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The definitive statement of the Knowledge Argument was formulated by Frank Jackson, in a paper entitled “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 I will also describe the main points of alleged similarity and dissimilarity between these two arguments.

The knowledge argument aims to refute physicalism, the doctrine that the world is entirely physical. Physicalism (also known as materialism) is widely accepted in contemporary philosophy. But some doubt that phenomenal consciousness.

I argue that the knowledge argument is best understood as an argument for the existence of non-physical properties of material objects, or colours. I suggest that the knowledge argument is standardly presented as an argument for the existence of qualia because it is implicitly assumed that physics “tell us” that what it is like to perceive colour is determined, not by properties of material objects, but by properties of perceiving subjects; hence any gaps in Mary’s knowledge must be gaps in her knowledge about perceiving subjects. If nothing else, this physicalist assumption is odd given that the knowledge argument is supposed to be an argument against physicalism. Using the knowledge argument as an argument for the existence of non-physical colours is consistent with the transparency of perceptual experience. Moreover, rejecting the physicalist assumption behind the orthodox interpretation of the knowledge argument undermines the motivation for thinking of non-physical colours as epiphenomenal.

The knowledge argument is an argument against physicalism that was first formulated by Frank Jackson in 1982. While Jackson no longer endorses it, it is still regarded as one of the most important arguments in the philosophy of mind. Physicalism is the metaphysical thesis that, roughly speaking, everything in this world—including tables, galaxies, cheese cakes, cars, atoms, and even our sensations— are ultimately physical. The knowledge argument attempts to undermine this thesis by appealing to the following simple imaginary scenario: Mary is confined to a black-and-white room, is educated through black-and-white books and through lectures relayed on black-and white television. In this way she learns everything there is to know about the physical nature of the world. She knows all the physical facts about us and our environment, in a wide sense of ‘physical’ which includes everything in completed physics, chemistry, and neurophysiology, and all there is to know about the causal and relational facts consequent upon all this, including of course functional roles. (Jackson 1986, p. 291) The knowledge argument says that if physicalism is true, Mary knows everything in this world. However, it seems obvious that her knowledge is not yet complete. Suppose that..

Frank Jackson argued, in an astronomically frequently cited paper on 'Epiphenomenal qualia'[Jackson 1982 that materialism must be mistaken. His argument is called the knowledge argument. Over the years since he published that paper, he gradually came to the conviction that the conclusion of the knowledge argument must be mistaken. Yet he long remained totally unconvinced by any of the very numerous published attempts to explain where his knowledge argument had gone astray. Eventually, Jackson did publish a diagnosis of the reasons why, he now thinks, his knowledge argument against materialism fails to prove the falsity of materialism [Jackson 2005. He argues that you can block the knowledge argument against materialism - but only if you tie yourself to a dubious doctrine called representationalism. We argue that the knowledge argument fails as a refutation of either representational or nonrepresentational materialism. It does, however, furnish both materialists and dualists with a successful argument for the existence of distinctively first-person modes of acquaintance with mental states. Jackson's argument does not refute materialism: but it does bring to the surface significant features of thought and experience, which many dualists have sensed, and most materialists have missed.

I argue that Frank Jackson's knowledge argument cannot succeed in showing that qualia are epiphenomenal. The reason for this is that there is, given the structure of the argument, an irreconcilable tension between his support for the claim that qualia are non-physical and his conclusion that they are epiphenomenal. The source of the tension is that his argument for the non-physical character of qualia is plausible only on the assumption that they have causal efficacy, while his argument for the epiphenomenal character of qualia is plausible only on the assumption that they are non-physical. Since these two arguments cannot be combined coherently, the most Jackson's argument can establish is that qualia are non-physical.

The knowledge argument aims to refute physicalism, the view that the world is entirely physical. The argument first establishes the existence of facts (or truths or information) about consciousness that are not a priori deducible from the complete physical truth, and then infers the falsity of physicalism from this lack of deducibility. Frank Jackson (1982, 1986) gave the argument its classic formulation. But now he rejects the argument (Jackson 1998b, 2003, chapter 3 of this volume). On his view, it relies on a false conception of sensory experience, which should be replaced with representationalism (also known as intentionalism), the view that phenomenal states are just representational states. And he argues that mental representation is physically explicable.

Frank Jackson's knowledge argument against physicalism has caused an extensive debate. In this paper, I sketch and examine a new argument against Jackson's view, an argument which appears to retain more of physicalism than other replies to Jackson. this argument draws strength from a causal theory of knowledge, and hold that there is no knowledge of epiphenomenal qualia, hence that Jackson's main conclusions from the thought experiment are incorrect. There are still problems with this argument, however, so the question remains how much of the mental that can be accounted for in physicalist terms.