Further or Farther?

Use Farther when referring to physical distance; use further in all other cases. 

Examples of Further and Farther in a Sentence

The restaurant is farther down the road. (The statement refers to physical distance)

Again, if you’re referring to distance, use farther; if you’re referring to degree, abstractions, or nonphysical or metaphorical distance, use further.Enter your text here...

Shall we inquire further into this problem? (Here, the speaker is asking if we should continue our inquiry [metaphorical or temporal distance])Enter your text here...

If you do not rest your swollen ankle, you will cause further damage. (i.e., Additional damage or a higher degree of damage)

Caveat

The further/farther distinction seems to be more of an issue in American English than in British English.

Also, these words are so frequently mixed up that they have become borderline interchangeable. In fact, writers have been using them interchangeably since the Middle Ages, and the practice of reserving farther for physical distance is a recent occurrence according the American Heritage Dictionary. 

More Examples of "Further" in a Sentence

1. The teacher decided to further explain the topic, but it was of no use.
2. “I refuse to discuss the matter with you further,” she shouted before slamming the door in his face.
3. I continue to work hard to further my career in the investment firm.
4. Economic suggests an employee will earn more working fewer hours as they move up further on the labor backward bending curve.
5. Mrs. Hatch motivated the crowd to donate to further her aim of ending animal cruelty.
6. The relationship will not move further if you do not compromise.
7. “We could spend our afternoons at the grandma’s house, which was further down the road,” he reminisced.
8. The interviewer asked further questions to clear misconceptions regarding his job description and working rank.

More Examples of "Farther" in a Sentence

1. The farther I moved away, the closer you pulled me back.
2. As we drove deeper into the countryside, the houses grew farther apart.
3. Rain showers are expected this summer farther inland than last year.
4. If we walk in this direction two blocks farther, we can eat at the new Chinese restaurant.
5. I saw them walk a bit farther before taking a turn.
6. The nighttime shrinks as we travel farther east.
7. She said to him, “I cannot walk any farther.”
8. “How often do you use the word farther in the sentence?” the teacher asked the student.
9. The access to the cave was farther than we anticipated.
10. The map misled us into walking farther north.
11. I decided to jog farther than my usual route because I wanted to lose an extra pound before the wedding.