The Philosopher Who Refuted His Own Famous Argument

Mary lives her whole life in a black-and-white room, watching the world through a black-and-white monitor. She is, in the setup, the world's leading neuroscientist of color — she knows every wavelength, every cone-cell response, every neural pathway involved in red. One day someone opens the door and she walks outside.

Does she learn something new?

The Australian philosopher Frank Jackson published this thought experiment in 1982, in a paper called "Epiphenomenal Qualia" in The Philosophical Quarterly. The argument was tight. If physicalism is true, all facts are physical facts. Mary already had all the physical facts. But she clearly learns something — what red is like — when she sees a tomato. So there are non-physical facts. So physicalism is false.

Mary's Room became one of the most-cited thought experiments in late-twentieth-century philosophy of mind. Generations of undergraduates have walked her out of the room. The argument was Jackson's career-defining piece.

Thirteen years later he turned on it.

In a 1995 "Postscript on 'What Mary Didn't Know'," reissued and expanded in essays through 2003 and 2007, Jackson conceded that his own argument went wrong. The mistake, he decided, was in how he had thought about sensory experience. Mary's new state, when she sees the tomato, is a representational state — her visual system is representing a property of the tomato that physicalism can describe in full. There is no extra non-physical fact she is acquiring. There is just a brain doing what brains do.

It is a strange thing for a philosopher to do — keep teaching an argument by refuting it. Jackson does. He still publishes the original Mary, walks her out of the room, lets the intuition land, and then explains why the intuition fools you. The room is a good philosophical machine. It is also, by its inventor's account, a trap.