动词 “need” 的意思是 “需要，必须”。它的否定形式有两种：“not need to” 和 “needn't”。它们有区别吗？现在时态和过去时态下的这两个否定形式在用法上一样吗？

用法总结

1 在现在时态下，“(do) not need to” 和 “needn't” 表达的意思通常是一样的，即 “不需要，用不着”。“Needn't” 比 “not need to” 稍微更正式一点。

You don't need to worry about the exam, you've studied lots. 

You needn't worry about the exam, you've studied lots.

I don't need to go to work tomorrow as it's a holiday.

I needn't go to work tomorrow as it's a holiday.

2 在过去时态下，“(did) not need to” 常用来表达我们之前没有做某事，因为 “不需要”。

He didn't need to worry about the exam. He had already passed the course.

I didn't need to go to work today, so I stayed in bed.

3 在过去时态下，“needn't + have + 动词过去分词” 常用来表达我们之前做了某事，但其实 “本不必” 做。

He needn't have worried about the exam. It was really easy.

I needn't have gone to work today. I didn't realise it was a holiday. What a mistake!