The terms farther and further are sometimes used interchangeably by some writers because they both denote “at a greater distance.” However, there are different uses of the word further in which farther cannot be substituted.
Example: The library is farther from my house than the bookstore.
Example: The country was getting wilder and the homes were farther apart.
Further also deals with distance, but not in the physical sense. We use further when we’re talking about figurative distance or a general advancement. Further also indicates a greater degree of something. Some terms that are synonymous with further include furthermore, moreover, and in addition.
Example: They chatted further about general matters—mutual friends, and from Weller, some advice on campaigning.