could

aux v

• ① can¹的过去式[表示过去的事实]
  • She complained that she couldn't sleep.她抱怨说睡不着觉。
  • It was very difficult to find a house that she could afford.很难找到她买得起的房子。

• ② can¹的过去式1[在从属子句中,为求时式之一致性,作can¹的过去式]2[用于间接引用语句]
  • He thought he could beat them.他认为他能击败他们。
  • He said (that) he couldn't go.他说过他不能去(参照He said, "I can't go.")。
  • He asked me if he could see her.他问过我他能不能见她(参照He said to me, "Can I see her?")。

• ③ can¹的过去式[用于假设法]1[表示与事实相反的条件或想像][在条件子句中]2[在结果子句中]3[表示委婉或礼貌]
  • If I could go, I would be glad.假如我能去,我会很高兴(事实上我不能去)。
  • I could do it if I wanted [would].[表示现在]假如我愿意,我能做得到(然而我不愿意)。
  • I could have done it if I had wanted [wished] to.[表示过去]假如我当时想做,我能做得到(然而我未曾那么做)。
  • I couldn't sing.我恐怕不会唱(even if I tried被省略)。
  • The news could not be true.那消息不可能是真实的。
  • Could I use your phone?我可以借用你的电话吗?
  • Could I speak to Alice, please?我可以跟爱丽丝说话吗?
  • Could you come and see me tomorrow?明天能请你来见我吗?(比Can you ...?的语气更客气;比Will you ...?的语气更亲切)
  • I could shout [could have danced] for joy.我高兴得真想大叫一番[大跳起舞来]。
  • You could have at least phoned me!你至少本来可以打电话给我﹗