VOA一分鐘英語：Not need to 和 needn't 區(qū)別是什么？

動詞 “need” 的意思是 “需要，必須”。它的否定形式有兩種：“not need to” 和 “needn’t”。它們有區(qū)別嗎？現(xiàn)在時態(tài)和過去時態(tài)下的這兩個否定形式在用法上一樣嗎？
 
Hi, everybody. I’m Sam, and in this lesson I’m going to talk about ‘need’. Do you know the difference between needn’t and not need to?
Look at these two sentences in the present – is the meaning the same or different?
You don’t need to worry about the exam, you’ve studied lots.
You needn’t worry about the exam, you’ve studied lots.
They’re the same, right? Maybe needn’t is a little bit more formal, but the meaning is that there is no necessity for you to worry.
Now look at these two sentences in the past:
He didn’t need to worry about the exam. He had already passed the course.
He needn’t have worried about the exam. It was really easy.
These are different! In the first sentence, he had already passed the course, so he knew he didn’t need to worry. In the second sentence, he didn’t know the exam was going to be easy, so he was worried but he needn’t have been.
 
用法總結(jié)
1 在現(xiàn)在時態(tài)下，“(do) not need to” 和 “needn’t” 表達(dá)的意思通常是一樣的，即 “不需要，用不著”。“Needn’t” 比 “not need to” 稍微更正式一點(diǎn)。
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 在過去時態(tài)下，“(did) not need to” 常用來表達(dá)我們之前沒有做某事，因?yàn)?“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 在過去時態(tài)下，“needn’t + have + 動詞過去分詞” 常用來表達(dá)我們之前做了某事，但其實(shí) “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!