able

• able adjective (≠ unable)
• ably adverb
• ability noun (≠ inability)
• disabled adjective
• disability noun

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。

• and with passive infinitives. 并与不定式的被动形式连用：

  The DVD can be rented from your local store. 这 DVD 可在你们当地的商店租借。

• 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. 否定句也可用 could not：

  • 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。