The definitive statement of the knowledge argument was formulated by Frank Jackson in a paper titled "Epiphenomenal Qualia" that appeared in the Philosophical Quarterly in 1982. Arguments in the same spirit had appeared earlier (Broad 1925, Robinson 1982), but Jackson's argument is most often compared with Thomas Nagel's argument in "What Is It Like to Be a Bat?" (1974). Jackson, however, takes pains to distinguish his argument from Nagel's. This entry will follow standard practice in focusing on Jackson's argument, though it also describes the main points of alleged similarity and dissimilarity between these two arguments.

The knowledge argument targets physicalism about the mind, which claims that, as Jackson puts it in a follow-up article, "the actual world … is entirely physical" (1986, p. 281). The argument provided one of the chief sources of doubt about physicalism in the late twentieth century, and continues to shape discussion of the mind-body problem into the...