1、could, should 和 would 除了分别是 can，shall 和 will的过去式，还有其他的用法，有人学英语多年还容易将其搞混淆，因此使用时要特别注意：1.could 的用法(1)表示惊异、怀疑、不相信等态度：How could John be so arrogant？约翰怎么这么傲慢？He couldnt be over forty. 他不可能有 40 多岁了。Where could she be now？ 她现在能在哪儿呢？以上三个句子可以用 can 代替 could，两者在时间上没有差别，只是用 could 时语气较缓和，用 can 时不相信程度更强一些。(2)比较委婉客
2、气地提出问题或陈述看法：Could(Can) you lend me your walkman？你能把随身听借给我用一下吗？Could I see your credentials？我可以看看你的证件吗？这时 could 和 can 没有时间上的差别。(3)在虚拟条件句中作助动词，与谓语动词一起构成谓语：I could do it (if I would).（假如我愿意的话）我是能办到这一点的。（指说话人不愿意）You could have done better if you had been more careful. 你要是再细心一点，是可以做得更好的。2.should 的用法(1)表示
3、惊异、赞叹、不满等情绪：It is simply a miracle that rice should grow in such a place. 稻子竟能在这样的地方生长，这实在是个奇迹。Its wonderful that you should get full marks. 你得了满分真了不起。Why should you be so late today？你今天怎么来得这么晚？(2)表示委婉地陈述自己的意见：I should think you are right. 我想你是对的。(3)（表示语气较强的假设）万一，竟然：If he should fail to come, ask To
4、m to work in his place. 万一他不来，就叫汤姆代替他工作。(4)（表示可能性、推测）可能，该：My sister should be home by now. 我妹妹现在应该到家了。(5)（表示建议、命令、愿意等）应该：I move that he should come with us. 我坚持他应和我们一起去。3.would 的用法(1)用在虚拟语气的主句中：If you went to see him, he would be delighted. 如果你去看他，他一定非常高兴。She would have come if she hadnt been so bus
5、y. 要不是忙她就来了。(2)委婉地提出请求、建议或看法：Would you take a seat？ 请坐！(3)表示意愿，在陈述语气和虚拟语气都可用：He would not leave before he finished his work. 他在完成工作以前不愿离开。(4)表示过去反复发生的动作：Now and then a blackbird would call. 不时会有山鸟叫。(5)表示过去的一种倾向:The wound would not heal. 伤口老不愈合。(6)表示推测：That would be in spring 1989. 那大概是在 1989 年春天。=sh
6、ould 和 would 都是情态动词，也是助动词，你应该知道，它们两个有时也可以不译。首先 should，在汉语中，我们常译为：应该。 而would 常译为：可以或者是将要。给个例子 you should clean the classroom。你应该打扫教室。It would be rain soon 。 不久将会下雨。而仅仅将这两个词做比较，显然 should 比 would 语气更强烈我今年刚高考完。还有几个需要提醒你，1 个用法sb shuold have done sth 某人应该做什么事（注意是应该，而实际上没做）。*should 和 would 的区别和用法 1）should
7、无词义，只是 shall 的过去形式，与动词原形构成过去将来时，只用于第一人称。 例如：I telephoned him yesterday to ask what I should do next week. 我昨天给他打电话，问他我下周干什么。 比较：“What shall I do next week?“ I asked. “我下周干什么？ “我问道。（可以说，shall 变成间接引语时，变成了should。） 2） would 也无词义，是 will 的过去形式，与动词原形构成过去将来时，用于第二、第三人称。 例如：He said he would come. 他说他要来。 比较：“I
8、 will go,“ he said. 他说：“我要去那儿。“ 变成间接引语，就成了： He said he would come. 原来的 will变成 would，go 变成了 come.。should 本应该做某事却没有做,表示责备和遗憾.如; You should ahve told me the news eariler.would 表示与事实相反。1。If I were a bird, I would be happy.(与现在事实相反)2. If I had told him the news, he would have cried(与过去事实相反)3. If I were t
9、o go tomorrow, I would take a plane(与将来事实相反)should have done 是翻译为本该做某事 而没做 would have filled 没有这个意思1 Like the rules governing the use of shall and will on which they are based, the traditional rules governing the use of should and would are largely ignored in modern American practice. Either should
10、or would can now be used in the first person to express conditional futurity:就象作为 shall 和 will 词的基础的限用的用法规则一样，适用于 should 和 would 这个词的传统使用规则在现代美国英语中也已被忽略了。 现在 should 或 would 这两个词中的任何一个都可以用于第一人称，表示条件式中的将来：If I had known that, I would (or somewhat more formally, should ) have answered differently.如果已经知
11、道了这个情况的话，我就（或正规一点用 should ） 不会那么回答了 ，2 But in the second and third persons only would is used:但在第二人称或第三人称中只用 would ：If he had known that, he would (not should ) have answered differently.如果他知道那个情况的话，就（不能用 should ） 不会那么回答了。3 Wouldcannot always be substituted for should, however. Should is used in all
12、 three persons in a conditional clause:但是 Would 并不是总是能由 should 代替。 Should 在三种人称的条件从句中都可以用：if I (or you or he ) should decide to go.如果我（或 你 或 他 ） 决定要去。4 Should is also used in all three persons to express duty or obligation (the equivalent of ought to ):Should 用于这三种人称的表示职责和义务的句子中（相当于 ought to ）：I (or
13、 you or he ) should go.我（或者 你 或者 他 ） 应该去 。5 On the other hand, would is used to express volition or promise:另一方面，would 用来表达决心或保证：I agreed that I would do it.我一定会做的。6 Either would or should is possible as an auxiliary with like, be inclined, be glad, prefer, and related verbs:而 would 或 should 都可以作助词和
14、 like，be inclined， be glad，prefer 及其相关词语一起使用：I would (or should ) like to call your attention to an oversight.我想（或 should ） 请你注意一下一个疏漏之处 。7 Here would was acceptable on all levels to a large majority of the Usage Panel in an earlier survey and is more common in American usage than should. Should have is sometimes incorrectly written should of by writers who have mistaken the source of the spoken contraction shouldve. See Usage Note at if, rather, shall在此处，在一次早期的调查中对大多数各阶层的使用者来说，would 是可以接受的， 且在美国用法中比should 更为常见。 有时书写者把 should have 误拼成 should of ， 因为他们把口头缩略形式 shouldve的来源给弄错了
