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 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 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 (2004)—which includes replies from such philosophers as Daniel Dennett, David Lewis, and Paul Churchland.
Thought experiment
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 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 happens when Mary is released from her black-and-white room or is given a color television monitor? Does she learn anything new or not? Jackson claims that she does.There is disagreement about how to summarize the premises and conclusion of Jackson's argument in this thought experiment. Paul Churchland did as follows:
Mary knows everything there is to know about brain states and their properties. It is not the case that Mary knows everything there is to know about sensations and their properties. 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." He suggests his preferred interpretation:
Mary (before her release) knows everything physical there is to know about other people. Mary (before her release) does not know everything there is to know about other people (because she learns something about them on her release). Therefore, there are truths about other people (and herself) which escape the physicalist story.
Later on, Amy Kind proposes another summary for the argument:
While in the room, Mary has acquired all the physical facts there are about color sensations, including the sensation of seeing red. 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. Therefore, there are non-physical facts about color sensations. [From1, 2] If there are non-physical facts about color sensations, then color sensations are non-physical events. Therefore, color sensations are non-physical events. [From3, 4] If color sensations are non-physical events, then physicalism is false. Therefore, physicalism is false. [From5, 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.
Background
Jackson says there are quite a few similar arguments that predate his formulation, even going back as far as John Locke.