Farther vs Further

Farther versus Further
Throughout history, farther and further have been used interchangeably. Even my friendly Merriam-Webster Dictionary states that the words are interchangeable; they are the inflected form of far. It is not until recent history that they are becoming distinguished by grammarians.

Farther
Farther shows a relation to physical distance. If you can replace the word farther with "more miles" then you have done it correctly.
• Our car drove farther than I thought it would on one tank of gas.
• I wanted to run farther, but I became too exhausted.
• Our house is farther away from the restaurant than yours.
Further
Further relates to metaphorical distance or depth. It is a time, degree, or quantity. It is also another way of saying "additional".
• I asked that there be further discussion on the matter.
• I need to look further into the logistics of moving farther from my office building.
• I hope that gas prices drop further for our road trip vacation.

Farther shows a relation to physical distance. If you can replace the word farther with "more miles" then you have done it correctly.
• Our car drove farther than I thought it would on one tank of gas.
• I wanted to run farther, but I became too exhausted.
• Our house is farther away from the restaurant than yours.
Further
Further relates to metaphorical distance or depth. It is a time, degree, or quantity. It is also another way of saying "additional".
• I asked that there be further discussion on the matter.
• I need to look further into the logistics of moving farther from my office building.
• I hope that gas prices drop further for our road trip vacation.

Well, I hope that this has helped you some. If not, let me know and we can discuss this further. Or was that farther?
Phil