Unit 18. for since ago
See Unit 17 How long have you … (Present Perfect 3)
for and since
We use for and since to say how long:
We use since + the start of the period (Monday/ 9 o'clock etc.):
- Barry has been in Canada since January. (= from January to now)
- Barry has been in Canada for six months. (not since six months)
- I've known her since 1980. (= from 1980 to now)
- I've known her for a long time. (not since a long time)
See Unit 92 from … to until since for
ago = before now:
- Susan started her new job two weeks ago. (= two weeks before now)
- "When did Tom go out?" "Ten minutes ago." (= ten minutes before now)
- I had dinner an hour ago. (= an hour before now)
- Life was very different a hundred years ago.
We use ago with the Past Simple (did/ had/ started etc.)
Compare ago and for:
- When did she arrive in London?
- She arrived in London four days ago.
- How long has she been in London?
- She has been in London for four days.