Jackson’s knowledge argument
A strong, and well known, illustration that there is “something more” to humans than the physical is the “knowledge argument” proposed by Jackson [i, ii, #12.1]. Briefly, the thought experiment envisages someone called Mary who is a super-smart scientist who has spent all her life in a black-and-white room. In the room, she learns all the physical facts about human colour vision. One day, she is able to leave the room and see a red tomato. “Wow!”, she says, “Now I know what red looks like” or “Wow! Now I know what it is like for other people to see red”. If Mary knew all the physical facts about colour vision but found out something new when she saw red, then the quality of seeing red cannot be physical.
Most authors, with a notable exception of Dennett [], agree that Mary knows “something more” but they disagree in interpretation and also in whether it implies the falsity of physicalism.
In Dennett’s deflationary view, if Mary knows everything there is to know about colour perception from “book learning”, then she already knows what it is like to see red. This view is described as implausible by Papineau [ page 53]. For instance, Mary’s new experience will enable her to recreate the experience in her imagination and to classify new experiences introspectively. “No amount of book learnin’ will tell her how to create a red experience in imagination”.
Ravenscroft[] describes four replies which have been given to the knowledge argument.
1. Some would distinguish “knowledge that” from “knowledge how” and would say that it was “knowledge how” which Mary gained when she saw red. She wasn’t in any way incapable of thinking thoughts about red experience. All she lacked was the ability to re-create that experience in imagination and classify it by introspection. This has been called the “ability hypothesis” [ page 59]. The argument is that what Mary gained was new skills such as being able to recognise red objects and to imagine them rather than knowledge of new facts. Jackson would dispute this by saying, for instance, that Mary learns something about other people and what it feels like to them to see red. The ability hypothesis upholds the basic physicalist line that Jackson’s argument does not imply any dualism of properties. But it does allow, contra Dennett, that Mary acquires new powers of imaginative re-creation and introspective classification. Papineau agrees that this hypothesis does not adequately answer Jackson’s argument [ page 61-62].
2. It is argued by Churchland [iii] that the knowledge argument can be used to prove that property dualism, as well as physicalism (and just about any other metaphysical theory of the mind) to be inadequate. Therefore, he says, there must be something wrong with the knowledge argument, although he doesn’t say what. However it could instead point to a fundamental limitation of any theory to tell us about qualia and phenomenal consciousness[ p176]. Lewis [iv] suggests this might be a consequence of how the brain is structured.
3. Jackson initially argued that, if physiology is a complete explanation, then the knowledge argument entailed a version of property dualism which was epiphenomenal. Later, he changed his mind in view of the difficulties with the epiphenomenal view and therefore said that “there must be a reply” which is as yet unknown. The alternative deduction that physiology is not complete was something that Jackson and Braddon-Mitchell[v] were very reluctant to do.
4. Did Mary know all the physical facts? Some would say not.
There appears to be no knock-down argument against the knowledge argument that physicalism is inadequate.
iF. Jackson, “Epiphenomenal qualia”, Philosophical Quarterly 32: 127-36, 1982
iiF. Jackson, “What Mary didn’t know”, Journal of Philosophy 83:291-295, 1986
iiiP. M. Churchland, “Reduction, qualia and the direct introspection of brain states”, Journal of Philosophy, 82:8-28, 1985
ivD. Lewis, “Knowing what it is like” Philosophical papers vol 1, 1983
vD. Braddon-Mitchell and F. Jackson, “Philosophy of Mind and Cognition”, Oxford; Blackwell, 1996