Unit 2 Let's Celebrate! Using language 情态动词课件-2023-2024学年高中英语外研版（2019）必修第二册

情态动词 Focus on 基本用法 Modal verbs be able to dare＆need have to had better 1. a) be able to 后接动词原形，表示某人做某事的能力，可用于大多数时态。 They were able to escape from the building when the fire broke out. 火灾发生时，他们设法从那栋建筑里逃了出去。 b) be able to 用于过去时态时，可以表示 “某人过去或当时成功地做了某事”。 2. a) dare 作情态动词时， 主要用于否定句、疑问句和条件从句中，一般不用在肯定句中。 ① I'm so afraid that I dare not move. 我吓得一动也不敢动。 ② Dare she ring him at the office? 她敢打电话到办公室找他吗？ b) need 表示 “需要”或 “必须”, 作情态动词时，用于否定句和疑问句中，在肯定句中一般用must, have to, ought to或should 代替。needn’t表示“不必；不需要”。 ① You needn’t tell him about it. He has known it. 你不必告诉他这件事。他已经知道了。 ② Need I pay the whole amount now? 我必须现在全部付清吗？ c) dare 和need 常用作实义动词，有时态、人称和数的变化。所不同的是，作实义动词时，在肯定句中，dare+带to的不定式；在否定句和疑问句中，dare+带to/不带to的不定式。 ① I dare to swim across this river. 我敢游过河去。 ② He didn't dare (to) say what he thought. 他不敢说出他的想法。 ③ He does not dare (to) answer. 他不敢回答。 3. a) have to 的含义与must相似，两者往往可以互换使用，但have to 有各种时态，且强调客观需要，意为 “不得不”。 ① It’s dark now. I have to go home. 现在天黑了，我必须回家。 ② I have to leave because of the bad weather. 因为天气不好，我不得不离开了。 ③ Do you have to wear uniforms at school? 你在学校必须穿校服吗？ You don’t have to/needn't go if you don't want to. 如果你不想去，就不必去。 b) 否定形式是don't have to，相当于needn't。 4. had better 后接动词原形，意为 “最好”, 用于现在或将来时，可用于一切人称，没有任何词形变化。 had better 的否定式是在其后加not,疑问式是把had和not 提前。 ① You'd better sit here and have a rest. 你最好坐在这儿休息一下。 ② She had better not tell lies any more. 她最好再也别撒谎了。 ③ Hadn't the doctor better see him? 医生是不是去看看他比较好？ I. 用适当的情态动词填空，每空一词。 1. You __________ go to school tomorrow, because it is Saturday. 2. I'm a