情态动词 专升本英语语法详细讲解课件课件.ppt

助动词 动词表示动作形态，但英语里有些动词并不表示动作形态，而是协助主动词表示时态（tenses）或语态（voices）。这些动词叫助动词（auxiliary verbs） 英语中助动词主要有两类： 一是基本助动词，如have, do, be； 二是半助动词, 如 be about to等 三是情态助动词，如may, must, need等。 基本助动词 助动词可表示动词时态和语态,构成疑问句和否定句,例如 “have, has, had”用来构成完成时态； “be, is, are, am, been, was, were, being” 构成被动语态 What do you do every day? Betty has completed her work on time . Jason is writing a new book. A rat was caught by a cat. 构成疑问句附加语，如： Mr. Chen has not become a businessman, has he? Jasons lectures are clear and easy-to-understand, arent they? 构成简短答语，如： -Will you help us with the gardening? 　 Yes, I will. /No, I wont. -I have seen that film before. 　 -So have I. -William isnt a teacher. 　 -Neither is his wife. He is unwilling to help me with my English. Every clause is obliged to obtain a finite verb. We were about to start when it rained. He seems to be very disappointed. I don’t have to buy a new house.  情态动词 情态动词有 can (could), may (might), must, need, ought to, dare (dared), shall (should), will (would) .  在肯定句中它们后边都要接 动词原形. 在否定句中，can, may, must 和dare后边加not；have to和ought to分别在have和ought后加not；had better和would rather的否定式分别是had better not和would rather not。 这些情态动词与现在完成时连用在某种意义上有一定的虚拟性。 情态动词+动词原形 情态动词+动词完成式 情态动词+动词进行式 情态动词+动词完成进行式 某些情态动词的特殊用法 一、情态动词+动词原形 can表示体力或脑力方面的“能力”、“技能”或根据客观条件能做某种动作的“可能性” My grandma is over seventy, but she can still read without glasses. 但表示人体力或智力的具体动作时须用 be able to He was able to do that without any help. may表示“允许，可以”，相当于be allowed to You may go now.　 May I use your computer? may或might可和as well连用，表示“建议”，译为“还是……的为好” You may as well keep a certain distance from that mad man. 　　 You might as well go home now. must表示“必须”或“应当”、“一定” 在回答must引起的问题时，如果是否定的答复，不能用mustn’t，而要用needn’t或don’t have to，因为mustn’t是“一定不要”、“一定不能”的意思。 You must come to the classroom before eight. “Must we do it now?” “No, you needn’t.” have to 加动词原形，表示“不得不”，“必须”，它比must更强调客观 have to可用于多种时态，而must一般用于现在时，其过去时与将来时分别由had to与sh