Do we go farther or further? The two words are very close, but there is one small difference.
When you talk about real distance (how far you walk, drive or travel), you can use farther or further. Farther is more common in American English, further in British English.
When it is not about real distance, use only further. It can mean “more”, “extra” or “to a higher level”.
Real distance → farther or further (both are fine)
Anything else (more, extra, to a higher level) → only further
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