Question

should have done ;could have done; might have done 有什么区别

Answer 1

should have done:本应该做而没做某事，强调“本来应该”；
could have done:本可以做却没做某事，强调“本来可以”；
might have done: 可能已经作了某事，强调猜测。

前两个都是假设，是与实际情况相反的假设。第三个是猜测。除此之外，should have done还明显含有懊悔或责怪之意。

举例来讲：

小明把家里的钥匙放在教室忘记带了。回到家打不开门一直蹲在门口等到晚上10点多加班的爸爸妈妈回来，很晚才进了家门。此场景下

1. 小明到家后发现钥匙忘带很懊悔。此时他可能会抱怨自己：I should have brought the key with me.

2. 那时的小明除了在门外等待爸爸妈妈回来，还有别的解决方案却没做：He could have come back to school to get the key but he didn't.

又如，当爸爸妈妈那么晚回来发现小明在门外，问明原因后，爸爸妈妈问他为什么当时不返回学校拿钥匙。爸爸妈妈认为若小明当时返回学校拿了钥匙的话可能早就进去了。爸爸妈妈可能会说：You could have come in much ealier if you came back school to get the key then.

3. 关于为什么当时没有返回学校拿钥匙，小明解释到：I thought the gate might have already been closed by that time.(学校大门那时候可能早已经关了）

For your reference. Tks!

Answer 2

should have done 是当初该(有义务)做什么事但是没做的
could have done 是当初能（有能力）做某事但没做的
might have done 是可能做过了某事（表不确定）