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

　　結構︰主詞＋need not have＋過去分詞

　　說明︰此句型意為原本不必但卻。表示與過去事實相反的假設語氣，即做了沒有必要做的事。而didnt need to＋原形動詞則表示過去的事實，譯為當時不必而且也沒。need not have 在疑問句中表對過去之必要性的強烈疑問，即有的必要嗎？。

　　You need not have bought extra oil for this short trip.在這么短的旅程中，你實在沒有必要多買油。

　　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? 他有必要到車站去接她嗎？

　　He need not have come. (But he came.) 當時他不必來。（但卻來了）

　　He didnt need to come. (And he didnt come.) 當時他不必來。（而且也沒來）

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

　　那天天氣很好，我原本不必帶傘的（但卻帶了）。