Mary's Room

Mary is a brilliant scientist who has spent her whole life in a room without colour. She has studied vision exhaustively and knows every physical fact about it: the wavelengths, the receptors, the neural pathways, the processing, everything there is to know from the outside. One day she is released, and she sees a tomato.

Does she learn anything?

If she does, the argument runs, then the physical facts she already possessed did not include it, and not all facts are physical facts. The argument is valid, which means the entire dispute is about that second premise. Every physicalist reply has to explain away a very strong intuition that Mary learns something on leaving the room, and the replies differ mainly in how they do that rather than in whether they must.

Thomas Nagel had approached the same territory from another angle in 1974, and his version is about method rather than about colour. We could learn everything there is to know about echolocation (the physics, the neurology, the behaviour) and still not know what it is like to be a bat. His point is that objective description advances precisely by abstracting away from any particular point of view; that is what makes it shareable and checkable. But an experience is a point of view. So the standard method looks like it must leave out the very thing under study. Nagel does not conclude that physicalism is false. He concludes, more carefully, that we do not currently understand how it could be true.

What happened next to Jackson's argument is rare enough to be worth pausing over: he abandoned it. He became a physicalist and offered the ability reply: that what Mary gains on release is a set of capacities, to recognise, to imagine, to remember the colour, rather than a new fact about the world. Knowing how is not knowing that, and only the second kind of knowledge was ever at stake. Whether an ability is really all she gains is exactly what the argument was about, so this is a position rather than a refutation, and it is held by the man who invented the objection to it.

A common complaint is that the case is impossible: nobody could have every physical fact, and a life without colour would alter the visual system in ways that make the experiment incoherent. This misses what the case is for. The question is conditional, if somebody had complete physical knowledge, would anything remain? And objecting that nobody could have it leaves the conditional untouched. It is the same complaint made about the trolley problem, and it is beside the point in the same way. These cases are built to isolate one variable, not to be feasible.

The word qualia deserves a note of suspicion, since it is used throughout this literature as though it were neutral. It is meant to pick out the felt qualities of experience: the redness of red, the particular awfulness of a headache. Some philosophers argue the term bundles several different claims together and quietly imports the assumption that experience has intrinsic, private, ineffable properties, which is precisely what is in dispute. Using the word is already a small step towards one side, and it is better to know that than to use it innocently.

Finally, the case has a modern application that clarifies what it can and cannot do. A system trained on every scientific paper about colour can describe red accurately in any context you like. That settles nothing, because its behaviour is exactly what both the physicalist and the anti-physicalist would predict. This is the general shape of most confident claims in this area: a capability is demonstrated and a metaphysical conclusion is drawn that the demonstration could not support in either direction. Noticing the pattern is worth more than having a settled view about Mary.