情态动词+have done的用法总结否定形式

　　一、“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.

　　二、“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.

　　三、“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.

　　四、“need + have + 过去分词”表示过去做了不必做或不需要做的事情，或过去做某事纯属多余。如：

　　Need they have done it last week?

　　I needn't have bought so much wine—only five people came.

　　五、“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）

　　六、“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.