,一、must的含义,1. 表示义务、意图或建议:必须 You must do your homework first. I must get up early. 2.表示推测:一定,必定 He must be at home. The pen must be Jims.,二、must的用法：,1、肯定式：must + V原； You must finish your homework. 2、 否定式：must + not + V原； You mustnt smoke here. must not表示禁止,3、疑问式：Must + 主语? Must I clean the room at once? 我必须马上打 扫房吗？ Yes, you must. 是的，你必须马上打扫。 No, you dont have to (=neednt) . 不必啦。,在回答must引起的问句时，如果是否定的答复，可用dont have to或neednt(不必) ， 但不能用mustnt,三、must 与have to 的区别,1、must 强调主观上认为“必须”做某事,而 have to 强调客观上要求“不得不”做某事。,I have to look after my sister. For my mother went out.,I must work hard.,客观需要,主观意愿,I had to clean my bedroom yesterday. He has to work hard. He doesnt have to work hard. -Does he have to work hard? -Yes, he does./ No, he doesnt.,2、在肯定句中， have to 随人称和时态的不 同而变化。其否定式和疑问式 的构成与行 为动词have相同，需使用助动词。,请用must或have to的适当形式填空 1. We _ be polite to our teachers at school. 2. You _ go outside to play as it is snowing heavily. 3. Must I get to the station before 5 p.m.? Yes, you _. / No, you _. 4.I got up late this morning, so I _ take a taxi to school. 5. Does she _ stay at home? No, she doesnt.,mustnt,must,had to,have to,must,dont have to / neednt,