Before I became an editor, whether to use “farther” or “further” was the sort of question I would never have looked up for fear that it would have an annoying, complicated answer requiring a thorough knowledge of things like nominal adjectives or gerunds. Now it’s my job to look these questions up, and I’m happy to say that this is one issue that is gratifyingly easy to resolve. Farther refers to literal distance. Further refers to figurative distance. You see? That wasn’t so bad.
For those who enjoy tracking down more information, this rule is enshrined in both Strunk and White (fourth ed., p. 46) and The Chicago Manual of Style (16th ed., p. 281).
- Further versus Farther (rickybruce.wordpress.com)
- Which Word Wednesday: Farther vs. Further (fillingmypatchofsky.com)