The Farther I Go, the Further Behind I Get(farther and further)

The easier of the two words, "farther," is the comparative degree of "far." (far, farther, farthest)  It means "at a greater distance" and refers to actual spatial measurement.

The following sentences use "farther" correctly:
        We arrived at the airport later than they did because we live
            FARTHER away.
        My new car drives FARTHER on a tank of gas than my old one.
        I'm too tired to walk any FARTHER.
        Plant the tree FARTHER than ten feet from the house.
        We can't drive any FARTHER on this road without chains.
        She jogs a mile FARTHER than I.
        Boston is FARTHER from Los Angeles than from Las Vegas.
        Our house is FARTHER from town than theirs.

In the above sentences, notice the following:
       1. The word "farther" can be replaced by "(at a) greater distance."
       2. The distance is physical, spatial, or geographical.
       3. The word "farther" has "far" in it.


The word "further" means "to a greater extent or degree" or "additional."  It is a more abstract term, is not physical or tangible, involves no actual measurement of distance, and is not related to the word "far."

The following sentences use "further" correctly:
             Let's discuss this idea FURTHER in my office.
             Because of new evidence, the trial faces FURTHER delay.
             We won't be able to answer your questions until we are FURTHER    
                 along in our research.
             I'll consider the matter FURTHER.
             This topic requires FURTHER study.
             The hospital provided no FURTHER details on his condition.
             Their techniques have been FURTHER refined.
             We'll pursue the subject FURTHER in our next class.
             The judge is expecting FURTHER proof.
             They plan to study the proposal FURTHER.
             The lawyer needs FURTHER evidence to support his case.
              If there are no FURTHER questions, we'll proceed.
             The jury needed time for FURTHER deliberation.

In the above sentences, notice that there is no mention of physical distance.

The following sentences use both words correctly:
   1. To FURTHER prove that she increased her stamina, she rode two              
          miles FARTHER.
   2. The FARTHER I travel from the office, the FURTHER behind schedule I am.


Confusion can arise when it seems that a distance is involved, but it's not an actual physical distance, as in these sentences:
    1. Nothing could be FURTHER from the truth.
    2. We drifted FURTHER apart.
    3. This relationship can go no FURTHER.
    4. The dispute has driven the two sides FURTHER apart.

In sentences like the above, it can be argued that "farther" and "further" are
interchangeable, with the following guidelines:
    1. Sometimes "farther" can be used in a figurative or metaphorical sense.
    2. In any situation, if you aren't sure about which to choose, use "further"  
         unless the statement involves actual physical distance.


P.S. It should be noted that "further" can also be a verb that means "to
advance," as in "further his cause," "further your education," or
"further your career."