1、情态动词情态动词表示说话人对某一动作或状态的态度，认为“可能” “应该” “必要”等。情态动词本身词义不完全，不能单独用作谓语，必须和不带 to 的不定式（即动词原形）连用。情态动词没有人称和数的变化。情态动词的否定式一般是在它们的后面加否定词 not 构成。朗读时，情态动词的肯定式一般不重读。一、 can 和 could 的用法（一）can 的用法1. 表“能力” 。Eg. Our company can keep pace with changes in the market.Specially-trained dogs can smell out drugs.2. 表“许可” 。Eg.
2、- Can I use your mobile phone?- Im afraid not. I am expecting a call.3. 表“可能性” 。多用于否定与疑问句中，但也可用于肯定句中表示理论上的可能性。Eg. Can there be life on Mars?You cant be tired -youve only been working for an hour.You cant have slept through that thrilling performance.4. 表其他。如“请求” “命令” “惊讶” “迷惑” “不相信”等态度。Eg. Can you h
3、elp me to lift it, please?If you wont keep quiet, you can get out！She has left her husband, but can you blame her after the way he treated her?You cant be serious!（二）could 的用法：1. 表“过去能够做某事”这样一种事实，但不指具体的某次行为。Eg. I could read when I was three years old.He was so drunk that he couldnt find the front do
4、or.2. 表“过去的可能与许可” 。多用于间接引语中。Eg. Father said that I could go swimming in the river with my friends.Jack said he couldnt complete his collection in such a short time.3. 表“现在的可能与能力” 。只是其可能性比 must 表示的可能性要小得多。Eg. My wife is in hospital. Our baby could arrive at any time.Whats for dinner? I could eat a ho
5、rse.4. 表“现在的许可” 。主要用于疑问句（不可用于否定句） ，语气比较委婉，其答语只能用 can.Eg. -Could you baby-sit for us on Friday?-Of course, I can.5. 表“轻微的责备” 。多用于第二人称。Eg. You could be a bit more careful!6. 表“请求或命令” 。多用于第二人称。Eg. You could give me a band with the cooking.7. 表“建议” 。Eg. If she is not at home, you could try phoning her a
6、t the office.二、 may 与 might 的用法1. 表“许可” 。might 可指现在的时间，也可指过去的时间，语气更委婉。Eg. You may / might take whatever you like.He told me that I might borrow his dictionary.- May / Might I ask for a photo of your baby?- Certainly. 注意: 在回答 may 或 might 的问句时，应尽量避免使用 may 或 might 这个词，而应用其他方式来回答。如：Yes, please. / Certai
7、nly. / Please dont. / Youd better not. / No, you mustnt.等，以免显得太严肃或太不客气。2. 表“可能” 。这时 might 和 may 可以互换，might 可指现在的时间，也可指过去的时间，但语气更加不肯定，即可能性更小。Eg. The road may / might be locked.She may /might be waiting for you in the entrance hall.3. might 可用于虚拟语气，may 不能。Eg. If she were here, you might get some help
8、from her.I might have told him the news if I had known it.4. may 置于句首时表示愿望、祝愿，这也是虚拟语气的一种特殊形式。Eg. May God bless you.May you succeed.5. 用于 may/might as well 结构中Eg. I might as well go.You may as well tell him what you think of him.His appearance had changed so much that you might as well not recognize
9、him.三、 shall 和 should 的用法(一) shall 的用法1. 多用于疑问句中以表示征求对方一件或指示，这时一般用于第一人称和第二人称。Eg. What shall we do this evening? Shall we go dancing?Shall he come to your office?2. 用于第二人称和第三人称，表“允诺” “警告” “命令” “决心” “必然”等。Eg. Dont worry. You shall get the book this afternoon.You are a naughty boy! You shall get what y
10、ou deserve.He shall be punishes if he breaks the rule.Nothing shall stop us from carrying out the plan.(二) should 的用法1. 表“义务，责任” 。Eg. You should send her a note.2. 表“劝告或建议” 。Eg. I often see lights in that empty house. Do you think I should report it to the police?Each of us should have a passionate
11、pursuit in our life.We should learn about the computer and make full use of it.3. 表对现在货将来比较有把握的“推测，推断” 。Eg. It is 8 oclock now. He should be here at any moment.I should have finished reading it by next Friday.4. Should 与完成时连用，表示“过去应做而未做的事” 。Eg. You should have told her about ir last week.5. 构成虚拟语气。E
12、g. It is suggested that we should start out early tomorrow morning.If it should rain, the crops would be saved. I am anxious that he should be well cared for.6. 与 think，imagine ，say 等连用，表达不成熟的意见。Eg. I should say she is over forty.四、 will 和 would 的用法1. 表“意愿” 。will 表示现在的意愿， would 表示过去的意愿。Eg. KMT chair
13、man Lien Chan has visited Nanjing and will continue his visit to Xian and Shanghai after Beijing.Present Bush yesterday announced that American forces would withdraw from Iraq.2. 表示征求意见或提出请求。Eg. Will you do me a favour?Would Sunday night suit you?Id like to see your new bike.3. 表示习惯和倾向性。Eg. June is
14、known as Black June in China because high school graduates will take the most important exam in their life-the national college entrance exam.G id for gold, but gold will not buy everything.4. 表示“推测” 。Will 用于谈论现在，would 用于谈论过去。Eg. They will climb the mountain and help collect rubbish to improve the e
15、nvironment.Every family would have some sort of trouble.5. 表示“执意，决心” 。Eg. The man who has made up his mind to win will never say “impossible”.He would do it, though I told him not to.五、 must 和 cant 的用法（一） must 的用法：1、 表示“必须” 。mustnt 译为“一定不要，不准” 。Eg. I must shut the door, or the dog will come in.Plant
16、s must have water in order to live.- Must I return your book this week?- Yes, you must.- No, you neednt.2、 表示“推测” 。译为“准是，一定是” 。（1 ） “must+v.”表示对现在情况的推测。Eg. He must be mad.（2 ） “must+have+过去分词”表示对过去的推测。Eg. She didnt come to school. She must have been ill.（3 ） “must+be+v.ing”表示对将来或现在进行时态动作的推测。Eg. Acco
17、rding to the weather report, it must be raining tomorrow.He must be watching TV.You must be joking.3、 表示“应当” 。相当于 should，ought to .Eg. You must say hello to her.4、 表示“偏偏” ，表达对某事的不满或责备等情绪。Eg. Why must it rain on Sunday？5、 表示抱怨或讽刺。“must+be+v.-ing”表示对将来或现在进行时态动作的推测。Eg. Why must you always be finding fa
18、ult with me?（二） cant 的用法：1. 表示“不能，不许”等。Eg. I cant swim in the lake.They cant wear jeans lake.2. 表示“推测” 。（1 ） 表示对现在和将来的推测。Eg. Can he have said so?He cant have said so.（2 ） 表示对过去的推测。3. 用于某些固定结构，如：cant help doing sth 表示“不禁，忍不住，不得不（做某事） ”。Eg. Hearing the news, I cant help laughing.4. Cannottoo 不论怎样都不过分。Eg. You cant be too careful when driving.5. Cannot help but 后接动词原形，表示“不禁” “忍不住” “不得不” 。Eg. I cant help but he sorry about it.We cant help but admire her courage.6. Cannot but do sth 表示“除此之外，别无他法” 。Eg. I couldnt but laugh on his funny face.
