/kən;strong form kæn ||; kən; kæn/modal verb (
negative cannot /ˈkænɒt
||; ˈkænɑt/
short form can't /kɑ:nt;
US kænt
||; kænt/
past tense could /kəd
||; kəd/
strong form /kʊd
||; kυd/
negative could not short form couldn't /ˈkʊdnt
||; ˈkυdṇt/)
1 used for showing that it is possible for sb/sth to do sth or that sb/sth has the ability to do sth 表示可能性或能力: Can you ride a bike? 你会骑自行车吗？He can't speak French. 他不会讲法语。
Can has no infinitive or participle forms. To make the future and perfect tenses, we use be able to He's been able to swim for almost a year. Could have is used when we say that somebody had the ability to do something but did not do it She could have passed the exam but she didn't really try. can 没有不定式，也没有分词形式。如要表示将来时及完成时，可用 be able to：He's been able to swim for almost a year.他学会游泳差不多一年了。could have用于表示有能力做某事而没有做：She could have passed the exam but she didn't really try.要是她肯努力，这次考试她早该及格了。 2 used to ask for or give permission （用于提出要求或表示准许）: Can I have a drink, please? 请问有喝的吗？He asked if he could have a drink. 他问有喝的没有。
When we are talking about general permission in the past could is used I could do anything I wanted when I stayed with my grandma.However, when we are talking about one particular occasion we do not use could They were allowed to visit him in hospital yesterday. 表示过去某段时间内的准许用 could：I could do anything I wanted when I stayed with my grandma.从前我跟外婆住在一起，我做什么都没人管。指某一特定场合不用could：They were allowed to visit him in hospital yesterday.昨天他们获准到医院探望他。 3 used to ask sb to do sth （用于请求某人做某事）: Can you help me carry these books? 你可以帮我拿这些书吗？
4 used for offering to do sth （用于表示愿意做某事）: Can I help at all? 用得着我吗？
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 to talk about sb's typical behaviour or of a typical effect （用于指特有的行为或效应）: You can be very annoying. 你有时候挺ni4人。Wasp stings can be very painful. 叫黄蜂蜇着很不好受。
6 used in the negative for saying that you are sure sth is not true （用于否定式，指某事并非属实）: That can't be Maria -- she's in London. 那不可能是玛丽亚呢？她人在伦敦呢。Surely you can't be hungry. You've only just had lunch. 你肯定不觉得饿。你不是刚吃过午饭吗？
7 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, we use can I can smell something burning.NOT I'm smelling… 这些动词不用于进行时。若指进行中的动作可用 can： I can smell something burning.我闻到什么东西烧着了。不可说I'm smelling…