ESL learners are often unable to decide when to use for instead of since. Take a quick look at these sentences:
- INCORRECT: Susie has been here since ten days.
- CORRECT: Susie has been here for ten days.
- INCORRECT: That house has been empty since three months.
- CORRECT: That house has been empty for three months.
Both for and since can be used with a present perfect to talk about duration up to the present, that is, to say how long something lasts. However, for is followed by the period of time; since is followed by the starting point of time.
for + period of time
- I trust him. I've known him for more than five years.
- The Leaning Tower of Pisa has been saved for another 300 years according to its engineers.
- How long have you been here for? I've been here for six hours.
since + starting point
- Regina's songs have been used in various TV programs and movies since 2005.
- They have held rights to the book since the early 1970s.
- I have not seen any of them since that evening.