By request, this post will be about further and farther. You guys have been giving me so many great requests; it has truly humbled me to realize how many questions you have that I cannot answer without research. Not only are you learning, but I’m learning. That being said, thank you–and let’s get on with the post!
Farther is what you use when referring to PHYSICAL distance. An easy memory hook is to think of “far,” which clearly denotes distance. For example, if a child is sitting through a long car ride, he or she might ask “How much farther?” Although knowing most children, they’ll end up saying further! 😛
Further is used for figurative distance–as in, something that cannot be measured. It’s actually more commonly used as “furthermore” when used as an addition. Let’s look at an example: “I was annoyed further by the cat’s misbehavior.” You cannot measure my level of annoyance (although my husband may disagree!).
Sometimes you’re not quite sure if something is a physical distance or not, like in the example, “I’m further along in my book than you are.” It can be physical distance as in pages, or a theoretical distance. In cases like this where you cannot differentiate if the sentence is referring to physical distance, use further. It is safer to use since it is not bound to a literal distance.