A Place for Consciousness

Reinventing nature is hard work. I could not have done even the little bit of it that I do here without a lot of support from others, both intellectually and emotionally. My intellectual interests and capacities have grown slowly, and my debts are owed to many. My time at Indiana University has been wonderful and invigorating, and the path that took me here was long and winding. I want to begin by acknowledging my debts to those who helped to steer me along that path, so that I finally found my way to philosophy.

I would like to thank Anthony Nemetz for first introducing me to the world of intellectual questioning when I was an undergraduate business major. His demanding eloquence was a revelation to me at that time in my life, as nothing in my background had previously exposed me to intellectual life.

I would like to thank Douglas Hofstadter, whose books "Metamagical Themas" and "Gödel, Escher, and Bach" serendipitously fell into my hands about that same time, steering me towards the philosophy of mind and cognitive science. My interactions with him here at Indiana University have been challenging and provocative.

I owe my deepest debts from my time at the University of Georgia to Donald Nute. Not only did he direct my master's thesis when I was studying Artificial Intelligence there, but he has encouraged and supported me every step of the way since: first in my decision to move into philosophy, and then by encouraging me to come to Indiana University to do my Ph.D..

I would like to thank Ned Block for the helpful conversations we had during my time at MIT in 1991. His insistence that ideas as unusual as mine need to be very strongly motivated has always stuck with me, acting as a burr whenever I have been tempted to cut corners in my writing or thinking.

When I arrived at Indiana, I was already convinced of the explanatory gap between the facts of consciousness and the physical facts, and suspected that there must be a deep link between consciousness and causation. I was extremely fortunate to come here with those interests at the same time that David Chalmers was finishing his dissertation on the very same topic, working through some very similar intuitions. That first year with David was very energizing, as well as exasperating. It was he who convinced me that, given my understanding of the problem, intellectual integrity required me to give up my commitment to physicalism; he also helped me to see that giving up on physicalism was a very different thing from giving up on explaining consciousness. I can scarcely say what this work would look like without his feedback and patience over the last few years, nor could I be sure it would even exist. I am, at heart, an intellectual conservative and a physicalist, and many times I felt discouraged by the distance I was traveling from my intellectual home. Without David's continued assurance that the work was interesting and worthwhile, it would have been very tempting to take the easier path.

The faculty at Indiana have also been very supportive. I would especially like to thank the members of my committee. I would like to thank Mike Dunn for taking the time to read each chapter of this dissertation over the last six months, and for providing his comments. The work would be much poorer without that feedback. Most importantly, I would like to thank him for being liberal enough to let me pursue these ideas.

I would like to give special thanks to Anil Gupta, not only for the helpful discussions we have had over the years, but for providing me with a role model for the way a true philosopher should conduct himself. His probity, patience, gentleness, and integrity have been an inspiration to me.

I would like to thank Tim O'Connor for his enthusiasm, incredible energy, and time at our long lunches. His intellectual support the last few years provided much needed reassurance for me here in Bloomington, reassurance that helped me to keep myself on track.

In the last year Indiana was very fortunate to add Brian Cantwell Smith to its cognitive science program, and I was fortunate to add him to my committee. Like me, Brian is a computer scientistcumphilosopher, and the perspective that gives is difficult to put into words. I am especially grateful to Brian for the long hours he invested trying to help me improve my writing. Without his help, this already difficult piece of work would be almost unreadable.

As anyone who has completed an advanced degree knows, graduate students learn more outside of class from our peers than we do inside class from professors. Nothing can substitute for heated arguments over beer that last late into the night. I almost have too many of these informal debts to list, mostly to my fellow graduate students in the philosophy department. I would like to single out for special thanks a handful that have provided especially memorable philosophical conversation over the last few years: Tony Chemero, Diarmuid Crowley, Stephen Crowley, Eric Dalton, Craig DeLancey, Jim Hardy, and Adam Kovach. I would also like to thank the Indiana University philosophy faculty for their support over the years, but most especially David McCarty and Paul Spade.

Here in Bloomington, my warmest and most deeply felt thankyou's are owed to Leslie Gabrielle. Not only has she provided me with an important intellectual sounding board, but her friendship and support over the last four years have been priceless on a personal level. Work in graduate school in a highly specialized field can sometimes be isolating, and the connectedness she provided for me was desperately needed. I would not have gotten through some of the rougher times over the last few years without her. Along those same lines, I would like to thank my friends from back home in Atlanta, especially Allen Domenico and Bob Lauth for their support and encouragement. The most precious friendships are the ones that you know will last a lifetime.

Finally, my most speechless thanks are reserved for my parents, Sally and Donald, and for my brother Alan. They have made an investment in my life and identity that is truly staggering to consider. Every word in here reflects their love.

Preface

So, why write about consciousness and causation?

Those two problems are each tough philosophical chestnuts individually, and it's not clear why thumping them together would help us to crack either one of them. The burden of this dissertation is not only to argue that they need to be treated together, but to actually show, in a very concrete way, how they in fact do go together. I argue, in effect, for the radical thesis that conscious experience is an aspect of causation itself, and one that is absolutely vital to it. And I argue that all this is incompatible with physicalism while, nevertheless, being perfectly compatible with physical science. This is a tough ledge to walk in the current intellectual climate. Accordingly, the aims I have for this work exist at several levels, each a bit more ambitious than the previous.

At the least ambitious level, I wish for this dissertation to provoke readers. Within it I defend a bevy of ideas that are at odds with the physicalist orthodoxy within the philosophy of mind. I believe the world picture I begin to flesh out in this work should at least make physicalists uncomfortable, as it brings to the forefront the possibility that a dual aspect or property theory needn't be supernatural, naturalistically untenable, or hopelessly vague. My chief hope for this work is that, after reading it, no physicalist should be able to rest comfortably with an easy assumption that any alternative view must lead to empirical absurdity.

At the next level, I hope that this dissertation challenges readers. Possible challenges come on two fronts. On one front, readers who remain convinced that physicalism is likely true need to find better arguments for it than currently exist. Almost all parties agree that embracing physicalism requires biting some large bullets, but physicalism's strongest support has been the widespread intuition that rejecting it seems to lead to even greater absurdities than does accepting it. Especially, many assert that physicalism is required to guarantee the causal relevance of experience.

One challenge coming out of this dissertation is to show vividly that, if one wishes to hold onto this physicalist shibboleth, one's background theory of causation needs to be fully articulated. For what this dissertation does above all else is present a case that, under at least one possible and substantial view of causation, a view that seems compatible with physical science, the physicalist shibboleth turns into a chimera. Not only does experience turn out to have a place in the causal order even if physicalism is false, I make a case on grounds completely independent of the mindbody problem that it, or something nearly exactly like it, is required for causation to exist.

A second kind of challenge exists for those less sympathetic with physicalism: many open questions remain at the end of this work, and these questions present the possibility for an actual empirical and philosophical research program. The challenge is to see if these open questions lead to fruitful avenues of research, or if, instead, they show that the ideas here lead down a dead end.

At the third and most ambitious level, I hope that this dissertation may actually convince some readers. While I propose some unusual ideas here, I try very hard to accompany my proposals with substantive philosophical arguments. The generic position I suggest, which I call Liberal Naturalism, is currently a minority position, but it at least has contemporary precedents within philosophy, especially in the work of philosophers like David Chalmers and Frank Jackson. My more specific proposal, which I call The Carrier Theory of Causation, involves experience directly in the fundamental causal character of the world. This more specific proposal seems very radical when stated baldly, but I have not pulled a rabbit out of a hat, nor have I motivated it by appeal to any strange aspects of quantum mechanics. I have tried to work with acceptable rigor using only some fairly mundane intuitions about the world, and about consciousness. And I have tried, always, to respect science. While the case I make is not airtight, few philosophical or scientific arguments ever are. It is, nevertheless, highly detailed and rationally motivated. When viewed as a whole, I think it has a pleasant kind of elegance, and promises to be potentially fruitful. I consider those properties its greatest strengths.

Finally, I want to say that this dissertation is intended to be as much philosophical narrative as it is a collection of philosophical arguments, although arguments are produced in abundance. For that reason, the argumentative structure of this dissertation should, in some respects, be viewed as secondary to it. My chief concern when writing it was to convey a possible way of looking at the world. In that sense, I hope the reader comes away with a feeling that there is a cosmological vision that is worth thinking about lying in the vicinity of the ideas here, and that it promises to make the world a rich and interesting place if true. Within philosophy, its closest kin is to be found in the process philosophy descended from Bergson and Whitehead, and I owe Whitehead a debt for inspiration.

The most important thing to know about this dissertation before you begin reading it is that, although it is long, it is possible to take a short tour and still come away with the main thrust of argument. For those interested in the short tour, I recommend reading chapters one through three to understand the setup of the problem. From there, skip to chapters ten and eleven, and then to chapters fourteen and fifteen. If the short tour has peeked your interest, go back and read the rest. Especially, those who believe in the adequacy of one or all of the standard replies to the antiphysicalist arguments should read Part I. Part II gives more thorough reasons than the short tour does for believing that someone interested in understanding consciousness should look hard at causation itself. Finally, a full and careful reading of Part III is interesting independently of one's views on the mindbody problem, especially the detailed treatment of receptivity in chapter twelve, and the arguments against actualism, and for the reducibility of spacetime, in chapter sixteen.

Chapter 1

Liberal Naturalism

1.1 The Sliding Tile Puzzle

The mystery of consciousness is both profound and exciting. To anyone who has thought hard and long about it, the questions it raises linger and deepen upon reflection. Eventually, they seem to transcend specific questions about consciousness, touching insecurities about our understanding of nature herself. One begins to suspect that solving the puzzle of nature may not be like piecing together a jigsaw puzzle, with pieces nestled stably in their proper place. To solve the puzzle of conscious experience, we may have to view the project as being more like trying to solve a sliding tile puzzle.

What is a sliding tile puzzle? A sliding tile puzzle consists of a rectangular frame with movable tiles within it, each tile decorated with a different part of the puzzle. Initially the tiles are scrambled, and the goal is to unscramble them to retrieve the puzzle's picture. The rectangle contains one empty space, and the puzzle solver must rearrange the tiles by sliding them into and out of this empty space. By doing this, the puzzle solver hopes to undress the confusion and reveal the puzzle's ornamental face.

Sliding tile puzzles contain a trap, a seductive property that lures the unsuspecting. Often the puzzle solver can bring order to almost all of the puzzle, perhaps fitting every piece into its proper slot except the last two tiles. These last two tiles might be transposed, for instance, each in the other's slot. The trap is sprung when the puzzle solver holds stubbornly to the hard won order in the rest of the puzzle, afraid that disturbing it too much will cause it to disappear, never to return. Seduced by the order already in the puzzle, the puzzle solver searches desperately for a minimally disruptive solution, one that places the pieces without disturbing the rest of the puzzle very much.

Unfortunately, we cannot usually solve tile puzzles this way. To fit the final two pieces in place one has to regress first, and then rebuild the old order from a new direction. The trap is that, since the puzzle solver flinches at every challenge to the old order, the ideal of completing the puzzle becomes a hopelessly elusive goal. The irony is that the hard won old order will eventually reappear within a more completely ordered context, but only if it is first challenged and, temporarily, relinquished.

In writing this book, I have approached the problems of consciousness and causation like they are the final two pieces in a sliding tile puzzle. I wish to help put them into their proper places within a naturalist framework, and believe that sound arguments exist that this achievement will carry a cost. This cost will require ruffling, just a bit, the hard won order science has brought to our understanding of nature. The cost is this: we must concede that materialism is an inadequate version of naturalism.

Materialism is an ontological thesis. Within metaphysics, ontology is the study of what exists, with particular emphasis on the different ways of existing possessed by different kinds of things. Traditionally, philosophers studying ontology have been very much concerned with identifying fundamental categories of properties, objects, events, or processes whose existence they could see as grounding the existence of other kinds of things. Materialism (which I will also call physicalism) is the thesis that all other kinds of things derive their existence from the existence of the physical. Among these "other kinds of things" are minds, value, the good, justice, beauty, and meaning.

Materialism has been a dominating influence in this century, and as a working hypothesis it has severely constrained the avenues of explanation open to scientists and philosophers. The constraint it provides has proved very fruitful in the empirical sciences, and a bit less so in philosophy. My own opinion is that its overall effect has been positive. Because of it, we have uncovered a great deal of the startling beauty and subtle order in the puzzle of nature.

I have great intellectual admiration for, and sentimental attachment to, materialism. And yet, in this book I will argue that materialism is false. The book has a positive thesis also. Despite the failure of materialism, I do not believe we should abandon the goal of naturalism, as we should not identify naturalism with materialism. We do best when we think of naturalism as a methodological requirement. It requires that we place human beings in the world without special, ad hoc assumptions that are discontinuous with what else the natural sciences tell us about nature.

Among naturalists, those such as McGinn (1989) occupy one extreme. They are so impressed by the difficulty of the problems associated with explaining consciousness that they have concluded that it is just not soluble. Their opponents on the other extreme have dubbed them, a bit derisively, "The New Mysterians". These opponents sometimes continue to hold out for more traditional science (Churchland & Churchland, 1990; Flanagan 1992), and sometimes simply deny the existence of the phenomenon at issue (Dennett 1988; Wilkes 1988). We can call those on this other extreme, again a bit derisively, "The GungHo Reductionists".

The position I will begin to develop in this dissertation is a Liberal Naturalism. Like materialism, Liberal Naturalism holds that the world is composed from a single set of fundamental properties and entities, related by a single set of fundamental laws. However, unlike materialism, Liberal Naturalism holds that some of these properties and laws are not physical properties and laws. I am a Liberal Naturalist, as is David Chalmers, an earlier version of Frank Jackson, Nagel in some of his moods, and Wilfrid Sellars on some ways of reading his work. The Liberal Naturalists recognize the possibility that what is described by physics, and what subsists in physics, may not circumscribe nature's limits. That allows them comfortably to step outside the standard physicalist ontology, while retaining a naturalist world view. From The GungHo Reductionist and New Mysterian standpoints, this is something of an endaround⁽¹⁾.

The positive project in this book is to identify what these nonphysical properties are; to explain why they should exist; and to give reasons for believing that a story exists showing how they fit cohesively within a scientific and naturalistic world view. I will pursue these goals by introducing a substantive view of causation that goes beyond the physical. If successful, this rich picture of causation will provide the bridge that takes us from the physical to consciousness. The view I will develop respects the effective closure of the physical. I attempt to complete our views of causation by adding elements that are complementary to the structure of activity described by physical science, and, for that reason, are every bit as essential to it as the physical.

1.2 The topics: causation and consciousness

Causation  The human body is a wondrous system, a marvel whose subtlety and complexity test the word "machine", making it sometimes seem like a recklessly inadequate characterization. Natural science tells us that the body is made ultimately of very tiny and exotic physical entities, and we know that it consists in the motions of, and interactions among, delicately layered physical structures. Our bodies are spatiotemporal organizations of these tiny entities, driven by an enormous number of microphysical interactions between and among them.

According to physical theory, the entire being of these entities consists in the active dispositions that produce their intrinsic dynamics, and their intimate couplings. The mystery of consciousness is the question of why this assembly, this whirlwind of causation, should ever feel. Why cannot this causation go on without feeling, without sensation, without experiencing at all? Viewed in the large, these finely layered patterns are dynamical wonders, but it is hard not to wonder why the dynamics should be conscious. Causation produces motion, but why should a congerie of motion, however complex, ever feel? Many working philosophers of mind consider the task of finding an answer to this fundamental question the greatest obstacle to the task of naturalizing the mind.

A recent resurgence  The problem of consciousness is currently a very live topic of interdisciplinary debate. New journals devoted to the topic of consciousness, such as The Journal of Consciousness Studies and Psyche, have appeared in the last few years. In 1987, Ray Jackendoff ventured a computational analysis of consciousness in his book Consciousness and the Computational Mind. Marcel and Bisiach's anthology Consciousness in Contemporary Science (1988) presaged and helped to legitimize the growing scientific interest in the topic, as did Bernard Baar's substantive proposal about the functional and biological organization of consciousness in A Cognitive Theory of Consciousness (1988). More recently, major books on the topic by Nobel laureates like Gerald Edelman (1989) and Francis Crick (1994) have lent scientific prestige to the topic.

Within contemporary analytic philosophy, a slow but steadily building discussion existed in the 1970's and 1980's, provoked largely by contemporary antiphysicalist arguments. The key figures producing this pressure were Saul Kripke (1972), Thomas Nagel (1974), and Frank Jackson (1982). In the late 80's, William Lycan presaged the philosophical resurgence of the topic with his book titled simply Consciousness.

The book that ultimately broke the dike was Daniel Dennett's flamboyantly titled, and popularly successful, Consciousness Explained (1991). Dennett galvanized forces on all sides through his ingenious efforts attempting to explain consciousness by contentiously arguing it out of existence. Though widely read, Dennett's work has garnered more opposition than conversions.

I believe another recent book, David Chalmers' The Conscious Mind (1996), marks a modern watershed of sorts. The Conscious Mind succeeded in systematizing the dispersed and often sketchy versions of antiphysicalist arguments, expressing them within a powerful and perspicuous metaphysical framework. While the logic and metaphysics underlying these arguments stand to be refined even further, the conclusions at stake seem to be these. First, Chalmers argues that we have very good reasons to believe that an inprinciple explanatory gap exists between explanations in the physical sciences, and the facts about consciousness. These facts include even the seemingly brute fact that consciousness exists. Second, he argues that the existence of such a gap has ontological repercussions, and cannot be dismissed as a mere epistemic shortcoming. A theory's ontological completeness is bound to its explanatory power by unbreakable chords. In the rest of this book, I use the term antiphysicalists to refer to the group of philosophers who, like me, accept these conclusions.

After defending this negative thesis, Chalmers suggests that we may explain consciousness even if physicalism is false. When reductive explanation fails, he points out, we may turn to nonreductive explanation. The physical facts would play a large and essential role in such an explanation, but they would not be the whole story. In some ways the present book is a sequel to Chalmers' book, taking another few steps down the road of explaining consciousness within a nonreductive framework.

Consciousness  Given all this commotion, some readers may wonder what it is that I will be trying to explain. "Consciousness" is a multiply ambiguous term⁽²⁾, and not all senses of the term pose equally severe problems. This book focuses on what philosophers call phenomenal consciousness, but, unfortunately, no easy way to define phenomenal consciousness seems at hand. An understanding of what consciousness is is as much a matter of acquaintance as definition. At best, one can call attention to it in an increasing level of detail. I will tarry over the task for only a little while here. Along the way, I cite more thorough sources that interested readers are encouraged to turn to for more detail.

The most succinct way to convey the meaning of the term is through a phrase popularized by Thomas Nagel. A creature's phenomenal consciousness is responsible for the facts concerning what it is like to be that creature. For instance, part of what it is like to be a visually normal human being is for purple things to visually appear in a certain way, as having a certain kind of visual quality. Once one becomes aware of these visual qualities as qualities, one may naturally wonder what the colors from a larger color space look like. For example, some birds discriminate color more finely than any human. What is the experience like when these birds see the extra colors presumably available to them? Once we know about their ability, a question about the character of their conscious experience remains. Similarly, just as human visual sensations are different from human auditory sensations, one can wonder what a bat's echolocation is like for it; one may also wonder what the qualities and sensations associated with a manta ray's sensing of electromagnetic currents on the ocean floor are like. At the extreme, one may even wonder, however implausibly, whether there is anything at all that it is like to be these creatures. Perhaps they are unconscious automatons, all "dark inside"?

All of these wonderings seem to involve legitimate questions about matters of fact. Solving the mystery of consciousness requires understanding just what kind of facts these are. Are they ordinary physical facts, explainable in the same basic way that other physical facts are explainable? This book will ask: given all the physical facts the facts about the motion and structure of bodies why are there facts like these at all?

Each of these wonderings addresses an informational deficit in our knowledge of the world. The information about the character of these qualities constitutes phenomenal information for subjects of experience.⁽³⁾ Additionally, the exact organization of the qualities of experience, and perhaps even their character, seems to be very responsive to conceptualization. One sees this phenomenon when staring at visual illusions like the Necker cube: the qualitative experiences associated with seeing its face as oriented upward or as oriented downward are very distinct. This suggests a location for the world's repository of facts concerning phenomenal consciousness. For a particular creature, the facts concerning what it is like to be that creature arise from (i) its capacities for obtaining phenomenal information in the first person, and (ii) its way of conceptualizing the world.⁽⁴⁾

Moving just slightly beyond Nagel's slogan, one may deliver longer descriptions of the intended target. The following paragraph by Brian Loar (1997) does a good job of concisely expanding the slogan, "What it is like to be...."

On a natural view of ourselves, we introspectively discriminate our own experiences and thereby form conceptions of their qualities, both salient and subtle. These discriminations are of various degrees of generality, from small differences in tactual color experience to broad differences of sensory modality, e.g. those among smell, hearing and pain. What we apparently discern are ways experiences differ and resemble each other in respect of what it is like to have them. Following common usage, I will call those experiential resemblances phenomenal qualities; and the conceptions we have of them, phenomenal concepts. Phenomenal concepts are formed "from one's own case". They are typedemonstratives that derive their reference from a firstperson perspective: 'that type of sensation', 'that feature of visual experience'. And so thirdperson ascriptions of phenomenal qualities are projective ascriptions of what one has grasped in one's own case: 'she has an experience of that type.'

At the next higher level of detail, one can move on from descriptions like this by cataloging varieties of phenomenal experience. By asking the reader to attend to varieties of consciousness available in his or her own case, such efforts hope to direct and refine each reader's awareness of the subject matter. Chalmers engages in this sort of approach in the first chapter of his The Conscious Mind. He calls attention to, and gives short accounts of, the fascinating variety of phenomenal content found in experiences as diverse as: visual experiences, auditory experience, tactile experiences, olfactory experiences, taste experiences, experiences of temperature, pains, other kinematic and proprioceptive sensations, mental imagery, conscious thought, emotions, and the sense of self. Such catalogs are often effective at making the subject matter vivid.

At the most extreme level of detail one can isolate the meaning of 'phenomenal consciousness' by comparing and contrasting it with other senses of the term 'consciousness'. The most detailed contemporary exposition of the meaning of the term seems to be in Charles Siewert's (1994) Understanding Consciousness. Siewert delves into extreme detail, with much care, in an attempt to isolate the sense of the term that picks out the mystery, drawing it out from its hiding place among the other senses of the term. His exposition runs over two hundred pages, and I recommend it to readers who are hungry for further clarification.

1.3 The structure of the book

As the discussion of phenomenal consciousness attempts to progress, new proposals all flounder on the same basic problem: naturalized explanations of consciousness seem forced to postulate unexplainable identities between conscious states and the ontology of the proposed theoretical machinery. Some proposals claim that conscious states are primitively identical with certain kinds of computational states (e.g., JohnsonLaird 1988); others claim that they are primitively identical with biologically based brain states (e.g., Kinsbourne 1988); still others claim that conscious feelings are identical to special kinds of representational contents (e.g., Tye 1995); and so on. Since each of these features is at least arguably present in the one type of consciousness we have access to, our own, and since none of the proposed theories can establish their explanatory power without first appealing to the contentious identities, adjudicating between them is as difficult as reliably generalizing from them.

The sticking point seems to be that what we know about physical causation just does not seem to contain, even implicitly, anything that would ground the possibility of conscious experience. This wellknown "explanatory gap" between our physical image of the world and conscious experience forces theorists to treat these identities as primitive, and these, in turn, vitiate the explanatory force of the proposals that use them. Our ontological commitments are embedded in our explanatory frameworks, so failures of explanation signal incompleteness in our ontological commitments. That is, in a nutshell, why physicalism fails.

Within contemporary philosophy of mind, physicalism is something of a church orthodoxy. Antiphysicalists are not completely hostile to the church's principles. Rather, the arguments they produce stand to physicalism in a way that is something like Lutheran attacks on aspects of Catholic orthodoxy and practice. In an effort to fend off these reformist attacks, the Church elders produce a standard set of maneuvers designed to defend the faith.

In part one of this book, Against Physicalism, I argue that a physicalist metaphysics cannot adequately account for consciousness. To establish physicalism's failure, I examine four of the most prominent shields held forth by the architects of this philosophical Restoration, arguing that none of them effectively blunts the blow. Chapter two examines the charge that the reformers are arguing from ignorance, and also offers a working analysis of the physical. Chapter three formulates a version of physicalism that is weak enough so that any plausible version will fail if it fails, and then uses the results from chapter two to argue that it fails. Chapter four examines the prospect that some opaque, metaphysical necessity may restore the orthodoxy, allowing for a nonreductive physicalism. Chapter five examines an analogous appeal to identity, one that proposes the existence of identities that do not follow from any deeper explanatory connection. Chapter six discusses an appeal to alternate conceptions of explanation and ontology stemming from meaning holism.

The last two parts of the book build a defense against a fifth objection, an objection that is perhaps the most simple and powerful available to the Restoration. This fifth objection is simply that physicalism must be true if we are to avoid absurdity. The absurdity arises from an unsavory dilemma that antiphysicalism is supposed to reduce to: consciousness either is epiphenomenal (i.e., causally irrelevant), or interacts in a spooky way with the physical. By entering into a detailed analysis of causation, and thereby producing a third alternative, I will argue that this is a false dilemma.

The case I will build is divided into two parts, one occupying the middle third of the book, and the other presented in the final third. In part two of the book, Puzzles, Paradoxes, and Tensions, I spend time exploring problems and tensions created by the antiphysicalist conclusion that there must exist fundamental nonphysical properties. How can the world have both physical and phenomenal aspects? And why would it? By searching the places where these two aspects seem most incompatible with one another, I try to discover clues about where the incompleteness in our knowledge might lie. Among other conclusions, I argue that the existence of consciousness is evidence for hidden structure within nature. Also, I argue that, at every turn, our search points us toward the need to more fully understand causation itself.

I devote the final part of this book, The Two Faces of Causation, to a direct analysis of causation and the mystery of causal interaction. Perhaps the metaphysics of causation is richer than materialists usually suppose? I will argue for an analysis of causation in which experience shows up as a result of special sorts of causal interactions, interactions in which a set of effective individuals share a common receptive field. As a first point, I build a case that, like the explanation of consciousness, the explanation of causation also requires nature to have two aspects. As a second point, I argue that a realist account of causation needs to posit a structure to the causal nexus. I will argue for a conception of the causal nexus as the connecting point where effective elements of the world become receptive to one another.

An intriguing twist arises from the analysis of the structure needed to understand the causal nexus. On grounds completely independent of the problem of consciousness, I will argue that this structured entity must have properties that precisely parallel the troublesome properties of consciousness. The nexus requires a partially nonphysical nature, a kind of privacy, unity, apparent irrelevance from the perspective of physical explanation, a variety of intrinsic properties, and it contains ties to both individuation and identity.

Given these precise parallels, I will argue that an appealing case exists for postulating that the existence of conscious experience is intimately related to this nonphysical aspect of causation. As such, it turns out that the place of consciousness in the natural world intrinsically connects it to a larger, metaphysical background via its intimacy with causation itself. Under the kind of realist account of causation I will detail, a picture emerges that does not drive a wedge between consciousness and the physical world. Instead, it locates us within a world that is richer than the one previously available. The resulting view provides the foundations for a possible Liberal Naturalism.

1.4 Beginning the journey

If I may be granted the patience to indulge in one final metaphor, in many ways this book will be like a slow boat ride down a long and lazy river. We will travel through an exotic set of landscapes, lingering to take into our sights a sometimes disorienting variety of unusual beasts. Before the trip ends, we will explore questions about the nature of the physical, the meaningfulness of claims involving necessity, the status of highlevel token identities within physicalism, the possibility of panpsychism, the boundaries of consciousness, the nature of causation, the primitiveness of space and time, the relation between actuality and possibility, and the very idea of an intrinsic property. With luck, the richness of the landscape will serve to make the journey worth the investment.

I will begin by clarifying why Liberal Naturalism is needed in the first place, and that means understanding why an explanation of consciousness will elude us within a purely physicalistic framework. That is the task taken up in the next five chapters, and it will carry us through the first third of our journey. Pack your bags, it should be fun.

1. An 'end-around' is a misdirection play in American football. The offensive team makes the defensive team believe it is taking the ball in one direction, but then hands it to the splitend, who runs in the other direction around the startled defense. In this case, the Liberal Naturalist rejects any form of physicalism, but goes around traditional forms of defense against dualism by retaining naturalism. The endaround is a high risk/high reward play. If all goes well, it results in a large gain. If it develops poorly, usually a large loss results as the splitend gets tackled behind the line of scrimmage.

2. Baruss (1990) catalogs twentynine separate definitions of the term, which he groups into three categories. Chalmers himself distinguishes eight senses of the term in his first chapter.

3. For an extended defense of the existence of phenomenal information see Lycan (1996). Lycan is a physicalist.

4. I do not mean to suggest in any way at all that these are independent capacities.

Chapter 2

The Form of the Argument

2.1 The dialectic

Recent antiphysicalist arguments have relied on a variety of thought experiments, claiming that these point to inevitable limits on the physicalist program for explanation, and, by implication, the metaphysical position of physicalism. The physicalist's response to these maneuvers has wavered between polite incredulity, and a zealous patience with businessasusual science. This response frustrates the antiphysicalists with its apparent blindness to the deep philosophical issues that seem, from their perspective, to be at stake.

Perhaps the seminal modern paper on the issue is Nagel's What is it like to be a bat? (1974). Nagel argues that the subjectivity of points of view will be left out of any physicalist account of the universe. According to Nagel, our inability to discover what it is like to be creatures very different from ourselves, despite knowing their physiology, makes this failure evident.

Among others, Frank Jackson (1982) and recently David Chalmers (1996) have refined Nagel's guiding intuitions. In Jackson's well known thought experiment, he asks that we consider a superneuroscientist named Mary. From within a black and white room, through books and observation of a black and white TV, Mary learns everything there is to know about the visual system. Jackson maintains that, nevertheless, Mary learns something the first time she is exposed to color. She learns what the experience of blue is like, for instance. Thus, physicalism must be false because we can know all the physical facts without being able to know, even in principle, all the facts.

Chalmers asks us to conceive a universe physically identical to ours from big bang to big crunch, but with the twist that our counterparts have no conscious mental life. They are phenomenal zombies. Chalmers argues that such a universe is conceivable and, furthermore, logically possible. He argues that this shows the falsity of physicalism by showing that the facts about qualitative consciousness are further facts, not determined in the appropriate way by the physical facts.

If the antiphysicalists are akin to Lutheran reformers, the Churchlands have quite accurately summarized one typical response by defenders of the faith (1990),

The negative arguments here all exploit the very same theme, viz. our inability to imagine how any possible story about the objective nuts and bolts of neurons could ever explain the inarticulable subjective phenomena at issue.

In the quote above, the Churchlands seem to be accusing the antiphysicalists of producing arguments from ignorance. In this chapter I will defend the antiphysicalist arguments against this charge, arguing that this physicalist attempt at restoration fails. I will lay out the form of the argument. On the way to doing this, I will need to suggest a working analysis of the physical, defend the position that knowledge of phenomenal facts comes from observation, and offer a diagnosis of why the phenomenal facts do not logically supervene on the physical. Although the analysis in this chapter is primarily intended as a clarification of current arguments, I believe the endproduct also counts as a substantial new argument in its own right.

2.2 The game of Life

A simplified physics  In this section, I will try to clarify the antiphysicalist's understanding of the arguments by developing a detailed analogy between the physical and the cellular automaton called Life. The Life world has been used in discussion of the mindbody problem before, most notably in Dennett (1991a). Along the way I will use examples to introduce the philosophical notion of logical supervenience, but only later will I discuss the relevance of this notion to the issues. The immediate purpose is to lock onto intuitive conceptions of what it means to be physical, and to logically supervene upon the physical facts. I do this by drawing out the categorical structure of physical theories, identifying the kinds of information they convey, and exposing the kinds of conditions that make physical properties the kinds of properties they are.

Life is the name of a kind of cellular automaton that evolves on a twodimensional grid. Cellular automata consist of points, or cells, in an abstract space, all of which can have kinds of "causal" properties. We can start an automaton off by assigning properties to cells at random. The automaton then evolves, changing states according to rules that apply pointwise to the space. Typically, the rules that determine which properties a cell will have at a given time are a function on the properties of neighboring cells at an immediately preceding time.

In Life, we think of each cell on the grid as square, and as having eight neighbors: a neighbor touching it on each side, and a neighbor touching it on each corner. Additionally, a cell can have exactly one of two properties, being "on" or being "off", at any given time step. Figure one pictures a cell and its neighbors. Three simple rules govern the evolution of a Life automaton:

1) If a cell has exactly two on neighbors it maintains its property, on or off, in the next time step.

2) If a cell has exactly three on neighbors it will be on in the next time step.

3) Otherwise the cell will be off in the next time step.

Despite its simple structure, the Life automata can evidence a tremendous variety of patterns. For instance, the mathematician who invented it, John Conway, has proven that a Life grid can act as a universal Turing machine. More remarkably, he has proven that the grid can support extremely complex patterns that are selfreplicating in Von Neumann's sense of nontrivial selfreplication (Poundstone 1985). These patterns have functional properties similar to DNA and provide the motivation for the name Life. Let us imagine a possible world that is a Life universe consisting of an infinite grid. The two properties possessed by grid cells, "on" and "off", are the basic physical properties in the Life universe. The rules governing the grid's evolution are that universe's laws of physics. When thought of in this way, Life becomes a perfect modeling ground for understanding the notion of logical supervenience that we will discuss later.

Entities called gliders may serve as a simple example of how logical supervenience works in the Life universe. A glider consists of a sequence of patterns, each exactly five contiguous cells, that move across the screen in a characteristic fashion (see figure 2.2). Other cellular automata can also produce gliders, so we cannot define the property of being a glider using Life physics. Life can present sufficient conditions for the existence of gliders, but fails to be necessary for them.

The point that will be most important to the discussions in this chapter, and in the next few, is that the kind of sufficiency Life facts present for other kinds of facts is a very strong kind of sufficiency. It is not the kind of sufficiency that one might assert of causal conditions, as there's not even an air of contingency about it. Given a set of facts about Life cells, the very facts about what it means to be a glider go the rest of the way towards establishing the facts about the existence of gliders in the given situation. In this sense, it is not even conceivable that the facts about gliders could be different, given a set of facts about a Life world. So the kind of sufficiency being pointed to is a kind of logical sufficiency, in a sense of "logical" that determines what philosophers sometimes call "broadly logical" possibilities and necessities.

This is an issue that I will come back to later, but the sense of "logical" at work does not require meanings that are formally definable, nor does it require strict derivation within a formal system. In fact, gliders already give us an example of how reductive definition is inessential. The existence of particular gliders may be logically necessitated by Life facts in an intuitively clear way, and, just as clearly, the type is not definable in terms of structures specifically involving Life's "on" and "off" properties (as pointed out above, other cellular automata, with other kinds of basic properties, may support the existence of gliders).

Understanding these intuitively clear relations in a rigorous way is a project for a metatheory. No doubt, difficult and subtle issues exist in the metatheory here. These issues concern what meaning is, how well the behaviour of meanings may be captured by logical syntax, and how to formally understand logical sufficiency. The unsettled character of these philosophical metaprojects should not distract us from the fact that the antiphysicalist arguments are applied arguments. As applied arguments, what is most important to judging their soundness is adequate competence (i.e., skill), and not necessarily an adequately formalized metatheory regarding what concepts and meanings are. Such competency issues should be addressed at the applied level. On the face of things, finding a completely adequate metatheory for logic and meaning is no more pertinent to judging the arguments to follow than it is to judging other arguments, inside and outside of science, that require using various interesting concepts.

I will come back to these issues later in this chapter when I discuss just what the physicalist claim is. In the meantime, one of the purposes of this section is to illustrate the sense of logical sufficiency at issue via simple and clear examples. For instance, upon analysis, we see that all it means to be a glider is to have a certain structure and to exhibit a certain evolutionary behavior. The structure produces an orderly and predictable range of successive states that, lacking interference by other phenomena, glide across the grid. Once we have achieved this insight, we may easily see that there might be some circumstances in a Life world that would be logically sufficient to produce the existence of gliders. After all, the physics we are considering will allow for structure to arise, and for the evolution of those structures, and that is not difficult to see. To rule out the possibility that gliders could exist in a Life universe, we would need a specific proof that the physics was insufficient to produce them.

The kind of logical sufficiency being pointed to in the example of gliders is what I will mean by "logical supervenience" in what follows. We may accurately think of it as a kind of necessitation relation: the facts in the supervenience base necessitate the facts in the higherlevel ontology by being logically sufficient to produce them. Now, could a complex organization of the properties in Life similarly necessitate the existence of consciousness in that kind of world? The case of gliders suggests a way of approaching this question. We can try to discover the most general classes of properties that can logically supervene on the physics of a Life universe. If these do fall into a few general classes then that fact could be a great guide to us. When trying to decide whether the Life universe could exhibit a property, we could try to give an analysis of the property in terms that one or more of those classes could satisfy. If we find that kind of analysis, then we must hold open the epistemic possibility that the Life universe could realize the property in question⁽¹⁾. Our forbearance would hold until presented with more specific proof, either an existence proof or an impossibility proof. Conversely, if the property in question avoids such analysis, then we must conclude that a pure Life universe could not realize it.

The properties possessed by the atomic cells of Life fall into three general classes: location, their "powers", and their ancestor/descendent relations. The class of causal powers consists of the properties of being "on" or being "off" (for the sake of argument, I will stipulate that being "off" designates a property). Let us call a property a causal role property if it meets two conditions. It must be a property of a basic object (Life cells, in this case), and it must play a counterfactually supportive role in the determination of the causal powers of other basic objects. In the present case, both properties of location and causal powers are causal role properties.

Additionally, a cell's current property may be an antecedent or consequent in a chain of causation to or from other cells. We can define an ancestor and descendent relation using the idea of counterfactual consequence. Let us say the state of a set of cells at a given time is just the conjunction of the states of its member cells. Imagine a set of cells X that is in some state at some given time, and a set of cells Y that was in some state earlier. The state of X at the later time is a counterfactual consequence of the earlier state of Y IFF a change to the state of Y at that earlier time would have led to a change in the state of X at the later time.

One can then define ancestor and descendant relations in the obvious way. Let <x,p,t> denote the state p of cell x at a given time t, and <Y,P,t> denote the state P of a set of cells Y at a given time t. A cell state <x,p,t> is a descendant of some earlier <Y,P,tn> just in case <x,p,t> is a counterfactual consequence of <Y,P,tn>. Ancestor relations are the converse of descendant relations. A consequence of these definitions is that they make a cell state at a given time a descendant of any superset of an ancestor, but that does not matter. Here, as with the definitions that follow, being too liberal will not undermine the basic work the analysis will do. If this is bothersome, one can tack on a minimal set condition.

What sorts of properties can exist in a world with just these properties as fundamental? The properties of the combinatorial structures of these basic cells will be supervening properties. For clarity, I will stipulate that structures are a set of contiguous cells in Life. 'Contiguous' means that every cell in the set is reachable from any other cell in the set without having to cross a cell not in the set. The morals that I am going to draw from this analysis will apply to messier notions of structure also.

The ancestral and descendant properties generalize easily to structures. What other interesting properties do structures have? We can see that the world will support other properties analogous to properties that physical things possess. Among these properties, two important classes should be singled out: the evolutionary relations between structures, and their interactive relations. An evolutionary property is instantiated by a structure when it is a member of an evolutionary sequence. For instance, a structure has the property of being a glider if its state is one of the states that occurs in the evolution of a glider. In the general case, an evolutionary sequence is a set of successive states each of which is sufficient to produce the next if no other phenomenon interferes with it. Many interesting phenomena, such as gliders, consist of many different structures linked through time, evolving sequentially from one another in this way.

The class of evolutionary properties is very broad, and all sorts of uninteresting evolutionary properties are specifiable. At every time step the whole grid has at least one evolutionary property, and any random region within a grid will usually have more than one evolutionary property. As before, this liberality should not matter to the later points. We can usefully analyze a whole host of interesting Life properties as evolutionary, from being a glider (which moves across the screen) to being a blinker (which moves back and forth horizontally and vertically) to being a traffic light (which twinkles like a star).

Some objects, like "eaters",⁽²⁾ are interesting because of evolutionary properties in combination with properties like interactive properties. The idea of an interactive property casts a broad net over the whole array of effects a structure may have. Consider gliders again. As already related, gliders are structures of five cells that move across the grid as they evolve. During its evolution, a glider may meet other structures, and each interaction will produce some disruption or change to both phenomena. The range of possible interactions and results form the interactive properties of gliders. If we wished, we could represent any interactive property using a set of structures and their states, specifying points of contact, and describing the state of the structure that would result in the next time step.

Like with the other properties we have discussed, we can be very liberal about interactive properties. In fact, any given Life object will have an infinity of such properties. It will have one for every possible interaction it might have with other Life objects, and one for each description of the result.

Perhaps a bit surprisingly, we now seem to have sufficient resources for analyzing all the welldefined and really interesting, general classes of properties that can logically supervene on a Life automaton. For example, one can describe the history of any Life object as a sequence of different structures whose evolutions are punctuated by the exemplification of one or more of its interactive properties. Each punctuation results in a new structure, or set of structures. They begin to evolve, exemplify further interactive properties, and so on.

Supervenience, definition, and illdefined properties  Something important about the above treatment is that even the welldefined properties are not reducible, in the sense of being theoretically definable, in terms of Life. These welldefined properties only supervene on potential Life automata, as Life may present sufficient but not necessary conditions for them. Additionally, Life objects that are less welldefined than structures will exist, and these will have less welldefined properties. We have to accommodate this vagueness in a way compatible with the idea that the Life world consists, at bottom, only of welldefined properties.

A proper analysis will proceed by giving accounts of the vague properties involved. Any successful analysis would connect an illdefined property to the Life world by designating similarity classes of the welldefined properties, allowing members of this class to act as potential realization bases for properties in the illdefined categories.⁽³⁾ To see why, note that if one asserts of anything that it is an x or has property y one must be able to justify the assertion based on some aspect of its history, including its present. This implicitly reduces to the assertion that some such combination of welldefined basic properties is logically sufficient for realizing the less welldefined properties. Any adequate analysis of the vague properties will have to show how this can be.

Generally, the introduction of illdefined properties by using similarity classes just bifurcates each of the basic categories. Each basic category becomes a genus with two species. The category of structural properties breaks into precise structural properties, as defined above, and vague structural properties realizable by a similarity class of welldefined structures. Interactive properties split into a species of precise interactive properties, as defined above, and vague interactive properties realizable by a similarity class. The other properties receive a similar treatment. Always, particular exemplifications of imprecisely defined properties occur through reference to a set of precisely defined properties. Figure three depicts the logical structure of the situation.

Two kinds of reduction  Like the welldefined categories, we can naturally construe the vaguer interactive and structural properties to include possibilities that do not involve specific Life facts and physics. So no theoretical reduction, in the sense of defining one category in terms of the other, is at hand, for either the vague or the welldefined properties.

Even so, in another sense of 'reduction', gliders may be reduced to Life facts in virtue of logically supervening on them. This other sense is that the existence of things like particular gliders may be wholly dependent on Life facts and physics, despite the fact that the category outruns definition in those terms. That is, the existence of particular gliders may reduce, even if their categorical being does not. Thus, theoretical reduction fails, but ontological reduction succeeds (pending a deflationary, intentional account of the categorical slack). Furthermore, even though theoretical reduction fails, the kind of reduction that succeeds clearly hinges, partially, on facts about meaning: the circumstances in Life may produce the existence of particular gliders by satisfying the concept that picks out the property of being a glider.

One might think that one could continue to define new sorts of interesting properties in the Life universe by considering systems. A system would be a collection of structures and take into account their relations. However, as we have defined structure, we can view a system as just a larger, more complicated structure. As a structure, a system also has only evolutionary properties, structural properties and interactive properties. Facets of its internal dynamics will be what makes it a system.

2.3 Could a Life universe possess phenomenal consciousness?

The challenge Now that we have done this preliminary work, we can return to the problem of consciousness. Might qualitative consciousness arise in a universe that consisted only of facts satisfying the specifications of Life? This is a serious question. Life can exhibit phenomena of indefinite complexity. Who knows what properties structures of quadrillions of cells might exhibit and what interesting phenomena might arise? Can we rule out the presence of phenomenal consciousness in a pure Life universe?

In such a pure world, any kind of phenomenon that can exist will be, in principle, of a kind that allows Life to exhibit logically sufficient conditions for its existence. Ultimately, this means allowing for entailment by:

(1) Causal role properties

(2) Ancestral properties

(3) Structural properties

(4) Evolutionary properties

(5) Interactive properties

(6) Some overlapping combination of 15

Such a world may possess all sorts of "emergent" properties via combinations of (1) (5), along with, perhaps, the addition of vagueness. For instance, we cannot rule out such a universe exhibiting some kind of genuine life. We already know it may contain selfreplicating phenomena. That these entities might eventually lead to the existence of animate objects is at least an epistemic possibility. These objects (epistemically) might metabolize elements of their environment, act in a goaldirected manner, evolve to be increasingly complex, and, generally, possess a suite of functional properties sufficient for regarding them as alive. Given that life might exist, ecologies might exist. Given that ecologies might exist, even economies might arise in a Life universe. We can analyze economies into kinds of functional relations between objects within an ecological system, and functional relations are a combination of evolutionary and interactive properties.

So, overall, logical supervenience does not give us grounds to rule out many kinds of phenomena in such a universe. Nevertheless, I will argue that no pure Life world can necessitate the existence of consciousness, or the specific character of its phenomenal qualities. By a "pure" Life world, I mean a world in which the only fundamental facts are those completely describable by the physics of Life. The purity condition is extremely strong, and very important for the discussion to follow. The purity of our hypothetical Life world means that it contains no properties, features, entities, or aspects other than those laid out in the specification of Life's physics. Nothing, absolutely nothing, may be smuggled in. In particular, it cannot be imagined to be "implemented" by anything other than "pure" dispositions corresponding to "on" and "off" properties, whatever might be meant by this (the possibility of such a world is, indirectly, a concession to physicalists, and does not illegitimately help the defense of antiphysicalist arguments I give below).

Arguing for negative conclusions of this type requires producing reasons that justify believing that we cannot properly analyze the property in a certain way. At one level, such assertions will seem brute, simply relying on an adequate grasp of the concept that picks out the property. At other levels, we may approach the proposed analyses from a variety of more concrete perspectives, note the systematic failures, and the general reasons behind the failures. That is the strategy that I will pursue below.

To set the stage for a more vivid articulation of the point, I want to emphasize that we must remain constantly aware that the Life universe is not our universe. We are to imagine an alien dimension, a dimension fully described by Life's physics. No one can decide the question of whether any conscious feeling at all can exist in a pure Life universe by an appeal to firstperson evidence, or analogy, or verbal reports. This takes out of play certain groundlevel intuitions that affect the discussion about consciousness in our universe. For instance, we cannot claim that we will empirically discover a coordination between different kinds of descriptions (Flanagan, 1992), a coordination that will allow us to attribute an identity or supervenience relation between feeling and the functionality of Life objects.

Establishing such coordination requires us to access facts of both kinds, and the problem is precisely to access the phenomenal facts in a pure Life world, if any. Conversely, if we had access to the phenomenal facts, if any, we would obviously not need any process of "coordination" between them and other kinds of facts. Those other kinds of facts would have been the entailment base from which we obtained our phenomenal information. So the Life universe is alien to us, and only logical supervenience could bring consciousness into existence within it. To satisfy the requirement of logical supervenience we need to look for conceptual connections between the welldefined properties, or life history, of a Life object and the presence of consciousness.

The skeptic's claim I will defend the skeptic's claim, which is merely this: we may consistently acknowledge any kind of structure and functionality for Life objects, and deny the presence of feeling in a Life universe. Thus, positive facts about consciousness cannot logically supervene on the facts about a Life universe. I will begin the defense of the skeptic's claim in this way. At bottom, the basic shortcoming seems to be that Life is only able to present facts about patterns of bare difference. A bare difference between entities is a difference that is merely formal, ungrounded in any further facts about internal structural differences between those entities, or internal relations of difference between a structureless intrinsic content possessed by those entities.

Bare differences are difficult to conceive of, and I believe it is reasonable to doubt the intelligibility of the notion. However, a pure Life world would seem to need such facts, and, as I will argue later, a purely physical world would also need them. So as not to win a cheap victory against the physicalist, then, I am going to grant the intelligibility of these kinds of stipulated bare differences between primitive dispositional properties. I think the best way to conceive of a bare difference between two properties, x and y, is to think of the relation as primary, with the existence of the relata, such as they are, derivative on their participation in an ungrounded relation of difference. In contrast, a contentful notion of difference reverses the order of primacy: the existence of the difference is derivative on further facts of intrinsic difference between the natures of the relata. A pure Life world must instantiate bare differences between the "on" and "off" properties, as a contentful difference requires smuggling in further intrinsic facts about the "on" and "off" properties, facts aside from those stipulated by Life's physics. This bareness is what allows them to exist as pure dispositions.

The skeptic maintains that facts about bare difference are always consistent with the absence of feeling, since the difference structures instantiated by phenomenal consciousness involve differences in particular, qualitative contents. Our taste space, for instance, contains different tastes, and our color space contains different colors. The relevant premise is that these tastes and colors are contents instantiating a structure of difference relations, not structures instantiated merely by difference relations.

No one denies that we can catalog the differences between different colors and different tastes along relevant dimensions. If we do this, we can surely abstract out a contentfree difference structure. The skeptic's objection is to the further move of analyzing conscious qualities into the abstract patterns of difference between them. Our acquaintance with the phenomenal qualities yields information about them as contents occupying slots within these difference structures. Reification of the difference structure as basic requires ignoring the content instantiating those structures. That move ignores the grounding of those differences in this specific case.

Qualia as observables For the skeptic about feeling in the Life world, these conclusions about the elements of consciousness are not mere "intuitions". Colors, tastes, sounds, and other sensations have the status of observables, and these "intuitions" have the status of observations. As observations they might be wrong, but it takes very powerful arguments to overturn them.

The claim that qualia are observables is controversial to some. The most common worry is that modeling our knowledge of qualia on perception is misleading, so people are unsure how we can be "observing" them. Some people argue from these kinds of worries to eliminativist conclusions, but, minimally, opponents sympathetic to these worries hold that the knowledge grounding the skeptic's conclusions is highly refined, theoretical and corrigible.

To these worries, the skeptic replies that the objector seems to have an unreasonably narrow concept of observation. By insisting that something can achieve the status of an observable only if we obtain the information about it through perception, the objector is making too strong a claim. The physicalist's objection rules out of court a huge amount of information about consciousness that we have access to, and that a theory of consciousness should have to explain. As examples, here are two statements most would agree express facts that should have the status of observables:

(A) Last night I thought about my childhood.

(B) Sometimes I think about my childhood when no one is around.

By calling these things observables I mean that they meet these four conditions: (1) They belong to a type whose members are potential objects of awareness; (2) We can become aware of them without the aid of special instruments; (3) The dubitability of our belief in facts of the relevant type is almost zero; (4) Our awareness of instances of the type is reliable. These characteristics allow facts like (A) and (B) to attain the status of useful falsifiers for scientific and other theories. For instance, a theory of mind fails to account for some of our evidence about ourselves if it fails to account for how we can sometimes think about our childhoods when no one is around.

The skeptic about the possibility of consciousness in the Life world is claiming only that facts like (A) and (B) are no more problematic than many other facts we count as "observable". The fact that perception does not mediate our awareness of them seems to be a redherring. Thus, if anything can count as an observable, (A) and (B) both can. Our skeptic firmly insists that a science of consciousness must allow such observables if it wants to be treated as legitimate. Since facts like (A) and (B) turn out to be no more problematic as observables than perceptually mediated facts, a straightforward argument delivers the phenomenal qualities as observables also.

Last night, I lacked behavioral evidence that I was thinking about my childhood. I was not writing about it, nor talking about it, nor acting on it. I was, in fact, scouring my bathtub. How do I know what I was thinking about? What was the evidence of my thoughts? It was the presence of certain kinds of conscious phenomenal imagery, verbal, imagistic, and kinematic. That imagery may have been identical to the thoughts, or it may just be a concomitant of thinking that gives evidence for thoughts.

In either case, my awareness of the conscious phenomenal imagery cannot be considered more dubitable than my awareness of my thoughts. Since the phenomenal imagery is the evidence for such thoughts, it is easy to argue⁽⁴⁾: the sentence (A) has the status of an observation claim IFF the phenomenal imagery that is my evidence for it has the status of being an observable. Similarly, I obtain my knowledge of types of thoughts like those referred to in sentence (B) from observables IFF I also obtain my knowledge of types of phenomenal qualities from observables.

Arguments such as this, the skeptic maintains, establish that we obtain knowledge of what the phenomenal qualities (colors, feelings, sounds, imagery, other sensations) are like through conscious awareness of them. For example, I obtain my knowledge of what the shades of blue look like to me by consciously experiencing them. Consequently, phenomenal qualities are observables (which is not to say observation of them is always either easy or incorrigible). Through observation the skeptic obtains phenomenal information that explanations and theories must be held accountable for.

The fact that awareness of these things is not perceptually mediated should not count against them. For centuries we had no idea how perception worked, but that did not stop us from treating information delivered by perceptual awareness as being information about observables. Similarly, the lack of a sound theoretical understanding of nonperceptual awareness should not stop us from recognizing that it also delivers information about observables.

David Lewis (1995) has argued that physicalists can grant the existence of qualia, but only if they deny that we have special, unmediated access to their natures. The claim that qualia are observables does not violate Lewis' injunction. To possess phenomenal information, our skeptic does not need to have a more direct access to qualia than to any other kind of observable. The skeptic is chiefly concerned with the character of the connection between phenomenal qualities, as disclosed through the phenomenal information we do have available, and their hidden natures, if they have hidden natures. Does the phenomenal information we have about qualia logically supervene on the properties of their hidden natures, or is there an opaque, nomic connection? The skeptic merely claims that if the hidden nature of qualia is that of a structure of bare differences, the connection between our phenomenal information and this nature is not one of logical supervenience.

The character of the supervenience base in Life If we can show that the pure Life world can only support bare difference spaces, and patterns of bare difference spaces, the phenomenon of qualitative consciousness would then seem to avoid analysis into the possible categories of explanation available. Any proposed solutions to the problem of consciousness that do not go beyond Life's resources would necessarily be from a different game altogether, and not even eligible to win this one.

Our skeptic can make this concrete case by taking a closer look at the materials available in the Life universe. What does it mean to be an "on" or "off" property? The only two requirements are that (i) they be distinct, and (ii) they should be instantiated in patterns conforming to the counterfactual dependencies described by the laws. In short, the distinction between being "on" or being "off" is a merely formal one. "On" and "off" designate bare, contentfree difference.

The Life specification is, at heart, a structural schema for a universe. It specifies certain patterns of contrast between being, patterns that must hold for a universe to count as a Life universe. As we ascend to higher levels of organization in the Life world, we do not escape from the circle of bare difference. Appending schemas to schemas only yields more schemas. A Life structure is a pattern of bare difference, mere contrast.

In Life we have a world potentially consisting of a huge number of simple, bare differences lying side by side, with reliable, regular transitions between them. Does this world present logically sufficient conditions for the existence and specific nature of a higherlevel consciousness with qualitative, subjective content? We know from observation that the difference between red and green is not a mere formal difference. The question is therefore equivalent to the question of whether or not qualitative contents like the shades of green are patterns of bare difference.

A pattern of differences between colors can produce another color. For instance, a field of tightly packed yellow and red dots may yield an experience of orange under the right viewing conditions. We can observe that the shade of orange that results is not produced by the mere pattern of difference, though. It has to be a pattern of difference between the appropriate colors, thus providing no explanation of color in terms of mere patterns of difference. If we try to abstract the pattern of difference from their contentful bases, viewing them as mere difference structures, we see that the result is multiply realizable and some of the realizations do not yield orange.

For instance, one can instantiate the same structure of differences between two other colors whose hues lie at the same distance from each other as red and yellow (e.g., yellow and green). A pattern of dots of these colors will yield a different color from orange (e.g., brown). Therefore, we can observe an identical structure of formal difference, but different colors. The fact that, even allowing that we start with colors, one cannot reduce some colors to the mere difference structure among other colors is suggestive. After all, the skeptic is maintaining a much weaker position.

The position the skeptic is defending is that patterns of bare differences do not entail the facts about the phenomenal qualities. Patterns of bare differences are difference structures whose identity obtains because of a mere formal difference, ungrounded by content. The skeptic notes that orange cannot even be reduced to the structure of difference between red and yellow once we abstract from the phenomenal content of red and yellow themselves. We can observe more straighforwardly that red and yellow are not constituted by patterns of mere difference, without any content at all.

As an analysis of phenomenal content, the idea that something like a shade of red is a pattern of bare, merely formal differences is observationally inadequate. To make it work, something must be added. The only tool Life presents for constructing phenomenal content out of patterns of bare difference is its counterfactual content. Unfortunately, known logics of counterfactuals only add things like consistency constraints, or metrics over similar possible worlds, to our toolkit. These are not even the right kind of thing to add to a collection of formally distinct properties to make them add up to properties that are not merely formally distinct. A pattern of bare differences does not become a phenomenal content because another world contains a similar pattern, or because it is consistent with patterns that occur elsewhere in that same world. Yet that is all we have here. If one tells a skeptic that a pattern of bare differences transitions to another pattern of bare differences, the skeptic can consistently deny that either pattern has to support a feeling. Nothing in the logic of counterfactuals requires that the transition should feel like something either. The Life schema thus seems to underdetermine the story about qualitative content. We seem to have good reason for believing that the skeptic's claim is consistent.

Transferring information between worlds Why might someone believe that the skeptic's claim is inconsistent? Sometimes unwarranted assumptions predicated on beliefs about our world might tempt us to smuggle phenomenal facts into the Life universe. Qualia in our world may perform some functions, or correspond to some specific internal structures or processes. Perhaps performance of these functions is necessary to their being objectively classified as pain feelings rather than feelings of another type (phantom pains, maybe). Maybe, in our world, performances of these kinds of functions are always accompanied by the feels.

Even if we grant ourselves the assumption that phenomenal feelings perform some functions in our world, a further question looms. Are we telling the complete story about experiences when we tell the story about their function? We have to avoid automatically assuming that a similarly functioning element of the Life world feels pain. That is to beg the question about the completeness of the functional explanation in our world. More strongly, the Life world presents us with an opportunity to investigate that question. What phenomenology, if any, would similarly functioning objects in the Life world logically require us to attribute to them?

At that point, the alien character of the Life world presents a problem. Given our remove from that universe, we have no firstperson knowledge that even one conscious state exists in it. Without even that small bit of information, making grandiose generalizations about the existence of consciousness across these alien worlds, ours and the Life world, becomes tricky business. We need some supporting story about how the facts in this alien world can be sufficient to support facts about consciousness. This supporting story cannot assume the existence of consciousness in that world

We clearly need a supporting story that goes beyond the mere coextensiveness of facts in our world if we want to generalize from our world to a hypothetical Life universe. Our alienation from it seems to block transferring the information so naively. At this point, the existence of an explanatory gap in our world, admitted even by many physicalists, is evidence that mere coextensiveness, or "coordination", is all we really have. If this is so, then the functional information alone cannot be the whole story. It seems to follow that a skeptic is consistent if he admits to any kind of functioning at all in the Life world, and denies that the activity supports consciousness.

Adapting antiphysicalist arguments to Life We can also approach the conclusion through meaning, since the type of logical necessitation we are looking for should have a grounding in meaning. Whatever pattern of events might occur in the Life world, it is very implausible that such patterns satisfy what it means to be conscious. As evidence for this, one may observe how holding that Life physics can support consciousness seems completely ad hoc. Why assert that anything possesses a subjective, qualitative aspect in a Life world? What work would the claim do? It does not seem to explain anything that cries out for explanation within Life's closed world. (this observation corresponds to the sort of argument found in Stapp 1996).

The only temptation one can possibly have is an extension of something one might believe about functioning in our world into another world very different from ours, one where we have no firsthand evidence about the existence of phenomenal consciousness at all. Since any kind of interactive, evolutionary, or structural conditions that a Life world meets are already complete, albeit extrinsic, we are left with an explanatory gap, "Why should this combination of Life properties feel like anything at all?" Such an explanatory gap could not exist if all it meant to have a conscious experience was to instantiate a complicated pattern of formally distinct differences.

The skeptic could also weave a tale about an imaginary superLife scientist who knew all the facts about possible Life phenomena. He might ask, "should such a scientist conclude that there is a quality of experience for certain Life phenomena?" We know that to justify a consciousness claim all our Lifescientist could point to would be instantiations of properties from the welldefined basic categories that logically supervene. Since the facts about these aspects of consciousness cannot be discovered by knowing the facts about interactive properties, structure, or evolution in the Life universe, the claim goes beyond anything that can logically supervene. The superLife scientist could never justify a positive claim. Thus, concluding that qualitative consciousness exists in that universe would be illegitimate for the Lifescientist (this argument adapts Jackson's knowledge arguments from his 1982 to our Life world).

The skeptic might ask if we can conceive of a universe obeying all, and only, the Life physics, one which exhibited properties as complex as you please, but which did not have qualitative consciousness at all. The skeptic might help us by pointing out that the extrinsic and formal specification of the Life schema is presumed to completely circumscribe the world. The extant understandings of what makes for truthconditions on counterfactuals, and of what a formal distinction is, seem to straightforwardly allow for the conceivability of this zombie Life world (this argument adapts Chalmer's Zombie arguments in his 1996).

The skeptic might challenge us by asking,"What is it like to be a (given) Life object?" By asking this, the skeptic intends to call our attention to our irremediable ignorance about the real character of the qualities we might be attributing. If they truly logically supervened, such severe ignorance would not exist (this adapts Nagel's worry in his 1974).

If some people insisted that phenomenology could exist, for instance visual phenomenology, the skeptic might correct them by asking if they could conceive of the visual experiences of Life objects inverted in a variety of ways. Perhaps these critics imagine that the "on" and "off" properties of a realized Life universe would not merely be formally distinct, but would have to be implemented by something with an intrinsic nature (someone might plausibly claim that they cannot make sense of the idea of a mere formal distinction, ungrounded in intrinsic difference)⁽⁵⁾. If so, this is a further fact relative to the Life specification. One way to get such critics to consider the possibility of inverted spectra is to point out that the Life specification really does need only the bare distinction between the "on" and "off" properties. As long as they are distinct, and play their roles, the intrinsic natures they might have are irrelevant to the question of whether or not it is a Life universe. Since their intrinsic distinctness should remain even if their job description changes, we should be able to imagine inverting whatever intrinsic natures are supposed to be playing those roles. The Life universe is, in principle, multiply realizable. From this, the possibility of inverted spectrum seems to threaten.

These thought experiments are just vivid ways of trying to make the same general point: qualitative consciousness just does not logically supervene on Life facts and physics. Regardless of how successful one thinks these kinds conceptual tests are when applied to our universe, the Life case seems much more clear cut. We can see the answer directly by considering the kinds of properties that can logically supervene in that universe, and noting that there is no analysis of phenomenal consciousness that allows such properties to entail its existence.

In the end, these arguments for the skeptic's claim do not have the form of arguments from ignorance. They do not have the form, "I cannot imagine how suchandsuch could possibly explain consciousness, so suchandsuch cannot explain consciousness." They have the form, "We have reasons for thinking that suchandsuch can only explain facts of type Y. Since we have observational evidence that the facts of consciousness are not facts of type Y, we have good reason to believe that suchandsuch cannot explain the existence of consciousness." Its essential form is an argument from a theory to that theory's failure of prediction. To paraphrase Dennett, a perception of failure is not the same thing as a failure of perception. The successful perception, in this case, is of a failure of prediction.

1. Epistemic possibility is the widest space of possibility, including the space of logical possibilities as a proper subset. For instance, given a mathematical conjecture that has not been proven, we must hold it open as an epistemic possibility that it is true, and also that it is false. Still, only one of those is a logical possibility. I suggest thinking of epistemically possible situations this way: a situation S is epistemically possible for an agent A just in case A cannot discern an inconsistency in the description of S.

2. Eaters are structures that can "absorb" other structures.

3. The questions about how these similarity classes might be specified are interesting. Rosenberg (1997) makes some foundational observations about how circular conceptual systems might pick out such classes.

4. The relevant premise for the argument is (P): If x has the status of being an observable, the evidence for x must also have the status of being observable. For example, if I can observe that it is cold outside based on the evidence that there is snow on the ground, the snow on the ground must also be something that I can observe. Similarly, if I observe a photon in the cloud chamber based on the evidence that a cloud has appeared, then the cloud must be an observable also. The premise (P) gains its plausibility from the principle that the epistemic status of evidence cannot be less secure than the status of that which it is evidence for.

5. In chapter fourteen I will pursue this sort of objection in detail, finally endorsing it.

Chapter 3

A Formulation of Physicalism

3.1 How to get nonphysical facts "for free"

The role of logical supervenience  In chapter two I did a lot of work analyzing Life. In section three of that chapter I argued at length that positive facts about phenomenal consciousness do not logically supervene on facts about Life. To understand why doing this is helpful, we need to become clearer about what the physicalists' claims commit them to. We can then home in on the precise nature of the antiphysicalist qualms. I will not go into full detail here since that has been done well in other places (notably Jackson 1993; Chalmers 1996; Kirk 1994 and Poland 1994 do so as physicalist sympathizers), but I wish to at least outline the intuitive idea and the way it must be captured within a principled metaphysical framework. The basic intuition behind physicalism is that the particular physical facts in the world somehow exhaust, or fix in a very strong way, all the particular facts in the world. These intuitions are more fundamental than identity claims because identity claims must fail if these intuitions fail.⁽¹⁾ Every fact fixes itself in the requisite sense. In general, the physicalist must claim that for free connections exist between the particular physical facts in our world, and the particular facts of other ontologies. In David Armstrong's phrasing⁽²⁾, given all the microphysical facts about our world, all the other facts are an ontological free lunch.

Essentially, its proponents ground the physicalist program on the possibility that the highlevel description of any particular fact in economic (or psychological or sociological or . . . .) terms is just a redescription of some physical circumstance using another, more abstract conceptual structure. As a different conception of already existing physical stuff, such facts require no fundamentally new ontological posit. To express this insight, the physicalist has enlisted supervenience. The basic idea underlying supervenience is that if the truth of token facts of one type, called the base facts, in the right way guarantees the truth of token facts of another type, called the supervenient facts, then we require only the base facts in our most fundamental ontology.

The basic idea behind supervenience is simple but, as it stands, will not serve the physicalist's purposes. It has several variations, and some of these variations are compatible with dualism. The nuances we must get comfortable with relate to the modality and the scope of the supervenience claim. Supervenience may come in two relevant modalities, natural and logical⁽³⁾, that are sometimes not distinguished from each other.

Natural supervenience asserts that the base facts determine the supervenient facts in virtue of some law of nature connecting the two. We can paraphrase the nomic supervenience claim as follows. Let the base facts be the A facts, and the supervenient facts the B facts. Then,

The particular B facts naturally supervene on the particular A facts IFF the laws of nature ensure that whenever the particular A facts hold, the particular B facts will also hold.

A short (and potentially misleading) way of stating the natural supervenience relation is to say that the base facts cause the supervenient facts. Clearly, natural supervenience is not what the physicalist has in mind. Almost any antiphysicalist will freely admit that laws of nature exist to connect the physical facts of the body to the phenomenal facts that are claimed to be nonphysical. The problem here is that laws of nature are contingent relative to the facts they connect, and contingent connections cannot support ontological reduction. As an example, consider the connection between gravity and electromagnetism in physics today. Nature connects them only naturally, and therefore we must consider them quite independent and equally fundamental forces. Not distinguishing natural from logical supervenience sometimes gets philosophers into ontological trouble. Searle's position, for instance, seems to be one of natural supervenience and yet he surprisingly believes he is defending ordinary physicalism (1992).

How can the physicalist get the requisite "for free" connections? We can think of it this way. What, in a physicalist world, allows us to assert statements such as, "There are tables."? The ontological category 'tables' is not part of the fundamental physicalist ontology. Such statements are true just in case the conditions existing in our purely physical world are such that at least one object meets the application conditions of the concept 'table.' The physicalist can then say that the world realizes tableness, exhibits an instance of it. In other words, tables exist in a purely physical world because it presents logically sufficient conditions for predicating 'table.' Whether or not the physical world can support such a predication is a matter both of empirical fact (what the particular physical facts happen to be), and the meaning of the concept (do those particular facts present logically sufficient conditions for satisfying it).

That is the sense in which the physicalist can have tables in the world for free, and dollar bills and inflation as well. So, given a full understanding of the physical facts, the logical room for the highlevel facts to vary must disappear. This is the sense in which the particular physical facts necessitate the particular economic facts. This logical room is given partly by the concepts involved, and it involves truths of meaning. Indeed, how else can the physicalist justify the claim that economic facts are nothing new over and above the physical facts since truths of meaning are the only things a physicalist can possibly hope to get for free? We say, therefore, that the physical world makes real (or realizes) the particular highlevel fact. So to account for given highlevel facts, the physicalist needs to uphold the formula physical facts + conceptual truths yield highlevel facts.

An example of logical supervenience at work would be the determination of the shape of a Rubik's cube. Does its (roughly) cubical shape logically supervene on the physical facts about it? The answer seems to be clearly 'yes.' Given all the physical facts about a Rubik's cube, facts that include all the spatial relationships between its component parts, a sufficiently intelligent being would be able to determine that it is (roughly) cube shaped. Its shape is entailed by the physical facts alone with no further ontological suppositions being required. It follows that there is no possible world where all the physical facts about the Rubik's cube are the same, but its shape is different.

One final wrinkle: the supervenient properties of an object may be either local or global in character. If supervenience is local, then the base facts of that object alone are sufficient to set the supervenient facts. Facts about the heat of the sun are of this character. If global supervenience holds, then the supervenient facts about an object also require the base facts involved in its context. Economic facts are globally supervenient. For instance, the fact that a particular piece of paper is money is due to a complex social and historical context that it is embedded in. The same goes for the particular fact that Trey Kirven paid $4.71 for his lunch yesterday at 12:51.

3.2 Formulating Physicalism

Generally, I will say that a fact, S, logically supervenes on a set of facts B just in case there is no logically possible world in which the B facts are true and the S fact is false. Now, this automatically means that all necessary truths, such as mathematical truths, logically supervene on the physical for trivial reasons. Physicalism should not rule out Platonism by fiat, so I will leave open the relationship between the physical facts and truths about abstract entities. With this in mind, we can now state a very weak version of the physicalist position: Physicalism is true IFF all the contingent, particular, positive facts in the world are globally (spatially and temporally), logically supervenient on the particular physical facts including, perhaps, the physical laws.⁽⁴⁾

Some things that logical supervenience is not A typical reaction to the discussion so far is to claim that very little logically supervenes on the physical, as the "logical" criteria is far too strong. From the antiphysicalist side, Chalmers (1996) addresses this reaction by sketching examples of how one might establish logical supervenience in particular cases,⁽⁵⁾ as does Jackson (1994). They also offer some general considerations concerning why logical supervenience should hold almost universally. From the physicalist side, Kirk (1994) also defends the claim⁽⁶⁾, as do Horgan (1984) and Armstrong (1982). For more detail regarding the positive case, I refer interested readers to these authors. Below, I will address the common basis people's doubts seem to rest upon.

Why do some people believe that logical supervenience fails quite generally? Commonly, the requirement that one set of facts follows "logically" from another is thought to be a very, very strong requirement, too strong to capture the general relationship between the highlevel facts and the physical facts. The chief source of this doubt seems to reside in the impression that the notions of "logical", "consistent", and "analytic" must be understood in terms of syntactic derivability within a formal system. For example, some people believe that the supervenience conditionals at issue here could only be "analytically true" if one could produce a syntactically wellformed deduction of the consequent facts (i.e., the supervenient facts) from the antecedent facts (i.e., the base facts). To these people, it seems that the Afacts could logically supervene on the Bfacts only if one could produce definitions of the Afacts in Bfact terms, and then use these definitions to syntactically derive the truth of the supervening Afacts from the base of Bfacts.

The inevitable failure of most highlevel facts to meet this condition seems patently obvious. They should fail to meet the syntactic derivability condition for one (or both) of two reasons: (i) most of the highlevel concepts at issue will evade perspicuous definition altogether; or (ii) to the extent that one might be able to define any highlevel concept, the definition will not be expandable to purely physical terms, and so will not be in a form appropriate for use in a derivation from a purely physical base of facts. I will not take issue with either of these worries. Instead, my strategy in answering the doubts they raise will be to argue that these worries arise because the successes of modern logic have caused a too strong identification between theory and phenomena.

The relevant observation is that logical consequence, analyticity, and consistency are semantic phenomena. The formal syntactic representations that inform our modern understanding of these notions are merely theories invented to help us explore the phenomena. They are tools for modeling them, nothing more and nothing less. The apparatus of these theories is extraordinarily useful, but also incomplete in important ways. Because they embody theories, both the models built with these tools and the tools themselves must answer to the informal competence we possess (or may develop) with the use of our concepts, with meaning, with consistency, and with logical consequence. Only if they pass these tests may we accept them as completely adequate theoretical tools. Thus, to raise this objection against logical supervenience requires defending some very strong claims about the adequacy of logical syntax to capture informal semantics. These claims are that (i) the syntax of logical definition adequately models the structure and behavior of meanings for nonprimitive concepts; and (ii) the logical satisfaction of concepts is adequately analyzed within formal logic.

I believe few people, when the point is put so starkly, will wish to defend these claims. The phenomena that argue against them are ubiquitous, and difficult to deny. In the end, resisting the counterexamples is selfdefeating, as it requires abandoning the confidence in our native competencies that we need to justify accepting these modeling tools in the first place. I will argue primarily against claim (i), that the syntax of logical definition adequately models the meaning of nonprimitive concepts, because I believe that claim (ii) fails if claim (i) fails.

To argue against claim (i), one may point out that it is in conflict with one important source of the original skepticism about logical supervenience. It conflicts with the claim that most interesting highlevel concepts do not have definitions. As an example, consider the concept of "friendship". Perhaps some incisive analysis will yield a crisp, formally modelable definition, but, for the sake of argument, let us assume that no such definition will ultimately be forthcoming. Few would want to claim that the concept of "friendship" is, as a consequence, meaningless, nor, I think, would many want to claim that it is a primitive term. "Friendship" is a meaningful concept whose meaning is neither primitive, nor completely analyzable in terms of a formal definition involving other concepts related to one another by the logical constants. This is trouble for someone needing to defend claim (i) above, as it seems to suggest that meaning outruns the resources of formal definition.

"Friendship" does seem to be just this sort of concept. However, do we need to conclude from this that notions of logical consequence and satisfaction do not ever apply to it? That seems like an extremist reaction. When one considers concrete cases, some conditions certainly present themselves as being entitled to the claim that they logically satisfy the concept of friendship, irrespective of its resistance to formal definition. To see this point, imagine two people, Allen and Gregg, who have known one another for twelve years, genuinely liked one another, shared many experiences, secrets, and adven

A Place for Consciousness

Probing the deep structure of the natural world

Table of Contents

Dedication

Acknowledgments

Preface

Abstract

Chapter 1. Liberal Naturalism

Part I. Against Physicalism

Chapter 2. The Form of the Argument

Chapter 3. A Formulation of Physicalism

Chapter 4. The Objection from Metaphysical Possibility and Necessity

Chapter 5. Logical Supervenience, Entailment, and Identity

Chapter 6. The Objection from Holism and the Rejection of Analyticity

Part II. Puzzles, Paradoxes, and Tension

Chapter 7. Rethinking Nature: On the Possibility of a Benign Panpsychism

Chapter 8. Puzzles for Liberal Naturalism

Chapter 9. The Boundary Problem For Phenomenal Individuals

Chapter 10. Transitions

Part III. The Two Faces of Causation

Chapter 11. Receptive Connections

Chapter 12. A Tutorial: Some simplified models

Chapter 13. Does Receptivity Logically Supervene on the Physical?

Chapter 14. The Carrier Theory of Causation

Chapter 15. The Consciousness Hypothesis

Chapter 16. Space, Time, and the Unity of the World

Chapter 17. Conclusion

Appendix A. David Lewis' Similarity Metric

**Appendix B. Prolog program for the Life world's ingressions**