Usage Note: Many writers since the Middle English period have used farther and further interchangeably. A relatively recent rule, however, states that farther should be reserved for physical distance and further for nonphysical, metaphorical advancement. The Usage Panel has favored this rule for some time. In our 1987 survey, 74 percent of the Usage Panel preferred farther in the sentence If you are planning to drive any farther than Ukiah, you'd better carry chains, while 64 percent preferred further in the sentence We won't be able to answer these questions until we are further along in our research. While the use of both adverbs was acceptable in these examples in our 2009 survey, only 62 percent accepted the use of further in the drive sentence quoted above, and only 58 percent accepted farther in the research example. Approval of usage following the rule was nearly unanimous.