Is it farther or further?
"theory of knowledge," 1856, coined by Scottish philosopher James F. Ferrier (1808-1864) from Greek episteme "knowledge," from Ionic Greek epistasthai "know how to do, understand," literally "overstand," from epi "over, near" (see epi-) + histasthai "to stand," (see histo-).
The scientific (as opposed to philosophical) study of the roots and paths of knowledge is epistemics (1969). Related: Epistemological; epistemologically.
The branch of philosophy concerned with the nature and origin of knowledge. Epistemology asks the question “How do we know what we know?”