could

modal verb

/kəd/, strong form /kʊd/

动词形式

could not
couldn't	/ˈkʊdnt/ /ˈkʊdnt/

Idioms

used as the past tense of ‘can’（用于 can 的过去式）
- She said that she couldn't come.她说她来不了。
- I couldn't hear what they were saying.我听不见他们在说些什么。
- Sorry, I couldn't get any more.对不起，我无法弄到更多了。
Grammar Point can / could / be able to / manage
can / could / be able to / manage
- Can is used to say that somebody knows how to do something:can 表示懂得做：
  Can you play the piano?你会弹钢琴吗？
  It is also used with verbs of seeing, noticing, etc:该词亦与表示看见、注意到等的动词连用：
  I can hear someone calling.我听见有人在呼叫。
- Can is also used with passive infinitives to talk about what it is possible to do:
  The podcast can be downloaded here.播客可在此下载。
- Can or be able to are used to say that something is possible or that somebody has the opportunity to do something:can 或 be able to 表示某事情有可能或某人有机会做某事：
  Can you/are you able to come on Saturday?你星期六能来吗？
- You use be able to to form the future and perfect tenses and the infinitive:用 be able to 构成将来时、完成时和动词不定式：
  You’ll be able to get a taxi outside the station.在车站外可搭乘出租车。
  I haven’t been able to get much work done today.我今天未能干多少工作。
  She’d love to be able to play the piano.她很希望能弹钢琴。
- Could is used to talk about what someone was generally able to do in the past:could 表示过去通常能做：
  Our daughter could walk when she was nine months old.我们的女儿九个月大就会走路了。
- You use was/were able to or manage (but not could) when you are saying that something was possible on a particular occasion in the past:关于在过去特定情况下可能的事用 was/were able to 或 manage，但不用 could：
  I was able to/managed to find some useful books in the library.我总算在图书馆找到了一些有用的书。
  I could find some useful books in the library.
  In negative sentences, could not can also be used:
  We weren’t able to/didn’t manage to/couldn’t get there in time.我们未能及时赶到那儿。
  Could is also used with this meaning with verbs of seeing, noticing, understanding, etc:亦可用 could 加表示看见、注意到、明白等的动词表示此义：
  I could see there was something wrong.我发觉出事了。
- Could have is used when you are saying that it was possible for somebody to do something in the past but they did not try:表示过去有可能做某事但没有做，用 could have：
  I could have won the game but decided to let her win.我本可以赢得那场比赛，但还是决定让她赢了。
used to ask if you can do something（询问是否可做某事）能，可以
- Could I use your phone, please?请让我用一下你的电话可以吗？
- Could we stop by next week?我们下周能过来一下吗？
used to politely ask somebody to do something for you（礼貌地请求别人做事）能，可以
- Could you babysit for us on Friday?你星期五帮我们看一下孩子好吗？
used to show that something is or might be possible（表示可能性）可能
- I could do it now, if you like.如果你愿意的话，我现在就可以做这事。
- Don't worry—they could have just forgotten to call.别担心，他们可能只是忘了打电话。
- You couldn't have left it on the bus, could you?你不可能把它落在公共汽车上了吧？
- ‘Have some more cake.’ ‘Oh, I couldn't, thank you (= I'm too full).’“再来点蛋糕吧。” “谢谢你，我吃不下了。”
Topics Doubt, guessing and certaintyb1
used to suggest something（用于建议）可以
- We could write a letter to the director.我们不妨给主管写封信。
- You could always try his home number.你总可以试着给他往家里打电话呀。
Topics Suggestions and adviceb1
used to show that you are annoyed that somebody did not do something（对某人未做某事表示恼怒）本来可以
- They could have let me know they were going to be late!他们要晚来，也该早告诉我一声呀！
(informal) used to emphasize how strongly you want to express your feelings（强调感觉）真想
- I'm so fed up I could scream!我烦透了，非大喊大叫不可！
Grammar Point modal verbs
modal verbs
- The modal verbs are can, could, may, might, must, ought to, shall, should, will and would. Dare, need, have to and used to also share some of the features of modal verbs.can、could、may、might、must、ought to、shall、should、will 和 would 均为情态动词。dare、need、have to 和 used to 亦具有情态动词的某些特性。
- Modal verbs have only one form. They have no -ing or -ed forms and do not add -s to the 3rd person singular form:情态动词只有一种形式，没有 -ing 或 -ed 形式，第三人称单数也不加 -s：
  He can speak three languages.他会说三种语言。
  She will try and visit tomorrow.她明天将设法去参观。
- Modal verbs are followed by the infinitive of another verb without to. The exceptions are ought to, have to and used to:情态动词后跟不带 to 的动词不定式，但 ought to、have to 和 used to 例外：
  You must find a job.你必须找到一份工作。
  You ought to stop smoking.你应当戒烟。
  I used to smoke but I gave up two years ago.我过去抽烟，但两年前就戒了。
- Questions are formed without do/does in the present, or did in the past:疑问句现在时不用 do/does，过去时不用 did：
  Can I invite Mary?我可以邀请玛丽吗？
  Should I have invited Mary?我本该邀请玛丽吗？
- Negative sentences are formed with not or the short form -n’t and do not use do/does or did.否定句用 not 或简约式 -n't，不用 do/does 或 did。
You will find more help with how to use modal verbs at the dictionary entries for each verb.情态动词的不同用法可参考本词典里各情态动词词条。

Idioms

could do with something

(informal) used to say that you need or would like to have something（表示需要或希望有）想要
- I could do with a drink!我真想喝一杯！
- Her hair could have done with a wash.她的头发该洗一洗了。