高中情态动词专项总复习
一、can （could）1、can表示能力，用在过去时中，could表示过去所具有的一般的能力；经常表示能够做某事，事实上不一定去做，而was / were able to则表示过去做成了某事（=managed to do, succeeded in doing）。在否定句中两者可通用。例如：
① Two eyes can see more than one. 两只眼比一只眼看得清。
② Could the girl read before she went to school? 这女孩上学前能识字吗？
③Mary can play the piano. She has been able to play it since she was 5.玛丽会弹钢琴。她五岁起就会弹了。
④He could swim across the English Channel. But he didn't feel like it that day. 他能游过英吉利海峡，但那天他不想游。
⑤Yesterday I was able to get home before the heavy rain.昨天我在下大雨前赶到了家里。
⑥He tried many times, then at last, with the help of his math teacher, he was able to work out the difficult problem.
2、表示可能（理论上或是逻辑判断上），可用于肯定句，否定句和疑问句。can在肯定句中表可能性时是表示理论（道理）上的可能性，普遍、一般情况下可能，而不是表示具体某事发生的可能性；表示这样的意思时要用could，may或might。can't （couldn't）表示不可能，与must意义相反。
①Accidents can happen.意外情况是可能发生的。
②Scotland can be very warm in September.九月的苏格兰可以非常暖和。
③Will you answer the phone? It could （may /might） be your mother. 你去接电话好吗？可能是你妈妈打来的。（不能说It can be）
④He can't （couldn't） have enough money for a new car.他不可能有足够的钱买新车。
⑤You mustn't smoke while you're walking around in the wood. You could start a fire.在林子里走时勿吸烟，那样可能会引起火灾。
⑥When many people surf on the Internet, the speed can （could） be very slow.
⑦During rush hours, streets can （could） be vey crowded.
●can （could） have done表示对过去发生事情的推测，can have done只能用于疑问句和否定句中（可能已经了吗 不可能已经），肯定句中用could have done。
①Where can （could） he have gone?他会上哪儿去了呢？
②He can't （couldn't） have gone to school-it's Saturday.他不可能是去上学了，今天是星期六
③He could have gone off with some friends.他可能是和几位朋友出去了。（不说can have gone）
3、could+完成式还可用来表示虚拟（不用can）（也可表推测），过去本能做而未做以及用来责备某人在过去本可以做某事但未做。如：
①You were stupid to go skiing there you could have broken your leg. 你到那个地方去滑雪真傻，你可能会摔断腿的。
②You could have told me the boss was angry.你本该告诉我老板生气了。
4、表示给予许可、允许或征求意见（=may）。
① Can I have a look at your new pen? 我可以看一看你的新钢笔吗？
② He asked whether he could take the book out of the reading—room.他问他可不可以把书带出阅览室。
③You can take this book home to read more carefully.你可以把书拿回家更详细地阅读。
5、表惊异、怀疑、不相信等态度。主要用于否定句、疑问句或感叹句中。
① Where can （could） they have gone to? 他们会去哪儿了呢？
② How can you be so careless? 你怎么这么粗心？
6、比较委婉客气地提出问题或陈述看法。
① Can （Could） you lend me a hand? 帮我一把好吗？。
② I'm afraid we couldn't give you an answer today.恐怕我们今天不能给你答复。
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