一、情态动词的"三不"特征
情态动词（modal verbs）是高一英语语法里"看起来简单、考起来易错"的一类词。先记住它的三个基本特征，很多错误就能自动避免：
- 不能单独作谓语，必须和动词原形一起构成谓语。❌ He can English. ✅ He can speak English.
- 没有人称和数的变化，第三人称单数也不加 -s。❌ She cans swim. ✅ She can swim.
- 后面永远跟动词原形（包括 be 动词）。❌ You must to go. ✅ You must go.
高一最常考的情态动词有：can/could、may/might、must、should、would、need、dare。
二、can 与 may：能力、许可与请求
can / could 表能力：can 指现在的能力，could 指过去的能力。 - I can play the piano, but I couldn't play it three years ago.
can / may 表许可： - can 用于非正式场合：Can I use your pen? - may 用于正式场合：May I come in, sir? - could 表示更委婉的请求：Could you help me with this box?（此处不是过去时，而是礼貌语气）
⚠ 易错点：回答 Could you...? 或 May I...? 提问时，习惯用 can 而不是 could：—Could you lend me your bike? —Yes, of course I can.
三、推测的"三种温度"：这是高一最重要的考点
表示"对现在情况的推测"时，情态动词按可能性从高到低排列： - must：一定、肯定（可能性极高，只用于肯定句）； - may / might：可能、也许（可能性和语气 weakest，might 比 may 更不确定）； - can't / couldn't：不可能（表示否定推测，不能用 mustn't 代替）。
例句对比： - He must be at home — the light is on.（他一定在家，灯亮着。） - He may be at home, but I'm not sure.（他可能在家，但我不确定。） - He can't be at home — I saw him in the library just now.（他不可能在家，我刚才在图书馆看见他了。）
四条必须牢记的规则： 1. must 表推测只能用于肯定句，疑问句和否定句要用 can/could：Can he be at home? / He can't be at home. 2. mustn't 表示"禁止、不许"，不表示推测。You mustn't smoke here.（此处不许吸烟。） 3. 推测过去的情况用 must have done / may have done / can't have done： - The ground is wet. It must have rained last night.（地面是湿的，昨晚一定下雨了。） - She can't have finished the work so quickly.（她不可能这么快就完成了工作。） 4. 反意疑问句要根据情态动词后的事实来选择： - He must be a teacher, isn't he? - He must have finished it, hasn't he?（若句中含过去时间状语，则用过去式：He must have finished it yesterday, didn't he?）
四、must 与 have to：两者不能随便替换
- must 表示说话人主观认为有必要：I must finish my homework tonight.（我自己认为必须完成。）
- have to 表示客观情况迫使：I have to wear glasses because of my poor eyesight.（视力不好，客观需要。）
- 时态上：must 没有过去式，过去情况用 had to；have to 有人称和时态变化（has to / had to / will have to）。
五、need 与 dare：既能当情态动词，也能当实义动词
这是高一易错题的高频来源。
作情态动词（多用于否定句和疑问句）： - You needn't worry about it.（needn't = 不必） - Need I say more?（我需要再说吗？） - She dare not tell the truth.
作实义动词（有人称、时态变化，后面可跟 to do）： - He needs to see a doctor. - She doesn't dare to speak in public.
判别方法：看否定和疑问是否借助 do/does/did，以及后面有没有 to。有 do/does/did 或 to，就是实义动词。
六、例题精析
【例1】— Must I hand in the report today? — No, you __. You ____ finish it by Friday. A. mustn't; must B. needn't; can C. can't; may D. needn't; need
解析：must 引导的疑问句，否定回答用 needn't / don't have to（不必），不能用 mustn't（禁止），排除 A、C；D 中第二个空 need 作情态动词不能用于肯定句，排除。答案 B。
【例2】Look at the dark clouds. It ______ rain soon. A. must B. can C. may D. need
解析：乌云密布只是"有可能"下雨，不是"必然"，用 may 表推测最恰当。答案 C。
【例3】The dictionary ______ be Li Ming's. Look! His name is on it.
解析：有"名字写在上面"的确凿证据，表示把握极大的肯定推测，填 must。
【例4】— I didn't see Mary at the party last night. — She ______ have gone there. She was preparing for the exam all night.
解析：由"整晚在准备考试"可知她不可能去过，用 can't。
七、分层练习
基础题（用适当的情态动词填空）： 1. __ you please open the window? It's hot in here. 2. He _ swim when he was only five years old. 3. You (not) play computer games before finishing your homework. 4. — ___ I use your dictionary? — Of course, here you are.
提高题： 5. Tom __ be in the classroom. I saw him go home just now. 6. She _ have forgotten the appointment; she is always so careful. (表示"不可能") 7. You (not) go to the station to meet him; he knows the way. 8. It ___ (be) rainy tomorrow, so take an umbrella with you. (表示"可能")
参考答案： 1. Could/Would 2. could 3. mustn't 4. May/Can 5. can't 6. can't 7. needn't 8. may/might be。
八、复习建议
- 建立"功能表"记忆：把情态动词按"能力 / 许可 / 推测 / 义务 / 必要性"五类列表，每类写2个例句，考前只背自己的例句。
- 抓住三条红线：must 不用于推测的否定句与疑问句；mustn't 是禁止不是推测；must have done 表示对过去的肯定推测。
- 做题先判"是不是推测"：一旦识别出是推测语境，就在 must / may / can't 三个词中选择，其他词基本可以排除。
- 每天一句语感训练：把课本课文中的情态动词句子抄下来，遮住情态动词自测，两周即可形成稳定语感。