【正文】 ago. 他可能在家嗎？不，他不可能在家，因?yàn)槲?分鐘之前才在街上遇到他。 may (might) 1）表示請(qǐng)求、可以、允許。 You may drive the tractor. 你可以開(kāi)那臺(tái)拖拉機(jī)。 2)表建議（可和as well 連用） You may（might）as well stay where you are. 你還是原地待著好。（may as well 有“還是……的好”的含義）3）表可能（事實(shí)上）。可以指過(guò)去時(shí)間，也可以指現(xiàn)在時(shí)間，但語(yǔ)氣更加不肯定，只能用于肯定句和否定句。 He may be at home. 他可能在家。 She may not know about it. 她可能不知道這件事。 He was afraid they might not agree with him. 他擔(dān)心他們可能不同意他的意見(jiàn)。 They might be having a meeting, but I’m not sure. 他們有可能在開(kāi)會(huì)，不過(guò)我不肯定。 must 1）表示必須、必要 We must do everything step by step .我們必須按部就班地做一切事情。 2)must 的否定式有兩個(gè)：當(dāng)回答由must引起的問(wèn)題時(shí)，否定答復(fù)要用needn’t或don’t have to 表示“不必”、“無(wú)須”、“用不著”、“ 3）表示推測(cè)語(yǔ)氣的用法，意為“準(zhǔn)是、一定”等，只用于肯定句，并且要有充足的理由說(shuō)明。 He must have passed the exam, because he looked so happy. 他一定通過(guò)考試了，因?yàn)樗雌饋?lái)如此的開(kāi)心。 4. have to have to的含義與must是很接近的,只是have to 比較強(qiáng)調(diào)客觀需要，must著重說(shuō)明主觀看法。 I must clean the room.（主觀想法）I have to clean the room.（客觀需要） 另外，have to 能用于更多時(shí)態(tài)： We had to be there at ten .我們得在十點(diǎn)鐘到那里。 We will have to reconsider the whole thing. 這一切我們將不得不重新加以考慮。 have to 的否定式：don’t have to do 表示“不必做……”之意。 would. 1）表意愿。 They would not let him in because he was poorly dressed. 他們不讓他進(jìn)去因?yàn)樗轮婆f。 I said I would do anything for you. 我說(shuō)過(guò)我愿意為你做任何事。 2）表過(guò)去反復(fù)發(fā)生的動(dòng)作或過(guò)去的一種傾向。 Every time she was in trouble, she would go to him for help. 她每遇到麻煩都會(huì)向她求助。他告訴我盒子打不開(kāi)了。 ought to . 表義務(wù)，意為“應(yīng)該”（因責(zé)任、義務(wù)等該做），口氣比should稍重。 You are his father. You ought to take care of him. 你是他父親，應(yīng)當(dāng)管他。 You oughtn’t to smoke so much. 你不應(yīng)該抽這么多煙。 used to . 表示過(guò)去的習(xí)慣動(dòng)作或狀態(tài)，現(xiàn)在不復(fù)發(fā)生或存在。疑問(wèn)式和否定式有兩種。 He used to live in the countryside, but now he lives in the ，現(xiàn)在住在城里。 There used to be a building at the street corner, but it has been pulled down. 街道拐角處過(guò)去有座樓房，現(xiàn)在拆了。 I usedn’t (didn’t use) to smoke. 我過(guò)去不抽煙。 Used you (Did you use) to go to school on foot? 你過(guò)去常步行去學(xué)校嗎？ 難點(diǎn)釋疑：（一）need和dare的用法比較 need和dare既可用作情態(tài)動(dòng)詞，也可用作實(shí)義動(dòng)詞。用作情態(tài)動(dòng)詞時(shí)，主要用于否定句和疑問(wèn)句。用作實(shí)義動(dòng)詞時(shí)，可用于各種句式。 You needn’t telephone him now. 你現(xiàn)在不必打電話給他。 I don’t think you need worry. 我想你不必發(fā)愁。 She dare not go out alone at night. 她晚上不敢一個(gè)人出去。 Not one of them dared mention this. 他們誰(shuí)也不敢提這件事。 You don’t need to do it yourself. 你不必親自做這件事。 We need to tell them the news. 我們需要把這消息告訴他們。 The table needs painting (to be painted.). 桌子需要油漆一下。 We should dare to give our own opinion. 我們要敢于提出自己的觀點(diǎn)。 He did not dare (to) look up. 他不敢抬頭看。 （二）情態(tài)動(dòng)詞后跟完成式和進(jìn)行時(shí)的用法 ，表“應(yīng)當(dāng)已經(jīng)……”，“想必已經(jīng)……”，“本來(lái)可以……”等意。 I should have finished the work earlier. 我應(yīng)當(dāng)早一點(diǎn)完成這項(xiàng)工作的。 He isn’t here. He must have missed the train. 他還未到，一定是沒(méi)趕上火車。 Where can (could) he have gone? 他能到那里去了呢？ You may (might) have read about it. 你可能在報(bào)上已經(jīng)讀到這件事了。 You could (might) have been more careful. 你本來(lái)可以更細(xì)心的。 He needn’t have worried about it. 他本不必為此事?lián)摹?There was a lot of fun at yesterday’s party. You ought to have e, but why didn’t you? 昨天的聚會(huì)非常有意思。你本應(yīng)該來(lái)，為何不來(lái)呢？ 2. 情態(tài)動(dòng)詞后跟進(jìn)行時(shí)，表示“想必正在……”，“可能正在……”，“應(yīng)當(dāng)正在”等意。 It’s twelve o’clock. They must be having lunch. 現(xiàn)在是十二點(diǎn)。他們一定正在吃飯。 They may be discussing this problem now 他們可能正在論討這個(gè)問(wèn)題。 六、不定式1. 不定式的構(gòu)成 1) 不定式的一般式. 不定式的一般式所表示的動(dòng)作通常與主要謂語(yǔ)的動(dòng)作同時(shí)或幾乎同時(shí)發(fā)生，或是在它之后發(fā)生。如： They invited us to go there this summer. 他們邀請(qǐng)我們今年夏天去那兒。 He stood aside for me to pass. 他站到一邊讓我通過(guò)。 2) 不定式的完成式 . 不定式的完成式所表示的動(dòng)作在謂語(yǔ)所表示的動(dòng)作之前發(fā)生，它在句中可作表語(yǔ)、狀語(yǔ)、賓語(yǔ)，有時(shí)也可作主語(yǔ)、定語(yǔ)等。如： She seemed to have heard about this matter. 她似乎已聽(tīng)說(shuō)過(guò)這件事。 I am sorry to have kept you waiting so long. 我很抱歉讓你等了這么久。 I meant to have told you about it, but I happened to have an important thing to do. 我本來(lái)想告訴你這件事的，但我碰巧有一件重要的事要做。It has been an honor for me to have traveled so much in your country. 對(duì)我來(lái)說(shuō)，在你們國(guó)家旅行這么多地方是一件很榮幸的事情。 3) 不定式的進(jìn)行時(shí) . 不定式的進(jìn)行時(shí)表示正在進(jìn)行的與謂語(yǔ)動(dòng)詞同時(shí)發(fā)生的動(dòng)作。它在句中可以用作除謂語(yǔ)以外的所有成分。如： He pretended to be listening to the teacher carefully. 他假裝在認(rèn)真地聽(tīng)老師講課。 4) 動(dòng)詞不定式的否定形式是由not或never加不定式構(gòu)成。 Try not to be late again next time. 盡量下次不要再遲到。 He wished us never to meet her again. 他希望我們永遠(yuǎn)不要再見(jiàn)到她。 5) 疑問(wèn)詞+動(dòng)詞不定式： 不定式和疑問(wèn)詞whether, what, which, whom, where, when, how, why等連用可以在句中起名詞的作用，通常跟在tell, know, show, decide, learn, wonder, explain, advise, teach, discuss, find out等動(dòng)詞后面作賓語(yǔ)，有時(shí)也可以充當(dāng)主語(yǔ)、表語(yǔ)等。如： On hearing the news, he didn’t know whether to laugh or to cry. 聽(tīng)到這個(gè)消息，他不知道該哭還是該笑。 When to hold the meeting has not decided. 什么時(shí)候開(kāi)會(huì)還沒(méi)有決定。 The most important problem is how to get so much money. 最重要的事情是如何搞到這么多錢。 介詞后一般不直接接不定式，但可以接疑問(wèn)詞+不定式短語(yǔ)作賓語(yǔ)。如： Mary gave some advice on how to learn English. 瑪麗提了一些如何學(xué)習(xí)英語(yǔ)的建議。 I have no idea of how to do it. 我不知道該怎么做。 2. 不定式的語(yǔ)法作用 . 1) 不定式作主語(yǔ)： To see once is better than to hear a hundred times. 百聞不如一見(jiàn)。 To master a foreign language is not an easy thing. 掌握一門外語(yǔ)不是一件容易的事。 在很多情況下，人們通常用it作為形式上的主語(yǔ)，而把不定式短語(yǔ)移到謂語(yǔ)之后，使句子顯得平穩(wěn)一些。如： It’s good manners to wait in line. 排隊(duì)等候是很有禮貌的。 It made us very angry to hear him speak to his mother like that. 聽(tīng)到他那樣跟他媽媽說(shuō)話我們很生氣。 2) 不定式作表語(yǔ)： The most important thing is to put theory into practice. 最重要的事情是把理論付諸實(shí)踐。 The greatest happiness is to work for the happiness of all. 最大的幸福就是為大家的幸福而工作。 I feel it a great honor to be invited to speak at the meeting before so many students. 我覺(jué)得被邀請(qǐng)?jiān)跁?huì)上面對(duì)這么多學(xué)生發(fā)言是一件很光榮的事情。 4) 不定式作補(bǔ)語(yǔ)：. ①不定式可以和名詞或代詞一起構(gòu)成復(fù)合結(jié)構(gòu)作動(dòng)詞的賓語(yǔ)，這時(shí)不定式被稱為賓語(yǔ)補(bǔ)足語(yǔ)。如： I would like you to help me with my English exercises. 我想請(qǐng)你幫我做英語(yǔ)練習(xí)。I never expected the shoes to be worn out so soon. 我從來(lái)沒(méi)想到鞋這么快就穿破了。注意：動(dòng)詞help后面接不定式作賓語(yǔ)或賓語(yǔ)補(bǔ)足語(yǔ)可以帶to也可以不帶to。如： Who can help me (to) carry this heavy box? 誰(shuí)能幫我拎這個(gè)重箱子？ ②在make, let, have等使役動(dòng)詞和see, watch, notice, hear, feel等感官動(dòng)詞后的復(fù)合賓語(yǔ)中，動(dòng)詞不定式不帶to。 I often hear her sing in the next room. 我經(jīng)常聽(tīng)到她在隔壁唱歌。 They make the baby go to bed at 7:00 . every day. 他們每天讓孩子晚上7：00上床睡覺(jué)。 注意：當(dāng)使役動(dòng)詞和感官動(dòng)詞變?yōu)楸粍?dòng)語(yǔ)態(tài)時(shí)，不定式就成了主語(yǔ)補(bǔ)語(yǔ)，作主語(yǔ)補(bǔ)語(yǔ)的不定式必須加to。如： Though he had often made his little sister cry, today he was made to cry by his little sister. 盡管他經(jīng)常弄哭他的小妹妹，但今天他卻被他的小妹妹弄哭了。 He is often heard to sing the song. 經(jīng)常有人聽(tīng)到他唱這首歌。 ③以be said, be reported, be known, seem, happen, prove, appear等構(gòu)成謂語(yǔ)的句子中，動(dòng)詞不定式通常也可看作主語(yǔ)補(bǔ)語(yǔ)。如： More than 20 people were reported to have been killed in the accident. 據(jù)報(bào)道，有20多個(gè)人死于事故。 I happened to be talking with him when he was hit by a car. 他被汽車撞的時(shí)候，我碰巧在和他談話。