Lesson Nine,情態(tài)動(dòng)詞,情態(tài)動(dòng)詞,情態(tài)動(dòng)詞的特征,在形式上，情態(tài)動(dòng)詞沒有人稱、數(shù)的變化 ，也沒有非謂語形式，只有could, would, might等幾個(gè)過去式。其它如 must, ought to 等的過去式皆與現(xiàn)在式同形。 2. 在意義上，大多數(shù)情態(tài)動(dòng)詞有多個(gè)意義。如can可表“能夠”、“可能”或“允許”等。,1、 情態(tài)動(dòng)詞的基本用法 (1)can、be able to 和could can和be able to都表示能力，意思上沒多大區(qū)別。但can只有現(xiàn)在和過去時(shí)，而be able to則有更多的形式。但當(dāng)成功地完成某一具體動(dòng)作時(shí)，通常不用could而用was/were able to來表示。這時(shí)was/were able to 相當(dāng)于managed to，表示經(jīng)過一番努力，終于能夠完成某事。 Can you use chopsticks? The wounded man still was able to get to the village and was saved in the end.,can和could can和could都可以表示能力、技能、許可、建議或請(qǐng)求和可能性。但比較委婉客氣地提出問題或陳述看法，一般用could，回答時(shí)則用can。 Could you help me carry the bag? Can I help you?,He may be sick.(生病的可能性較大) He might be sick.(生病的可能性較小),(2)may/might may/might表示可能，但may比might可能性大。如：-Why isnt he in class?,may/might表示“允許”，may用于現(xiàn)在時(shí)或?qū)頃r(shí)，might常用在間接引語中表過去時(shí)，但might也可用于現(xiàn)在時(shí)間，表示比較委婉的語氣，回答用may。 He says we may leave. He said we might leave.,Yes, you can / may. No, you mustnt,may / might 表示建議或請(qǐng)求，但might比may 更客氣，意思更肯定而無過去時(shí)態(tài)的含義。,May / Might I use your bike?,（3）must must表示必須，應(yīng)該，沒有時(shí)態(tài)變化。 You must do everything as I do. must表示肯定的推測(cè)。 The light is still on, so he must be at home. mustnt 表示禁止做某事。 You mustnt smoke in the office.,（4）have to have to 表示“必須、不得不”，是由于某種外界（客觀）原因而“必須”，“不得不”做某事，也可表示經(jīng)常的或習(xí)慣性的事“必須”做。have to的否定形式表示不必。have to可用于多種時(shí)態(tài)中。 You will have to clean your own boots when you join the army. I have to be at my office every evening.,（5）should / ought to should和ought to表示應(yīng)當(dāng)、應(yīng)該，前者比后者語氣輕。 You should / ought to work hard. should / ought to work hard Since she is not here, we should / ought to be in the classroom. should / ought to的否定形式表示禁止之意。 Children shouldnt smoke.,should可表示陳述意見，推出建議或請(qǐng)求；而ought to可以表示勸告之意。 You ought to respect your parents. He suggested that they should leave at once. （6）will / would will 用于各種人稱表示“意志”、“意愿”或“決心”等，否定式wont + 動(dòng)詞。 I will tell you all about it. Tom wont do such a thing.,will用于疑問句中，常用在第二稱時(shí)表示說話人向?qū)Ψ教岢觥罢?qǐng)求”或“詢問”。 Will you please tell her the news when you see her? will 表示習(xí)慣性的動(dòng)作，有“總是”、“慣于”的含義。 Fish will die out of water. would 表示客氣的請(qǐng)求、建議或意愿。 Would you please be quiet? Would you like coffee?,would 表示過去反復(fù)發(fā)生的動(dòng)作。 When I passed my school I would see my teachers who taught me 5 years ago. （7）need need 作“必要”講，既可作情態(tài)動(dòng)詞，也可作實(shí)義動(dòng)詞。作實(shí)義動(dòng)詞時(shí)后面的動(dòng)詞不定式要帶to，其變化與一般動(dòng)詞相同。 I need to think it over.,（8）dare dare表示“敢”的意思。作為情態(tài)動(dòng)詞時(shí)，主要用在疑問句和否定句中。dare若作實(shí)義動(dòng)詞，后面可帶to的不定式，此時(shí)to也可以省略。dare與need的用法相似。 How dare you say that? She doesnt date (to) ask her father.,（9）used to used to表示過去常常發(fā)生的動(dòng)作或存在的習(xí)慣，但現(xiàn)在已不復(fù)存在了。 He used to smoke. （10）shall shall作為情態(tài)動(dòng)詞用于第二、三人稱，表示說話人的意愿，有“命令”、“警告、威脅、強(qiáng)制”和“允許”等意思。 We shall do as our teacher says. You shall