"Since " is used to specify a point of
time in the past. Since is also used to mention a reason or a
"For" is used when we mention a duration of period and not a point of
time. For is also used for telling the reason of doing some activity.
I have been in this city since
I have been in this city for the last
four years. (2010-2014)
here, duration of
4 years is mentioned.
"Since" is used for telling a reason. I traveled by an auto since the bus had not arrived
For : I prayed God for the good of my family.