Expert Disagreement as a Reason for Doubt about the Metaphysics of Mind (Or: David Chalmers Exists, Therefore You Don't Know)

Probably you have some opinions about the relative merit of different metaphysical positions about the mind, such as materialism vs. dualism vs. idealism vs. alternatives that reject all three options or seek to compromise among them. Of course, no matter what your position is, there are philosophers who will disagree with you -- philosophers whom you might normally regard as your intellectual peers or even your intellectual superiors in such matters – people, that is, who would seem to be at least as well-informed and intellectually capable as you are. What should you make of that fact?

Normally, when experts disagree about some proposition, doubt about that proposition is the most reasonable response. Not always, though! Plausibly, one might disregard a group of experts if those experts are: (1.) a tiny minority; (2.) plainly much more biased than the remaining experts; (3.) much less well-informed or intelligent than the remaining experts; or (4.) committed to a view that is so obviously undeserving of credence that we can justifiably disregard anyone who espouses it. None of these four conditions seems to apply to dissent within the metaphysics of mind. (Maybe we could exclude a few minority positions for such reasons, but that will hardly resolve the issue.)

Thomas Kelly (2005) has argued that you may disregard peer dissent when you have “thoroughly scrutinized the available evidence and arguments” on which your disagreeing peer’s judgment is based. But we cannot disregard peer disagreement in philosophy of mind on the grounds that this condition is met. The condition is not met! No philosopher has thoroughly scrutinized the evidence and arguments on which all of her disagreeing peers’ views are based. The field is too large. Some philosophers are more expert on the literature on a priori metaphysics, others on arguments in the history of philosophy, others on empirical issues; and these broad literatures further divide into subliteratures and sub-subliteratures with which philosophers are differently acquainted. You might be quite well informed overall. You’ve read Jackson’s (1986) Mary argument, for example, and some of the responses to it. You have an opinion. Maybe you have a favorite objection. But unless you are a serious Mary-ologist, you won’t have read all of the objections to that argument, nor all the arguments offered against taking your favorite objection seriously. You will have epistemic peers and probably epistemic superiors whose views are based on arguments which you have not even briefly examined, much less thoroughly scrutinized.

Furthermore, epistemic peers, though overall similar in intellectual capacity, tend to differ in the exact profile of virtues they possess. Consequently, even assessing exactly the same evidence and arguments, convergence or divergence with one’s peers should still be epistemically relevant if the evidence and arguments are complicated enough that their thorough scrutiny challenges the upper range of human capacity across several intellectual virtues – a condition that the metaphysics of mind appears to meet. Some philosophers are more careful readers of opponents’ views, some more facile with complicated formal arguments, some more imaginative in constructing hypothetical scenarios, etc., and world-class intellectual virtue in any one of these respects can substantially improve the quality of one’s assessments of arguments in the metaphysics of mind. Every philosopher’s preferred metaphysical position is rejected by a substantial proportion of philosophers who are overall approximately as well informed and intellectually virtuous as she is, and who are also in some respects better informed and more intellectually virtuous than she is. Under these conditions, Kelly’s reasons for disregarding peer dissent do not apply, and a high degree of confidence in one’s position is epistemically unwarranted.

Adam Elga (2007) has argued that you can discount peer disagreement if you reasonably regard the fact that the seeming-peer disagrees with you as evidence that, at least on that one narrow topic, that person is not in fact a full epistemic equal. Thus, a materialist might see anti-materialist philosophers of mind, simply by the virtue of their anti-materialism, as evincing less than a perfect level-headedness about the facts. This is not, I think, entirely unreasonable. But it's also fully consistent with still giving the fact of disagreement some weight as a source of doubt. And since your best philosophical opponents will exceed you in some of their intellectual virtues and know some facts and arguments, which they consider relevant or even decisive, which you have not fully considered, you ought to give the fact of dissent quite substantial weight as a source of doubt.

Imagine an array of experts betting on a horse race: Some have seen some pieces of the horses’ behavior in the hours before the race, some have seen other pieces; some know some things about the horses’ performance in previous races, some know other things; some have a better eye for a horse’s mood, some have a better sense of the jockeys. You see Horse A as the most likely winner. If you learn that other experts with different, partly overlapping evidence and skill sets also favor Horse A, that should strengthen your confidence; if you learn that a substantial portion of those other experts favor B or C instead, that should lessen your confidence. This is so even if you don’t see all the experts quite as peers, and even if you treat an expert’s preference for B or C as grounds to wonder about her good judgment.

Try this thought experiment. You are shut in a seminar room, required to defend your favorite metaphysics of mind for six hours (or six days, if you prefer) against the objections of Ned Block, David Chalmers, Daniel Dennett, and Saul Kripke. Just in case we aren’t now living in the golden age of metaphysics of mind, let’s add Kant, Leibniz, Hume, Zhu Xi, and Aristotle too. (First we’ll catch them up on recent developments.) If you don’t imagine yourself emerging triumphant, then you might want to acknowledge that the grounds for your favorite position might not really be very compelling.

It is entirely possible to combine appropriate intellectual modesty with enthusiasm for a preferred view. Consider everyone’s favorite philosophy student: She vigorously champions her opinions, while at the same time being intellectually open and acknowledging the doubt that appropriately flows from her awareness that others think otherwise, despite those others being in some ways better informed and more capable than she is. Even the best professional philosophers still are such students, or should aspire to be, only in a larger classroom. So pick a favorite view! Distribute one’s credences differentially among the options. Suspect the most awesome philosophers of poor metaphysical judgment. But also: Acknowledge that you don't really know.

[For more on disagreement in philosophy see here and here. This post is adapted from my paper in draft The Crazyist Metaphysics of Mind.]