Thought experiment 9: Mary’s Room

The Australian philosopher Frank Jackson used the tale of a colour-deprived prodigy to argue for a world beyond the physical. But is it so black and white?

By David Edmonds

Illustration by Marie Montocchio / Ikon Images

Mary has had an unusual upbringing. She’s been raised entirely alone in a black-and-white room. The furniture is black and white. The paintings are black and white, as is the TV. The food shoved under the door has all been dyed black and white.

It’s not a fun existence, but there is no shortage of books (all black and white, obviously), and she has access to the internet (with a black-and-white screen), so Mary has entertained herself by studying. Understandably, her obsession is colour. She has read everything there is to know about colour – the physics, the biology, the neuroscience. She knows about the wavelengths of various colours. She knows how these stimulate nerves in the retina and how the brain interprets the electric signals. It’s no exaggeration to say that Mary is the world’s leading scientific expert on colour.

And not just the science of it. She’s taken on board CP Snow’s concerns, first aired in the New Statesman, about the gulf in intellectual life between science and the humanities and has read all the novels and poetry that reference colour, and all the associations with emotions, such as love and anger and envy. She’s particularly fond of Robert Burns’s “A Red, Red Rose”.

And then comes a day Mary had long anticipated. The door of her room swings open and she is able, finally, to exit her monochrome life. And there in front of her, the very first thing she sees, is a red rose.

Frank Jackson, the son of two philosophers, entered the family business after switching as a student from mathematics. He was teaching at Monash University in Melbourne when he was asked to give a talk to the psychology department. “In the spirit of interdepartmental cooperation I said ‘yes’ that sounds like a good idea. But then I had to think of something to talk about.”

The reason they wanted to hear from him was that they’d discovered he was a rarity among philosophers in not being a physicalist. A physicalist, crudely put, holds that everything is physical, that everything can be explained in physical terms.

Jackson had just read HG Wells’s short story “The Country of the Blind”, in which an explorer, Nunez, discovers a people who have no sight. In the story, Nunez tries to explain vision to the blind locals, but they refuse to believe there is this extra sense.

At the time, Jackson thought that the Mary’s Room thought experiment showed that physicalism was wrong. Whatever her knowledge of how the world worked, Mary did learn something when she saw the red rose. She had what philosophers call a phenomenal experience; she learnt how “redness” looks to a perceiver. That had to be something extra to the physical brain, argued Jackson, because Mary already knew all about brains.

Later, Jackson came to abandon his original position. He became increasingly worried about the claim that colour and other experiences were epiphenomenal. The epiphenomenalist believes that the sensation of colour plays no causal role in the physical universe. It is a by-product of brain activity, but it has no effects of its own.

But how could that be? The sensation of seeing a red rose inspired Burns to write a poem. So it clearly did have a causal effect on the physical world. The way colours look to us, the way food tastes to us, or music sounds to us, moves us to action.

However, here’s the problem for the physicalist. After seeing the red rose, Mary surely has acquired something new. She has new power to imagine what a red rose looks like, a new way to think about it. How can the physicalist explain this? “The standard physicalist response,” says the physicalist David Papineau, of King’s College London, “is that Mary merely has a new concept of red. Suppose you know who Cary Grant is, but later discover that Cary Grant was born Archie Leach. Cary Grant and Archie Leach are different concepts, but they both refer to the same thing (person).”

Similarly, red can be described in two ways. It can be described from the inside, as it were – the phenomena, in terms of how it feels, how it is experienced. Or it can be described, as a scientist would, in terms of light travelling to the retina etc. These are merely different means of referring to the same thing.

The real value of the Mary thought experiment is not that it undermines physicalism, says Professor Papineau, “it’s that it forces us to acknowledge the very distinctive nature of phenomenal concepts”, such as feeling pain, or seeing red. After all, the inspiration for Burns’ “A Red, Red Rose” was phenomenal experience – it was not from learning about oscillations in the primary visual cortex.