Growl, growl, grumble ... I just spent half an hour on this ansd instead of publishing it just disappeared. Growl and grumble some more ...
Oh well - the really simple rule comes at the end. First the explanation and examples all of which come either from the Cobuild dictionary or the
Cobuild concordancer.
Both forms can be used to refer to physical distance :
... the awesome Jotunheim mountains a few miles further north
...I walked further than I intended
... Further to the north, the British infantry ...
... optional EF excursions can take you farther afield to other countries
... and some twenty metres farther on it ended
... striped with forest, stretching farther and farther until the mists
But
further has a lot of additional (further!) uses:
1. more / to a greater extent / additional :
The situation was further complicated by/ he sank further into debt/ a further five hundred pounds
2. In addition :
He said XXX. He further argued that ..
3. prior, subsequent, longer time :
I can't remember further back than 1970 / Three years further on / I won't detain you further
4. Following, subsequent to :
Further to your telephone call, ...
5. In set expressions :
go further (= say something more extreme) ;
take something further
6. As a verb :
to further your career
So, the simple rule is : always use
further and you'll always be correct (and ignore all those silly sites on the net that tell you otherwise).
But an almost as simple rule is : use
farther for physical distance if you really want to, but
further in all other contexts.
Hope that's
furthered your understanding
Further or Farther ? 
Linear Mode
