Unit 3语法专项— 情态动词should与have to课件 2025-2026学年外研版八年级英语下册

教学课件 外研英语八年级下册 Unit 3语法专项—— 情态动词should与have to 全解精讲+分层练习 1 学习目标 1.理解情态动词should和have to的核心含义与本质区别 2.掌握should/have to的肯定、否定形式及基本用法 3.能根据语境正确区分并使用should和have to 4.掌握相关句型转换技巧，熟练完成句式改写 5.能在填空、选择、改错等题型中灵活运用语法点 情态动词的基础概念 情态动词用来表达说话人的语气、态度或情感 后接动词原形，无人称和数的变化 本单元核心：should（主观）和have to（客观） 二者均表“应该/必须”，但使用场景差异显著 should 核心含义与基本形式 核心含义：表建议、劝告、责任或轻微推测，语气委婉 肯定形式：should + 动词原形 否定形式：shouldn't (should not) + 动词原形 人称特点：所有人称通用，无需根据主语变化 should 表“建议/劝告” 用法+例句 这是should最常用的场景，用于给他人提建议、劝诫 1.You should talk with your parents about the problem. 2.She shouldn't spend too much time on phone games. 3.We should listen carefully in class. 4.You shouldn't be late for school every day. should 表“责任/义务” 用法+例句 用于表达分内该做的事，语气比must更温和 1.A student should finish his homework on time. 2.We should protect the environment around us. 3.A teacher should care about every student. 4.You should keep your promise to your friends. should 表“推测/预期” 用法+例句 表示根据情况对事情的发展做出合理推测 1.They should arrive at the station in ten minutes. 2.The movie should be very interesting; many people watch it. 3.He should finish the work by the end of this week. 4.The book should be on the desk; I put it there just now. have to 核心含义与基本形式 核心含义：表客观义务、必要，强调外界规则/要求 肯定形式：have to + 动词原形（有人称和数的变化） 否定形式：don't/doesn't have to + 动词原形（表不必） 核心：动作不是主观意愿，而是外界迫使必须做 have to 人称与数的变化规则 第一/二人称单复数（I/you/we/they）：用have to 例：I have to get up early every morning. 第三人称单数（he/she/it/单数名词）：用has to 例：She has to take a bus to school. 否定形式：对应变don't have to/doesn't have to have to 表“客观规则/要求” 用法+例句 因学校、家庭、社会等规则产生的客观义务 1.We have to wear school uniforms from Monday to Friday. 2.He has to finish the training before 6 p.m. 3.You have to follow the traffic rules when crossing the road. 4.They have to keep quiet in the library. have to 过去式（had to）用法+例句 表过去发生的客观必要，无人称变化，所有人称通用 结构：had to + 动词原形 / didn't have to + 动词原形 1.Yesterday I had to stay at home to look after my sister. 2.They didn't have to go to school last Sunday. 3.She had to take a taxi because the bus was late. have to 否定式 核心含义：不必 don't/doesn't have to = needn't，表“没有必要做某事” 1.You don't have to bring your textbook; I will share mine. 2.He doesn't have to finish the work today; it's due tomorrow. 3.We don't have to get up early on weekends. 注意：与“禁止”无关，仅表无客观要求 should 与 have to 核心对比表（基础） 情态动词 核心侧重 人称变化 否定含义 should 主观建议、劝告、责任 无 shouldn't 不应该（劝诫） have to 客观规则、外界要求 有（has to/had to） don't have to 不必（无要求） should 与 have to 语境辨析 例句对比 主观建议（should） You should exercise every day to keep healthy. You should read more books to improve your English. 客观要求（have to） You have to exercise for an hour at school every day. You have to read two books every month for your class. 易混点：don't have to 与 mustn't 区别 don't have to：表“不必”，无客观要求，可做可不做 例：You don't have to bring a gift to the party. mustn't：表“禁止”，绝对不能做，有严格规定 例：You mustn't run in the hallways at school. 核心：一个是“无要求”，一个是“严禁止” 小练习1——判断用法（should/have to） 判断下列句子该用should还是have to，标注原因 1._________ brush your teeth twice a day.（_________） 2._________ wear a helmet when you ride a bike.（_____________） 3._________ not play computer games for too long.（_________） 4._________ finish my homework before watching TV.（___________） should 表建议 have to 表客观规则 should 表劝诫 have to 表客观要求 句型转换1——陈述句变建议句 规则：It's a good idea to do sth. → You should do sth. 示例：It's a good idea to practice English every day. → You should practice English every day. 关键：保留动词原形，替换句式即可 句型转换2——客观必要句改写 规则：It's necessary to do sth. → 主语 + have to/has to do sth. 示例：It's necessary for her to get up early. → She has to get up early. 关键：根据主语变have to/has to 句型转换3——无需做某事改写 规则：don't need to do sth. → don't/doesn't have to do sth. 示例：You don't need to buy a new pen. → You don't have to buy a new pen. 关键：主语为三单时，用doesn't have to 句型转换4——否定劝诫句改写 规则：It's not right to do sth. → You shouldn't do sth. 示例：It's not right to shout at your parents. → You shouldn't shout at your parents. 关键：直接替换为shouldn't + 动词原形 句型转换 典型例题讲解（1） 原句：It's a good idea for us to join the English club. 解析：表建议，用should改写，保留动词原形 答案：We should join the English club. 技巧：忽略形式主语it，直接用真实主语作主语 句型转换 典型例题讲解（2） 原句：It's necessary for him to hand in the report today. 解析：表客观必要，主语he是三单，用has to 答案：He has to hand in the report today. 技巧：注意第三人称单数的形式变化 句型转换 典型例题讲解（3） 原句：She doesn't need to go to the office on Saturday. 解析：表不必，主语she是三单，用doesn't have to 答案：She doesn't have to go to the office on Saturday. 技巧：needn't与don't/doesn't have to可互换 语法易错点提醒（1） 1.should后接动词ing形式：错误，必须接动词原形 错误：You should reading more. 正确：You should read more. 2.have to的三单形式不变：错误，三单必须用has to 错误：He have to go to school early. 正确：He has to go to school early. 语法易错点提醒（2） 3.混淆shouldn't和don't have to：前者是“不应该”，后者是“不必” 错误：You don't have to be rude to others. 正确：You shouldn't be rude to others. 4.had to变否定加not：错误，过去式否定用didn't have to 错误：He had not to go yesterday. 正确：He didn't have to go yesterday. 专项习题1——用所给词正确形式填空 用should/shouldn't/have to/has to/don't have to填空 1.You ___________ eat too much junk food; it's bad for health. 2.He ___________ get up at 6 a.m. because his school is far. 3.We ___________ study hard for our exams. 4.You ______________ worry about me; I can take care of myself. 5.They ___________ follow the rules in the museum. shouldn’t has to should don't have to have to 专项习题2——句型转换（按要求改写） 1.It's a good idea to take a walk after dinner.（改为should句型） 2.It's necessary for us to clean the classroom every day.（改为have to句型） 3.You don't need to wait for me here.（改为don't have to句型） 4.It's not right to copy others' homework.（改为shouldn't句型） 5.She needs to finish the work before 5 p.m.（改为has to句型） You should take a walk after dinner. We have to clean the classroom every day. You don't have to wait for me here. You shouldn't copy others' homework. She has to finish the work before 5 p.m. 专项习题3——单项选择 1.You ______ drink more water when you have a cold. A. should B. have to C. doesn't have to D. shouldn't 2.He ______ wear a tie to work; it's the company rule. A. should B. has to C. don't have to D. shouldn't 3.You ______ go out at night; it's not safe. A. should B. have to C. don't have to D. shouldn't 4.We ______ take umbrellas; the sun is shining brightly. A. should B. have to C. don't have to D. shouldn't A B D C 专项习题4——改错（找出错误并改正） 1.You should to go to bed early every night. 2.My mother have to get up early to make breakfast. 3.He doesn't has to go to school on Saturday. 4.You don't have to be late for the meeting again. 5.We should playing sports every day to keep fit. 去掉to have→has has→have don't have to→shouldn't playing→play 专项习题5——补全对话（用适当词填空） A: Hi, Tom. You look worried. What's wrong? B: I have a math test tomorrow. I'm not good at math. A: You ____________ ask your teacher for help. She is very kind. B: I know, but I'm too shy. And I _________ finish my math homework first. A: You ___________ be shy; your teacher will be happy to help you. B: You're right. And I _______________ worry too much; I can try my best. A: That's good. We _________ go to the library and study together. should have to shouldn't don't have to should 语法知识梳理 should 1.含义：建议、劝告、责任、推测 2.形式：should/shouldn't + 动词原形，无人称变化 3.改写：It's a good idea to do → You should do have to 1.含义：客观规则、外界要求，表必要 2.形式：have to/has to/had to + 动词原形，有人称变化 3.否定：don't/doesn't/didn't have to 表“不必” 4.改写：It's necessary to do → 主语 + have to/has to do 课堂小结 1.本单元核心：情态动词should（主观）和have to（客观）的用法 2.should后接动词原形，无人称变化，否定为shouldn't（不应该） 3.have to有人称/时态变化，三单用has to，过去用had to，否定表不必 4.核心区别：should是“我建议”，have to是“外界要求” 5.易错点：后接动词原形、人称变化、don't have to与mustn't区分 教学课件 Unit 3语法专项—— 情态动词should与have to Thank you for listening! 33 $