The Rule

  • since + point in time (specific moment)
  • for + period of time (duration)

Scenarios

⏰ Describing Duration

Contextsince (point)for (period)
Worksince Januaryfor three months
Studysince 2020for five years
Livingsince I graduatedfor a decade

💬 Example Sentences

With since:

  • “I’ve been working here since 2021.” (从 2021 这个时间点开始)
  • “She’s been studying English since last Monday.”
  • “They’ve been collaborating since the project started.”

With for:

  • “I’ve been working here for four years.” (持续了四年这段时间)
  • “She’s been studying English for two months.”
  • “They’ve been collaborating for weeks.”

Quick Reference

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since + [具体时间/事件]
  - since Monday
  - since 2020
  - since last week
  - since I was born
  - since the beginning

for + [时间段]
  - for two weeks
  - for a month
  - for years
  - for a long time
  - for decades

Common Mistakes

❌ Wrong✅ CorrectNote
since two weeksfor two weeksDuration needs “for”
for 2020since 2020Point in time needs “since”
since a monthfor a monthDuration needs “for”

Memory Trick

Quick test: Can you replace it with “from X to now”?

  • ✅ Yes → Use since (starting point)
    • “from 2020 to now” → “since 2020”

Quick test: Can you add “a period of” before it?

  • ✅ Yes → Use for (duration)
    • “a period of two weeks” → “for two weeks”

Practice

Choose “since” or “for”:

  1. I’ve been learning English ___ 2020.
  2. She’s worked here ___ five years.
  3. They’ve been married ___ last June.
  4. We’ve known each other ___ a long time.

Answers:

  1. since (2020 is a point in time)
  2. for (five years is a period)
  3. since (last June is a point in time)
  4. for (a long time is a period)