by Tim Sommers
Children are natural philosophers. Some combination of imagination, maybe, and lack of knowledge. Philosophy is all theory and no data, after all. In any case, in my experience, one of the most popular philosophical puzzles among young people is this.
When I look at something red, it looks red to me. But it’s hard to say what “red” is other than not green, not blue, etc. How do I know that when you look at something red it doesn’t actually look like what I see as green – and vice versa. Philosopher’s call this “The Inverted Spectrum Problem”.
John Locke was the first to write about it. It’s surprising that no one wrote about earlier since, as I said, many, many people, including children, come up with the basic idea all on their own. I think that maybe the problem is a product of the way our view of the mind changed in the early modern period. Specifically, it’s a side effect of the increased emphasis on the idea of idea of a private, internal, inaccessible self. Anyway, in the end, Locke didn’t think it was very important. Maybe it isn’t. But like many philosophical puzzles, it points to something important.
Back up. We learn colors by being shown samples of colors and learning to name them. Back in my day, it was crayons. So, we learn colors by discrimination. But maybe colors are, beyond that, “featureless”, as the philosophical behaviorist said. Yet non-color-blind people are seeing something when they see a color. What is it?
When I ask my students what “red” is, I invariably get the answer, it’s a certain frequency of light. What frequency? I always ask. In the olden days, most of the time, they had to admit they didn’t know. Nowadays, they google it on their phone and say “between 635 and 700 nanometers”. But when you go to the grocery store you don’t tell red apples from green by looking for apples in a certain frequency range, do you?
Long before the science of optics and any understanding of the electromagnetic-spectrum, people saw and could identify colors. Philosophers from Locke and Hume down to today have called colors “secondary” properties. Other secondary properties include taste and smell and sound. Primary properties, on the other hand, are objective features of the physical world that can be measured quantitatively – like extension in space, mass, and velocity. Colors are an interaction between the objective world and our perceptual apparatus. Objects reflect different colors under different lighting conditions. Our perception of red is the way we see a certain frequency of light, usually (but not exclusively) as a reflection off an object under “normal conditions”. But what about the felt, phenomenal quality of redness? Analytic philosophers call bits of perceptual experience “qualia”. The inverted spectrum problem asks, if we can only identity colors by our qualia, and you have your qualia and I have mine, and we can’t compare them directly, how do I know that you don’t associate different qualia than I do with red? I am not sure that’s an improvement on the original way of putting the question. But it will help us get to a larger point in a minute.
But first, here are various ways of pushing back against the inverted spectrum problem. Some people think colors are associated with feelings. Red is hot. Red is excitement – whereas blue is melancholy. So, you might think, you could tell if I had blue qualia instead of red qualia when I saw what you call red things, because red things would make me sad. That’s too simplistic, of course, but you get the idea. Also, there are more different perceptible shades of color between some colors than others and so, maybe, we could detect it behaviorally if your color perceptions were inverted (relative to mine). And some people say that the currently dominant empirical theory of color perception, the Hurvich-Jameson model, shows that we can’t change the profile of our subjective color responses without rewiring our whole brain. Meaning, I guess that color inversions are possible, but if I did brain surgery on you, I could tell if your spectrum was inverted.
However, the deeper question behind the problem is this. Are qualia real? Some contemporary philosophers (Dennett, the Churchlands, et al) regard them as an illusion. But even if things like are experiences of colors are a perceptual illusion, perceptual illusion are still perceptual experiences. How can we make even sense of the idea that we don’t “really” have perceptual experience at all? But if we do have any kinds of perceptual experience, then aren’t qualia real? Doesn’t that show that there is more to the world than all the physical objects in it? Qualia, at least?
Maybe, Frank Jackson’s “knowledge argument” will help. Suppose, for some reason, Mary is confined to a black and white room for her whole life, prevented from seeing even her own body. Her only contact with the outside world is a black and white monitor. So, Mary has never seen color. Maybe as a response, she spends all her time studying color. She knows everything there is to know about the electromagnetic spectrum, the cones and rods in our eyes, how our brain processes visual information, even how people talk about color. She knows all the physical facts about color, although she has never seen anything colorful. Now, suppose one day she is able to leave the room. When she sees something red will she learn something new? We might say, now she knows what red looks like. She knew all the physical facts about red before, but now she knows what it’s like to have red qualia.
Obviously, you could deny that she learns anything new. There’s nothing to know about colors except all the physical facts about them, you could say. But if Mary does learn something new, it seems to be the case that subjective experience, qualia, the felt phenomenal quality of experience are, in fact, not reducible to merely physical facts. She knew all those before she left the room. Maybe, the world is not just physical, chemical, biological, and/or psychological. Maybe, the world has nonphysical stuff in it too. Like color qualia. And maybe your mind, as opposed to your brain, is not physical.