Thursday 7/25
What is it Like to See the Color Red?
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Today we took up a puzzle which is so daunting it has been called the hardest problem in physics today. Consider that my subjective experience of smelling the freshly brewed coffee has a qualitative character--what it is like for me to smell the coffee--and a subjective character--what it is like for me to smell the coffee. The conscious state I am in while enjoying the subjective experience of smelling the coffee is the state it is because of the distinctive qualitative character of the experience, but it is my conscious state in the first place in virtue of my having it. We say that my capacity for having subjective experiences is grounded in my capacity to enjoy phenomenal consciousness and that the qualitative character of my phenomenal consciousness is in turn a result of the bits and pieces of colors, sounds, smells, tastes, touches--all the raw feels, in short--out of which my subjective experience of the world is constructed, which we call qualia.
For reasons we sketched today, the problem posed by subjective experience is that there seems to be no physical basis for it to which we can point.
To see this, we followed Nagel in asking the odd question, what is it like to be a bat? Indeed, Nagel's classic article "What Is It Like to Be a Bat?" first sets out the enormous challenge subjective experience presents.
Setting Out the Problem
Phenomenal Consciousness is essentially the subjective character of experience. That is, phenomenal consciousness is what it is like to have this or that experience.
"[F]undamentally an organism has conscious mental states if and only if there is something that it is like to be that organism--something it is like for the organism."
Consider, for example, the bat. If the bat has subjective experiences, then there is something it is like to be a (particular) bat. But that something is wholly inaccessible to us.
There are facts accessible only from the first-person point of view of the organism. These facts consist of the facts of the qualitative character of subjective experience.
Materialism (Physicalism) proposes that every mental event is a physical event. The thesis of Reductive Materialism proposes that all the facts about mental events can be accounted for by facts about physical events.
The Problem
| 1. | If Reductive Materialism is true, then any fact of mental events can be explained in terms of facts about the physical events to which they reduce. | ||
| 2 | It is not the case that any fact of mental events can be explained in terms of facts about the physical events to which they reduce. | ||
| ∴ | 3 | Reductive Materialism is not true. | 1&2 |
This is a very general way of presenting the challenge accounting for the phenomenon of subjective experience poses not just for understanding the computational basis of mind, but for any physical basis of mind whatsoever, whether computational or otherwise.
There is, you see, an important aspect to mental states: There is something it is like to have them. To want a glass of red wine is, on the one hand, to have a desire for the glass, and, on the other hand, to feel the pull, if you will, of the red wine. There is further something it is like to actually drink the red wine and satisfy the desire for it. These raw feels or qualitative experiences associated with mental states collectively fall under the problem of phenomenal consciousness. Yet why should there be anything it is like to be in a mental state of any sort?
The problem of phenomenal consciousness is usually cast as a problem for physicalism: At least some mental facts--facts about phenomenal consciousness, in particular--are arguably not physical facts; hence no version of physicalism, including computationalism, is true. Thus phenomenal consciousness is opaque to science, since science only trades in physical facts. Put another way, science cannot, apparently, explain how phenomenal consciousness emerges in a purely physical universe.
The problem phenomenal consciousness presents is as simple as it is devastating. As Nagel points out, no study of bats can ever reveal what it is like to be a bat. As much as we might learn about echo-location and nocturnal navigation, a bat's phenomenal consciousness is intrinsically perspectival: We can never know what it is like without already having that perspective, which we would have only if we were already bats ourselves.
This is the hard problem of consciousness: For creatures like us there is something it is like to be, just how is there something it is like to be them? How does a squishy lump of greyish/whitish matter have phenomenal consciousness insofar as it is not merely aware of things in its environment, it has rich subjective experiences of them as having various qualities?
Today we considered a couple of thought experiments designed to show that phenomenal consciousness is not reducible to brain states or, really, any physical state whatsoever.
| The Knowledge Argument | |||
| 1 | If Physicalism is true, then it is not possible to know all the physical facts without knowing all the facts. | ||
| 2 | It is possible to know all the physical facts without knowing all the facts. | ||
| ∴ | 3 | Physicalism is not true. | 1&2 |
Fred is able to consistently sort tomatoes into two piles, because Fred is able to distinguish between two kinds of red (what he calls "red-1" and "red-2"). He calls the rest of us red-1 and red-2 color-blind, because we cannot distinguish between objects that are red-1 and objects that are red-2. Yet we can determine all the neurophysiological facts about Fred.
| The Case of Fred | |||
| 1 | We can determine all the physical facts about Fred, but we cannot determine what it is like for Fred to see red-1 and red-2. | ||
| 2 | If (1), then it is possible to know all the physical facts without knowing all the facts. | ||
| ∴ | 3 | It is possible to know all the physical facts without knowing all the facts. | 1&2 |
Mary is an expert in vision. She has, however, gained her expertise over black-and-white television while in a black-and-white room. Mary has never seen the color red, so she does not know what it is like to see red. What she does know are all the facts of neurophysiology pertaining to vision.
| The Case of Mary | |||
| 1 | Mary knows all the physical facts, but she does not know all the facts. | ||
| 2 | If (1), then it is possible to know all the physical facts without knowing all the facts. | ||
| ∴ | 3 | It is possible to know all the physical facts without knowing all the facts. | 1&2 |
The Knowledge Argument seems to force us to the unhappy conclusion that there is no physicalist account of the phenomenon of phenomenal consciousness. I say "unhappy" because the lack of a physical account of phenomenal consciousness entails we cannot build a mind: We have, after all, only the 'stuff' around us to use in building a mind; yet if these arguments are sound, no amount or combination of physical stuff will allow us to build a mind which enjoys phenomenal consciousness.
Thus much hinges on these arguments. No doubt this explains why the problem of phenomenal consciousness has been one of the most discussed problems in recent philosophy. Some of the best minds philosophy has to offer have been absorbed by it, and some physicists and neuroscientists have begun to notice the enormity of the challenge phenomenal consciousness presents.
Part of the appeal of the Knowledge Argument is surely the simplicity of its explanation. Our intuitions about phenomenal consciousness are teased-out and bolstered by two clever thought experiments, the case of Mary and the case of Fred, which provide us something like a graphic-novel approach to philosophy. Putting it that way is not to denigrate but to compliment: One of the reasons Jackson's original article, "Epiphenomenal Qualia", has generated so much discussion is the accessibility and clarity of the problem he describes.
In the forward to "There's Something About Mary: Essays on Phenomenal Consciousness and Frank Jackson's Knowledge Argument" (Peter Ludlow, Yujin Nagasawa, and Daniel Stoljar, eds., Cambridge, Mass: MIT Press, 2004), Jackson offers this brief on his argument:
There are two main parts to the knowledge argument (in the form in which I advanced it; there have been many versions of it): the part that says that complete physical knowledge is not complete knowledge tout court (or anyway not as far as the mind is concerned), and the part that says that if physicalism is true, it is. The final step is then modus tollens. The first part is the part supported by the plausibility of the contention that Mary would learn something about what the world is like on her release. As we might put it, she would acquire an enlarged view of the available dimensions of similarity in our world. Before her release, runs the first part, she knew a lot about how different people looking at ripe tomatoes typically were alike, both in themselves and in their relations to the tomatoes. She knew, for example, how the ripe tomatoes typically induced a tendency to use the word 'red' in such people, provided they were English speakers. After her release, she would realize that there was another dimension altogether to how they are alike, and to how they differ from people looking at, say, grass. The second part of the knowledge argument is the part where it is observed that because she knows all there is to know physically, this means that were physicalism true, there would be no dimensions of similarity instantiated in our world other than those she knows about in the room before her release. Therefore, physicalism is false.
In the same forward, Jackson repudiates what he formerly believed the argument demonstrated. Indeed, he is now confident the argument goes wrong somewhere, even if it is not clear where. As he puts it,
Although I no longer agree with the knowledge argument, I do think it has been, and continues to be, a major impetus to many important debates that have cast a great deal of light on some very hard problems in the philosophy of mind. In many ways, I which I could still accept it.
Let us expand a bit on the above case of Mary. Mary is the object of a sadistic philosophical experiment in which she is raised from birth in a black-and-white room. We might even imagine her being tatooed black and white herself to remove any possibility of her ever seeing color. We're not wholly sadistic. We give her a computer with which to learn things about the world. (You shouldn't have to ask: Of course it has a black-and-white monitor!)
Now let us suppose that the physics of color an the neurobiology of color perception are completed sciences. Thus all the physical facts about color and its effect on our neurophysiology are known. Mary, never having experienced color, uses her computer to become expert in these (completed) sciences. So she knows everything there is to know about the physical facts of color.
Now let's let her out of her black-and-white room. Just for fun, let's put a huge, juicy, ripe red apple on a table outside the door so it will be the first thing she sees on leaving the room. Surely she will learn something new, something she would not know before leaving the room: what it is like to see the color red. She will now know, to frame it as Jackson does above, that those seeing the color red are alike in a way she did not, and could not, have known before leaving the room. Yet she knows all the physical facts, so what she now knows is not a physical fact.
Broadly speaking, two responses to the knowledge argument have emerged corresponding to the two parts of the argument as Jackson described them above:
- Deny the proposition that "complete physical knowledge is not complete knowledge" (Jackson's own move, interestingly); or
- Deny the proposition that all knowledge is physical knowledge while maintaining that physicalism is nonetheless true.
The philosophical gymnastics involved in either response are complicated and fascinating. Suffice it to say that Jackson is correct: We learn much in coming to grips with the argument.
The current state of affairs is not, however, encouraging: There is no consensus on a final solution to the puzzle Mary presents. As puzzles go, it's a doozy.