-
would/could/might/should have
done
等
用法和区别
一、在虚拟语气中的用法（情态动词都是过去时态！）
1.
should
have
done
：原本应该做某事，
(
否
)shouldn't
have
done
:
原本不该做某事
2. ought to have done
原本应该做某
事，
(
否
) oughtn't to
have
done
:
原本不该做某事
注意：
ought to do
语气更强，常用于长辈对小辈的用语
或某规则上的要
求（严格的规则应用
must
）．
should do
可用语平辈朋友间，较为客气与口语化
3.
need
have
done
原有必要做某事
(
否
)
needn't
have
done
原
本没必要做某事
< br>注意：做情态动词，
need
的过去式仍然是
need;
做实意动词，
need
的过去式是
needed.
4.
could have
done
原本能够做某事
注意：
couldn't have done
无虚拟语气的用法，
只表推测，相
当于
can't
have done
：过去不可能做了某事
5.
might have done
原本可以做某事
注意：
might not have done
无虚拟语气的用法，
只表推测，
相当于
may not
have done
：过去可能没有做某事
have done
原本会做某事
1. I would have told you all about the
boy's story, but you didn't ask me.
二、对过去事情表推测的用法
(
情态动词用
原型或过去式都可以，只
是在说话者看来，可能性大小稍微有所不同而已
)
1.
must
have
done
：过去肯定做了某事。不存在
mustn't
have
done
的形式。其否定或疑问形式须用
can(could)have
done
：“不可能做
过某事”
来表示：
Since the road is wet, it must have
rained last night.
既然路是湿的，那昨天晚上肯定下雨了。
He can't/couldn`t have missed the way.
I drew him a map.
他不可能迷路。我（当时）给他画了张图。
“The dictionary
has
disappeared. Who could/can have taken
it?”词典不见了，（过去）谁可能把它拿走了？
2. may / might have done
may / might have
done
：过去可能做了某事，
may
比
might
表示可
能性稍大些。
may/might not have
done
过去可能没有做某事：
I
can't
find
my
keys.
I
may
/
might
have
left
them
at
the
school
yesterday.
我找不到我的钥匙了。我可能昨天把他们落在学校了。
John may/might not have passed the
exam; he looks very sad.
约翰可能没有通过考试。他看起来很忧伤。