For / since / ago

For、since 和 ago 都和时间有关，但用法各不相同：

例如：今天是星期四，阿兰星期一到了河内。同一件事可以有三种说法：

• Lan has been in Hanoi for three days.

  阿兰在河内已经三天了。

• Lan has been in Hanoi since Monday.

  阿兰从星期一起就在河内了。

• Lan arrived in Hanoi three days ago.

  阿兰三天前到了河内。

💡两个常见陷阱：中文“从 2019 年开始（到现在）”是 since 2019——from 后面通常要接 to/until（from 2019 to 2022）；“两年前”（从现在往回算）是 two years ago，不是 before two years。

For 回答 How long?，可以用于任何时态，不只是现在完成时。

• I've had this phone for three years.

  这部手机我已经用了三年了。（现在还在用）

• We lived in Hue for two years, and then we moved to Saigon.

  我们在顺化住了两年，然后搬到了西贡。（已经结束 → 一般过去时）

• I'm staying with my cousin for a week.

  我要在表哥家住一个星期。

• 用在现在完成时的否定句中：I haven't seen her for years。美式英语也常用 in：I haven't seen her in years。
• for + 一段时间（for two hours）和 during + 事件或时期（during the film、during the summer）不同：during 说的是什么时候，不是多长时间。
• for ages（口语）= 很久很久：I haven't been to the cinema for ages。

Since 给出起点——某一天、某一年、某件事——动作从那时一直持续到现在。所以主句通常用完成时（have/has + V3 或 have/has been + -ing）。

• My dad has worked at the hospital since 2015.

  我爸爸从 2015 年起就在这家医院工作。

• I haven't eaten anything since this morning.

  我从早上到现在什么都没吃。

• Binh has played football since he was little.

  阿平从小就踢足球。（since + 一般过去时从句）

• It's been two years since I last saw Minh.

  我上次见阿明已经是两年前了。

It's been (= It has been) + 一段时间 + since + 一般过去时 这个句型在口语中很常见。英式英语也说 It's two years since…，意思相同。

Ago 放在一段时间的后面，从现在往回算。它指的是已经结束的时刻，所以和一般过去时连用，不用现在完成时。提问用：How long ago…? 或 When…?

• Hung moved to Hanoi three years ago.

  阿雄三年前搬到了河内。

• How long ago did you start this job? — About six months ago.

  你多久以前开始做这份工作的？——大约六个月前。

• I called her ten minutes ago, but she didn't answer.

  我十分钟前给她打了电话，但她没接。

💡Ago 从现在往回算；before 从过去某个时刻往回算：She left Hanoi in 2020. She had moved there two years before（= 2018 年）。单独使用时，before 意思是“以前”：I've never been here before。

选时态之前先问自己：这件事还在继续，还是已经结束了？

同样的信息可以从一种句型换成另一种：

• I bought this bike two years ago. → I've had it for two years.

  这辆自行车我是两年前买的。→ 我已经骑了两年了。（bought → have had，不是 have bought）

• Minh started learning the guitar in 2023. → He's been learning it since 2023.

  阿明 2023 年开始学吉他。→ 他从 2023 年起一直在学。

• The last time I saw Hoa was in May. → I haven't seen Hoa since May.

  我最后一次见阿花是在五月。→ 从五月到现在我都没见过阿花。

• ✗I have studied English since five years.

  ✓I have studied English for five years.

  five years 是一段时间 → for。

• ✗I have lived here for 2019.

  ✓I have lived here since 2019.

  2019 是起点 → since。

• ✗We met each other before two years.

  ✓We met each other two years ago.

  “……以前”= 一段时间 + ago。

• ✗I have seen that film two weeks ago.

  ✓I saw that film two weeks ago.

  ago 指已经结束的时间 → 一般过去时。

• ✗I live here since 2020.

  ✓I have lived here since 2020.

  用 since 时主句要用完成时。

• ✗I'm waiting for an hour!

  ✓I've been waiting for an hour!

  说到现在为止持续了多久，用完成时，不用现在进行时。