情态动词的过去时各自是什么意思？

去看语法书

1.would have done.could have done.might have done都是对过去情况的推测,只是2.might have done的可能性最小.
3.should have done是应该做,注意一下,如果是should not have done是本不该做而做勒,有责备的意思
4.提醒你一下,考试经常这样设陷阱让你钻的:might have done即可以理解成may的过去时，对过去的推测，又可以理解成是might这个单词，而不是may的过去时，表比may的可能性更小的推测。

1.would have done: used for describing an action or event that would have happened if sth else had happened first(表示前一事件如果发生，后一事件也会紧接着发生。)如：If I had seen the advertisement in time I would have applied for the job.(我要是及时看到了这则广告，我就应聘那份工作了。)
2.could have done:本来可以。 They could have let me know they were going to be late!他们要晚来，也该早告诉我一声啊！
3should have done:真该；真应该。You should have seen her face when she found out!你真该看看她发现事情真相时脸上的表情。
4might have done:used to say that you are not surprised by sth(表示不感到以外)， I might have guessed it was you!我猜就是你！

“could + have + 过去分词”的疑问或否定形式表示对过去发生的行为怀疑或不肯定。
e.g. He couldn't have been to that town

“might + have + 过去分词”表示对过去发生的行为的推测。
e