J.M. NORTHUP

Generally speaking, FARTHER is used when discussing only true DISTANCE and FURTHER is used when measuring FIGURATIVE DISTANCE. However, that isn’t completely true. Why? Well, let’s discuss it.

Both FARTHER and FURTHER can be use as adverbs (modifies a verb, adverb, adjective, or phrase) and adjectives (modifies a noun or pronoun). When used in comparative (and superlative) forms, there really is no difference between them according to Cambridge Dictionary. However, there are times when you can use FURTHER, but not FARTHER (when used before a noun to mean “extra,” “additional,” or “higher level of”).

As Adverbs

As adverbs, further and farther are not confined to distance, and this leads to one clearer distinction between the words. Further has the meaning of “moreover” or “additionally,” one that is not shared by farther. Farther does not work very well as a sentence adverb, and so it would sound rather awkward to begin a sentence with “Farther, I’d like to address the issue of why these words are so confusing.”

https://www.merriam-webster.com/words-at-play/is-it-further-or-farther-usage-how-to-use

As Adjectives

When using these words as adjectives there are similar degrees of overlap and distinction. While both words are defined as carrying the meaning of “additional,” this role has now been almost entirely taken over by further.

https://www.merriam-webster.com/words-at-play/is-it-further-or-farther-usage-how-to-use

It is interesting to note that FURTHER can be used as a VERB while FARTHER cannot.

As Verbs

Finally providing use with a degree of clarity, further is the undisputed winner in the verb bloodfest (e.g., you attempt to further your career by pretending to work harder than you actually do). This is not to say that farther hasn’t also been used as a verb, but it is now rare enough that you can sneer at anyone who uses it in this fashion (just kidding; please do not sneer at people for their linguistic nonconformity).

https://www.merriam-webster.com/words-at-play/is-it-further-or-farther-usage-how-to-use

CONCLUSION:

Farther vs. Further – What’s the Gist?

Believe it or not, these two terms are somewhat related. They are both comparative degrees of the word far. There are some nuances of which to be aware, however.

• Farther is a modifier.
• Further functions both as a modifier and as a verb.

http://www.queens-english-society.com/farther-vs-further

I hope this helps. Happy writing/editing, my friends!