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for and since for Time

We lived there for five years.
He has been away since Tuesday.

We often use for and since when talking about time.

for + period: a "period" is a duration of time - five minutes, two weeks, six years. For means "from the beginning of the period to the end of the period".

since + point: a "point" is a precise moment in time - 9 o'clock, 1st January, Monday. Since means "from a point in the past until now".

Look at these examples:

for
a period
from start to end
since
a point
from then to now
>===< x===>|
for 20 minutes
for three days
for 6 months
for 4 years
for 2 centuries
for a long time
for ever
since 9am
since Monday
since January
since 1997
since 1500
since I left school
since the beginning of time
all tenses perfect tenses

for

For can be used with all tenses. Here are a few examples:

  • They study for two hours every day.
  • They are studying for three hours today.
  • He has lived in Bangkok for a long time.
  • He has been living in Paris for three months.
  • I worked at that bank for five years.
  • Will the universe continue for ever?

We do not use for with "all day", "all the time":

  • I was there all day. (not for all day)

since

Since is normally used with perfect tenses:

  • He has been here since 9am.
  • He has been working since he arrived.
  • I had lived in New York since my childhood.

We also use since in the structure "It is [period] since":

  • It was a year since I had seen her.
  • How long is it since you got married?
Both for and since also have other meanings, with no reference to time. Here are some examples:
  • This is for you.
  • Is this the train for London?
  • Since you ask, I'll say yes.
  • Since he didn't study, he didn't pass the exam.