In Consciousness Explained, Daniel Dennett proposes the following continuation to the story of Mary’s room:

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!”

I don’t intend to fully analyze this scenario here, and for that reason I left it to the reader in the previous post. However, I will make two remarks, one on what is right (or possibly right) about this continuation, and one on what might be wrong about this continuation.

The basically right or possibly right element is that if we assume that Mary knows all there is to know about color, including in its subjective aspect, it is reasonable to believe (even if not demonstrable) that she will be able to recognize the colors the first time she sees them. To gesture vaguely in this direction, we might consider that the color red can be somewhat agitating, while green and blue can be somewhat calming. These are not metaphorical associations, but actual emotional effects that they can have. Thus, if someone can recognize how their experience is affecting their emotions, it would be possible for them to say, “this seems more like the effect I would expect of green or blue, rather than red.” Obviously, this is not proving anything. But then, we do not in fact know what it is like to know everything there is to know about anything. As Dennett continues:

Surely I’ve cheated, you think. I must be hiding some impossibility behind the veil of Mary’s remarks. Can you prove it? My point is not that my way of telling the rest of the story proves that Mary doesn’t learn anything, but that the usual way of imagining the story doesn’t prove that she does. It doesn’t prove anything; it simply pumps the intuition that she does (“it seems just obvious”) by lulling you into imagining something other than what the premises require.

It is of course true that in any realistic, readily imaginable version of the story, Mary would come to learn something, but in any realistic, readily imaginable version she might know a lot, but she would not know everything physical. Simply imagining that Mary knows a lot, and leaving it at that, is not a good way to figure out the implications of her having “all the physical information”—any more than imagining she is filthy rich would be a good way to figure out the implications of the hypothesis that she owned everything.

By saying that the usual way of imagining the story “simply pumps the intuition,” Dennett is neglecting to point out what is true about the usual way of imagining the situation, and in that way he makes his own account seem less convincing. If Mary knows in advance all there is to know about color, then of course if she is asked afterwards, “do you know anything new about color?”, she will say no. But if we simply ask, “Is there anything new here?”, she will say, “Yes, I had a new experience which I never had before. But intellectually I already knew all there was to know about that experience, so I have nothing new to say about it. Still, the experience as such was new.” We are making the same point here as in the last post. Knowing a sensible experience intellectually is not to know in the mode of sense knowledge, but in the mode of intellectual knowledge. So if one then engages in sense knowledge, there will be a new mode of knowing, but not a new thing known. Dennett’s account would be clearer and more convincing if he simply agreed that Mary will indeed acknowledge something new; just not new knowledge.

In relation to what I said might be wrong about the continuation, we might ask what Dennett intended to do in using the word “physical” repeatedly throughout this account, including in phrases like “know everything physical” and “all the physical information.” In my explanation of the continuation, I simply assume that Mary understands all that can be understood about color. Dennett seems to want some sort of limitation to the “physical information” that can be understood about color. But either this is a real limitation, excluding some sorts of claims about color, or it is no limitation at all. If it is not a limitation, then we can simply say that Mary understands everything there is to know about color. If it is a real limitation, then the continuation will almost certainly fail.

I suspect that the real issue here, for Dennett, is the suggestion of some sort of reductionism. But reductionism to what? If Mary is allowed to believe things like, “Most yellows typically look brighter than most blue things,” then the limit is irrelevant, and Mary is allowed to know anything that people usually know about colors. But if the meaning is that Mary knows this only in a mathematical sense, that is, that she can have beliefs about certain mathematical properties of light and surfaces, rather than beliefs that are explicitly about blue and yellow things, then it will be a real limitation, and this limitation would cause his continuation to fail. We have basically the same issue here that I discussed in relation to Robin Hanson on consciousness earlier. If all of Mary’s statements are mathematical statements, then of course she will not know everything that people know about color. “Blue is not yellow” is not a mathematical statement, and it is something that we know about color. So we already know from the beginning that not all the knowledge that can be had about color is mathematical. Dennett might want to insist that it is “physical,” and surely blue and yellow are properties of physical things. If that is all he intends to say, namely that the properties she knows are properties of physical things, there is no problem here, but it does look like he intends to push further, to the point of possibly asserting something that would be evidently false.