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情态动词,刘延,语法特征,1） 情态动词不能表示正在发生或已经发生的事情，只表示期待或估计某事的发生。2） 情态动词 除ought 和have 外，后面只能接不带to 的不定式。3） 情态动词没有人称，数的变化，即情态动词第三人称单数不加-s。4） 情态动词没有非谓语形式，即没有不定式，分词，等形式。,主要情态动词,Can, couldMay, mightMustOughtNeedDare, dared,can,表能力：I can read very fast.表客观可能性：Mary cant be the leader.表允许：You can take it away.表怀疑：How can you finish it?,could,表能力/可能性：Could you finish it soon?表怀疑：He could not be 50.委婉地提出问题：Could you show me the pass?用于虚拟：If you had come, you could have got a wonderful gift.,may,询问或说明可不可以做：May I ask you a question?表可能会发生：He may get angry.表目的或让步的从句：Come here in time so that you may see the singer.,might,表可能的事：（同may）表目的从句： （同may）用于虚拟： If you had finished it, the boss might have given you some promotion.,must,表必须做的事：You must hand in your homework this Friday.表揣测：It must have rained last night.表“偏偏”的意思：He must get a fever when we were ready to get off.,ought,表应该做的事：You ought to do it carefully.表非常可能的事：He ought to be here by now.,need,表需要；主要用于否定句或疑问句：We neednt hurry.可用于否定意思的句子：I dont think you need do it.作及物动词，和不定式连用：He didnt need to say that to her.,dare,表“敢于”，主要用于疑问句、否定句和条件从句：He dare not tell him the news.作及物动词，与不定式连用：We dont dare to enter the house.,情态动词接不同形式的用法,情态词 + 不带 to 的不定式情态词 + 进行时 情态动词的过去时 情态词 + 完成式 情态动词表不同的“肯定”程度 练习,情态词 + 不带 to 的不定式,在这种结构中 ， 所有的情态动词都可以指直接的现在或将来 。 e.g. I may / can / must go there now . 我也许 / 可能 / 应该现在去那里 。He cant leave yet . 他现在还不能走 。 I may / can / must go there tomorrow . 我也许 / 可能 / 应该明天那儿 。 另外 ，此种结构也可用来一 “ 推测 ”， 但这时情态动词后的动词 ，仅限于静态动词 。 e.g. He must be at home , since the light in his room is still on . 房里的灯还亮着 ，他一定在家 。 He must know the answer . 他一定知道答案 。,情态词 + 进行时,这种形式往往可用来表示 ： A . 可能或推测 ： Meg may be phoning her fiance . 梅格可能在给他的未婚夫打电话 。 You must be joking ! 你准是在开玩笑 。 He cant be leaving yet . 他现在还不会走 。 B . 使语气更委婉 ： We must / may / should be leaving soon . 我们必须 / 也许 / 应该马上走 。 C . 其它用法 ： You must be working when the inspector comes in . 检查员进来时你必须在工作 。,情态动词的过去时,would , could , might 和 should 在形式上都可以说是过去时 ， 但这一点与其用法和意义并无多大关系 。我们一般把其用于间 接引语时叫做 “ 过去时 ” 。 e.g. He said you could / would / might leave early . 但在更多的情况下，might 表示比 may 更不肯定的情况 。 在疑问句中 ，could ,would 比 can , will 更客气 , should 是 “ 应该 ” ， 表一种义务 。 e.g. I might see you tomorrow . Could you help me , please ? Would you please show me the way ? He said I should see a doctor .,情态词 + 完成式（一）,它包括两种形式 ： 1）“ 情态词 + have + 过去分词 ” ； 2）“ 情态词 + have been + 现在分词 ”。,情态词 + 完成式（二）,它们的用法如下 ： 非推测性用法 ： “ could + 完成式 ” ， 即用于肯定句中 ，可以表示“ 本 来可以完成而未完成的动作 ” 。 E.g.- We could have walked to the station;it was so near . -Yes . A taxi wasnt at all necessary . “ neednt + 完成式 ” ，即用于否定句中 ，意为“ 本来 不必 ” ，指实际上做了本来不必做的事 。 E.g. There were plenty of time . She neednt have hurried .,情态词 + 完成式（三）,“ ought to / should + 完成式 ” ，表示“ 本来应该 ”，指本 该做而实际未做的事 ， 否定句则表示实际做了本不应该做的事 。 E.g. The plant is dead , I should have given it more water . / We shouldnt have waited for her because she never come . “ might + 完成式 ” ，那用于肯定句 ，可以表示本来可以做 而实际未做的事 ，暗含一种责备 ， 此时不可用 may 替代 。 E.g. He might have given you more help , even though he was very busy .,情态词 + 完成式（四）,推测性用法 : 对过去的事情进行推测时 ，我们可以采取“ 情态词 + 完成式 ” 形式 。 “ can / could + 完成式 ” 表推测时多用于疑问句或否定句中 ，不用于肯定句 。 E.g. He cant / couldnt have forgotten you address so soon. /Can she have lost the book ? “ must + 完成式 ” 意为“ 准是已 ”往往用于肯定句中 ，其否定形式是 cant , 不是 mustnt . He must have left early . ( 否定 ：He cant have left early . ) / He must have been working late . ( 否定 ： He cant be working late . ),情态词 + 完成式（五）,“ may / might + 完成式 ” 表示“ 可能已经 ” ， “ 或许已经 ” ，是对已经发生事情的 不太肯定的推测 ，其中 may 一般不用于疑问句中 。 E.g. You may ( might ) have read about it in the papers . /He may ( might ) not have finished the work . 另外 ， 有时亦可用 should和ought to 表“可能”或“推测”， 但由于 should 和 ought to 常表示 “ 义务 ” 因而会产生歧义 ， 所义并不常用 。 John ought to / should have left by tomorrow . 在疑问句和否定句中 ，通常不用 should 和 ought to 来表示 “ 可能 ” 或 “ 推测 ” 。,情态词 + 完成式（六）,有时候 ， 如果表示的 “ 可能 ” 或 “ 推论 ” 的依据几乎可以 肯定的话 ，也可以用 will 和 would . E.g. That will be Roland , I can hear him at the door . / That will have been Roland . He said hed be back at. / That wont be Roland . I am not expecting him yet .,情态动词表不同的“肯定”程度（一）,不同的 “ 肯定 ” 程度可按下列层次排列 ：He is at home . ( 事实 ） He must be at home .（ 非常可能） He could be at home .（ 很可能 ） He ought to be at home .（ 很可能 ） He may be at home .（ 仅仅可能 ）,情态动词表不同的“肯定”程度(二),He might be at home .（ 或许 ） He isnt at home .（ 事实 ） He cant be home .（ 接近肯定 ） He couldnt be at home .（ 不及 cant 肯定 ） He may not be at home . （ 可能 ，但不肯定 ） He might not be at home .（ 不及 may 肯定 ）。,补充,can&be able tohad betterwould rather,can&be able to,1）can/could 表示能力；可能 (过去时用could), 只用于现在式和过去式(could)。be able to可以用于各种时态。2）只用be able to a. 位于助动词后。 b. 情态动词后。 c. 表示过去某时刻动作时。 d. 用于句首表示条件。 e. 表示成功地做了某事时，只能用was/were able to， 不能用could。,had better,had better 相当于一个助动词，它只有一种形式，它后面要跟动词原形。had better do sth had better not do sthe.g. It is pretty cold. Youd better put on my coat.e.g. Shed better not play with the dog. 注意：had better have done sth表示与事实相反的结果，意为本来最好。You had better have come earlier.,would rather,would rather dowould rather not dowould rather than 宁愿而不愿。还有would sooner, had rather, had sooner都表示宁愿、宁可的意思。e.g. If I have a choice, I had sooner not continue my studies at this school.e.g. I would rather stay here than go home. = I would stay here rather than go home.,练习,1.The traditional goal of science is to discover how things are,not how they ought .A toB to beC beD have been 2.Although Oriental ideas of womans 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,练习,3) It around nine oclock when I drove back home because it was already dark. A had to be B must be C was to be D must have been 4) Johns score on the test is the highest in the class; A he should study last nightB he should have studied last nightC he must have studied last nightD he must had to study last night,练习,5) You yesterday if you were really serious about your work.A ought to come B ought to be comingC ought to have comeD ought have come 6) “We didnt see him at the lecture yesterday.”“He it.” Amustnt attended Bcouldnt have attendedCwould have not attended Dneednt have attended,练习,7) You all these parcels yourself. The shop would have delivered them if you had asked a shop assistant. A didnt need to carryB neednt have carriedC neednt carryD didnt need carry 8) “Did you cri