BBC news 2010-12-12 加文本

could have猜测

1)may / might + have + 过去分词”表示对已发生的动作或存在的状态进行不肯定的推测，might的语气比may弱一点。这种结构主要用于肯定句和否定句，疑问句改用can或could。如：

They may not have known it beforehand.

You might have read about it in the papers.

2)“must + have + 过去分词”表示对过去发生的事情或状态进行推测，语气比较坚定，通常只用于肯定句。如：

It must have rained last night, for the ground is wet. 

You must have been mad to speak to the servant. 

3)“can / could + have + 过去分词”表示对过去某种情况的怀疑或不确定。can和could一般用于否定句和疑问句，could的语气较can弱。如：

I didn't see her at the meeting this morning; she can't / couldn't have spoken at the meeting.

He can't have finished the work so soon. 

4)“should / ought to + have + 过去分词”表示过去本该做某事但没做，其否定式表示过去不该做某事但做了，这种句式含有不满或责备之意，ought to的语气比should强一些。如：

You ought to / should have studied harder. 你本应该更努力学习的。（但没有）

He oughtn't to / shouldn't have done that. 他本来就不该做那件事。（可是做了）

5)“would ＋ have ＋ 过去分词”表示对过去的某种情况进行猜测，或本来要做某事却因某种原因未做成，通常用来说明某一情况，但不像用should或ought to那样含有责备之意。如：

I guess the poet would have been about twenty when she wrote her first poem.

Another worker wouldn't have acted like that.