needn't do
didn't need to do
didn't have done
这些词组都是什么意思？在用法上有何区别？

“need”双重角色的用法及其区别

“need”既可以作情态动词，也可以作实义动词，但是它们的用法不同。

作为情态动词的“need”的用法与其他情态动词“can”，“may”，“must”的用法基本相同：在限定动词词组中总是位居第一，没有非限定形式，即没有不定式、-ing分词或-ed分词等形式；第三人称单数现在时没有词形变化；情态动词之间是相互排斥的，即在一个限定动词词组中只能有一个情态动词。下面是“need”作为情态动词的用法：

一、need表示“需要”或“必须”，通常用于否定句和疑问句。例如：

1．You needn't do it again．你不需要再做了。

2．He needn't worry about it．这件事他无需担心。

3．Need he do this homework first？他需要先做这些作业吗？

4．Need they fill in the form？他们需要填表吗？

二、在否定句中，可以用need的否定形式＋不定式完成体。例如：

1．We needn't have worried．其实我们不必要慌。

2．You needn't have mentioned it．你本来不必提起这件事。

3．You needn't have said that when he asked．当他问的时候，你其实不必要说。

三、needn't后的不定式间或也能用进行式或被动语态。例如：

1．He needn't be standing in the rain．他不必要站在雨中。

2．We needn't be waiting in this place．我们不必要在这儿等。

3．The hedges needn't be trimmed thisweek．本周树蓠不必要整修。

“need”作为实义动词时，通常用法是：

人＋need ＋to do

物＋need ＋doing

物＋need ＋to be done

另外，“need”后还可以直接跟名词。请看下面的例子：

1．We need to collect the parcel before we leave for England．去英国之前，我们需要收拾好行李。

2．We need to tell him the truth．我们需要告诉他真相。

3．My car needs repairing．我的汽车需要修理。

4．The flowers need watering．这些花需要浇水。

5．His leather shoes needs to be mended．他的皮鞋需要修补。

6．Her room needs cleaning．她的房间需要打扫。

7．It is aquestion that needs very careful consideraton．这是一个需要慎重考虑的问题

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needn't have（done）和didn't have 的区别


A needn't have done意指没必要干某件事但多余地干了，即浪费了时间：

You needn't have watered the flowers，for it is going to rain．

你本不必浇那些花，因为就要下雨了。（你浪费了时间。）

You needn't have written such a long essay．The teacher only asked for

300 words，and you have written 600．

你本不必写这么长的文章。老师只要求写300个字而你却写了600个字。

He needn't have bought such a large house．His wife would have been quite happy in a cottage．

他没必要买这么大一所房子。他的妻子住在一个小房子里也会感到很满意的。（浪费了钱）

You needn't have carried all these parcels yourself．The shop would have delivered them if you had asked them．

你本来没有必要自己拿着这些大包小裹的。要是当时你跟商店说一声，他们就会把东西送来的。

B didn't have／need to do意指不一定非干某事，而通常也并没有这样做：

I didn't have to translate it for him for he understands Dutch．

我用不着替他翻译，因为他懂荷兰语。

I didn't have to cut the grass myself．My brother did it．

我用不着自己修剪草坪。我的兄弟修剪过了。（无义务，而且无行动）有些人的确把didn't have to／didn't need to用于表示已完成的动作，这时 have或 need都要加以重读：You didn't 'have to give him my name通常意味着没有必要告诉他我的姓名，但是你却告诉了他。但当一个不必要的动作实际已完成了时，还是用needn't have+过去分词为好：

You needn't have given him my name．

你本来没必要把我的姓名告诉他的。