for a long time / since Monday

Grammar notes

For or Since?

Use for with a length of time and since with a starting point. Both are very common with the present perfect. They help answer the question How long?

• Example: I have lived here for three years.
• Example: She has been ill since Monday.

Quick Rule

• for + period of time
• since + starting point

One points to the whole distance, and the other points to the starting line.