情态动词 can和could的用法

【来源：易教网 更新时间：2013-07-15】

can和could can的词义 

 表示体力或脑力方面的"能力"或客观上的"可能"。如：  Can you ride a bike? Yes，I can.你能骑自行车吗?是的，我能骑。 Can Mr. Smith use chopsticks? No，he can't . 史密斯先生会用筷子吗?不，他不会。  Most women here can read and write now.这里的多数妇女都能识字，也会写字。  In China even barren mountains can be turned into fertile fields.   在中国，荒山也能变成良田。 

can用在否定句和疑问句中时  在这种句子中，can常可意谓"可能"，表示猜测和推理。如：  It surely can't be six o'clock already? 不可能已经六点钟了吧? You can't be hungry so soon，Tom. You've just had lunch. 顿姆，你不可能饿得这么快，你刚吃过午饭。  She cannot be so careless. 她不可能这么粗心。 Where can he be? 他会在什么地方呢? What can he mean? 他会是什么意思呢?  It surely can't be six o'clock already? 不可能已经是六点钟了吧?

[注一] can加动词的进行时态，也可表示"可能"。如： 

What can he be doing all this time? 他一直会是在干什么呢? She cannot be playing ping-pong now.她现在不可能在打乒乓球。  [注二] 在日常会话中，can可代替may表示"允许"，may比较正式，如： You can drop in any time. 你随时都可以来串门。  Can I use your basin? of course，you can.我可以用你的脸盆吗?--当然可以。  You can have my seat，I'm going now.我要走了，你坐我的座位吧。

 Could  could是Call的过去式，表示与过去有关的1)能力和2)可能(在否定和疑问句中)。如：  1

)We were sure that he could do the work. 我们肯定他能做这工作。 He was a farmhand. He could not afford to send his son to school. 他是个雇农，他供不起儿子上学。 

2)At that time we thought the Story could not be true.那时我们以为所说的事不可能是真的。  [注] could可代替can表示现在，但语气较为婉转。如： could you wait half an hour?请你等半个小时好吗?  could you please ring up again at six? 六点钟请你再来电话好吗? could we visit a kindergarten? I've been wanting to see one ever since I came to China.我们可以访问一个幼儿园吗?我自从到中国来以后，一直想看一所幼儿园。  [注二]表示过去的能力并已完成一具体动作时须用were (was) able (to)，不可用could。如：  I am glad we were able to catch the train. 我很高兴我们能赶上火车。但如未完成一具体动作，则可用could not。如：  I am sorry we couldn't (或weren't able to) catch the train.我很遗憾我们没有能赶上火车。 

can的形式 页  can只有现在式can和过去式could两种形式，能表示现在一般和过去一般两种时态，有时也能表示将来。所有其他时态(包括将来)须用be able加动词不定式来表示。如：  With their help, we shall be able to finish the work in a few days. 有他们的协助，我们将会在几天之内完成这项工作。  They have not been able to come to Boston. 他们没有能到波斯顿来。 Mr. Johnson rang up just now to Say that he won't be able to come over this evening.约翰逊先生刚来电话，说今天晚上他来不了。 

 can，could用于否定或疑问句中 can (could)用于否定或疑问句中后面跟动词原形的完成式时，表示对过去发生事件的"可能性"。而could较can更加表示说话人的"不肯定的"语气。如：  Can he have left already? 他会是走了吗?  Could she have forgotten my address? 她会把我的地址忘记了吗? It couldn't have been henry. He has gone to the factory. 不可能是亨利，他已经去工厂了。  Surely she can not have arrived so early. 他当然不可能这么早到这里的。  [注] could加动词的完成式时，有时表示"过去可能完成但事实上并没有实现的动作"。如：  You could have done the work better.你本来可以做得更好些。(事实上你做得不那么好)  You could have got the early train.你本来可以搭上早班火车的。(事实上没搭上)