助动词need和行为动词need
need指主语的主观特需情况而使之必要。need既可以作助动词，又可以作行为动词。 作助动词时，need没有人称和数的变化，后接不带to的不定式（动词原形），否定式为needn't.作行动动词时，need同别的行为动词一样，有人称和数的变化，后接带to的不定式，否定式要在前面加don't（doesn't, didn't），疑问句用do (does, did)提问。例如：
There need be no hurry, need there?
He need never know. (=He never needs to know.)
I need only add a few words. (= I only need to add a few words.) 比较：
Father sent me the book, so I didn't need to write to him for it. 父亲把那本书寄来了，所以我不必为此给他写信了。（信没写） Father sent me the book, so I needn't have written to him for it. 父亲把那本书寄来了，所以我本不该为此再写信给他的。（信已写） Note:
作助动词用时，need只用于疑问句中和否定句中，在肯定句中常用must, have to, should,ought to等。例如：
Need you do it right now? I needn't, but he must. She doesn't need to be told. She has already known it.
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（客观情况使得告诉她没有必要： 她已经知道）
She needn't be told. We should keep it secret from her. （主观上不愿告诉）
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