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29.9.12

"Mary's room" tells us nothing

I have a low tolerance for philosophical thought experiments that posit strange situations that nobody has actually encountered -- "experience machines," violinists hooked up to innocent people's kidneys, planets where water's chemical formula is XYZ, etc. I think they make a fundamental mistake about what intuition is. Intuition is a practical skill. Therefore it is rooted in actual experience of encountering decisions to be made in real life. Intuition has some weight in those situations. So I have no in-principle objection to philosophical arguments that demonstrate that one's beliefs about one situation must be wrong because they imply a counterintuitive result in some other familiar situation. But there seems to me to be no reason to think that an intuition about an unfamiliar case should carry any weight at all.

Consider the classic "Mary's room" thought experiment. The point of this scenario is supposed to be to demonstrate that subjective experiences ("qualia") exist in addition to the physical facts about the universe. Here's how Ian Pollock summarizes it:

Mary is a genius neuroscientist. She knows everything there is to know empirically about how the mind and brain work, and in particular she exhaustively knows every single scientific fact that bears on color vision: optics, how the retina works, how the retina’s signals get processed in the brain, et cetera.

However, Mary has had an unusual upbringing. Raised by philosophers (a sketchy proposition in the best of times), she has been kept in a monochrome room for her entire life and has never seen primary colors — never seen a red rose, or a green leaf, or a blue sky. (Nitpicky readers will notice that this would be actually pretty hard to accomplish — for one thing, she would have to have her skin painted monochrome, never look at a bright light through her closed eyelids and see the red color that results, never dream in color... but never mind. This! Is!! PHILOSOPHY!!!)

Eventually, her philosophical zookeepers take a day off from heroically pushing obese people off bridges, and they take her out of her monochrome cage. She comes out into the world and sees a dandelion for the first time, saying “Wow, so that’s what yellow looks like! Cool!” You can imagine all her other epiphanies for yourself.

The gotcha being that she appears to have learned something new — what it’s like to see yellow — on being released. But we stated that she already knew all the scientific facts! Therefore, there must be facts out there that are beyond the reach of science, even in principle — mental facts, or subjective facts, perhaps. Facts about what it is like to have certain experiences. That’s the idea, anyway.

Here's the problem: To decide whether Mary learned anything new upon first seeing the color yellow, we have to try to imagine knowing everything about color without having seen it. But that's not something any of us have any experience with. So our intuitions are going to be dominated by imagining what it's like to know quite a lot about something. But in the latter case everyone would agree that direct experience teaches you something new. Intuitions about "Mary's room" are useless in demonstrating whether qualia are non-physical facts. At best, this thought experiment can just illustrate the opposing positions. And perhaps some enterprising scientist with no respect for the IRB could use it to design an empirical test of the issue. But probing the thought experiment conceptually does nothing because we haven't had the right kind of experiences to callibrate our intuitions with.

(As a side note, my heavily Pragmatist outlook leads me to doubt the conceptual coherence of the idea of complete scientific knowledge of some topic, of the sort Mary is hypothesized to have. Scientific knowledge is a matter of approximate yet useful models. The idea of a complete cataloging of every fact strikes me as a sort of naive "mirror theory" of truth.)

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