needn't have done和didn't need to do 有什么不同

Question

如题所述

Answer 1

不同之处为：
needn't have done表示某件事没必要做却已经做了。表示已经做了这件事。
didn't need to do指在过去某件事不必做，是否做了不清楚。

例句：
needn't have done
1、We spent a hell of a lot of money that we needn't have spent.
我们花了很多本来不需要花的钱。
2、I was nervous when I announced my engagement to Grace, but I needn't have worried.

我宣布和格雷丝订婚时有点紧张，但我本不必担心的。
3、You needn't have waited for me.
你本不需要等我的。
4、You needn't have told me that much.

你不必和我讲那么多。

didn't need to do
1、Because the threat never developed, we didn't need to take any real counter measures.
威胁从未加剧，因此我们没有必要真采取什么对策。
2、I didn't need to know that Coca-Cola has added a lot of value.

“我没有需要知道，可口可乐公司增加了大量的价值”。
3、I didn't need to think about it.

我根本不需要考虑。
4、She is very reliable and I knew I didn't need to encourage her.

她非常可信赖，我知道我没有必要给她鼓励。

Answer 2

动词的分类上，前者的need为情态动词，后者为实意动词。
意思上，前者表示某件事没必要做却已经做了，表示已经做了这件事；而后者只是主语在过去时表示某件事必不必要做，做了没有并不清楚。本回答被提问者和网友采纳

Answer 3

needn't have done中的need 相当于是个情态动词，就是没必要做（已经做过了）；
didn't need to do中的need 是个谓语动词，意思是 不需要做；
同一个词在不同的短语中充当的成分不一样。（这不就是自己写的吗，还什么修改建议....）