/kəd;strong form kʊd ||; kəd; kυd/modal verb (
negative could not short form couldn't /ˈkʊdnt
||; ˈkυdṇt/)
1 used for saying that sb had the ability or was allowed to do sth （用于表示曾经有能力或被允许做某事）: I could run three miles without stopping when I was younger. 我年轻一点的时候一口气能跑三英里。Elena said we could stay at her house. 埃琳娜说我们可以住在她家里。
If something was possible on one occasion in the past, use was/were able to or managed to The firemen were able to/managed to rescue the children.But in negative sentences could not can be used, too The firemen couldn't rescue the children. 若指某事在过去可能发生，可用was／were able to或managed to：The firemen were able to/managed to rescue the children. 消防员成功把孩子们救出。否定句中也可以用could not：The firemen couldn't rescue the children. 消防员无法把孩子们救出。 2 used for saying that sth may be or may have been possible （用于表示某事有可能或本来有可能发生）: I could do it now if you like. 你喜欢的话，我现在就可以做。She could be famous one day. 她有朝一日会出名的。He could have gone to university but he didn't want to. 他本来可以上大学的，但他不想。You could have said you were going to be late!(= I'm annoyed that you didn't) 其实你可以预先说好会迟到的！
3 used for asking permission politely （用于礼貌地请求准许）: Could I possibly borrow your car? 我可否借用你的车子？
4 used for asking sb politely to do sth for you （用于礼貌地请求别人做某事）: Could you open the door? My hands are full. 请你替我开门行吗？我两手都拿着东西。
For more information about modal verbs, look at the Quick Grammar Reference section at the back of this dictionary. 有关情态动词的详细用法，参看本词典末“语法便览”部份。 5 used for making a suggestion （用于提出建议）: ‘What do you want to do tonight?’ ‘We could go to the cinema or we could just stay in.’ “你今晚想做什么？”“我们可以去看电影，或者就待在家里。”
6 used with the verbs ‘feel’, ‘hear’, ‘see’, ‘smell’, ‘taste’ （与feel、hear、see、smell、taste等动词连用）
These verbs are not used in the continuous tenses. If we want to talk about seeing, hearing, etc at a particular moment in the past, we use could We could hear/see children playing outside. (NOTWe were hearing…) 这些动词不用于进行时。若指曾经看见、听见等可用could：We could hear／see children playing outside. 我们听见／看见孩子们在外面玩耍。（不可说We were hearing…）