Knowledge argument

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The knowledge argument (also known as Mary's room or Mary the super-scientist) is a philosophical thought experiment proposed by Frank Jackson in his article "Epiphenomenal Qualia" (1982) and extended in "What Mary Didn't Know" (1986). The experiment is intended to argue against physicalism — the view that the universe, including all that is mental, is entirely physical. The debate that emerged following its publication became the subject of an edited volume — There's Something About Mary (2004) — which includes replies from such philosophers as Daniel Dennett, David Lewis, and Paul Churchland.


Mary's Room is a thought experiment that attempts to establish that there are non-physical properties and attainable knowledge that can be discovered only through conscious experience. It attempts to refute the theory that all knowledge is physical knowledge. C. D. Broad, Herbert Feigl, and Thomas Nagel, over a fifty-year span, presented insight to the subject, which led to Jackson's proposed thought experiment. Broad makes the following remarks, describing a thought experiment where an archangel has unlimited mathematical competences:

He would know exactly what the microscopic structure of ammonia must be; but he would be totally unable to predict that a substance with this structure must smell as ammonia does when it gets into the human nose. The utmost that he could predict on this subject would be that certain changes would take place in the mucous membrane, the olfactory nerves and so on. But he could not possibly know that these changes would be accompanied by the appearance of a smell in general or of the peculiar smell of ammonia in particular, unless someone told him so or he had smelled it for himself.[1]

Roughly thirty years later, Feigl expresses a similar notion. He concerns himself with a Martian, studying human behavior, but lacking human sentiments. Feigl says:

...the Martian would be lacking completely in the sort of imagery and empathy which depends on familiarity (direct acquaintance) with the kinds of qualia to be imaged or empathized.[2]

Nagel takes a slightly different approach. In an effort to make his argument more adaptable and relatable, he takes the stand of humans attempting to understand the sonar capabilities of bats. Even with the entire physical database at one's fingertips, humans would not be able to fully perceive or understand a bat's sonar system, namely what it is like to perceive something with a bat's sonar.[3]

Thought experiment[edit]

The thought experiment was originally proposed by Frank 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? [4]

In other words, Jackson's Mary is a scientist who knows everything there is to know about the science of color, but has never experienced color. The question that Jackson raises is: once she experiences color, does she learn anything new? Jackson claims that she does.

There is disagreement about how to summarize the premises and conclusion of the argument Jackson makes in this thought experiment. Paul Churchland did so as follows:

  1. Mary knows everything there is to know about brain states and their properties.
  2. It is not the case that Mary knows everything there is to know about sensations and their properties.
  3. Therefore, sensations and their properties ≠ brain states and their properties.[5]

However, Jackson objects that Churchland’s formulation is not his intended argument. He especially objects to the first premise of Churchland’s formulation: "The whole thrust of the knowledge argument is that Mary (before her release) does not know everything there is to know about brain states and their properties, because she does not know about certain qualia associated with them. What is complete, according to the argument, is her knowledge of matters physical." He suggests his preferred interpretation:

  1. Mary (before her release) knows everything physical there is to know about other people.
  2. Mary (before her release) does not know everything there is to know about other people (because she learns something about them on her release).
  3. Therefore, there are truths about other people (and herself) which escape the physicalist story.[6]

Most authors who discuss the knowledge argument cite the case of Mary, but Frank Jackson used a further example in his seminal article: the case of a person, Fred, who sees a color unknown to normal human perceivers. We might want to know what color Fred experiences when looking at things that appear to him in that particular way. It seems clear that no amount of knowledge about what happens in his brain and about how color information is processed in his visual system will help us to find an answer to that question.


Whether Mary learns something new upon experiencing color has two major implications: the existence of qualia and the knowledge argument against physicalism.


First, if Mary does learn something new, it shows that qualia (the subjective, qualitative properties of experiences, conceived as wholly independent of behavior and disposition) exist. If Mary gains something after she leaves the room — if she acquires knowledge of a particular thing that she did not possess before — then that knowledge, Jackson argues, is knowledge of the qualia of seeing red. Therefore, it must be conceded that qualia are real properties, since there is a difference between a person who has access to a particular quale and one who does not.

Refutation of physicalism[edit]

Jackson argues that if Mary does learn something new upon experiencing color, then physicalism is false. Specifically, the knowledge argument is an attack on the physicalist claim about the completeness of physical explanations of mental states. Mary may know everything about the science of color perception, but can she know what the experience of red is like if she has never seen red? Jackson contends that, yes, she has learned something new, via experience, and hence, physicalism is false. Jackson states:

It seems just obvious that she will learn something about the world and our visual experience of it. But then it is inescapable that her previous knowledge was incomplete. But she had all the physical information. Ergo there is more to have than that, and Physicalism is false.[4]


Jackson believed in the explanatory completeness of physiology, that all behaviour is caused by physical forces of some kind. And the thought experiment seems to prove the existence of qualia, a non-physical part of the mind. Jackson argued that if both of these theses are true, then epiphenomenalism is true — the view that mental states are caused by physical states, but have no causal effects on the physical world.

  Explanatory completeness
of physiology
 + qualia
(Mary's room)
= epiphenomenalism

Thus, at the conception of the thought experiment, Jackson was an epiphenomenalist.


Objections have been raised that have required the argument to be refined. Doubters cite various holes in the thought experiment that have arisen through critical examination.

Nemirow and Lewis present the "ability hypothesis", and Conee argues for the "acquaintance hypothesis". Both approaches attempt to demonstrate that Mary gains no new knowledge, but instead gains something else. If she in fact gains no new propositional knowledge, they contend, then what she does gain may be accounted for within the physicalist framework. These are the two most notable[citation needed] objections to Jackson's thought experiment, and the claim it sets out to make.

Design of the Thought Experiment[edit]

Some have objected to Jackson’s argument on the grounds that the scenario described in the thought experiment itself is not possible. For example, Evan Thompson questioned the premise that Mary, simply by being confined to a monochromatic environment, would not have any color experiences, since she may be able to see color when dreaming, after rubbing her eyes, or in afterimages from light perception.[7] However, Graham and Horgan suggest that the thought experiment can be refined to account for this: rather than situating Mary in a black and white room, one might stipulate that she was unable to experience color from birth, but was given this ability via medical procedure later in life.[8] Nida-Rümelin recognizes that one might question whether this scenario would be possible given the science of color vision (although Graham and Horgan suggest it is), but argues it is not clear that this matters to the efficacy of the thought experiment, provided we can at least conceive of the scenario taking place.[3]

Objections have also been raised that, even if Mary’s environment were constructed as described in the thought experiment, she would not, in fact, learn something new if she stepped out of her black and white room to see the color red. Daniel Dennett asserts that if she already truly knew "everything about color", that knowledge would necessarily include a deep understanding of why and how human neurology causes us to sense the "qualia" of color. Moreover, that knowledge would include the ability to functionally differentiate between red and other colors. Mary would therefore already know exactly what to expect of seeing red, before ever leaving the room. Dennett argues that functional knowledge is identical to the experience, with no ineffable 'qualia' left over.[9] J. Christopher Maloney argues similarly:

If, as the argument allows, Mary does understand all that there is to know regarding the physical nature of colour vision, she would be in a position to imagine what colour vision would be like. It would be like being in physical state Sk, and Mary knows all about such physical states. Of course, she herself has not been in Sk, but that is no bar to her knowing what it would be like to be in Sk. For she, unlike us, can describe the nomic relations between Sk and other states of chromatic vision...Give her a precise description in the notation of neurophysiology of a colour vision state, and she will very likely be able to imagine what such a state would be like.[10]

Surveying the literature on Jackson’s argument, Nida-Rümelin identifies, however, that many simply doubt the claim that Mary would not gain new knowledge upon leaving the room, including physicalists who do not agree with Jackson’s conclusions. Most cannot help but admit that “new information or knowledge comes her way after confinement,” enough that this view “deserves to be described as the received physicalist view of the Knowledge Argument.”[3] Some philosophers have also objected to Jackson’s first premise by arguing that Mary could not know all the physical facts about color vision prior to leaving the room. Owen Flanagan argues that Jackson’s thought experiment “is easy to defeat,” He grants that “Mary knows everything about color vision that can be expressed in the vocabularies of a complete physics, chemistry, and neuroscience,” and then distinguishes between “metaphysical physicalism” and “linguistic physicalism”:

Metaphysical physicalism simply asserts that what there is, and all there is, is physical stuff and its relations. Linguistic physicalism is the thesis that everything physical can be expressed or captured in the languages of the basic sciences…Linguistic physicalism is stronger than metaphysical physicalism and less plausible.

Flanagan argues that, while Mary has all the facts that are expressible in “explicitly physical language,” she can only be said to have all the facts if one accepts linguistic physicalism. A metaphysical physicalist can simply deny linguistic physicalism and hold that Mary’s learning what seeing red is like, though it cannot be expressed in language, is nevertheless a fact about the physical world, since the physical is all that exists.[11] Similarly to Flanagan, Torin Alter contends that Jackson conflates physical facts with “discursively learnable” facts, without justification:

…some facts about conscious experiences of various kinds cannot be learned through purely discursive means. This, however, does not yet license any further conclusions about the nature of the experiences that these discursively unlearnable facts are about. In particular, it does not entitle us to infer that these experiences are not physical events.

Nida-Rümelin argues in response to such views that it is “hard to understand what it is for a property or a fact to be physical once we drop the assumption that physical properties and physical facts are just those properties and facts that can be expressed in physical terminology.”[3]

Ability hypothesis[edit]

Several objections to Jackson have been raised on the grounds that Mary does not gain new factual knowledge when she leaves the room, but rather a new ability. Nemirow claims that "knowing what an experience is like is the same as knowing how to imagine having the experience". He argues that Mary only obtained the ability to do something, not the knowledge of something new.[12] Lewis put forth a similar argument, claiming that Mary gained an ability to "remember, imagine and recognize."[13] In the response to Jackson's knowledge argument, they both agree that someone makes a genuine discovery when she sees red for the first time, but deny her discovery involves coming to know some facts of which she was not already cognizant before her release. Therefore, what she obtained is a discovery of new abilities rather than new facts; her discovery of what it is like to experience color consists merely in her gaining new ability of how to do certain things, but not gaining new factual knowledge. In light of such considerations, Churchland distinguishes between two senses of knowing, “knowing how” and “knowing that,” where knowing how refers to abilities and knowing that refers to knowledge of facts. He aims to reinforce this line of objection by appealing to the different locations in which each type of knowledge is represented in the brain, arguing that there is a true, demonstratively physical distinction between them.[14]

In response, Levin argues that a novel color experience does in fact yield new factual knowledge, such as “information about the color’s similarities and compatibilities with other colors, and its effect on other of our mental states.”[15] Tye counters that Mary could have (and would have, given the stipulations of the thought experiment) learned all such facts prior to leaving the room, without needing to experience the color firsthand. For example, Mary could know the fact “red is more like orange than green” without ever experiencing the colors in question.[16]

Earl Conee objects that having an ability to imagine seeing a color is neither necessary nor sufficient for knowing what it is like to see that color, meaning the ability hypothesis does not capture the nature of the new knowledge Mary acquires upon leaving the room. To show that ability is not necessary, Conee cites the example of someone who is able to see colors when she is looking at them, but who lacks the capacity to imagine colors when she is not. He argues that while staring at something that looks red to her, she would have knowledge of what it is like to see red, even though she lacks the ability to imagine what it is like. In order to show precisely that imaginative abilities are not sufficient for knowing what it is like, Conee introduces the following example: Martha, "who is highly skilled at visualizing an intermediate shade that she has not experienced between pairs of shades that she has experienced...happens not to have any familiarity with the shade known as cherry red". Martha has been told that cherry red is exactly midway between burgundy red and fire red (she has experienced these two shades of red, but not cherry). With this, Martha has the ability to imagine cherry red if she so chooses, but as long as she does not exercise this ability, to imagine cherry red, she does not know what it is like to see cherry red.[17]

One might accept Conee’s arguments that imaginative ability is neither necessary nor sufficient for knowing what it is like to see a color, but preserve a version of the ability hypothesis that employs an ability other than imagination. For example, Gertler discusses the option that what Mary gains is not an ability to imagine colors, but an ability to recognize colors by their phenomenal quality.[18]

Acquaintance hypothesis[edit]

Due to his dissatisfaction with the ability hypothesis, Earl Conee presents another variant. Conee's acquaintance hypothesis identifies a third category of knowledge, “knowledge by acquaintance of an experience,” that is not reducible to factual knowledge nor to knowing-how. He argues that the knowledge Mary actually acquires post-release is acquaintance knowledge. Knowing an experience by acquaintance “requires the person to be familiar with the known entity in the most direct way that it is possible for a person to be aware of that thing”. Since “experiencing a quality is the most direct way to apprehend a quality," Mary gains acquaintance with color qualia after release.[17] Conee thus defends himself against the knowledge argument like this:

  1. Qualia are physical properties of experiences (and experiences are physical processes). Let Q be such a property.
  2. Mary can know all about Q and she can know that a given experience has Q before release, although — before release — she is not acquainted with Q.
  3. After release Mary gets acquainted with Q, but she does not acquire any new item of propositional knowledge by getting acquainted with Q (in particular she already knew under what conditions normal perceivers have experiences with the property Q).[3]

Tye also defends a version of the acquaintance hypothesis that he compares to Conee’s, though he clarifies that acquaintance with a color should not be equated to applying a concept to one’s color experience.[19]

In Conee’s account, one can come to know (be acquainted with) a phenomenal quality only by experiencing it, but not by knowing facts about it as Mary did. This is different from other physical objects of knowledge: one comes to know a city, for example, simply by knowing facts about it. Gertler uses this disparity to oppose Conee’s account: a dualist who posits the existence of qualia has a way of explaining it, with reference to qualia as different entities than physical objects; while Conee describes the disparity, Gertler argues that his physicalist account does nothing to explain it.[18]

The Neural Basis of Qualia[edit]

V.S. Ramachandran and Edward Hubbard of the Center for Brain and Cognition at UCSD argue that Mary might do one of three things upon seeing a red apple for the first time:

  1. Mary says she sees nothing but gray.
  2. She has the "Wow!" response from subjectively experiencing the color for the first time.
  3. She experiences a form of blindsight for color, in which she reports seeing no difference between a red apple and an apple painted gray, but when asked to point to the red apple, she correctly does.

They explain further: "Which of these three possible outcomes will actually occur? We believe we've learned the answer from a colorblind synesthete subject. Much like the theoretical Mary, our colorblind synesthete volunteer can not see certain hues, because of deficient color receptors. However, when he looks at numbers, his synesthesia enables him to experience colors in his mind that he has never seen in the real world. He calls these "Martian colors." The fact that color cells (and corresponding colors) can activate in his brain helps us answer the philosophical question: we suggest that the same thing will happen to Mary."[20]

Ramachandran and Hubbard's contribution is in terms of exploring "the neural basis of qualia" by "using pre-existing, stable differences in the conscious experiences of people who experience synaesthesia compared with those who do not" but, they note that "this still doesn’t explain why these particular events are qualia laden and others are not (Chalmers’ ‘hard problem’) but at least it narrows the scope of the problem" (p. 25).[21]

Dualist Responses[edit]

Jackson’s argument is meant to support dualism, the view that at least some aspects of the mind are non-physical. Nida-Rümelin contends that, because dualism is relatively unpopular among contemporary philosophers, there are not many examples of dualist responses to the knowledge argument; nevertheless, she points out that there are some prominent examples of dualists responding to the Knowledge Argument are worth noting.[3]

Jackson himself went on to reject epiphenomenalism, and dualism altogether. He argues that, because when Mary first sees red, she says "wow", it must be Mary's qualia that causes her to say "wow". This contradicts epiphenomenalism because it involves a conscious state causing an overt speech behavior. Since the Mary's room thought experiment seems to create this contradiction, there must be something wrong with it. Jackson now believes that the physicalist approach (from a perspective of indirect realism) provides the better explanation. In contrast to epiphenominalism, Jackson says that the experience of red is entirely contained in the brain, and the experience immediately causes further changes in the brain (e.g. creating memories). This is more consilient with neuroscience's understanding of color vision. Jackson suggests that Mary is simply discovering a new way for her brain to represent qualities that exist in the world. In a similar argument, philosopher Philip Pettit likens the case of Mary to patients suffering from akinetopsia, the inability to perceive the motion of objects. If someone were raised in a stroboscopic room and subsequently 'cured' of the akinetopsia, they would not be surprised to discover any new facts about the world (they do, in fact, know that objects move). Instead, their surprise would come from their brain now allowing them to see this motion.

Despite a lack of dualist responses overall and Jackson’s own change of view, there are more recent instances of prominent dualists defending the Knowledge Argument. David Chalmers, one of the most prominent contemporary dualists, considers Jackson’s thought experiment to successfully show that materialism is false. Chalmers considers responses along the lines of the “ability hypothesis” objection (described above) to be the most promising objections, but unsuccessful: even if Mary does gain a new ability to imagine or recognize colors, she would also necessarily gain factual knowledge about the colors she now sees, such as the fact of how the experience of seeing red relates to the physical brain states underlying it. He also considers arguments that knowledge of what it is like to see red and of the underlying physical mechanisms are actually knowledge of the same fact, just under a different “mode of presentation,” meaning Mary did not truly gain new factual knowledge. Chalmers rejects these, arguing that Mary still necessarily gains new factual knowledge about how the experience and the physical processes relate to one another, i.e. a fact about exactly what kind of experience is caused by those processes.[22] Nida-Rümelin defends a complex, though similar, view, involving properties of experience she calls "phenomenal properties."[23]

See also[edit]


  1. ^ Broad 1925, p. 71
  2. ^ Feigl 1958, p. 431
  3. ^ a b c d e f Nida-Ruemelin, Martine. "Qualia: The Knowledge Argument". Stanford Encyclopedia of Philosophy. 
  4. ^ a b Jackson 1982, p. 130
  5. ^ Churchland, Paul M. (1985-01-01). "Reduction, Qualia, and the Direct Introspection of Brain States". The Journal of Philosophy. 82 (1): 8–28. doi:10.2307/2026509. 
  6. ^ Jackson, Frank (1986-01-01). "What Mary Didn't Know". The Journal of Philosophy. 83 (5): 291–295. doi:10.2307/2026143. 
  7. ^ Thompson, E. Colour Vision, 1995
  8. ^ Graham, George; Horgan, Terence (2000-05-01). "Mary Mary, Quite Contrary". Philosophical Studies. 99 (1): 59–87. doi:10.1023/A:1018779425306. ISSN 0031-8116. 
  9. ^ See Dennett 1991, p. 398 & Dennett 2006.
  10. ^ Maloney, J. Christopher (1985-03-01). "About being a bat". Australasian Journal of Philosophy. 63 (1): 26–49. doi:10.1080/00048408512341671. ISSN 0004-8402. 
  11. ^ Flanagan, Owen J. (1992-01-01). Consciousness reconsidered. Cambridge, Mass: MIT Press. ISBN 0262061481. 
  12. ^ Lycan, William G., ed. (1990-01-01). Mind and cognition: a reader. Cambridge, Mass., USA: Basil Blackwell. ISBN 0631160760. 
  13. ^ Lewis, David. Philosophical Papers Volume I - Oxford Scholarship. doi:10.1093/0195032047.001.0001. 
  14. ^ Churchland, Paul M. (1989-01-01). A neurocomputational perspective: the nature of mind and the structure of science. Cambridge, MA: MIT Press. ISBN 0262031515. 
  15. ^ Levin, Janet (1986-01-01). "Could Love Be like a Heatwave?: Physicalism and the Subjective Character of Experience". Philosophical Studies: An International Journal for Philosophy in the Analytic Tradition. 49 (2): 245–261. 
  16. ^ Tye, Michael (2000-01-01). Consciousness, color, and content. Representation and mind. Cambridge, Mass: MIT Press. ISBN 0262201291. 
  17. ^ a b Conee, Earl (1994-06-01). "Phenomenal knowledge". Australasian Journal of Philosophy. 72 (2): 136–150. doi:10.1080/00048409412345971. ISSN 0004-8402. 
  18. ^ a b Gertler, Brie (1999-03-01). "A Defense of the Knowledge Argument". Philosophical Studies. 93 (3): 317–336. doi:10.1023/A:1004216101557. ISSN 0031-8116. 
  19. ^ Tye, Michael (2009-01-01). Consciousness revisited: materialism without phenomenal concepts. Representation and mind. Cambridge, Mass: MIT Press. ISBN 9780262012737. 
  20. ^ Ramachandran, V.S.; Edward M. Hubbard. (April 14, 2003). "More Common Questions about Synesthesia". Scientific American. Retrieved 2007-03-12. 
  21. ^ Ramachandran, V.S.; Edward M. Hubbard. (January 1, 2001). "Synaesthesia – A window into perception, thought and language". Journal of Consciousness Studies. Retrieved 2011-05-02. 
  22. ^ Chalmers, David John (1996-01-01). The conscious mind: in search of a fundamental theory. Philosophy of mind series. New York: Oxford University Press. ISBN 0195105532. 
  23. ^ Nida‐Rümelin, Martine. Grasping Phenomenal Properties. pp. 307–338. doi:10.1093/acprof:oso/9780195171655.003.0013. 


Further reading[edit]

  • Ludlow, Peter; Nagasawa, Yujin; Stoljar, Daniel, eds. (2004). There's Something about Mary: essays on phenomenal consciousness and Frank Jackson's knowledge argument. Cambridge: MIT Press. ISBN 0-262-12272-3. 

External links[edit]