The story of Frank Jackson's Mary is a philosophical thought experiment proposed by Jackson in his article "Epiphenomenal Qualia"(1) and extended by him in his "What Mary Didn't Know"(2). The argument is intended to motivate what is often called the "Knowledge Argument" against physicalism.
The thought experiment was originally proposed by Jackson as follows:
"Mary is a brilliant scientist who is, for whatever reason, forced to investigate the world from a black and white room via a black and white television monitor. She specializes in the neurophysiology of vision and acquires, let us suppose, all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like 'red', 'blue', and so on. She discovers, for example, just which wavelength combinations from the sky stimulate the retina, and exactly how this produces via the central nervous system the contraction of the vocal cords and expulsion of air from the lungs that results in the uttering of the sentence 'The sky is blue'. [...] What will happen when Mary is released from her black and white room or is given a color television monitor? Will she learn anything or not?"(1)
In other words, Jackson's Mary is an omniscient scientist who knows everything there is to know about the physical science of colour, but has never experienced colour. The question that Jackson and the essay title raises is - once she experiences the colour red for the first time, does she learn anything new? And if she does learn something new, does that show that physicalism is false?
More formally laid out, the following argument is contained in the thought experiment:
(P1) Physicalism is true, and all mental phenomena are in some way really physical. In other words, all knowledge is physical knowledge.
(P2) Mary knows all and every piece of physical knowledge in regards to human colour vision, prior to her release from the black-and-white room. In other words, Mary knows all the knowledge that is available about colour vision.
(P3) Upon leaving the room and witnessing the colour red first-hand, she obtains new knowledge -- what experiencing the colour red actually "feels like".
(C) There was some knowledge about human colour vision Mary did not have prior to her release. Therefore, not all knowledge is physical knowledge. And therefore, (P1) (physicalism) is false
Given this context, the essay's title question is asking whether Mary does in fact learn something when she first experiences the colour red -- is (P3) true? And if she does learn something, is the above outlined argument sound, and physicalism false?
But Jackson's description of this thought experiment contains a subtle trap -- in an inviting equivocation of meaning for the concept "physical knowledge". Because the (P1) premise of the formalized argument is not explicitly stated by Jackson, he leaves available two different ways that the concept of "physical knowledge" can be understood. One the one hand, if one accepts the implied instruction to hold physicalism true (to consider P1 to be true), then the concept of "physical knowledge" must, ex hypothesi, include the physical basis underlying the first-person "feels-like" experience of seeing red for the first time -- even though Jackson never offers a way that Mary could learn that information. He just stipulates that she has acquired it. On the other hand, if one glosses over the implied instruction to hold P1 true, then the concept of "physical knowledge" can be limited to only the third-person objective (cum scientific) knowledge that is usually meant by the term "physical knowledge". Then she does learn something when she acquires the first-person experience that does along with the third-person physical knowledge. So the apparent paradox presented by Jackson's Mary can be seen to rest on an equivocation.
Most people, including most philosophers, approach this thought experiment with an already preconceived notion of the answer. Most people unconsciously employ a dualist mentality when they envisage the kind of knowledge that Mary possesses -- separating the third-person objective "scientific" knowledge from the first-person subjective "feels-like" knowledge. They unconsciously do not consider the kind of first-person subjective "feels like" knowledge acquired by an experience of the colour red as falling within the label of "all and every piece of physical knowledge in regards to human colour vision". So most people fail to follow Jackson's implied direction to consider physicalism true and will admit, readily or with angst, that Mary does learn something when she first experiences the colour red. And this answer poses a serious problem for those philosophers who would rather be physicalists.
But as pointed out by Daniel Dennett(3), people who approach this though experiment with the unconscious adoption of a dualist theory of subjective consciousness are not following the instructions laid down by Jackson. If one reads the article within which Jackson presents his though experiment, he clearly intends to start off with the assumption (if only for the sake of argument) that physicalism is true. Otherwise, there is no point to his though experiment. In other words, without the starting presumption that physicalism is true, the though experiment begs the question. From the context of the article, the rational assumption is that Jackson knew this.
If you start off with the assumption that the subjective first-person "feels like" experience is not amongst the physical knowledge available to Mary, then obviously she learns something upon her release from her room. And obviously, by both pre-supposition and by logical conclusion, physicalism is false. But if physicalism is true by pre-supposition, then necessarily, the subjective first-person "feels like" experience must fall within "all and every piece of physical knowledge in regards to human colour vision". And that means that before she leaves the black-and-white room, Mary must know, by stipulation, what the subjective first-person "feels like" experience of red will feel like.
However, the trap arises because Jackson does not provide the reader with any visualizable means that Mary might employ to acquire all that first-person subjective "feels-like" physical knowledge she is credited with. He does provide some example means of her acquiring all the third-party scientific physical knowledge. But he does not provide any clues to how she might acquire the first-person subjective-perspective knowledge that he stipulates must be physical. He simply stipulates that she has acquired it. And that leaves the reader primed to fall into the trap of assuming this first-person subjective-perspective "feels-like" knowledge cannot be among the "all and every piece of physical knowledge in regards to human colour vision". What is lacking, in other words, is imagination.
Even Howard Robinson(4), in his critique of Dennett's solution to the puzzle of Mary, falls into the same trap. His objection is -
"But she will not know by looking at the banana what physical colour impression that is, what input of light waves it is giving her unless she already has some way of relating how it experientially feels and her current physical states. It might be argued that she knows what the physical stimulus is as part of knowing 'all the physical information', but here the ambiguity enters. . . . She may have 'written down in exquisite detail, exactly what effect a yellow object would have' on her nervous system, but she couldn't tell by looking at an object whether it was having that effect, so wouldn't know that that look was the yellow or the blue one. Dennett's implication that Mary could, through physical knowledge, acquire the ability for direct recognition of colours is mistaken."
Dennett's argument is that if physicalism is presumed to be true, then Mary's "ability for direct recognition of colours" is necessarily part of the physical knowledge she is stipulated to possess. Of course Mary can tell by looking at a red object whether it was having the proper "reddish" effect on her. By stipulation of the thought experiment, that knowledge and ability is part of the physical knowledge she is credited with having.
The answer one gives to the question of whether Mary will learn something on first seeing red will depend upon how one views the Mind-Body relationship. If one is pre-disposed to consider that physicalism is true, then one will conclude that Mary learns nothing -- thus "showing" that physicalism is true. But if one is pre-disposed to consider that physicalism is false, then one will conclude that Mary does learn something -- thus "showing" that physicalism is false. All based on whether one is inclined to include within the scope of "all the physical knowledge" the first-person subjective "feels-like" experience of seeing red. In other words, all based on whether one is pre-disposed to think that the subjective first-person conscious experience of red is nothing more than the physical reactions of the physical components within the physical brain.
Of course, because the conclusion one reaches is a reflection of the starting premise about physicalism that one starts with, the argument does not really "show" anything. Any conclusion you reach is based on the fallacy of begging the question.
(1) Jackson, Frank; "Epiphenomenal Qualia" in The Philosophical Quarterly, Vol 32, No 127 (Apr. 1982), pp 127-136, URL=<http://www.jstor.org/stable/2960077>
(2) Jackson, Frank; "What Mary Didn't Know" in The Journal of Philosophy, Vol 83, No 5 (May 1986), pp 291-295, URL=<http://www.jstor.org/stable/2026143>
(3) Dennett, Daniel C.; Consciousness Explained, Little Brown and Company, Boston, Massachusetts, 1991, ISBN 0-316-18065-3. Pgs 399-400.
(4) Robinson, Howard; "Dennett on the Knowledge Argument" in Analysis, Vol 53, No 3 (Jul 1993), pp 174-177, URL=<http://www.jstor.org/stable/3328467>
Graham, George & Horgan, Terence; "Mary, Mary, Quite Contrary" in Philosophical Studies: An International Journal for Philosophy in the Analytic Tradition, Vol 99, No 1 (May 2000) pp 59-87, URL=<http://www.jstor.org/stable/4321045>
Howell, Robert J.; "The Knowledge Argument and Objectivity" in Philosophical Studies: An International Journal for Philosophy in the Analytic Tradition, Vol 135, No 2 (Sep 2007), pp 145-177, URL=<http://www.jstor.org/stable/40208745>
Kallestrup, Jesper; "Epistemological Physicalism and the Knowledge Argument" in American Philosophical Quarterly, Vol 43, No 1 (Jan 2006), pp 1-23, URL=<http://www.jstor.org/stable/20010220>
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