Farther or further: does the distinction still hold?

The standard guidance is that farther refers to measurable physical distance, as in the store is farther than I thought, while further refers to degree, extent, or additional amount, as in further discussion, nothing could be further from the truth, or further research is needed. Only further works as an adverb meaning moreover and as a verb meaning to advance something, as in furthering a career, which is a useful asymmetry to remember: farther has a narrow job while further does everything.

The historical reality is messier than the rule suggests. Both derive from the same Old English root and were used interchangeably for centuries, and the physical-versus-figurative distinction is a relatively recent prescriptive tidying that has never been fully observed in practice. British usage in particular has long favored further for both senses, and corpus evidence shows further gaining ground in American usage as well. Dictionaries note the overlap rather than treating farther for figurative distance as an outright error.

The practical position is that the distinction is worth following in formal and edited writing, because readers who know the rule will notice a violation and because it costs nothing, while using further for physical distance is unlikely to be marked wrong by anyone. When in genuine doubt, further is the safer choice given its broader acceptance. This sits in a family of distinctions with the same character, including between over and more than for quantities, where the supposed rule was a newspaper style convention rather than a grammatical one and was formally abandoned by the AP in 2014, and between since and because, where the objection was never well founded.