| #2 (permalink) Tue Apr 20, 2010 13:46 pm "a day before" vs "the day before"
'A day before' suggests not necessarily the exact day ( as 'the' day before would) but the period of time that has elapsed - in other words 24 hours.
'Ago' suggests back from the present as in: Two days ago, where we are going back two days from now. 'Before' can be used from now and from then as in: Before today we were able to buy tickets at the office but as from today you have to buy tickets online. Before the war prices were much cheaper.
In your sentence: The U.S. economy had been in a state of what is called stagflation since several years before, we are using 'before' to describe that time in the past (had been) and 'since' suggests from that time. In that case 'ago' wouldn't work because, as I said, it has to be a period back from now.
Hope this makes sense.
English as a Second Language
You can read my ESL story Present Simple
Joined: 27 Sep 2003