While waiting for reader submissions, I suppose I will start things off. My selection today for "underappreciated philosophy" is Gregg Rosenberg's 2005 Oxford University Press book, A Place for Consciousness: Probing the Deep Structure of the Natural World.
I'm not sure that Rosenberg's book counts as underappreciated simpliciter. It seems to be appreciated by a certain type of philosopher (it has been cited 74 times according to Google Scholar, mostly by people sympathetic with panpsychism and Russellian/Neutral Monism). My sense is that it is underappreciated by philosophers at large, however, and by people interested in the metaphysics of consciousness and causation.
I guess I will begin with a little background on Rosenberg. He was, apparently, a student under (CORRECTION: with) David Chalmers back when Chalmers was at Indiana. According to the back flap of the book, Rosenberg left the discipline after grad school, patented some form of technology, started a venture-capital funded company, and sold it (for a lot of money presumably) in 2001. He then went back to his dissertation, wrote it up as a book, and got it published through OUP. Pretty remarkable.
Anyway, here's why I think the book is underappreciated. Here's a first pass: it's a book that more or less singlehandedly caused me, a one-time staunch physicalist, to become a mind-body dualist. I know this is just a personal anecdote, but still, I think it is worth dwelling on for a moment. I started out my undergraduate career doing philosophy of mind at Tufts with Dan Dennett, one of the hardest-core physicalists out there. I was completely on board with him. Dualism had always seemed silly to me, and completely at odds with any scientifically respectable account of reality. And reading David Chalmers' book The Conscious Mind didn't sway me at all. The Zombie Argument -- the argument that Chalmers' entire book was based on -- immediately struck me then (just as it does now) as utterly question-begging. It seemed to me that will share Chalmers' intuition that zombies are conceivable, and so metaphysically possible, if one antecedently finds dualism attractive. Since I didn't find dualism attractive in the slightest, the Zombie Argument seemed silly to me.
Anyway, I more or less remained a physicalist...until I read Rosenberg's book. What was it about the book that did it for me? What was it that converted me into dualist? The first preface of Rosenberg's wonderful premise hits the nail on the head. Rosenberg writes on p. ix:
My intention in writing this book was to create something whose importance lies beyond the details of its arguments. I myself consider this primarily a book of ideas. Of all my hopes, my dearest is this: that A Place for Consciousness should provide inspiration to those like me who were raised with the physicalist orthodoxy, accepting it but not fully comfortably, whose disquiet always has been silenced at the end by the baffling question: How could it be otherwise? I believe this book points to a place in the space of philosophical ideas where something truly new and interesting exists. I am, above all, trying to lead readers to that place so that they can return without me to explore it on their own...
...
Both Russell and Whitehead argued that physical science reveals only a structural aspect to nature. If physics is all structure, it is natural to suppose that intrinsic properties related to the intrinsic properties we experience in consciousness are the intrinsic content of the physical. The suggestoin raises several questions: (1) Why should the intrinsic properties of a physical system be experiential? (2) Why do they exist above the level of the microphysical...? (3) Why should they form a unity of the kind we are acquainted within consciousness? and (4) Why should phenomenal content, as the intrinsic content of the physical, correspond so closely to the information structure within the brain? By constitutively linking experience and causation, I answer these questions from first principles. (my bolding/italics)
The sections I have bolded here are key. Professional philosophers today seem to emphasize rigor above all else. This has long puzzled me (see here, here, here, and here), given that most of the Greats (the Platos, the Aristotles, the Kants, etc.) almost "to a T" went beyond what they could rigorously show, opening up important new ways of thinking in the process. Kant never successfully established categorical normativity -- but so what? He was the first person to even get us thinking about it explicitly. And that was a great advance.
Rosenberg's book accomplished something similar for me. In contrast to other work defending some form of dualism (such as Chalmers' work), Rosenberg's book painted the first picture of reality to me that made dualism seem more plausible than physicalism. This was in large part because -- and here's the real thing that gripped me about his book -- Rosenberg shows (pretty convincingly in my view) that it is not just consciousness that science has trouble accounting for; science cannot account for causation either. And it can't account for it for the same simple reason: science deals with structure, whereas consciousness and causation -- properly understood -- both seem utterly simple and intrinsic. (note: it was really the second half of Rosenberg's book -- the part on causation, not the first part (on consciousness) -- that "got" me)
Indeed, Rosenberg got me to fundamentally "see the world in a different way" -- a way in which the idea of there being intrinsic qualities (such as primitive consciousness and causation) just have to be a part of any remotely plausible metaphysical picture of reality. For here, essentially, is what the book got me to see. First, every substance or property (note: I think there is no coherent distinction between substances and properties) we would ordinarily call physical -- mass, charge, the weak and strong nuclear forces, books, motorcyles, whatever -- are all fundamentally relational, or structural, in nature. An electon just is defined in terms of a particular function. So is mass. So is charge. Etc. But -- and this is the second thing that Rosenberg's book got me to see -- you can't have relations without relata. There have to be intrinsic properties "behind" the relations we observe (as physical things) for there to be those relations in the first place. This is, by the way, something that I think Kant knew too (with the phenomena/noumena distinction), and which Daniel Stoljar has focused on recently as well (though I think he is wrong in his analysis of its implications).
So, anyway, it wasn't the detailed arguments of Rosenberg's book that got me. I suspect some (or even much) of his own theory of causation, and how consciousness emerges from large-scale causal nexus in the brain, is false. Be that as it may, Rosenberg got me to thinking, for the very first time -- on broadly Kantian grounds, but also simply focusing on the phenomena of consciousness, causation, and structure -- that any world at all (let alone ours) just has to be dualistic in nature: at least in the sense of there being (A) "physical"/structural properties that can be measured by science, and (B) intrinsic/non-structural properties which cannot. (Readers might also note that these are ideas I explore and put to use in the new metaphysical model of the world and quantum mechanics that I developed in my recent Phil Forum paper "A New Theory of Free Will". Among other things, I argue that *any* world whatsoever must be constructed on a hardware/software duality that maps onto precisely the structural/intrinsic distinction that motivates mind-body dualism).
That, in a nutshell, is why I am a dualist today. I think Rosenberg's point is fundamentally right, that it persuasively shows what's wrong with physicalism, and that it persuasively shows what is fundamentally wrong with all purported defenses of physicalism, including the phenomenal concept strategy (which I agree with Chalmers to be a blind alley: either phenomenal concepts can be made sense of in relational/physical terms, in which case they fail to account for the intrinsic/non-relational elements of experience, or else they are understood in a non-physical way, in which case the strategy is self-defeating). And that is why I think Rosenberg's book is underappreciated.