Farther usually refers to physical distance. Further refers to an extension of time or degree. But see the usage notes below.
Also see: Avoid These 10 Words in Formal Writing.
- We drove farther south, making excellent time on the almost empty roads.
- The meeting ended without any plans for further discussions.
- We traveled farther in one week than any of us had expected. The trip took us even further into debt.
- "Since the Middle English period many writers have used farther and further interchangeably. According to a relatively recent rule, however, farther should be reserved for physical distance and further for nonphysical, metaphorical advancement. Thus 74 percent of the Usage Panel prefers farther in the sentence If you are planning to drive any farther than Ukiah, you'd better carry chains, and 64 percent prefers further in the sentence We won't be able to answer these questions until we are further along in our research. In many cases, however, the distinction is not easy to draw. If we speak of a statement that is far from the truth, for example, we should also allow the use of farther in a sentence such as Nothing could be farther from the truth. But Nothing could be further from the truth is so well established as to seem a fixed expression."
("farther," The American Heritage Dictionary of the English Language, 4th ed., 2000)
- "Farther and Further are historically the same word, so it is not surprising that the two have long been used more or less interchangeably. . . .
"As adjectives, both words could at one time be used in the sense 'additional.' . . .
"But in present-day English further has taken over this use entirely. . . .
"Farther has been relegated as an adjective to instances where either literal or figurative distance is involved. . . .
"And even in this function further is presenting formidable competition. . . .
"So for the adjective we can see that further has squeezed farther out of the 'additional' sense and is giving it considerable pressure in the 'more distant' sense. . . .
"In adverbial use further dominates when there is no sense of distance and as a sentence adverb, but both farther and further are in flourishing use whenever spatial, temporal, or metaphorical distance is involved."
("farther, further," Merriam-Webster's Dictionary of English Usage, 1994)
- "No one misuses farther for further, and you're safe with further provided that you don't apply it to distance. Several usage critics have even predicted that further will eventually absorb the meaning 'more distant,' driving farther into extinction."
(Claire Kehrwald Cook, Line by Line: How to Edit Your Own Writing. Houghton Mifflin, 1985)
(a) We need to explore this problem ______.
(b) Simon walked ______ into the woods.