Farther/Further?

These two words are commonly used interchangeably, but there is a difference between them.

"Farther" refers to physical or geographic distance.

Example: The apartment I want is farther from my office.

"Further" is more abstract. It refers to time or degree or quantity. It's another way of saying "additional."

Examples:

I have to look further into the question of moving farther from my office.
There was no further discussion.

Use farther when you're talking about physical distances.

Farther down the road.
They're further along in their plans than I expected.

Additionally, forgetting grammar rules:

You can also ask the question 'How far is it?'

Sentence to use: The apartment I want is farther from my office.

Use farther or further????????

The question: The apartment is how far from my office?

Use FARther for the word FAR as it refers to physical distance. You wouldn't say "The apartment is how FUR from my office?

And I always thought that 'farther' is American English while 'further' is the British equivalent.

I will always use "further". Maybe it's because I'm a purist, and Australian, but I do not use "farther" in any context.
See, if I say "It is further away", "futher" is correct because it is being used in the time context, even though distance is inferred...

In most (not all) cases, further can be used in place of farther, but there are more cases where farther can not be used in place of further.

Farther is used in reference to distance
Further is used in reference to time or quantity

According to the American Heritage Dictionary, since the Middle English period many writers have used farther and further interchangeably.

That is be true, John, but there are certainly examples where "further" cannot be replaced by "farther". "Further" may also mean "additional" while "farther" cannot.
"Here are further examples of this" cannot be replaced by "Here are farther examples of this." and you have never heard "farthermore", have you?:)

Good point!

"Farther" also means "more far."

Correct?

In the UK most of us use 'further' for everything, as Fowler, who disapproved of this new rule, predicted. For more details, you can read my post:

http://random-idea-english.blogspot.co.uk/2011/10/q-further-or-farther-british.html

What if you want to use further/farther "down the road of destruction"? it's not literally a physical distance... so can you use further in this case?