Here’s a quick, easy trick to remember the difference between these two adverbs.
Simply put, farther refers to geographical distance, and it has the word “far” in it.
Further is conceptual in nature.
So, you can go far
ther down the road, but you can’t go further down the road. You can go far, but you can’t go fur.
You can further your education, but you can’t farther it.
Ask yourself, “Am I referring to distance?” If so, use farther!
So, next time you find yourself wondering, “Do I use farther or further?” simply ask if you are talking about distance. If so, use farther!