Consider the unfortunate French abbreviation, S.D.F., which normally means "sans domicile fixe". Those three letters, for our purposes, represent since, during and for. Here's how that's going to help us:
SINCE is with STARTING POINTS -- SS [I haven't seen him since last week]... from a starting point in the past until now. A starting point can be an hour, a day, a year, etc.
DURING is with DEFINED PERIODS -- DD [My boss slept during the meeting]... we define how long a meeting, lunch, holidays, etc, are. These periods aren't fixed, they can be longer or shorter.
FOR is with FIXED PERIODS -- FF [We have lived here for 6 years]... six years is 312 weeks, or 2190 days. It's a fixed period. 2 minutes is fixed as well.
English, like any other language, isn't a hard science and some of it doesn't follow the rules as well as we'd like it to. But most of it does, and I hope that this little trick will help you use SDF correctly more often than not.
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