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:

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

since

Since is normally used with perfect tenses:

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

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.