Through GE Moore at Cambridge, he discovered Leibniz and Boole, and became a logician. Through Alfred Whitehead's influence, he travelled to Europe and met Gottlob Frege, who believed in a wholly logical language (and was borderline insane) and Georg Cantor, the inventor of "set theory" (who was locked up in an asylum) and a mass of French and German mathematicians in varying stages of mental disarray. Back home he and Whitehead wrestled with their co-authored Principles of Mathematics for years, endlessly disputing the foundations of their every intellectual certainty, constantly harassed by Russell's brilliant pupil Wittgenstein.
If the subject matter seems a little arid, with its theories of types, paradoxes and abstruse language (calculus ratiocinator?), and if its recurring theme of how logic and madness are psychologically intertwined seems a touch gloomy, don't let that put you off. Logicomix tells its saga of human argumentation with such drama and vivid colour that it leaves the graphic novel 300 (Frank Miller's take on the Battle of Thermopylae) looking like something from Eagle Annual.
Thursday, September 3, 2009
Sunday, August 9, 2009
Wednesday, July 29, 2009
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.
|Premise P1||Mary has complete physical knowledge about human color vision before her release.|
|Consequence C1||Mary knows all the physical facts about human color vision before her release.|
|Premise P2||There is some (kind of) knowledge concerning facts about human color vision that Mary does not have before her release.|
Therefore (from (P2)):
|Consequence C2||There are some facts about human color vision that Mary does not know before her release.|
Therefore (from (C1) and (C2)):
|Consequence C3||There 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.
That's a problem, though. If we adopt (LP), then Jackson's argument collapses into something that's trivially true (if not question-begging!).
Monday, January 12, 2009
It's important to emphasize that the truth-bar is almost never entirely full, except in some very special cases (e.g. conscious states to which you have immediate, incorrigible access). Take the case of a proposition based on basic sensory information--e.g. 'there is an apple on my desk.' In normal circumstances--good lighting, I can feel and see the apple, other people see the apple too, &c.--I; have very good reason to suspect that there really is an apply on my desk; the truth-bar for that proposition is (say) 99% full. Still, there are potential defeaters here: it might be the case that I am actually in some kind of Matrix scenario, and therefore it might be the case that there is no desk or apple at all. Still, based on other (fairly strongly justified) beliefs I have about the world, this Matrix scenario seems rather unlikely--that is, the truth-bar for 'I am in the Matrix' is very, very close to empty (though not entirely empty, as the proposition is still a logical possibility). Because this defeating proposition ('I am in the Matrix') has a very weak truth-bar, it doesn't weigh very heavily in my epistemic considerations--it's enough to keep the bar for 'there is an apple on my desk' from being 100% full, but that's about it.
This goes sharply against established epistemic tradition, according to which the primary goal of epistemology is truth. If we define truth as a 100% full bar, there are going to be very few propositions (aside from tautologies like 'all black things are black') that will enjoy an entirely full bar. Instead, the right way to think about epistemology--and about our epistemic responsibilities--is as a quest for justified belief, a quest for a reasonably full bar. What counts as 'reasonably full' is, again, going to vary based on contextual variables: when the stakes are rather low, I might assent to a proposition when (say) the truth bar is over 50% full. This might be the case when, for example, a friend tells me that there is a brown dog outside my house; I believe him, and if someone asks me 'is there a brown dog outside your house?,' I will be inclined to answer in the affirmative. My friend might be wrong or lying, but the stakes are low and I have very few strong defeater propositions in play--few good reasons to suppose that my friend speaks falsely, in other words. In more important cases (such as when engaged in technical philosophical deliberation, or when designing a passenger jet), I'm going to be inclined to withhold assent from propositions until the bar is almost entirely full: the consequences for assenting to the wrong belief are so potentially dire, that I will demand a higher standard of justification, investigation possible defeaters more thoroughly, &c.;
The emphasis here is on the contextually-dependent nature of epistemic action; rather than doing a lot of complex deliberating for every possible belief change entirely in our heads, we "offload" a certain amount of the work into the existing epistemic environment; that is, we use the existing epistemic landscape to simplify our decision-making by heuristically assigning various "values" to propositions that are related to the one under consideration, and performing a kind of Bayesian calculation to get a rough approximation of truth or falsity. We can make a direct parallel here with other work being done in extended/embedded cognition and extended mind theses--in just the same way that we use external props (e.g. written notes) as props to support certain cognitive processes (e.g. memory), we use our intuitive grasp of the existing epistemic landscape as a prop to support our own decision making. I call this approach "contextually embedded epistemology."