CET4语法（二）：need与have to 用法辨析

 　　1) need表示需要，主要用于否定句和疑问句。用于疑问句，肯定回答用must，否定回答用needn't。have to表示他人或客观情况要求“必须”，也可以翻译为“不得不”，have to否定形式意思是“不一定”或“没有必要”。

　　【例如】

　　You needn't come if you don't want to.

　　I don't think you need be so polite to her.

　　You don't have to work so hard if you just want to pass Band 4.

　　Because of the heavy rain, the children have had to get up earlier than usual this week.

　　It was very kind of you to do the washing-up, but you ____it. (CET-4 1998,6)

　　A) mustn't have done

　　B) would not have done

　　C) might not have done

　　D) didn't have to

　　本句译为：你把这些东西洗了，你真是太好了。但是你没有必要洗。must, would, might后面接动词的完成式，都很少用否定式，而didn't have to表示没有必要，符合题意，故答案为D.

　　2) need后面接动词的完成式，主要用于否定句，表示本可不必做某事。

　　【例如】

　　You ____ all those calculations¹! We have a computer to do that sort² of thing. (CET-4 1991)

　　A) needn't have done

　　B) must not have done

　　C) shouldn't have done

　　D) can not have done

　　“needn't +不定式完成式”表示“本来不必做，但实际做了”。题意是：你没有必要做全部计算，这类计算我们用计算机来做。故答案为A.

1 calculations   

n.计算( calculation的名词复数 )；盘算；自私的打算；推断

参考例句：

• We can exclude the possibility of total loss from our calculations. 我们可以在预测中把彻底失败的可能性排除在外。 来自《简明英汉词典》
• He scored out both calculations and did them again. 他把两个计算结果都划掉，又把它们计算了一遍。 来自《简明英汉词典》

2 sort   

v.排序，挑选，分拣；n.种类，类别，性质，程度

参考例句：

• She was a strange sort of person.她这个人有些古怪。
• I don't much care for that sort of man.我不太喜欢那种人。