When is it proper to use each of these? When is it not proper?
This is a relatively easy one. Farther is measurable distance. Further is unmeasurable - things like emotions.
His house is farther down this road.
I will go further to impress you with my love (unless I am talking about a walking contest).
His idea further complicated the situation.
what about with time? I think i say “I will not discuss this any further” and not “… farther”. but time is a measurable distance, kind of.
so is ‘farther’ talking strictly about physical distance, and everything else is ‘further’, or what?
I tell my students that “further” essentially means “more.”
The confusion comes in that sometimes we could get across essentially the same point by using either “further” or “farther”.
Most cases are relatively clear, though:
“His house is a greater distance down this road.”
“I will go to a greater extent to impress you with my love.”
“His idea even more complicated the situation.” (I know the grammar doesn’t work exactly with this one, but it still keeps the point of the sentence.)
In jb_farley’s example, we wouldn’t mean that we won’t discuss this for a greater distance, but “any more”, presumably.