情態動詞有can(能),may(可以),must(必須),have to(不得不),ought to(應該),dare(敢),used to(過去經常),had better(最好),would rather(寧願)，朗曼基礎語法9 情態動詞。在肯定句中它們後邊都要接 動詞原形 。在否定句中，can,may,must和dare後邊加not；have to和ought to分別在have和ought後加not；used to的否定式可用used not to，也可用didn't use to，但後者用得較多；had better和would rather的否定式分別是had better not和would rather not。這些情態動詞與現在完成時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動詞
一、情態動詞的現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工作。
2. may表示“允許，可以”，相當於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點為好。
You might as well go home now.你還是現在回家為好。
3. must表示“必須”或“應當”、“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更強調客觀
Tom had to work into the deep night everyday to earn a living. 湯姆為了生計每天都得工作到深夜。
5. should 表示“勸告”，“建議”或“義務”時，譯作“應當”，或表示“預測”和“可能”
He should take care of his parents as they are old enough not to live on themselves. 由於父母親老了，不能自理，他應當照顧他們。
He should be there now. 他可能到了。
should have done在虛擬語氣中表示“責備或後悔”［參見第三章第一節、二、2.］。
6. ought ，只有一種形式，即ought後必須加to，然後跟接動詞原形表示“有義務”或“必要”做某事，譯為“應當，應該”
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 可以用作情態動詞，後面跟不帶to的動詞不定式，這主要用於否定句中，它本身可有現在時第三人稱單數，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、情態動詞在一般時否定句中的用法
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. 現在他不可能寫完論文。
He may not sleep now. 他或許現在沒在睡覺。
You mustn't criticize her in that way. 你不應那樣批評她。
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。由於情態動詞can要求跟動詞原形，所以B和C都不對，can後雖然有被動形式，但在意義上和語法上與橫線後部分都無法銜接，所以D也錯，英語語法《朗曼基礎語法9 情態動詞》。
2) D錯。改為develop。may後要求跟動詞原形，而developing是現在分詞，顯然不符合要求，所以應改為develop。
3) A錯。改用 must occur，此處敘說的是客觀現象，而非強調正在發生的事，故用一般現在時。
4) B為正確答案。
5) B錯。改為ought not to。
6) B為正確答案。
II 情態動詞與完成時的使用
一、must+have+ED分詞：用於肯定句，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：用於肯定句和否定句，表示對已發生事情的不肯定的推測，相當於“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發生的.事卻沒有發生；否定句表示已發生了本不該發生的事。前者可譯為“本應，”後者為“本不該”
You should have apologized to her for not soon replying to the letter. 你本應向她道歉，說明為什麼沒能及時回信。(可你沒這麼做)
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，可能因為大霧而耽擱了。當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，因為她那時才5歲。
五、“could+have+ED分詞”有時用於表示過去的時間，說明某事可能或不可能已發生；有時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. 我簡直不明白他怎麼會犯那樣的錯誤。
He walked there,but he could have taken a taxi. 他走著去了，可當時完全可以坐出租。
“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“其實不必”
6) You all these parcels 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 表示過去的習慣動作或狀態，現在已不存在，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，後者表示be accustomed to “習慣於某種狀態”，而且跟接名詞或ING形式，而used to後接動詞原形，試比較
He used to drink. 表示“他過去經常喝酒”而現在不喝了。
He is used to wine (He is used to drinking wine) at each meal. 表示“他現在已養成習慣，每頓飯喝點葡萄酒。”
八、had better表示“最好……”，後接動詞原形，其否定式為had better not＋動詞原形
You had better not follow his behavior. 你最好不要學他。
