It depends on whether you’re moving or staying put.
Farther refers to moving in the literal sense.
The farther we traveled, the more tired we became.
Further, on the other hand, is used to describe some sort of change, often a gain or improvement in a function or skill.
The students have progressed further than expected.
It’s possible to use both in a sentence.
She walked farther to further her knowledge of the native plants.
If you found value in this post, could you do me a favor and share it with others? You may use any of the links below. Feel free to comment, as well. To contact me, send an email.
Follow me on Twitter.
Follow my Facebook page. (May need to log in.)
Connect with me on LinkedIn.