need to do sth实义动词
need do sth. 没有这种用法，有need doing，表被动
needn`t do sth情态动词
don`t need实义动词


“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

1) Depending on the sense,the verbneed  behaves sometimes like an auxiliary verb (such as can  or may ) and sometimes like a main verb (such aswant  or try ). When used as a main verb,need agrees with its subject, takesto  before the verb following it, and combines withdo  in questions, negations, and certain other constructions:  

根据语义，动词need 有时当作助动词来使用（如 can 或 may )， 有时象实义动词（如want 或 try )。当用作实义动词时，need 和主语一致， 把to 放在其后面动词的前面， 在疑问句、否定句或某些特定的造句法上和do 连用：  

He needs to go.
他想走。
Does he need to go so soon?
他这么快就要走吗?
He doesn't need to go.
他不需要走。

2) When used as an auxiliary verb,need does not agree with its subject, does not taketo  before the verb following it, and does not combine withdo :  

当用作助动词时，need 不用和主语一致， 不用把to 放在其后动词的前面， 并且不用和do 连用：  

He needn't go.
他不必走。
Need he go so soon?
他这么快就要走吗?

3) The auxiliary forms ofneed  are used primarily in present-tense questions, negations, and conditional clauses. They differ subtly in meaning from the main verb forms in that they always refer to an externally imposed obligation.Hence one might sayYou needn't  (or less formally, don't need to ) fill out both forms,  but where the sense of necessity is internal to the subject,only the main verb can be used:

Need 的助动词形式主要用于现在时态的疑问句、否定句和条件句中。它们在意思上和用作实义动词的形式有细微的区别，它们总指外部加强的压力。因此我们可以说你没必要 （或不太正规的 don't need to ) 填两份表格 ， 但是对于物体来说需要的意思是内在的，所以只能用实义动词：

I don't need to (not needn't ) be told how to manage my own affairs.  
我不需要（而不是 needn't ) 被告诉怎知管理自己的事情 。

4) Note also that the use ofneed  as an auxiliary is often accompanied by a presupposition that the activity in question has in fact been performed.The boys needn't have spoken frankly  implies that they did in fact speak frankly, whereas the sentenceThe boys did not need to speak frankly  does not; only the latter could be followed by a clauselikethey conveyed their meanings by indirection.  

还需注意need 用作助动词时经常伴随一个先决条件， 质问的动作事实上已经完成了。那些男孩们本来不需要坦诚相告的意味着他们事实上已经坦率地说了， 然而这个句子男孩们不需要坦诚地说话 就没有这个意思；只有后者可以在其后跟这样一个句子，如他们间接地表达他们的意思