Mary's room
A scientist who knows every physical fact about colour has never seen red. When she finally does, does she learn something new?
- Reading time
- 4 min
- Difficulty
- Intermediate
- Branch
- Mind
- First posed
- Frank Jackson, 'Epiphenomenal Qualia', 1982
The setup
Mary is a brilliant neuroscientist. For reasons we need not go into, she has lived her entire life in a black and white room, learning about the world through a black and white television monitor. She has never seen any colour.
Mary specialises in the neurophysiology of vision. She has learned everything there is to know about what happens when people see colours: every wavelength, every retinal response, every neural pathway, every fact about how the word 'red' is used. Imagine that she knows all the physical facts about colour vision, complete and perfect.
One day the door opens, and Mary steps outside. She sees a ripe tomato for the first time. The philosopher Frank Jackson, who devised the case in 1982, asked: does she learn something new?
It seems obvious that she does. She learns what it is like to see red. But by hypothesis, she already knew every physical fact. So if she learns something, there must be facts that are not physical facts, and physicalism, the view that everything is physical, is false. This is the knowledge argument.
Why it matters
Mary's room is one of the most famous arguments against physicalism, and one of the clearest ways to feel the pull of the hard problem. If complete physical knowledge leaves something out, the physical sciences cannot be the whole story about the mind.
The argument is unusual because its author later changed his mind. In the late 1990s Jackson came to accept physicalism and argued that his own argument must fail somewhere, though he and others disagree about exactly where.
Key terms
- Knowledge argumentFrank Jackson's argument from Mary's room: someone could know every physical fact about colour and still learn something new on seeing red, so not all facts are physical.
- PhysicalismThe view that everything that exists is physical, or is fixed by the physical facts.
- QualiaThe qualities of conscious experiences as they feel from the inside, such as the redness of red or the painfulness of pain. Singular: quale.
- Ability hypothesisA physicalist reply to the knowledge argument: when Mary first sees red, she gains no new fact, only new abilities, to recognise, remember and imagine red.
- Phenomenal conceptA concept of an experience that one can have only by having had the experience, such as the concept of what red looks like. Some physicalists use them to explain away Mary's new knowledge.
The positions
Mary learns a new fact
Mary learns a fact about experience that was not among the physical facts. So physicalism is false.
Mary gains an ability
Mary does not learn a new fact. She gains new abilities: to imagine, recognise and remember red.
Old fact, new concept
Mary learns an old fact in a new way. She acquires a new 'phenomenal concept' of something she already knew under physical concepts.
Mary learns nothing
If Mary really knew every physical fact, she would not be surprised. We cannot imagine what complete physical knowledge would be like.
Arguments and objections
Mary learns a new fact
- Best argument
- Before her release, Mary knew everything physical. After, she knows something she did not know: what seeing red is like. If she gained knowledge, there was something to know that physical knowledge did not include. The most natural explanation is that experiences have qualia, non-physical qualities.
- Strongest objection
- Learning something new does not show there is a new fact. You can learn a new way of thinking about an old fact: someone who knows that Hesperus is bright can learn that Phosphorus is bright, without learning a new fact about the world, since both are the planet Venus.
Mary gains an ability
- Best argument
- David Lewis and Laurence Nemirow proposed the ability hypothesis. Knowing what an experience is like is know-how, not know-that. Mary already knew all the facts; what she lacked was the capacity that comes from having the experience. This is no more a refutation of physicalism than the fact that reading about swimming does not teach you to swim.
- Strongest objection
- Mary seems to gain propositional knowledge too. She can now think 'so this is what my research subjects were seeing', which seems to be a thought with true-or-false content she could not entertain before.
Old fact, new concept
- Best argument
- On this widely held view, phenomenal concepts are special first-person ways of thinking about brain states, which can only be acquired by having the experience. Mary knew the physical fact about red-experiences under physical concepts; now she grasps the same fact under a phenomenal concept. Her epistemic progress is real, but the world contains nothing non-physical.
- Strongest objection
- If phenomenal concepts pick out physical states, critics ask why they reveal those states so differently, and so mysteriously, from all our other concepts. The explanation of phenomenal concepts may face its own hard problem.
Mary learns nothing
- Best argument
- Daniel Dennett argued that our intuition that Mary learns something comes from imagining a Mary who knows a lot, not one who knows everything. A truly omniscient physical scientist would be able to work out exactly what red would look like, and would recognise it at once. If you tried to trick her with a banana painted blue, she would spot the trick at once, because she would know that what she was seeing was blue.
- Strongest objection
- Most people find it hard to believe that any amount of reading could tell you what red looks like. Dennett's response seems to deny the very premise the thought experiment rests on.
Who argued what
- Mary learns a new fact Frank Jackson (1982), David Chalmers
- Mary gains an ability David Lewis, Laurence Nemirow
- Old fact, new concept Brian Loar, David Papineau
- Mary learns nothing Daniel Dennett, Paul Churchland
Variations
Real-life Marys
People who are colourblind from birth and later receive corrective lenses sometimes see certain colours for the first time as adults, often with strong emotional reactions. These cases are not perfect Marys, since the subjects do not know all the physical facts, but they make the scenario feel less abstract.
Mary and the robot
Imagine a robot that knows all the physical facts and has a perfect colour camera. When it first processes a red image, does it learn anything? If not, why should Mary? If so, what?
Go deeper
Jackson changes his mind
In 1982 Jackson used Mary to argue for epiphenomenal qualia. By 2003 he had become a physicalist, arguing that the intuition that Mary learns something must be explained away, since physicalism is better supported overall. He favoured a version of the view that Mary gains a new way of representing what she already knew. The fact that the author of the argument came to reject it says something about how hard it is to evaluate.
Related ideas
Further reading and sources
- EncyclopediaStanford Encyclopedia of Philosophy: Qualia: The Knowledge Argument
- WikipediaKnowledge argument
- BookThere's Something About Mary, Peter Ludlow, Yujin Nagasawa and Daniel Stoljar (editors)
- PaperEpiphenomenal Qualia, Frank Jackson
Open questions
- Is there something about seeing red that no textbook could ever teach?
- If Mary learns nothing, why does it seem so obvious that she does?
- Does knowing a thing and experiencing it differ only in degree?