Question

should have done ,shouldn't have done.could have done,couldn't have done ?什么意思？

Answer 1

should have done
本该做到但是没有做到
如:
you should have won the game,but you failed.
你本该赢了那场比赛,但是你输了.

shouldn't have done
本不该做的而做了
如:
you shouldn't have watered the flowers.
你本不该浇花的

could have done
本可以做而没有做
如:
you could have worked out the question,but you didn't
你本该解出拿到题的,但是你没有

couldn't have done
就不要我说了吧 类推~~~

Answer 2

这是虚拟语气的典型句子结构.
本应该 本不应该