The English language is ever changing, so some people find it difficult to know the proper use of words to write. There are words whose meanings are similar, but we need to know the appropriate use for them. In this case we can confuse “farther” and “further.” Farther versus further is just one of the many words that we can find in the English language. Farther and further are historically the same words, so it is not surprising that the two have long been used more or less interchangeably. People have been using them interchangeably for hundreds of years, and a few experts don’t even follow the distinction. Some people said that there are some advices to identify which word we can use, and others said that doesn’t matter which word we choose.
In the history of usage, “further” is the oldest word and according to the MERRIAM – WEBSTER DICTIONARY OF ENGLISH USAGE, it was 1906 when the first usage guide called on writers to make a distinction between “further” and “farther.” But, how we did know which word we can use in a sentence? Well, in the web www.gramarism.com states that the quick tip is to use “farther” for physical distance and “further” for metaphorical, or figurative, distance. It’s easy to remember because “farther” has the word “far” in it, and “far” obviously relates to physical distance. For example, imagine Robert and Michael are flying to a galaxy far, far way, but Robert gets bored and starts mercilessly bugging Michael. “How much farther?” He keeps asking in despair. Robert used “farther” because he was asking about physical distance. If Michael gets frustrated with Robert, which he surely will, he could respond, “If you complain further, I’m going to shoot you out the airlock.” Michael used “further” because he isn’t talking about physical distance, he’s talking about a figurative distance: the extent of Robert’s complaining.
We have another tip to know the difference between “farther” and “further.” According to GRAMMAR