... need not have V-ed ...

　　结构︰主词＋need not have＋过去分词

　　说明︰此句型意为原本不必但却。表示与过去事实相反的假设语气，即做了没有必要做的事。而didnt need to＋原形动词则表示过去的事实，译为当时不必而且也没。need not have 在疑问句中表对过去之必要性的强烈疑问，即有的必要吗？。

　　You need not have bought extra oil for this short trip.在这么短的旅程中，你实在没有必要多买油。

　　You need not have got up so early. 你不必起得那么早。

　　Need he have gone to the station to meet her? 他有必要到车站去接她吗？

　　He need not have come. (But he came.) 当时他不必来。（但却来了）

　　He didnt need to come. (And he didnt come.) 当时他不必来。（而且也没来）

　　It was fine that day, so I need not have brought an umbrella with me.

　　那天天气很好，我原本不必带伞的（但却带了）。