Knowledge argument


The knowledge argument is a philosophical thought experiment proposed by Frank Jackson in his article "Epiphenomenal Qualia", and extended in "What Mary Didn't Know".
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.
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".
The debate that emerged following its publication became the subject of an edited volume, There's Something About Mary, which includes replies from such philosophers as Daniel Dennett, David Lewis, and Paul Churchland.

Thought experiment

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.
The thought experiment was originally proposed by Jackson as follows:
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 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 knows everything physical there is to know about other people.
  2. Mary does not know everything there is to know about other people.
  3. Therefore, there are truths about other people which escape the physicalist story.
Later on, Amy Kind proposes another summary for the argument:
  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.
  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.
  6. If color sensations are non-physical events, then physicalism is false.
  7. Therefore, physicalism is false.

    Background

Jackson says there are quite a few similar arguments that predate his formulation, even going back as far as John Locke.
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:
In 1958, Feigl theorized that a hypothetical Martian, studying human behavior, will lack human sentiments.
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.

Implications

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

Qualia

If Mary learns something new upon seeing red, it shows that qualia 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

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.

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

Responses

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 objections to Jackson's thought experiment, and the claim it sets out to make.

Design of the thought experiment

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. 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. Nida-Rümelin recognizes that one might question whether this scenario would be possible given the science of color vision, 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.
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. 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.
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."
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. 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."