Wednesday, July 29, 2009

Having Your Qualia and Eating Your Physics Too

Can we coherently acknowledge the existence of qualia without being forced into a non-physicalist stance about the contents of the world? I'm back at CTY--as I am every summer--and today our philosophy of mind class got to Jackson's "Epiphenomenal Qualia." I was somewhat surprised, having not read the article since last year, to find that my own views on it seem to have changed considerably. Specifically, while I still agree with the main thrust of Jackson's argument (that is, that qualia exist), I'm much less impressed with the quality of his argumentation and the route by which he arrives at his conclusion; more specifically still, I'm incredibly skeptical that his "what Mary didn't know" argument shows anything like what it is purported to show. Qualia certainly deserve to be included in our ontology, but that emphatically doesn't imply that we ought to reject the physicalist picture of the world. Let me try and show how I think these two statements can be reconciled.

First, I suppose a bit of background is in order. Readers may already be somewhat familiar with the Mary case--Jackson's version of the knowledge argument against physicalism--so I won't waste a whole lot of time detailing the moves. Still, it's worth laying out exactly how the argument is supposed to proceed; as we shall see, the precise wording of one of the premises can make all the difference between soundness and total incoherence. Let's start with the informal presentation. Briefly, the standard presentation goes something like this.

Mary is a gifted neuroscientist who has dedicated her life to studying human color perception. She's learned everything there is to know about the physical process of seeing color: she knows everything about how the surface spectral reflectance of various objects interacts with environmental variables to produce changes in the photoreceptors of the eye, how those changes produce neural excitations, how those excitations are processed in the brain, and so on. She knows all the physical facts about how humans perceive color. Somewhat ironically, Mary herself has never perceived color. Her eyes (say) have been surgically altered so that she is only able to view the world in shades of grey. Nevertheless, her studies have proceeded beautifully, and she is now in a position of perfect physical knowledge. With this complete knowledge in hand, Mary undergoes an operation to reverse her perceptual idiosyncrasy; the procedure to keep her from being able to see color is reversed, and Mary's biology is returned to normal. When Mary awakens from the operation, she is presented with a red rose, and actually sees red for the first time. Does Mary learn something new?

On the standard interpretation, we're now presented with two horns of a dilemma: we're either forced to say that no, Mary has learned nothing new when she first sees color--an ostensibly counter-intuitive position to hold--or we're forced to say that yes, Mary learns something new when she sees the rose. If we take this second horn, though (so the argument goes), we must also admit that there are facts about color experience that are not physical; after all, ex hypothesi Mary knows all the physical facts about color vision--if she learns something new by actually seeing color, that new fact must be a non-physical fact. Therefore, the physicalist picture of the world is, while perhaps not strictly false, incomplete in an important way: it is incapable of accounting for the qualitative character of conscious experience. Thus, we must appeal to more than physics when describing a world that contains conscious creatures.

Here's a more formal presentation of the argument (taken from the SEP):

Premise P1Mary has complete physical knowledge about human color vision before her release.


Consequence C1Mary knows all the physical facts about human color vision before her release.
Premise P2There is some (kind of) knowledge concerning facts about human color vision that Mary does not have before her release.

Therefore (from (P2)):

Consequence C2There are some facts about human color vision that Mary does not know before her release.

Therefore (from (C1) and (C2)):

Consequence C3There are non-physical facts about human color vision.

This is, at first glance, a very plausible argument. Jackson's own conclusion was a version of epiphenomenalism: at the time of the article's publication, he held that whatever non-physical knowledge Mary acquired must lack any kind of causal efficacy, thus maintaining the causal closure of the physical universe. That seems to me to be a pretty desperate move, though, and apparently Jackson eventually agreed--he's since recanted this position, and now holds that there must be something wrong with the Mary case. I'm not sure if he's put any work into figuring out what it is, but other people certainly have. I'm going to more or less ignore all of them, as is my wont.

Here's what struck me when I was reading this argument today while preparing to lecture to the class on it: Jackson is deeply ambiguous, confused, or otherwise mistaken about what he means in (P1). The argument never even gets off the ground just because he's wrong about the kinds of things that Mary would be able to know from her particular position in her gray scale world. Let's tease this apart a little more.

What does it mean to say that Mary knows all physical facts about color perception? Presumably, just this: for every predicate, relation, or process P that relates to human color vision, if P is constrained by the laws of physics, then Mary knows P. This should be relatively non-controversial--"physical facts" are those (and only those) facts that are about the behavior of physical systems (and nothing else). The physicalist position is that the set of these facts is identical with the set of all facts that are necessary to explain the workings of the universe; that is, the physicalist position is the position that knowing all the physical facts amounts to knowing everything worth knowing. More narrowly, the physicalist position vis-a-vis color perception is just that knowing all the physical facts about color perception is both necessary and sufficient to give a complete account of how color perception works.

Good. We're homing in on the problem. The next question that we need to answer is this one: how do we go about learning physical facts? The physicalist "bite the bullet" style response to Jackson's argument just denies that Mary learns anything new when she's exposed to color for the first time--it asserts that if she knew all the physical facts, then she'd know what the experience was like. This is not very intuitive; we have a deep intuition that no matter how much I study some subject (via books, laboratory experiments, and so on), there are just some facts--like what it's like to see color--that just won't be accessible to me. That is, we have an intuition that there are some relevant facts that either can't be written down, or can't be discerned through objective experimentation: the what-it-is-likeness of color experience is, presumably, counted among these facts. This is the intuition that Jackson's argument exploits.

It's worth proceeding carefully here, though. Is saying that some particular fact F can't be written down or accessed through objective, third-person experimentation--that is, can't be described from a "view from nowhere"--equivalent to saying that F isn't a physical fact? Can all physical facts (to put it another way) be written down and accessed from a third-person viewpoint? Recall our definition of 'physical fact' above:

"Physical facts" are those (and only those) facts that are about the behavior of physical systems (and nothing else)
Let's rephrase the question, then: can all the behavior of every physical system be represented in third-person accessible formats? If we answer this question in the affirmative, we've adopted the position that Flannagan, in Consciousness Reconsidered, terms "linguistic physicalism," and there seems to be good reason to think that we've made a mistake somewhere in our reasoning. If we answer the question in the affirmative (that is), we've committed ourselves to the following position.

(LP) What it means for some fact F to be a physical fact is for F to be representable in some observer-neutral, third-person accessible form (e.g. public language).

That's a problem, though. If we adopt (LP), then Jackson's argument collapses into something that's trivially true (if not question-begging!).

(1a) Mary knows all linguistic (i.e. third-person accessible) facts about color perception.
(2a) Mary learns something new about color perception when she sees the rose.
(3a) Therefore, there are some facts about color perception that are not representable linguistically.

Of course this is true: it's part of what it means for something to be qualitative (that is, to be a conscious experience) that it's essentially private--that it's essentially accessible only from the first-person perspective. The question, then, becomes whether or not we are justified in adopting (LP); can we give an account of what's going on that doesn't require us to adopt it? Sure: we just have to allow that there might be some physical facts--facts about the behavior of some physical systems--that aren't capturable in third-person accessible representations. If we make this concession, then explaining what's going on in the Mary case becomes very easy: while black-and-white Mary has learned all the linguistically representable physical facts about color perception, this set of facts is not identical to the set of all physical facts about color perception--that is, there are aspects of the behavior of some relevant physical systems that cannot be captured from the third-person "view from nowhere." These facts, of course, are facts about what it is like to be in a certain physical state. To put it another way, there are facts about the state of Mary's own brain--which is, of course, a physical system--that can't be known from a third person perspective: she actually has to be in that state in order to know everything about it. When she's exposed to red for the first time, then, she's adding another bit of physical knowledge--which just is, recall, knowledge about the behavior of physical systems, which includes her brain--to her knowledge-base: that bit of knowledge, though, is one that is only accessible from the first-person standpoint.

Let me try to put this point as simply as I can. The problem with this thought-experiment is that Jackson is mistaken when he says that black-and-white Mary knows all the physical facts. What he means to say is that she knows all the linguistic physical facts--all the physical facts that can be accessed from the "view from nowhere." What Mary doesn't know is the set of physical facts--facts about the physical system that is her brain--that can only be accessed from the first-person viewpoint; she doesn't know what it's like to be in a particular physical state. That's what she learns when she leaves her black-and-white operating room.

To put it one more way, let me just say this. "Physical facts" is a term that refers not to a set of facts that is defined by a mode of access--that have in common something about how they can be known--but to a set of facts that is defined by the sort of system they deal with--that have in common a subject matter, not a kind of access. Physical facts are facts about the behavior of systems for which that behavior is totally describable in terms of the laws of physics, and it makes absolutely no difference (at least as far as we're concerned here) what the mode of access to those facts is. Some (many!) of the facts are expressable in observer-neutral language. Some are not. What matters is not this mode of access, but rather whether or not what is accessed is information about the behavior of a physical system.

Addendum: Please read the comment thread for more on this. Both Mark and Eripsa have given very insightful criticism and show that this argument needs refining. I've done my best to refine it below, and I might post an updated version later on. For now, though, the discussion in the comments is definitely worth following. Thanks to Lally, too, for providing vehement (and helpful) critiques off-thread.