What is the Difference Between "Farther" and "Further"?

The word "farther" is used to measure distance.
The word "further" is more abstract and is used to show time, quantity, or to what degree.

Examples of "farther":

She has run farther down the street than I have.

Argentina is farther south than Colombia.

Examples of "further":

We will discuss this matter further in order to come to an agreement.

The doctor will need to do further examinations to make a diagnosis.