The next time the Associated Press Stylebook looks to clean the cobwebs in the attic, the editors might want to take another look at farther/further.
The current entry, of long standing, restricts farther to physical distance, further to "extension of time or degree." This is one manifestation of editors' inevitable impulse to tidy up the language with minute distinctions invisible to most readers, or "dog whistle editing."
Further and farther have been interchangeable for most of the history of English, as the Blessed Henry Watson Fowler, the Oxford English Dictionary, Merriam-Webster's Dictionary of English Usage, and other authorities have acknowledged.
And thus have the people spoken. If you look up further in the current Merriam-Webster's Collegiate Dictionary, the Concise Oxford English Dictionary, and Webster's New World College Dictionary, you will see one of its core meanings listed as farther.
The American Heritage Dictionary has a usage note for farther, affirming the physical distance/abstract relations distinction. Significantly, the 74 percent of the Usage Panel's endorsement in 1987 had declined to 64 percent in 2009. Since the dictionary discontinued the Usage Panel in 2018, we are unable to see how much further erosion may have taken place. But Garner's Modern English Usage of 2016, while identifying the farther/further distinction as "punctilious usage," concedes in his Language-Change Index that further for physical distance is Ubiquitous but."
For the record, I dutifully enforced farther/further over four decades as a copy editor, though having done so does not leave me with a glow of professional pride. Time could have been spent on more significant matters.
So AP Stylebook, how about chucking this one into the dustbin?