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1、情态动词She can speak French and I cant. 什么叫情态动词？表示说话人对所述动作的看法，如需要、可能、意愿或怀疑等情感或状态。 情态动词的特征：He can speak English well,but I cant.We must stay here. 情态动词有词义，不能单独做谓语，无人称和数的变化，后面必须接动词原形。can/could/be able to1.三个都表“能力”could 是can的过去式。 eg: I couldnt speak English. I can speak English now. 将来能力使用shall/will/be ab
2、le to. eg: I will be able to speak French.2. can/could 表“请求、允许” could 比can 更委婉。 eg:Could I borrow your book?3. can/could 表“怀疑、推测” 可能性 cant be eg:It cant be Lilys bag.may/might1.表“请求、许可” might 比may更委婉、客气。 eg:May I come in? Might I come in?2. “可能”，表推测。 可能性 may be might beeg:He may come tomorrow. He mi
3、ght come tomorrow.必须must/have to 不得不1.must表个人意志和主观上的必要，意为“必须”“应该”用于一般现在时；I must go now.2.have to表客观上的必要。意为“必须”“不得不”除可用于现在时外，还可以表将来时shall/will have to和过去式had to。1.这台电视机不能用了，我们必须买台新的。 This TV doesnt work.We have to buy a new one.2.那时我们必须买台新的。 We had to buy a new one.3.我们将不得不买台新的。 We will have to buy a
4、 new one.I must study hard,because I want to go to Beijing University.I have to go shopping,because the fridge is empty now.should/would/ought to应该 愿意 理所应当1.You are his mother,you ought to look after him.2.You are a student,you should study hard.3.She would be glad if you would help her. 情态动词表推测must bemay bemight becant bedare , need既可作情态动词，又可作行为动词。做情态动词，无人称、数变化，主要用于否定句和疑问句情态动词类型1.只作情态动词的有：must,can(could),may(might)2.可作情态动词也可作实义动词的有need，dare3.可作情态动词也可作助动词的有will(would).shall(should)4.具有情态动词的某些特征的有have to,ought to
