Is there any difference between farther and further? Merriam-Webster’s online dictionary notes in a usage discussion that as an adverb, farther and further are used indiscriminately when literal or figurative distance is involved:
“How much farther do we have to go?”
“It’s just a mile further.”
“How much further do you want to take this argument?”
“I’ve taken it farther than I want to already.”
However, in adjectival form, a distinction has developed regarding use in these senses:
“My house is the farther of the two.”
“She needs no further introduction.”
Bryan A. Garner, in Garner’s Modern English Usage, advises, “In the best usage, farther refers to physical distances, further to figurative distances,”
Farthest and furthest, by extension, should maintain the same distinct meanings; use these forms in favour of the burdensome farthermost and furthermost. Furthering and furtherance are interchangeable noun forms that serve as synonyms for promotion or advocacy; there is no equivalent noun form for farther.
Further is also employed as a modifier, as in “Further, I see no reason to delay the proceedings”; furthermore is a variant. Farther, however, does not fit this role.