the shrewdness of apes

baseball announcers had me seething over the weekend with their misuse of the english language ("see how quick he gets rid of the ball here..."), so i figured it was time to uncover the answer to a question Dan and i had been having trouble with:

4. FURTHER vs. FARTHER

Use farther when referring to distance. Use further to indicate a continuation or extension in terms of time, degree, or anything else other than distance.

of course this couldn't be that easy. Merriam-Webster disagrees:

Farther and further have been used more or less interchangeably throughout most of their history, but currently they are showing signs of diverging. As adverbs they continue to be used interchangeably whenever spatial, temporal, or metaphorical distance is involved. But where there is no notion of distance, further is used . Further is also used as a sentence modifier , but farther is not. A polarizing process appears to be taking place in their adjective use. Farther is taking over the meaning of distance and further the meaning of addition .

basically, as long as you're not using "further" to describe distance, you're fine.