once(adv.)

在 I saw her once. 这个句子里, once 与过去时连用, 表示时间位置 (at some time in thepast)。上面的句子可以译为:我过去曾经见过她。而在 I have seen her once. 这个句子里, once 与现在完成时连用, 表示时间频率(one time only)。上面的句子可以译为: 我见过她一次。下面是类似的例子:

1. I once visited this city. 我过去曾访问过这座城市。

2. I've been in to see him once, he's sleeping. (Snow) 有一次我进去看他，他正在睡觉。once(conj.)1

用作连词的 once, 其意义为: as soon as(“一旦”“一……就”) 或 after(“在……之后”)。它常常表示从句中的动作业已完成, 因此 once 从句经常使用现在完成时:

1. Once you've finished your homework you can go out. 你一做完家庭作业就可以出去。

2. Once we have decorated the house, we can move in. 一旦我们把房间装饰好就能搬进去了。

3. Once you've learnt to swim, you'll never forget. 一旦你学会了游泳，你就永远也忘不了。

但是, once 也可以跟一般现在时、一般过去时或过去完成时连用:

1. Once you're in here, listen to your teacher. 你一旦进了这里，就要听老师的。

2. Once he understood, he did what he was told to do. 一旦他明白了,他就按照吩咐的去做了。

3. Once he had found somewhere to live he started looking for work. 他找到住处之后，马上就开始找工作。

4. I'll show you once we're safely inside the embassy. (Dan Brown, The Da Vinci Code) 我们安全进入使馆后，我会给你看的。(《达·芬奇密码》)