I simply can’t understand how he could have made such a mistake. 我簡直不明白他怎么會犯那樣的錯(cuò)誤。
He walked there,but he could have taken a taxi. 他走著去了，可當(dāng)時(shí)完全可以坐出租。
“couldn’t+have+ED分詞”還表示無論如何也不可能或沒有做到
I couldn’t have called you. I wasn’t near a telephone. 反正我也不可能給你打電話，我附近沒有電話。
5) “We didn’t see him at the lecture yesterday.”“He it.”
［A］ mustn’t attended
［B］ couldn't have attended
［C］ would have not attended
［D］ needn’t have attended
六、needn’t+have+ED分詞：表示對過去不必做的事情卻做了，可譯為“其實(shí)不必”
6) You all these parcels yourself.The shop would have delivered them if you had asked a shop assistant.
［A］ didn’t need to carry
［B］ needn’t have carried
［C］ needn’t carry
［D］ didn’t need carry
七、used to 表示過去的習(xí)慣動作或狀態(tài)，現(xiàn)在已不存在，在否定陳述句中，一般用didn't use to，也可用used not to；在疑問句中用“Did…use to”。used to還可與never,often,always等連用。注意used to與be used to的不同，后者表示be accustomed to “習(xí)慣于某種狀態(tài)”，而且跟接名詞或ING形式，而used to后接動詞原形，試比較
He used to drink. 表示“他過去經(jīng)常喝酒”而現(xiàn)在不喝了。
He is used to wine (He is used to drinking wine) at each meal. 表示“他現(xiàn)在已養(yǎng)成習(xí)慣，每頓飯喝點(diǎn)葡萄酒。”
八、had better表示“最好……”，后接動詞原形，其否定式為had better not＋動詞原形
You had better not follow his behavior. 你最好不要學(xué)他。
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