Qualia · about 4 minutes
Mary's Room
Mary is the greatest colour scientist who has ever lived. She knows every physical fact there is to know about colour -- every wavelength, every cone, every neuron. She has learned all of it inside a room with no colour in it, from screens and books exactly as grey as the one you are reading now.
Today Mary is being let out. So are you. But first you have to do her homework.
Fig. 1 -- one ripe tomato. Everything known about it is printed directly below.
Physical facts mastered: 0 of 7
You now know everything physical there is to know about colour. There is nothing further about it that can be written down, measured, scanned, or taught. Mary knew exactly this much, and not one fact more.
One question
Take a moment with it first. The tomato is up there, unchanged -- same object, same wavelengths, same reflectance curve, every number exactly as printed.
Did you just learn something new?
What just happened
This is Mary's Room, published by the Australian philosopher Frank Jackson in 1982, and it is one of the few thought experiments that can be performed on a visitor rather than described to them. The argument is three lines long and has been keeping philosophy departments in business for four decades:
- Mary knows every physical fact about colour.
- On leaving the room, Mary learns something.
- Therefore not every fact is a physical fact.
If that argument holds, physicalism -- the view that the physical story is the whole story -- is missing something. Not missing a detail. Missing a kind of thing.
If you said yes
You're with Jackson, at least the 1982 model. The complete physical account of colour was sitting right there in front of you, genuinely complete, and it did not contain the red. Something arrived through the door that no amount of study could deliver -- which suggests experience isn't just information you haven't got round to reading yet.
If you said no
You're in excellent company too, and the replies are sharper than they look. The ability hypothesis (Laurence Nemirow, David Lewis): Mary gains a skill, not a fact -- she can now recognise, imagine and remember red, the way learning to swim isn't learning a proposition about swimming. Know-how, not know-that. The phenomenal concept strategy: Mary learns an old fact in a new way, the way you can know Hesperus is Phosphorus for years before the evening star and the morning star click together as one object. Same fact, new handle.
And Daniel Dennett's, which is the rudest and hardest to shake: you never actually imagined Mary. You imagined a woman who knew a great deal about colour, because a mind that truly knew everything physical is not something any of us can hold in our heads. His Mary walks out, is shown a blue banana, and says nice try -- because she already knew precisely what her own visual system would do. If you find that unimaginable, Dennett would say: yes. That's the point. You've been running the experiment on a Mary you shrank to fit.
The fine print, and it's the best part. Frank Jackson changed his mind. The man who built the argument spent the following two decades taking it apart, and by the early 2000s was arguing in print that Mary learns nothing new and that he had been fooled by his own intuition. The most famous anti-physicalist argument of the century is disowned by its author, and philosophers go right on using it, because an argument doesn't belong to the person who made it. Put that on the meter.
Why it matters
Everything you were taught upstairs is true. The wavelengths are real, the cones are real, the opponent channels are real, V4 is real, and every one of those facts was known before you walked in. The question this room asks is not whether science is right about colour. It's whether being right about something is the same as having it -- whether the description of a thing and the thing could ever be the same size.
You picked your one true red back in Exhibit № 10. Nobody could see it then either. The difference is that this time you had all the numbers, and it still didn't help.
An honest asterisk. A real person raised without colour probably would not step outside and see the world as you see it -- the visual system needs early exposure to develop normally, and after long enough the wiring doesn't wait. Philosophers stipulate this away, as is their right, but it's worth knowing that Mary's room is a thought experiment all the way down and could not be built. Meanwhile the closest real thing exists: people with rod monochromacy live their whole lives in something very like the top of this page, and they are not waiting for a door.
Take it further
Jackson's original is "Epiphenomenal Qualia" (1982), four pages, very readable, and it also contains Fred, who can see two reds where you see one. For the recantation, look up Jackson's later Mind and Illusion. For the opposition at full strength, Dennett's "What RoboMary Knows." And if you'd like the same problem with the colour left in, the bat is waiting in Exhibit № 8.