modal动词可以；用于can的过去式；（礼貌地请求别人做事）能aux动词想；“can”的过去式；用于假设语气的条件句；用于虚拟语气的结论句网络能够；可能；会
动词
1. I would go if I could.
能去我就去。
2. could的意思
2. You could have been more considerate.
你本来可以更慎重些。
3. could
3. Could you do sth. for me?
你能替我做件事情吗？
4.
4. I could run faster then.
我那时能跑得更快一些。
5. Couldn't you try it again?
你可否再试一下？
传递信息
A：Could you give him this (message/ report/ document), please?
你可以把这个（口讯/报告/文件）给他吗？
B：No problem.
没问题。
还礼
A：You’ve been a big help.
你帮我大忙了。
B：I’m glad I could help.
能帮助您，我非常高兴。
请求帮助
1. 能;会
You use could to indicate that someone had the ability to do something. You use could not or couldn't to say that someone was unable to do something.
e.g. For my return journey, I felt I could afford the extra and travel first class...
至于回程，我觉得我能多花点钱坐头等舱。
e.g. I could see that something was terribly wrong...
我能觉察到有什么事很不对头。
2. 可能会;有时会
You use could to indicate that something sometimes happened.
e.g. Though he had a temper and could be nasty, it never lasted...
虽然他爱发脾气，而且有时还很讨厌，但向来都只是一阵儿。
e.g. He could be very pleasant when he wanted to.
他想要友好的时候会非常友好。
3. 本能够，本可以(表示某事本有可能发生但却并未发生)
You use could have to indicate that something was a possibility in the past, although it did not actually happen.
e.g. He could have made a fortune as a lawyer...
他本可以当律师挣大钱的。
e.g. You could have been killed!...
你差点儿就没命了！
4. (表示某事可能属实或可能发生)可能
You use could to indicate that something is possibly true, or that it may possibly happen.
e.g. Doctors told him the disease could have been caused by years of working in smokey clubs...
医生们告诉他这种疾病可能是由于多年在烟雾缭绕的俱乐部工作所致。
e.g. An improvement in living standards could be years away...
可能多年之后生活水平才能得到提高。
5. (表示某事不属实)不可能
You use could not or couldn't to indicate that it is not possible that something is true.
could
e.g. They argued all the time and thought it couldn't be good for the baby...
他们一直在争论，认为这对孩子肯定不好。
e.g. Anne couldn't be expected to understand the situation...
别指望安妮能弄明白当前情势。
6. (表示可能性、能力或机会)可能
You use could to talk about a possibility, ability, or opportunity that depends on other conditions.
e.g. Their hope was that a new and better East Germany could be born...
他们希望能够诞生一个崭新的、更加美好的东德。
e.g. I knew that if I spoke to Myra, I could get her to call my father.
我知道如果我同迈拉讲一声，就能让她给我父亲打电话。
7. 好像；仿佛
You use could when you are saying that one thing or situation resembles another.
could的翻译
e.g. The charming characters she draws look like they could have walked out of the 1920s.
她画的那些优雅迷人的人物就好像是从20世纪30年代走出来的一样。
8. (表示提议或建议)可以
You use could, or couldn't in questions, when you are making offers and suggestions.
e.g. I could call the local doctor...
我可以给当地医生打电话。
e.g. We need money right? We could go around and ask if people need odd jobs done or something...
咱们需要钱，对不对？咱们可以去周围打听一下看有没有人要找人做零工什么的。
9. (用于礼貌地提出请求或征得许可。当说话者意识到可能被拒绝时，可以用 couldn't 代替 could)能，可以
You use could in questions when you are making a polite request or asking for permission to do something. Speakers sometimes use couldn't instead of 'could' to show that they realize that their request may be refused.
e.g. Could I stay tonight?...
我今晚可以留下吗？
e.g. Could I speak to you in private a moment, John?...
约翰，我可以单独跟你说一会儿话吗？
10. (用以礼貌地打断某人或引出将要说的话)请允许我
People sometimes use structures with if I could or could I as polite ways of interrupting someone or of introducing what they are going to say next.
could的反义词
e.g. Well, if I could just interject...
嗯，请允许我插一句。
e.g. Could I stop you there?...
我能打断您一下吗？
11. (用以强调某人应该做所提及的事情，尤用于当说话者因为其没做该事而生气时)
You use could to say emphatically that someone ought to do the thing mentioned, especially when you are annoyed because they have not done it. You use why couldn't in questions to express your surprise or annoyance that someone has not done something.
could的近义词
e.g. We've come to see you, so you could at least stand and greet us properly...
我们都来看你了，你至少应该起身得体地打个招呼。
e.g. Idiot! You could have told me!...
蠢货！你本应该告诉我！
12. (表示想要做某事的强烈感情)
You use could when you are expressing strong feelings about something by saying that you feel as if you want to do the thing mentioned, although you do not do it.
could的近义词
e.g. I could kill you! I swear I could!...
我想杀了你！我发誓我真想杀了你！
e.g. 'Welcome back' was all they said. I could have kissed them!...
他们只是说，“欢迎回来。”我真想亲他们一下！
13. (用在if后以谈论没有能力或机会做但为考虑可能的结果而设想去做的事)
You use could after 'if' when talking about something that you do not have the ability or opportunity to do, but which you are imagining in order to consider what the likely consequences might be.
e.g. If I could afford it I'd have four television sets...
假如能买得起，我就会有4台电视机。
e.g. If only I could get some sleep, I would be able to cope.
要是能睡上一会儿，我就能应付了。
14. (与比较级连用，强调某物或某人具备某种特征的程度)太…，再…不过
You use could not or couldn't with comparatives to emphasize that someone or something has as much as is possible of a particular quality. For example, if you say 'I couldn't be happier', you mean that you are extremely happy.
e.g. The rest of the players are a great bunch of lads and I couldn't be happier...
剩下的选手是一帮很棒的小伙子，我太高兴了。
e.g. Darling Neville, I couldn't be more pleased for you...
亲爱的内维尔，我真太为你高兴了。
15. 怎么会(用在疑问句中强调对所发生的不愉快之事的感受)
In speech, you use how could in questions to emphasize that you feel strongly about something bad that has happened.
e.g. How could you allow him to do something like that?...
你怎么会允许他做那样的事？
e.g. How could I have been so stupid?...
我怎么会那么蠢？
16. 不用了(谢绝更多的食物或饮品)
You say 'I couldn't' to refuse an offer of more food or drink.
e.g. 'More cake?' — 'Oh no, I couldn't.'
“再来点蛋糕？”——“哦不，不用了。”
17. could do with -> see do