A scientist who knows everything about colour sees red for the first time.
Mary has spent her life in a black-and-white room, learning every physical fact about colour and vision. One day she walks out and sees a red tomato. Does she learn something new? If so, argued Frank Jackson in 1982, the physical facts can't be the whole story. Decades later, Jackson himself changed his mind.
The philosopher Frank Jackson introduced Mary in his 1982 paper 'Epiphenomenal Qualia' and returned to her in 1986. She is a brilliant scientist confined to a black-and-white environment, who has learned everything physical there is to know about colour: wavelengths, the eye, the brain. What she has never done is see colour.
The argument is aimed at physicalism, the view that everything, including the mind, is ultimately physical. If Mary already knows every physical fact, yet on seeing red for the first time she learns what it is like to see red, then there must be facts that are not physical. Jackson called that conclusion irresistible: there are more properties than physicalists talk about. These subjective qualities of experience are often called qualia.
The idea has older relatives. The philosopher C. D. Broad imagined an archangel who could work out the exact structure of ammonia but still could not predict how it smells. Thomas Nagel's famous essay 'What Is It Like to Be a Bat?' argued that no amount of physical data would let us grasp a bat's experience of echolocation.
Physicalists have fought back hard, and a whole book, There's Something About Mary (2004), collects the debate. David Lewis and Laurence Nemirow argue that Mary gains not a new fact but a new ability, to imagine, remember and recognise red, rather as passing a written driving test differs from being able to drive, an analogy offered by Amy Kind. Earl Conee suggests she gains acquaintance with the experience rather than new information. Daniel Dennett goes further: if Mary truly knew everything physical, she would already understand exactly what seeing red would be like, and would not be surprised at all. Jackson himself eventually became a physicalist, saying in 2023 that he no longer accepts the argument, though he still thinks physicalists must take it seriously.
Source: Wikipedia — Knowledge argument · Text summarised from Wikipedia (CC BY-SA 4.0)
