情态动词加have+done的用法
情态动词+have done
could/would have done
can have done
must have done
may have done
might have done
should / ought to have done
should not / ought not have done
1. 过去本来能够做但未实现：He could/would have finished it on time, but he was ill that day. （虚拟，*could表达惋惜之情）
2. 肯定、否定、疑问句中表推测（可能性）：Don't worry. They could have arrived home. / The guests would have arrived by that time.（对过去的推测，*would一般用于肯定句）
否定、疑问中表推测：He can't have slept with the noise. （把握性极大的推测）
Can he have gone to his office? （提出某种可能性）
想必 / 准是 / 一定： It must have rained last night, for the road is quite muddy. （把握性极大的推测）
注：否行形式为：can't / couldn't have done
也许 / 或许，一般用于肯定、否定句，不用于疑问句：It's too late. He may have gone to bed. （把握性不大的推测）
He may not have finished his work. （把握性不大的推测）
同上，比may语气更弱
本该做而实际上没做：You should / ought to have done this exercise more carefully. （表责备）
本不该做但是做了：You should't / oughtn't to have told her the truth. （表责备）
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