Prepositions

For and since

We use for and since to say how long.

For refers to a period of time.

• I've worked in this office for three years.

				now
2008		for three years		2011

Since refers to a point in time.

• I've worked in this office since 2008.

				now
since 2008				2011

For and since are often used with the present perfect to talk about actions that began in the past and continue now.

• I've lived in this apartment for three years.
  NOT: I live in this apartment for three years.

• I've lived in this city since last January.
  NOT: I live in this city since last January.