1、2016高考英语二轮：语法珍藏版笔记导学案（4）第四部分 几个用法的区别1、 can 和be able to的区别。can在表示“能力”时与be able to同义。但是can的时态形式不如be able to多。在一般将来时和现在完成时中只能用be able to。如：She will be able to dance in a week. 她再过一星期就会跳舞了。Nobody has ever been able to do it. 从来没有人能够做这事。在过去时中，could表示具备某种能力，但不一定做事；而was able to表示努力设法去做谋事，成功后说明有能力，相当managed
2、 to do或succeeded in doing。这时，could和was able to是不能互换的。例如：When he was a boy, he could swim across the river in fifteen minutes. 他小时侯，15分钟就能游过那河。（could表示能力，但不一定这么做）He was able to swim across the river in fifteen minutes last week.=He managed to swim across the river in fifteen minutes last week.=He suc
3、ceeded in swimming across the river in fifteen minutes last week.上周他15分钟就游过了那河。（was able to表示真这样做了，而且成功了。这里不能用could）2、must与 have to的比较。 Must 强调主观意志，也就是说，必要性来自说话者的主观意志。 have to 强调客观因素。例如：He must stop smoking. 他必须戒烟。（说话人认为他必须）This is an awful film. ？We really must go. 这部电影糟透了-我们一定要离开这里。（说话人认为必须）You ha
4、ve to go and see the boss. 你一定得去见见老板。（客观因素）Catholics have to go to church on Sundays. 天主教徒星期天必须去做礼拜。（客观因素，如教规等 ）注意：must not表示“绝对不可”; dont have to（或 havent got to ）表示“不必，没必要”，两者意思极为不同。英国英语中常用neednt来代替 havent got to 或dont have to,如：You mustnt tell Jenny. =Dont tell Jenny. 你一定不要告诉珍妮。You dont have to te
5、ll Jenny. =You can if you like but it isnt necessary. 你不必非要告诉珍妮。3、need 作为情态动词与行为动词的区别。作为情态动词，need 无过去式和将来时，故用had to, will have to替代，主要用在否定句、疑问句、条件句中，意思是“有必要”。例如：He need not come at once. 他不必马上就来。If you need go there, please tell me now. 如果你需要去那儿，请告诉我。Need he come at once? 他必须马上回来吗？（回答要用must, have to
6、, ought to, should等。例如：Need he come at once? Yes, he must/ought to /should/has to. No, he neednt /doesnt have to /mustnt.）neednt have done表示“本来不必做某事而实际上已经做了”。例如：We neednt have waited for him. 我们本来不必等他的。（实际上已等他了）用作实义动词时，need可用于肯定句、 否定句和疑问句，是“需要”之意。如：You need to wash your hands. 你需要洗手。Does he need to
7、take the medicine four times a day? 他需要每日服药四次吗？We didnt need to see him at all. 我们根本不必要看他(实际上也没去看他，请比较neednt have done的用法)need做实义动词时，后面的宾语如果是动名词，用主动形式表示被动意义，如果是不定式的被动形式，来表示被动意义。类似need的这种用法，还有require, want等。例如：The dinning room needs cleaning every day. =The dinning room needs to be cleaned every day.
8、 食堂需要天天打扫。My shoes need repairing. = My shoes need to be repaired. 我的鞋需要修理。4、would与 used to 的区别 .would 可表示反复发生的动作或某种倾向。used to表示过去的习惯动作或状态，强调现在已不存在。例如：She used to work into the night. 过去她常工作到深夜。（现在不了）She would work into the might. 以前她常工作到深夜。（不表示现在不了）People used to think that the sun went round the earth. 以前人们总认为太阳是围绕地球转的。（现在不这样认为了）I used to smoke quite a lot, but I have given it up. 我过去抽烟很凶，现在戒了。情态动词的重点和难点是：情态动词之间的区别；表示“推测”的表达方式；以及“情态动词+have+过去分词”的含义。