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The knowledge argument (also known as Mary's Room, Mary the Colour Scientist, or Mary the super-scientist) is a philosophical thought experiment proposed by Frank Jackson in his article "Epiphenomenal Qualia" (1982),[1] and extended in "What Mary Didn't Know" (1986).[2][3]

The experiment describes Mary, a scientist who exists in a black-and-white world where she has extensive access to physical descriptions of color, but no actual perceptual experience of color. Mary has learned everything there is to learn about color, but she has never actually experienced it for herself. The central question of the thought experiment is whether Mary will gain new knowledge when she goes outside of the colorless world and experiences seeing in color.

Did Mary learn something new?

The experiment is intended to argue against physicalism—the view that the universe, including all that is mental, is entirely physical. Jackson says that the "irresistible conclusion" is that "there are more properties than physicalists talk about". Jackson would eventually call himself a physicalist and say, in 2023, "I no longer accept the argument" though he still feels that the argument should be "addressed really seriously if you are a physicalist".[4]

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.[5]

Thought experiment

[edit]

Mary is the second character put forward by Jackson in his article Epiphenomenal Qualia. The other is a gifted person called "Fred" who "has better colour vision than anyone else on record"; specifically, Fred can see two different colours of red where ordinary colour vision only sees one.[1]: 128 

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 specialises 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...What will happen when Mary is released from her black and white room or is given a colour television monitor? Will she learn anything or not?

There is disagreement about how to summarize the premises and conclusion of Jackson's argument in this thought experiment. Paul Churchland did 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 are not the same (≠) as the brain states and their properties.

However, Jackson opposes it by saying 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."[2][3] 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.

Later on, Amy Kind proposes another summary for the argument:[6]

  1. While in the room, Mary has acquired all the physical facts there are about color sensations, including the sensation of seeing red.
  2. When Mary exits the Room and sees a ripe red tomato, she learns a new fact about the sensation of seeing red, namely its subjective character.
  3. Therefore, there are non-physical facts about color sensations. [From 1, 2]
  4. If there are non-physical facts about color sensations, then color sensations are non-physical events.
  5. Therefore, color sensations are non-physical events. [From 3, 4]
  6. If color sensations are non-physical events, then physicalism is false.
  7. Therefore, physicalism is false. [From 5, 6]

Background

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Jackson says there are quite a few similar arguments that predate his formulation, even going back as far as John Locke.[7]

C. D. Broad, Herbert Feigl, and Thomas Nagel, over a fifty-year span, presented insight to the subject. 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.[8]

In 1958, Feigl theorized that a hypothetical Martian, studying human behavior, will lack human sentiments.[9]

Nagel's essay "What Is It Like to Be a Bat?" takes a slightly different approach. He takes the perspective of humans attempting to understand the echolocation 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 sensory system, namely what it is like to "see" the world through sound.[10]

Implications

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

Qualia

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If Mary learns something new upon seeing red, it shows that qualia (the subjective, qualitative properties of experiences, conceived as wholly independent of behavior and disposition) exist. Therefore, it must be conceded that qualia are real, since there is a difference between a person who has access to a particular quale and one who does not.

Refutation of physicalism

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Jackson argues further, saying 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.[11]

Epiphenomenalism

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Main article: Epiphenomenalism

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.

Responses

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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".[12] 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

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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.[13] 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.[14] 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.[10]

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.[15] 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.[16]

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."[10] 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.[17] 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.[18]

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."

The three strategies

[edit]

Kind brings up three strategies that have been brought up in reaction to this argument: the ability analysis, the acquaintance analysis, and the old fact/new guise analysis.

Ability hypothesis

[edit]

Several objections to the argument 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.[19] Lewis put forth a similar argument, claiming that Mary gained an ability to "remember, imagine and recognize."[20] In the response to Jackson's knowledge argument, they both agree that Mary 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.[21] By distinguishing that Mary does not learn new facts, simply abilities, it helps to negate the problem posed by the thought experiment to the physicalist standpoint.

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."[22] 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.[23]

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, Brie 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.[24]

Kind offers a concrete and more realistic example: a driving test, where a person would have to complete a written test where their knowledge of road laws and facts will be tested, as well as an in-car exam, where they must display their ability to drive correctly while following the laws they know as well as putting their facts into practice. One can have all the knowledge-that (knowing all the safety rules related to driving) while having no knowledge-how (driving safely). Kind characterizes Mary's understanding of color sensation as what it's like knowledge, a sub-category of knowledge-that. She states that while Mary does learn something upon seeing the red tomato for the first time and gains knowledge-how; David Lewis claims Mary is now able to recognize, remember and imagine seeing the color red. Advocates of the ability analysis hold the belief that while Mary may have a surprised reaction to seeing red for the first time, she doesn't gain any new facts about the sensation of red.

Acquaintance hypothesis

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The acquaintance analysis argues that Mary is able to learn something new without obtaining accurate knowledge. Due to his dissatisfaction with the ability hypothesis, Earl Conee presents another variant. Conee's acquaintance hypothesis describes a third category of knowledge "by acquaintance of an experience".

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.

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. For example: A person may know facts about Sydney, Australia, but they won't actually be acquainted with it until they have been there in person. 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.[6]

The old fact/new guise analysis

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The response to the knowledge argument depends on whether we can accurately capture the new type of knowledge Mary gains when she leaves the room. Those who propose the ability analysis and the acquaintance analysis both agree that Mary learns something new, but they differ on whether this new knowledge can be reduced to factual knowledge or whether it requires direct experience. Another analysis, called the old fact/new guise analysis, denies that Mary learns something new at all. Instead, it suggests that Mary gains a new understanding of an old fact in a different way. This analysis depends on the idea that there are many ways to express the same fact. For example, the fact that Bruce Wayne is 6'2" tall can also be expressed as "Batman is 6'2" tall" or "Bruce Wayne mesure 1.8796 mètres" in French. Proponents of the old fact/new guise analysis argue that Mary gains a new understanding of an old fact through the acquisition of a phenomenal concept of red. They believe that Mary is now able to express an old fact about the sensation of red in a new way. However, whether this analysis is successful in responding to the knowledge argument depends on how phenomenal concepts are defined in a way that is compatible with physicalism.[6]

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 cannot 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."[25]

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).[26]

Dualist responses and Jackson's reconsideration of the argument

[edit]

Jackson's argument is meant to support mind–body dualism, the view that the mind, or at least some aspects of the mind, are non-physical. Nida-Rümelin contends that, because mind–body dualism is relatively unpopular among contemporary philosophers, and there are also 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 worth noting.[10]

Jackson himself went on to reject epiphenomenalism and mind–body 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 epiphenomenalism, 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 with 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.[27]

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.[28] Martine Nida-Rümelin defends a complex, though similar, view, involving properties of experience she calls "phenomenal properties".[29]

See also

[edit]

References

[edit]

Sources

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  • Broad, C. D. (1925). The Mind and His Place in Nature. Routledge & Kegan.
  • Dennett, Daniel (1991). Consciousness Explained. Boston: Little, Brown and Co. ISBN 978-0-316-18065-8. OCLC 23648691.
  • Dennett, Daniel (2006). "What RoboMary Knows". In Alter, Torin (ed.). Phenomenal Concepts and Phenomenal Knowledge. Oxford Oxfordshire: Oxford University Press. ISBN 978-0-19-517165-5. OCLC 63195957. Retrieved December 2, 2009.
  • Feigl, H. (1958). "The Mental and the Physical". In H. Feigl; M. Scriven; G. Maxwell (eds.). Concepts, Theories, and the Mind-Body Problem. Minnesota Studies in the Philosophy of Science. Vol. II. Minneapolis: University of Minnesota Press. pp. 370–497.

Further reading

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Knowledge argument

View on Grokipedia
from Grokipedia
The Knowledge argument, also known as Mary's room or the , is a philosophical challenge to —the thesis that all truths about the world are physical truths—developed by Frank Jackson in his 1982 paper "Epiphenomenal ." It posits a scenario in which Mary, a brilliant raised in a monochromatic black-and-white environment, acquires complete physical knowledge of human through textbooks, lectures, and black-and-white television, including all facts about wavelengths, neural firings, and behavioral responses to colors, yet has never herself experienced color. Upon exiting her room and seeing a ripe , Mary purportedly learns something new: the subjective, qualitative nature (or ) of seeing red, which cannot be captured by physical facts alone. The argument's structure rests on two core premises: first, that Mary's pre-experience knowledge exhausts all physical information about color; second, that her post-experience insight constitutes genuine new knowledge about the world. Jackson supports this with a parallel example of "Fred," a subject with hypersensitive color vision who can distinguish shades of red indistinguishable to others, where physical descriptions of his brain and eyes fail to reveal what it is like for him to see those shades. From these, the conclusion follows that phenomenal facts—what experiences feel like from the inside—are non-physical and irreducible, implying physicalism's falsity. This highlights an epistemic gap between objective physical descriptions and subjective conscious experience, central to debates on qualia and the hard problem of consciousness. Since its publication, the Knowledge argument has become one of the most influential critiques of physicalism, sparking extensive discussion in philosophy of mind and generating responses across representationalism, externalism, and compatibilist views. A prominent reply is the ability hypothesis, advanced by Laurence Nemirow and David Lewis, which contends that Mary's gain is not new propositional knowledge (facts) but practical abilities, such as imagining, recognizing, or discriminating color experiences, which are consistent with physicalism. Other critiques include Paul Churchland's charge of equivocation on "knowledge" and Daniel Dennett's dismissal of qualia as illusory, while defenders argue it underscores the irreducibility of first-person phenomenology. Notably, Jackson himself recanted the argument's anti-physicalist implications in the early 2000s, embracing a representationalist form of physicalism where Mary's new "knowledge" aligns with physical facts via conceptual shifts, though the thought experiment remains a touchstone for ongoing inquiry.

Background and Origins

Philosophical Context in Mind and Knowledge

, a dominant metaphysical thesis in late 20th-century , posits that everything is physical, meaning all facts about the world, including mental states and conscious experiences, are ultimately reducible to or supervenient upon physical facts. This view gained prominence through the influence of analytic philosophers like and David Armstrong, aligning with the rise of scientific naturalism and the rejection of Cartesian dualism in favor of explanations grounded in physics and . By the 1970s and 1980s, had become the prevailing position, shaping debates on by asserting that mental phenomena could be fully accounted for by physical processes without invoking non-physical entities. Central to challenges against are qualia, the subjective, phenomenal properties of conscious experiences that capture the "what it is like" aspect of sensations, such as the vivid redness of seeing a rose or the pain of a . These intrinsic qualities are directly accessible through and resist complete objective description, highlighting the first-person nature of . , in his seminal 1974 paper "What Is It Like to Be a ?", illustrated this subjectivity by arguing that even detailed physical knowledge of a bat's echolocation fails to convey the experiential "point of view" from which the bat perceives the world, underscoring qualia's irreducibility to third-person scientific accounts. In , the distinction between * knowledge provides a framework for understanding how propositions are justified: a priori knowledge is independent of sensory experience, derived through reason alone (e.g., "all bachelors are unmarried"), while a posteriori knowledge relies on from observation (e.g., "the sky is blue today"). Thought experiments play a crucial role in philosophical inquiry by testing these boundaries and intuitions without empirical testing, as seen in ' 1641 "evil demon" hypothesis in , which posits a deceptive entity manipulating perceptions to doubt external reality. Similarly, Hilary Putnam's 1981 "" scenario modernizes this , imagining a brain disconnected from its body and fed simulated inputs, to probe whether we can distinguish genuine experiences from illusory ones. Preceding later challenges to , early 20th-century epistemologists like explored gaps between physical descriptions and in his 1929 book Mind and the World-Order. Lewis introduced "the given" as the raw, pre-conceptual sensory content immediately presented in experience, distinct from the conceptual frameworks that interpret it into coherent knowledge. He argued that while the physical world is a conceptual construction built upon verifiable patterns, it does not exhaust the immediacy of the given, creating an irreducible divide between objective physical facts and the subjective immediacy of sensation. This conceptual emphasized that knowledge bridges but never fully eliminates the experiential gap, influencing subsequent debates on .

Frank Jackson's Formulation

Frank Jackson first fully articulated the knowledge argument in his 1982 paper "Epiphenomenal Qualia," published in The Philosophical Quarterly. In this work, Jackson presents the argument as a challenge to , the view that all phenomena, including mental states, can be fully explained by physical facts. He structures it around premises demonstrating that complete physical knowledge leaves out certain truths about conscious experience, specifically —the subjective, qualitative aspects of sensations. Jackson presents the knowledge argument to challenge . In the paper, he defends , the theory that are non-causal properties arising from physical processes but not reducible to them or causally efficacious in . He argued that , such as the phenomenal experience of seeing red, represent facts beyond the physical, thereby refuting the completeness of physicalist accounts of mind. To illustrate this, Jackson posed a involving a named Mary, who knows all physical facts about but has never experienced color herself; upon seeing red for the first time, he contends, she gains new . As he writes, "Will she learn anything or not? It seems just obvious that she will learn something about the world and our visual experience of it." The argument quickly garnered attention in 1980s philosophy of mind circles, sparking debates on and . It received endorsements from dualists, including , who highlighted its role in establishing the existence of non-physical properties of experience.

The Thought Experiment

Mary's Room Scenario

Mary is a brilliant who has spent her entire life in a black-and-white room, viewing the outside world solely through a black-and-white television monitor. From this controlled environment, she studies the of and masters every conceivable physical fact about it, including how light wavelengths interact with the , how neural signals are processed in the , and the behavioral responses they elicit, such as uttering the words "that's ." Despite her exhaustive of all physical processes and information related to color —gained through textbooks, lectures, and scientific instruments—Mary has never personally experienced the sensation of seeing color. Her encompasses every detail of the physical sciences concerning vision, yet she remains deprived of direct sensory exposure to hues like , , or . The pivotal moment occurs when Mary is released from her monochromatic confines and encounters a ripe for the first time. Upon seeing its vivid , she exclaims something to the effect of realizing what it is like to see , thereby acquiring new that was not part of her prior physical understanding. This experience reveals to her the subjective quality of color , which her scientific mastery had not captured. The thought experiment can be structured logically as follows: Premise 1 states that Mary knows all the physical facts about color vision before her release. Premise 2 asserts that, upon experiencing color, Mary learns something new—what it is like to see a specific color. The conclusion follows that there is knowledge beyond the physical facts, as her complete physical knowledge proves insufficient for grasping certain experiential aspects. While the scenario primarily focuses on visual color experience, Jackson briefly extends the idea to other senses, such as imagining a person who knows all physical facts about but has never heard , or variations involving heightened sensory discrimination, like distinguishing subtle hues that appear identical to others.

Core Premises and Assumptions

The Knowledge argument, as formulated by Frank Jackson, rests on a series of interconnected premises that challenge the completeness of physical regarding conscious experience. The first core premise posits that Mary, confined to a monochromatic environment, possesses exhaustive of all physical facts pertinent to , encompassing details from , , and behavioral dispositions. This includes on wavelengths of , retinal , neural firings in the , and functional roles of color perception in guiding behavior. Jackson describes Mary as acquiring all the physical there is to obtain about what goes on when we see , assuming this covers every scientifically describable aspect without direct experiential involvement. A second premise asserts that upon exiting her room and encountering color for the first time, Mary acquires novel —specifically, the phenomenal character or "what it is like" to see . This new is characterized as factual rather than merely a or , such as the capacity to recognize or imagine colors, which Mary already possesses through her scientific expertise. Jackson emphasizes that the revelation is substantive: "It seems just obvious that she will learn something about the world when she is first exposed to the relevant array of colours." The argument thus hinges on the assumption that this phenomenal knowledge constitutes a distinct category, irreducible to the prior physical information, and arises through direct acquaintance. Underlying these premises is the assumption drawn from physicalism's supervenience thesis, which holds that all facts about the world supervene on physical facts—meaning no additional facts can exist independently of the physical base. If physicalism is true, knowing all physical facts should preclude any further factual discoveries. The argument exploits this by contrasting the completeness of Mary's physical knowledge with the evident gain in phenomenal knowledge, implying a gap in physicalism's explanatory scope. Analyses of the argument formalize this as follows: Let PP represent the totality of physical facts about color, which Mary knows exhaustively; upon release, she comes to know QQ, the qualia of seeing red. Since QQ is not deducible from PP, it follows that Q⊈PQ \not\subseteq P, underscoring the premises' challenge to physical completeness. Potential ambiguities in the argument center on the demarcation of "physical facts." These are typically construed as those expressible in the vocabulary of the physical sciences, excluding first-person perspectives or subjective modes of presentation, though critics debate whether such exclusions beg the question against non-physical properties. Another ambiguity concerns the nature of the revelation: the new knowledge emerges through , not logical , yet it is presumed to be objective and factive, not merely perspectival. Jackson addresses this by insisting the argument makes no causal assumptions about , focusing solely on epistemic completeness.

Implications for Physicalism and Consciousness

Refutation of Physicalism

The knowledge argument refutes by demonstrating an epistemic gap between complete physical knowledge and phenomenal knowledge. In Frank Jackson's formulation, Mary, a confined to a black-and-white environment, acquires all physical facts about through scientific study, yet upon seeing color for the first time, she learns something new about the experience of . This new knowledge cannot be reduced to her prior physical , establishing that physical facts alone do not exhaust all facts about the world. As Jackson argues, "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 was incomplete. But she had all the physical . Ergo there is more to have than that, and is false." The argument targets both reductive and non-reductive forms of . Reductive , which posits that can be fully identified with physical states or processes, is directly undermined because Mary's exhaustive physical fails to capture the subjective of color , implying that phenomenal properties cannot be reduced to physical ones. Non-reductive , which allows mental properties to on physical ones without identity, is challenged on the grounds that logical or metaphysical should enable a priori deduction of phenomenal facts from complete physical ; the persistence of Mary's gap reveals that no such entailment holds, violating the thesis. Supporting this refutation are analogies to other epistemic or modal knowledge gaps, such as those in necessities where physical descriptions do not a priori reveal essential properties, suggesting a similar divide between physical and phenomenal domains. This gap implies that involves non-physical properties, as cannot account for the explanatory closure required to bridge it without invoking additional fundamental features beyond physics. The knowledge argument has had significant historical impact, bolstering property dualism by highlighting the irreducibility of experience and influencing David Chalmers' articulation of the "hard problem of consciousness," which questions why physical processes give rise to subjective experience at all. Chalmers integrates the argument to argue that phenomenal properties must be treated as fundamental alongside physical ones in a naturalistic dualist framework.

The Nature of Qualia

Qualia are defined as the ineffable, subjective properties of conscious experiences, such as the phenomenal "what it is like" to see the redness of , distinct from objective physical descriptions like wavelengths or neural firings. These properties capture the intrinsic, first-person feel of sensations, including the hurtfulness of or the of a , which cannot be fully conveyed through third-person scientific accounts. In the context of the knowledge argument, qualia represent the element Mary acquires upon her release from the black-and-white room, despite her exhaustive prior knowledge of all physical facts about , such as the 700 nm of or the responses of cells in the . Her pre-experience understanding encompasses objective mechanisms—like the functional roles of states and their relations to stimuli—but omits the subjective phenomenal character, revealing that qualia transcend complete physical descriptions. This gap underscores qualia's irreducibility, as Mary's new knowledge is not merely acquaintance with a fact but an experiential unavailable through propositional learning. Philosophical debates surrounding highlight their privacy and non-transferability via descriptive language, as seen in thought experiments like the , where two individuals might physically process colors identically yet experience inverted (e.g., one sees red where the other sees green). Such scenarios, exemplified by the case of "Fred" who discriminates colors differently from others due to unique , illustrate that are inherently private and cannot be shared or inferred solely from behavioral or physical evidence. This non-transferability reinforces the argument's point that elude exhaustive objective enumeration, challenging attempts to reduce them to . Frank Jackson originally posited as epiphenomenal—real non-physical properties that are causally inert with respect to but nonetheless essential to understanding . In his view, emerge as by-products of processes without influencing physical causation, yet their existence demands recognition beyond physicalist frameworks. is the view that mental states, such as , are causally inefficacious byproducts of underlying physical processes in the , much like steam rising from a engine—real phenomena that arise from but exert no downward causal influence on . The argument bolsters by highlighting a gap between complete physical and experiential understanding, as illustrated in Mary's scenario: despite knowing all physical facts about and accurately predicting behavioral responses to red without ever seeing it, Mary gains new upon direct experience, indicating that transcend physical information yet play no causal role in generating those predictions or behaviors. This supports the epiphenomenal view that exist non-physically but without causal powers, preserving the completeness of physical explanations for action. In his 1982 paper, Frank Jackson explicitly endorsed epiphenomenalism, deploying the knowledge argument to challenge identity theory and revive as a viable dualist alternative that accommodates irreducible . A key advantage of this position in relation to the argument is its compatibility with the principle, which holds that every physical event has a sufficient physical cause; by rendering causally inert, avoids overdetermination while accounting for the apparent novelty of Mary's knowledge. Nonetheless, critics argue that 's attribution of causal irrelevance to is problematic, as it renders such states evolutionarily implausible—natural selection would unlikely favor the emergence and persistence of features that provide no adaptive advantage in influencing or .

Responses and Criticisms

Critiques of Experimental Design

Critics have pointed out ambiguities in the Knowledge Argument's central premise that Mary knows "all the physical facts" about before experiencing it. argues that the term "physical facts" is unclear, questioning whether it encompasses only third-person scientific descriptions or also includes first-person phenomenal concepts, such as what it is like to see . If phenomenal concepts are themselves physical, then Mary's knowledge might already include them, rendering the argument's setup question-begging against . The isolation premise—that Mary can acquire complete physical of color without any personal —is also seen as methodologically unrealistic. This assumption posits a capacity for in a contrived environment, ignoring how typically integrates sensory with learning; without exposure to color, it is implausible that Mary could fully grasp even the physical mechanisms of color . Dennett illustrates this with thought experiments suggesting that practical would enable Mary to simulate or anticipate the , undermining the premise's isolation. Furthermore, the relies on intuition pumps that may prejudice intuitions against by design. contends that the argument's persuasive force stems from an in "knowing," shifting between propositional knowledge of facts and experiential acquaintance, which begs the question by assuming are irreducible without empirical justification. This methodological flaw highlights how the setup manipulates intuitions rather than rigorously testing . A more recent critique identifies gaps in treating experiential knowledge as purely factual rather than dispositional. Barbara Montero argues that the argument overlooks how understanding "what it is like" to see may require dispositional capacities activated only through experience, not deducible from factual physical truths alone; thus, Mary's apparent new knowledge upon seeing color reflects a shift in , not the discovery of non-physical facts, exposing a flaw in the experiment's assumption of complete factual exhaustiveness.

The Three Main Strategies

Physicalists have developed three primary strategies to counter the knowledge argument while preserving the view that all facts are physical facts. These approaches reinterpret what Mary gains upon her release from the black-and-white room, arguing that it does not constitute knowledge of non-physical facts but rather involves abilities, modes of acquaintance, or conceptual guises that do not imply an beyond . The ability hypothesis, as articulated by David Lewis, maintains that the "new knowledge" Mary acquires is not propositional of additional facts about the world but instead a set of practical abilities or know-how. Specifically, these include the skills to imagine, recognize, and remember what it is like to see red, which Mary lacked despite her complete physical . Lewis argues that such abilities do not reveal new physical or non-physical truths; they merely enable the application of existing physical information in imaginative or recognitional contexts, thus avoiding any challenge to . The acquaintance hypothesis, proposed by Earl Conee, posits that Mary's gain is —a direct, non-propositional familiarity with the phenomenal quality of —rather than knowledge by description of a new fact. Conee distinguishes this from her prior descriptive knowledge, emphasizing that acquaintance provides an experiential mode of access to the same physical without introducing novel propositions or properties. This hypothesis upholds by framing the difference as epistemic rather than metaphysical, where acquaintance enhances understanding without expanding the . The old fact/new guise analysis, advanced by Brian Loar in a manner echoing aspects of Thomas Nagel's discussion of subjective experience, contends that Mary does not learn a new fact upon seeing red; the physical fact remains the same, but she grasps it under a new phenomenal concept or "guise" derived from her direct experience. Loar describes these concepts as recognitional and quasi-indexical, allowing for an apparent epistemic novelty that arises from the subject's perspective without positing non-physical entities. This strategy reconciles the intuition of new knowledge with by attributing the difference to variations in conceptual representation rather than to hidden facts. Collectively, these strategies defend by recasting Mary's apparent acquisition of new as involving non-factual abilities, but non-propositional acquaintance, or re-presentations of established physical facts under novel conceptual modes.

Neuroscientific Counterarguments

Neuroscientific counterarguments to the knowledge argument emphasize that , such as the of , can be fully explained by physical processes in the , thereby eliminating any purported gap between physical and phenomenal . Pioneering work by and in the 1990s identified (NCC) that link specific sensory s to localized activity. For instance, they proposed that activity in the visual area V4 is crucial for , as neurons there respond selectively to color stimuli and contribute to the conscious of hue. In the context of Mary's room, this implies that her complete physical would encompass the functional and structural details of V4 activation, including how it generates the of , thus closing the without requiring . Building on such NCC research, illusionism posits that qualia are not intrinsic features of but introspective illusions arising from neural mechanisms that users misinterpret as ineffable properties. , in his 2017 book From Bacteria to Bach and Back, argues that once the full neural architecture of is understood—through detailed models of distributed processes—there is no remaining "hard problem" of qualia, as the apparent mystery dissolves into explainable cognitive judgments. This view aligns with empirical by treating phenomenal reports as user-illusions generated by the 's self-modeling, much like optical illusions, rather than non-physical facts that Mary would miss. Recent developments in further bolster responses by integrating predictive processing frameworks, which model experiential as in the rather than additional non-physical facts. In a 2023 analysis, Alex Moran defends grounding against the knowledge argument, contending that Mary's pre-experience in her black-and-white room omits certain physical facts about phenomenal grounding—such as how lower-level neural states metaphysically necessitate —allowing her to learn something new upon seeing without invoking non-physicalism. Complementing this, a 2025 study frames within predictive error coding (PEC), where the acts as an active generating "query acts" to minimize prediction errors from sensory inputs; here, the "what it is like" of emerges dynamically from these neural predictions, fully reducible to physical processes and resolvable via objective . Supporting evidence includes fMRI datasets from 2025 that map relational similarities among color to distributed cortical patterns, demonstrating how experiential content correlates with predictive neural hierarchies without extra facts. A lingering critique of these neuroscientific approaches notes that, even if qualia reduce to neural activity like V4 firing or predictive models, Mary's monochromatic environment prevents her from simulating the full experiential necessity assumed in the argument—her knowledge might describe the processes but not replicate the causal integration required for genuine qualia realization.

Dualist Rebuttals and Jackson's Reconsideration

Dualists have offered robust defenses of the knowledge argument, maintaining that it effectively demonstrates the existence of irreducible phenomenal facts beyond physical description. , in his analysis, argues that the argument reveals phenomenal truths—such as the subjective experience of color—that cannot be a priori deduced from complete physical , thereby supporting property dualism. He contends that this establishes an ontological gap, where involves non-physical properties essential to reality. Chalmers further rebuts prominent physicalist responses, such as the ability hypothesis, the acquaintance hypothesis, and the phenomenal concepts strategy, as question-begging or insufficient to bridge the . These strategies, he asserts, presuppose by reinterpreting Mary's new knowledge in physicalist terms without addressing why phenomenal facts appear non-deducible from physical ones, thus failing to refute the argument's core intuition. Frank Jackson himself underwent a significant reversal regarding the knowledge argument. In his 2003 essay "Mind and Illusion," he abandoned his earlier anti-physicalist stance, embracing physicalism and a form of indirect realism, influenced by advances in neuroscience that he saw as progressively closing the explanatory gap between physical processes and conscious experience. Jackson argued that empirical progress, including models of perception like predictive processing, supports the view that qualia are representational and fully accountable within a physical framework. In a 2023 interview, he explicitly stated, "I no longer accept the argument," reaffirming his commitment to physicalism while acknowledging the thought experiment's enduring pedagogical value. This shift undermines the argument's original intent to establish , as Jackson now views as causally efficacious representations rather than non-physical epiphenomena, attributing the reversal to neuroscience's success in explaining sensory and cognitive phenomena without invoking irreducible mental facts. Despite Jackson's reconsideration, the knowledge argument persists in philosophical debates, with recent analyses highlighting ongoing tensions between its intuitive appeal and physicalist critiques. For instance, a in Philosophia examines gaps in the argument's assumptions about , yet affirms its role in challenging reductive accounts of , ensuring its continued relevance even as evolves.

References

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