Mary the Color Scientist: A Boom Crutch Unveiled

Australian philosopher Frank Jackson's thought experiment about Mary the color scientist, often called “the Knowledge Argument,” has been pumping philosophers’ intuitions with remarkable vigor since it first appeared in 1982. For sheer volume and reliability, this must count as one of the most successful intuition pumps ever devised by an analytical philosopher. It is a classic, perennially on the list of required reading in undergraduate courses in the philosophy of mind all over the English-speaking world, and several weighty anthologies have been devoted to essays reflecting on its implications. It is interesting to note that its author has subsequently recanted, declaring that he no longer accepts its conclusion—but that has not diminished its popularity.

Here it is in its entirety, drawn slightly out of context perhaps, but still clear as a bell:

Mary is a brilliant scientist who is, for whatever reason, forced to investigate the world from a black and white room via a black and white television monitor. She specializes in the neurophysiology of vision and acquires, let us suppose, all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like “red”, “blue”, and so on. She discovers, for example, just which wavelength combinations from the sky stimulate the retina, and exactly how this produces via the central nervous system the contraction of the vocal chords and expulsion of air from the lungs that results in the uttering of the sentence “The sky is blue”. (It can hardly be denied that it is in principle possible to obtain all this physical information from black and white television, otherwise the Open University would of necessity need to use color television.) What will happen when Mary is released from her black and white room or is given a color television monitor? Will she learn anything or not? It seems just obvious that she will learn something about the world and our visual experience of it. But then it is inescapable that her previous knowledge was incomplete. But she had all the physical information. Ergo there is more to have than that, and Physicalism [i.e., materialism, the denial of dualism] is false. [Jackson, 1982, p. 130]

Is it a good intuition pump? Let’s turn all the knobs and see what makes it work. Actually, that would take us too long, but the job has been done, in the sizable literature on the topic. Here I will simply illustrate a few knobs that need to be examined, and leave the result as an exercise for you. (If you want, you can check your own results against the literature; two recent anthologies are referenced in Sources. Can you come up with a new twist?) More than twenty years ago, I conducted a preliminary exploration of the knobs, and issued a killjoy verdict that has been largely dismissed or disregarded: “Like a good thought experiment, its point is immediately evident even to the uninitiated. In fact it is a bad thought experiment, an intuition pump that actually encourages us to misunderstand its premises!” (Dennett, 1991a, p. 398). Let’s see if this is so. I claim that it is much more difficult to imagine the scenario correctly than people suppose, so they imagine something easier, and draw their conclusions from that mistaken base.

First knob: “a black and white room via a black and white television monitor.”

Presumably she wears black or white gloves and is forbidden to look at herself when she bathes, but the idea of cutting off all “external sources” of color is forlorn in any case. Would we have to rig some device that prevented her from rubbing her eyes (to create “phosphenes”—try it)? And couldn’t she have colors in her dreams before actually seeing them? If not, why not? Do the colors have to “get in via the eyes” before she can “store” them in her brain? A tangle of bad folk theory of color lies behind this simple suggestion.

Second knob: she “acquires, let us suppose, all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like ‘red’, ‘blue’, and so on.”

All the physical information there is to obtain? How much is that? Is that like having all the money in the world? What would that be like? It’s not easy to imagine, and nothing less than all will serve to make the thought experiment’s intended point. It must include all the information about all the variation in responses in all the brains, including her own, especially including all the emotional or affective reactions to all the colors under all conditions. So she will know in exquisite detail which colors calm her, annoy her, would grow on her with exposure, distract her, repel her, and so on. Is she forbidden to perform experiments on herself (without cheating, without smuggling any colored things into her cell)? If you didn’t imagine all this (and more), you didn’t follow directions. It’s like being asked to conceive of a chiliagon and imagining a circle instead. Lots of implications follow from one of these exercises of mental representation that don’t follow from the other. In this case, for instance, are we supposed to ignore the fact that if Mary acquired all this information, she would no doubt be in a state of total mental collapse, burdened with thousands of encyclopedia articles and diagrams?

If Jackson had stipulated that Mary had the God-like property of being “physically omniscient”—not just about color but about every physical fact at every level from the quark to the galaxy—many if not all readers would resist, saying that imagining such a feat is just too fantastical to take seriously. But stipulating that Mary knows merely all the physical facts about color vision is not substantially less fantastical.

“Imagine that Mary has a billion heads. . . .”

“Don’t be silly!”

“Ok. Make it a million heads. . . .”

“No problem!” (Really?)

In an earlier attempt to dramatize this problem of imagination, I encouraged people to consider a variant ending:

And so, one day, Mary’s captors decided it was time for her to see colors. As a trick, they prepared a bright blue banana to present as her first color experience ever. Mary took one look at it and said “Hey! You tried to trick me! Bananas are yellow, but this one is blue!” Her captors were dumfounded. How did she do it? “Simple,” she replied. “You have to remember that I know everything—absolutely everything—that could ever be known about the physical causes and effects of color vision. So of course before you brought the banana in, I had already written down, in exquisite detail, exactly what physical impression a yellow object or a blue object (or a green object, etc.) would make on my nervous system. So I already knew exactly what thoughts I would have (because, after all, the ‘mere disposition’ to think about this or that is not one of your famous qualia, is it?). I was not in the slightest surprised by my experience of blue (what surprised me was that you would try such a second-rate trick on me). I realize it is hard for you to imagine that I could know so much about my reactive dispositions that the way blue affected me came as no surprise. Of course it’s hard for you to imagine. It’s hard for anyone to imagine the consequences of someone knowing absolutely everything physical about anything!’ [Dennett, 1991a, pp. 399–400]

It is standardly assumed that things could not proceed this way. As Jackson disarmingly put it, “It seems just obvious that she will learn something about the world and our visual experience of it.” Or as George Graham and Terry Horgan (2000, p. 72) say, “Surely, [ding!], we submit, she should be both surprised and delighted.” That is a mistake, and that is what is wrong with Mary as a thought experiment. It just feels so good to conclude that Mary has a revelation of some sort when she first sees color that nobody wants to bother showing that this is how the story must go. In fact, it needn’t go that way at all.

Jackson’s intuition pump excellently exposes to the light a lot of naïve thinking about the nature of color experience and the brain that no doubt serves people well most of the time, so we might grant that he nicely draws out some of the implications of folk theory. But his aim was to refute a hypothesis about the capacity of the physical sciences to account for all color phenomena. Of course in any real-world situation, somebody in Mary’s imagined position would learn something new because however much she knew about color, there would be lots of facts about physical effects of color she didn’t know. It is only the stipulated extreme case that makes Jackson’s “just obvious” and Graham and Horgan’s “surely” out of place. If you are still inclined to think that my suggested alternative ending of the story would have to be impossible, see if you can work out an argued reason for your belief. It would be interesting to see if you come up with a consideration that has escaped the hundreds of philosophers who have labored over this for years. (Of course, that very fact might be taken to show that this is after all a wonderful intuition pump: it has provided employment for philosophers for three decades.)