1．基本语法特点 情态动词就是表示说话的语气或情态的动词。常见的情态 动词有 can, may, must, need, dare, shall, will, should, ought to, have to, used to, had better, would rather 等。 情态动词具有以下 3 个特点： 1)情态动词后面接动词原形并与动词原形一起构成谓语。 2)情
态动词虽有时态的变化，但却没有人称和数的变化， 即情态动词不会因为主语的人称或单复数的不同而用不同的 形式。 3) 变为疑问句或否定句时不需要助动词，而是将情态动 词移至主语前变为疑问句，直接在情态动词后加 not，构成否 定句。
2．表示能力的 can/could 和 be able to 的用法 1) can 表示具有某种能力或技能，意为“能，会”。如： Who can answer this question? 谁能回答这个问题？ 2)can 的过去式为 could，但它通常只表示过去一般性能 力，不表示过去特定场合下的能力，遇此情况要用 was/were able to。如： I could run faster then. 我那时能跑得更快一些。 They were able to jump into the sea before the boat was blown up. 他们在船爆之前跳入海里。
3．表示许可的 can/could/may/might/must 的用法 can/could/may/might 均可表示许可，只不过 may 较侧重讲 话人的许可，而 can 较侧重客观情况的许可；could/might 的语 气比 can/may 更委婉、客气；在答语中表示允许别人做某事要 用 can/may，不能用 could/might。如： — Could (Can, May, Might) I use it? 我可以借用它吗？ — Yes, you can (may)．可以。(不用 could/might) must 表示必须做某事， 其否定式 mustn't 表示“不可以”。 如： We must not speak of it again. 我们再也不要谈这事了。
4．表推测的 can/may/could/might/should/must 的用法 从所用句型来看：can 用于否定句和疑问句，may 用于肯 定句和否定式，两者均可用于否定句，但是含义不同(cannot ＝不可能，may not＝可能不)；could, might 和 should 可用于 肯定句、否定句和疑问句；must 表示推测通常只用于肯定句。 如： She can't be in the office now. 她现在不可能在办公室。 Might he know this? 他会知道这事吗？
5．shall 与 will 的用法 1) shall 除用于第一人称表示单纯将来外，还可用于陈述 句第二、三人称， 表示说话者的意图、警告、命令、决心等。 如： He shall have a bicycle for his birthday. 他可以得到一辆自行车作为生日礼物。 2) will 可以表示习惯和倾向性，意为“惯于， 老是， 终 归是”。如： The door won't open. 这门打不开。 3) Shall I (we)?？ 可用于征求意见等，Will you?？可用 于表示请求或邀请等。如： Shall I turn on the light? 要不要把灯打开？
6．need 和 dare 的用法 need 和 dare 可用作实义动词和情态动词，用作实义动词 时， 后接动词要用不定式， 有人称和数的变化， 可用于肯定句、 否定句和疑问句；用作情态动词时，主要用于否定句和疑问句 中，没有人称和数的变化，后接动词要用动词原形。如： You need not pay—it is free. 你不必付钱，这是免费的。 We need to have lots of patience. 我们需要有很大的耐心。 注意：need 表示“需要”，其后可接动名词，且要用主 动形式表示被动意义。 如： The room needs cleaning. 这房间需要打扫了。
7．“情态动词＋完成式”的用法 “情态动词＋have done”总体上是表示对过去所发生事 情的判断、推测等。 1)must＋have done：用于肯定句，表示推测，意为“一定 (已经)??”。 2)can＋have done：用于否定句或疑问句，表示推测，意为 “可能(已经)??”。 3)could＋have done：可用于肯定句、否定句或疑问句，表 示推测、 责备或遗憾等， 意为“可能??”， “本来可以??” 等。
4)should (ought to)＋have done：可用于肯定句、否定句或 疑问句，表示责备或遗憾等，意为“本来应该??”。 5)need＋have done：用于否定句或疑问句，用于否定时意 为“本来不必”，用于疑问句时意为“有必要??吗”。 6)may＋have done：用于肯定句或否定句，表示推测，意 为“可能(已经)??”。
7)might＋have done：用于肯定句或否定句，表示推测，意 为“可能(已经)??”(此时 might 可换为 may)；另外还可以 表示过去可能发生的事结果未发生，意为“本来会??”(此 时 might 不能换为 may)。 He can't have left so soon. 他不可能走得这么早。 I should have thought of it. 我本应想到这一点的。 You needn't have mentioned it. 你没有必要提及此事的。
You must have mistaken my intention. 你一定是误会了我的意图。 I might have come to a wrong conclusion. 我或许得出了错误的结论。 You could have helped me—why did you just sit and watch? 你本可帮助我的，为什么只坐在一旁瞧着？
8．“情态动词＋进行式”的用法 这类结构主要用于对一个正在进行的动作进行推测、责 备、描述等。如： He might be waiting for you. 他可能在等你。 He must be joking, or else he's mad. 他一定在说笑话，要不就是疯了。
if 引 导 的 条 件 从 句
类别 与现 在事 实相 反 与过 去事 实相 反 与将 来事 实相 反
用法 例句 从句动词：过去式(be 用 were) 主句动词： If he were here, he would help us. should/would/could/might＋动词 原形 从句动词：had＋过去分词 If I had been free 主句动词： yesterday, I would should/would/could/might＋have have visited you. ＋过去分词 从句动词： 过去式/should＋动词 If it should rain 原形/were＋不定式 tomorrow, we 主句动词： would not go should/would/could/might＋动词 camping. 原形
注意：主句中的 should 只用于 I，we，但在美国英语中， should 常被 would 代替；从句中的 should 可用于各种人称，且 不可以被 would 所代替。
二、混合虚拟结构 1．不同时间的虚拟 If he had listened to me, he would not be in trouble now.(从 句与过去事实相反，主句与现在事实相反) If he had told me yesterday, I should know what to do now.(从句与过去事实相反，主句与现在事实相反) If I were you, I would have gone to her birthday party.(从句 与现在事实相反，主句与过去事实相反) If you hadn't lent me some money, I couldn't have bought the new house and most likely I would be still living in the dangerous house now.(从句与过去事实相反，and 后面的主句与现在事实 相反)
2．虚拟与陈述的混合 He could have passed the exam, but he wasn't careful enough. You should have come earlier.The bus left a moment ago.
三、特殊句式虚拟结构 1．省略连词 if。在书面语中，如果虚拟条件从句中有助 动词或情态动词 were，had 或 should，可以把 if 省略，把这 几个词放到主语之前，构成主谓倒装。 Should he come (If he should come), tell him to ring me up. 他要是来了，让他给我打个电话。 Were I you (If I were you), I would not do it. 我要是你，就不做这事。
2．suggest, order, propose, request, require, demand, advise, insist＋宾语从句(should)do He suggested that we (should) save money for the future. The undergraduate insisted that he (should) go to work in the south. 注意：当 suggest 表示暗示，insist 表示坚持观点、事实时， 后接的宾语从句应当用真实语气。 His silence suggested that he agreed with my decision. He insists that doing morning exercises does good to people's health.
3． is suggested/advised/ordered/requested/required?＋that It 从句(should) do It is proposed that more students should go to university. 4 ． My advice/suggestion/request/requirement/order/proposal? ＋ is ＋ 表 语从句(should)do My advice is that you should practise speaking English as often as possible. The order from the commander was that the troops should set off for the front immediately.
5．His suggestion/advice/request/requirement?＋同位语从 句(should)do＋is? The request that they should get more is reasonable. 6．It is natural/necessary/strange＋that 从句 (should) do 表 惊奇、怀疑、惋惜、不满、理应如此等。 It's strange that he should have missed the train.(表竟然) It is important that we should learn from others.(表理应如此) It is a pity that he should not go with us.(表惊讶、不满)
7．wish＋that 从句(did/were 与现在相反) wish＋that 从句(would/could/might＋do 与将来相反) wish＋that 从句(had done 与过去相反) I wish I could go with them tomorrow. I wish I had never met him. 8．It is (high/about) time＋从句(did 或 should do) It is (high/about) time we went home. 9．would rather＋从句(did 与现在或将来相反)；(had done 与过去相反) I would rather you came tomorrow. I would rather you hadn't told her the news.
10．省去条件从句或主句：表示虚拟语气的主句或从句有 时可以省略，但其含义仍可以推知。 1)省去条件从句 You could have washed your clothes yourself. 你本可以自己洗衣服的。 省去了“If you had wanted to”。(事实是：你自己没洗衣服， 因为你不想洗)
2)省去主句(常用以表示愿望) If only＋从句(did/were 与现 在相反)/(would/could/might＋do 与将来相反)/(had done 与过去 相反) “要是??就好了” If my grandmother were with me! 如果我的祖母与我在一起多好啊！(事实是：祖母已不在 世) If only she had not left! 如果她没走就好了！(事实是：她已经走了) If only I had taken her advice! 如果我听从了她的建议就好了。(事实是：我没有听从)
注意：only if 是“只要”的意思，从句中用陈述语气。 11． if＋从句 (did/were 与现在相反)/(would/could/might as ＋do 与将来相反)/(had done 与过去相反) She treats Kate as if she were her own daughter. They talked as if they had been friends for years.
12． would like/was/were to have done sth. 表示 “本 打 算”“本计划”或“本应当”做的事而没有做成或没有发生 I would like to have attended the party, but one of my friends came to see me. 13．but for＋名词意为“要不是/如果没有??” But for your help we couldn't have succeeded in the experiment. 如果没有你的帮助，我们的实验不可能成功。
14．注意虚拟条件从句的特殊形式 Without electricity, human life would be quite different today. Without the air to hold some of the sun's heat, the earth at night would be freezing cold. 15．注意转折语气连词引导的虚拟语气 He hesitated for a moment before kicking the ball, otherwise he would have scored a goal. I told Sally how to get here, but perhaps I should have written it down for her. Yesterday, Jane walked away from the discussion.Otherwise, she might have said something she would regret later.
16．注意分词和独立结构引导的虚拟语气 Given more than two hours, we could have done the work better. Not having finished the work, he couldn't have seen this film.
一 、 用 所 给 词 的 适 当 形 式 填 空 。 1.If he had followed ________________(follow) my advice, he wouldn't have lost his job. have watched 2．I should not ________________(watch) that movie —it'll give me horrible dreams. 3 ． John went to the hospital alone.If he ________________(tell) me about it, I would have gone with him. had told expect 4．Just be patient.You cannot ________(expect) the world to change so soon.
5． George is going to talk about the geography of his country, but I'd rather he ____________(focus) more on its culture. focused 6．Mr.Johnson insisted that the problem worthy of attention (should) be discussed _________________________(discuss) at the meeting. 7．Had I known about this computer program, a huge amount would have been saved of time and energy _____________________(save)． have been 8．It must________________(be) Tom that parked the car here, as he is the only one with a car.
9．I can't leave.She told me that I ________ stay here until must she comes back. 10. He did not regret saying what he did but felt that he could have expressed ____________________(express) it differently. be writing 11．He must __________________(write) a letter to his girl friend now. 12．I think it's high time that she ________(make) up her made mind. 13．But for (＝if it had not been for) your help, I wouldn't have been ________________(be) successful. 14 ． I was so busy then, otherwise, I would have helped ________________(help) him. had been 15．I wish I ________________(be) there with them last week.
二、根据中文提示翻译下列句子。 1 ． You screamed in your sleep last You must have dreamed of something terrible night.____________________________________________( 你 一 定梦见什么可怕的东西了)． 2．It's a pity.________________ _____________________ You should have invited her to your graduation ceremony ____________(你本应该邀请她来参加你的毕业典礼的)． I had had your opportunities when I was young 3．I wish _______________________________________(我 年轻的时候有你们这样的机会)． 4．If only ______________________________________(他 he had known this disease is curable 知道这病是可以治好的)! Then he would not have killed himself.
they (should) set up a special 5．His proposal was that __________________________ board/committee to examine this problem __________________________________(他们成立一个专门委 员会来检查这个问题)． otherwise, it would have taken 6．I used my calculator; ____________________________ me more time to work out this question ___________________________________(否则，我会花更长的 时间才能算出这道题)． measures were taken to solve the 7．It's high time that ________________________________ problem of traffic jams ____________________(采取措施解决交通堵塞的问题)．
as though he were delivering a speech 8．Hugh usually talks _______________________________ at an assembly _________________(仿佛在大会上发表演说似的)． everyone (should) be prepared for 9．It is essential that _______________________________ emergency _____________________(每个人都为紧急情况作好准备)．
I would seize the opportunity without 10．Were I in your place, ____________________________ hesitation _________________(我会毫不犹豫地抓住机会)．