However, there is a subtle difference between "further" and "farther."
* Further is used for abstract distances, such as time, degree, or extent. For example: "We need to discuss this further."
* Farther is used for physical distances. For example: "I ran farther than you."
While both words can be used interchangeably in some contexts, it's generally best to use "further" for abstract distances and "farther" for physical distances to avoid confusion.