present perfect is often used with since and for to
denote periods of time up to the present. (Note that we do not use
present perfect with expressions that refer to a time period that
has finished, i.e. 'last week' or 'the day before yesterday'. Here
the simple past is used: 'I went to the cinema three times last week.')
you use since with the present perfect or present perfect
continuous, you are signalling when something started. If you use
for, you are signalling how long something has been going
- 'She has been living in Holland since the summer of 1992.'
- 'She has been living in Holland for the last nine years.'
is one use of since and for.
But since and for can also be used in a similar way
to as and because to give the reason for an action
or a situation. However, there are important differences between