D. Chalmers

A leading philosopher takes a mind-bending journey through virtual worlds, illuminating the nature of reality and our place within it. Virtual reality is genuine reality; that's the central thesis of Reality+. In a highly original work of "technophilosophy," David J. Chalmers gives a compelling analysis of our technological future. He argues that virtual worlds are not second-class worlds, and that we can live a meaningful life in virtual reality. We may even be in a virtual world already. Along the way, Chalmers conducts a grand tour of big ideas in philosophy and science. He uses virtual reality technology to offer a new perspective on long-established philosophical questions. How do we know that there's an external world? Is there a god? What is the nature of reality? What's the relation between mind and body? How can we lead a good life? All of these questions are illuminated or transformed by Chalmers' mind-bending analysis. Studded with illustrations that bring philosophical issues to life, Reality+ is a major statement that will shape discussion of philosophy, science, and technology for years to come.

At any given time, a subject has a multiplicity of conscious experiences. A subject might simultaneously have visual experiences of a red book and a green tree, auditory experiences of birds singing, bodily sensations of a faint hunger and a sharp pain in the shoulder, the emotional experience of a certain melancholy, while having a stream of conscious thoughts about the nature of reality. These experiences are distinct from each other: a subject could experience the red book without the singing birds, and could experience the singing birds without the red book. But at the same time, the experiences seem to be tied together in a deep way. They seem to be unified, by being aspects of a single encompassing state of consciousness.

What is consciousness? How does the subjective character of consciousness fit into an objective world? How can there be a science of consciousness? In this sequel to his groundbreaking and controversial The Conscious Mind, David Chalmers develops a unified framework that addresses these questions and many others. Starting with a statement of the "hard problem" of consciousness, Chalmers builds a positive framework for the science of consciousness and a nonreductive vision of the metaphysics of consciousness. He replies to many critics of The Conscious Mind, and then develops a positive theory in new directions. The book includes original accounts of how we think and know about consciousness, of the unity of consciousness, and of how consciousness relates to the external world. Along the way, Chalmers develops many provocative ideas: the "consciousness meter", the Garden of Eden as a model of perceptual experience, and The Matrix as a guide to the deepest philosophical problems about consciousness and the external world.

The chapter presents the Hegelian Argument for panpsychism. It is inspired by Hegel’s dialectical method in exploring the possibility of a conceptual middle-ground between materialism and dualism. It seeks a ‘synthesis’ between these two antithetical positions. The chapter establishes this synthesis by elucidating the opposition of materialism and dualism, as well as their respective strengths and weaknesses: Materialism is supported by causal arguments, which claim that causal explanations must be grounded in physical properties. If phenomenal properties are to be causally relevant, they have to be grounded in physical properties. This entails the truth of materialism. Conceivability arguments undermine the truth of materialism: There is no strong modal entailment between physical and phenomenal properties; physicalism requires that physical facts necessitate all other facts. Conversely, dualism is supported by conceivability arguments and heavily criticized by causal arguments. It presents constitutive Russellian panpsychism as a promising synthesis in this dialectic.

This chapter addresses another Kantian topic: the unity of consciousness. It looks at certain arguments that have been made against the unity of consciousness to determine whether they are good arguments against the unity thesis as we understand it. After fleshing out the unity thesis further, it applies the thesis to certain currently popular philosophical theories of consciousness, arguing that the thesis is incompatible with these theories: if the unity thesis is true, then these theories are false. The goal is not to conclusively prove the unity thesis, and indeed it is not certain that it is true. But it is suggested at least that the thesis is plausible, that it captures a strong intuition about the nature of consciousness, and that there are no knockdown arguments against it. If the thesis is true, it is likely to have important consequences for a theory of consciousness.

This chapter uses the movie _The Matrix_ to address issues about our knowledge of the external world. On the face of it, the movie raises a version of Descartes' skeptical challenge. Just as I cannot know I am not the victim of a evil genius, I also cannot know I am not in a matrix. And if I am in a matrix, so the challenge goes, most of my beliefs are false: I am not really seeing a table in front of me, I do not really live in Australia, and so on. It is argued that this thought, although initially compelling, is wrong. Even if I am in a matrix, there are still tables and cars, and most of my beliefs remain true. That is, the hypothesis that I am in a matrix is not a skeptical hypothesis, as traditionally thought. Instead, it is a sort of metaphysical hypothesis about the underlying nature of our world. If we are in a matrix, the physical world is more fundamentally a computational world, in which things are made of bits. This is an interesting new metaphysics, but it does not lead to skepticism. The chapter argues that much the same applies to many traditional skeptical hypotheses, such as the evil demon hypothesis and the hypothesis that my life is a dream. This does not provide a complete victory over skepticism, but it nevertheless helps in the project of vindicating knowledge of the external world.

This chapter takes up the issue of the contents of experience where Chapter 11 leaves off. It argues that the account of Fregean content in Chapter 11 has some important inadequacies concerning its relation to phenomenology and leaves some crucial issues unexplained. It develops a further account involving so-called Edenic content: content that represents primitive properties (such as primitive redness or greenness), properties that are not instantiated in our world but that one can imagine might have been instantiated in the Garden of Eden. The chapter brings this account to bear on many questions in the philosophy of perception, including questions about color constancy, spatial content, the representation of objects, and more.

This chapter analyzes aspects of the relationship between consciousness and intentionality. It focuses on the phenomenal character and the intentional content of perceptual states, canvassing various possible relations among them. It argues that there is a good case for a sort of representationalism, although this may not take the form that its advocates often suggest. By mapping out some of the landscape, the chapter tries to open up territory for different and promising forms of representationalism to be explored in the future. In particular, it argues for a nonreductive, narrow, and Fregean variety of representationalism, which contrasts strongly with more widely explored varieties. It concludes with some words about the fundamental relationship between consciousness and intentionality.

Confronted with the apparent explanatory gap between physical processes and consciousness, philosophers have reacted in many different ways. Some deny that any explanatory gap exists at all. Some hold that there is an explanatory gap for now but that it will eventually be closed. Some hold that the explanatory gap corresponds to an ontological gap in nature. This chapter explores another reaction to the explanatory gap. Those who react in this way agree that there is an explanatory gap, but they hold that it stems from the way we _think_ about consciousness. In particular, this view locates the gap in the relationship between our concepts of physical processes and our concepts of consciousness, rather than in the relationship between physical processes and consciousness themselves.

This chapter focuses on our knowledge of consciousness. The special phenomenal concepts of Chapter 8 lead to a distinctive class of “direct phenomenal beliefs,” which are argued to have many interesting epistemological properties. For a start, they support a sort of infallibility thesis: direct phenomenal beliefs cannot be false. This thesis can do only limited epistemological work, but analysis of these beliefs leads to a more substantial epistemological view that involves a central role for acquaintance. The framework is used to analyze two important issues in the epistemology of consciousness: epistemological arguments against nonreductive views of consciousness, as well as Wilfrid Sellars's arguments against the “given.”. The chapter concludes with some morals about the general role of consciousness in epistemology.

This chapter develops an account of the distinctive nature of phenomenal concepts, grounded in part in an analysis of the epistemological and conceptual observations that drive the arguments against materialism. It argues that phenomenal concepts behave in a way that is quite unlike most other concepts, involving a very strong sort of direct reference, on which the phenomenal qualities that are the referents of the concepts are also somehow present inside their sense. Here, the two-dimensional framework is again a useful tool in analyzing the phenomenon. The account in this chapter is in principle compatible with materialism; in recent years some materialists have developed closely related accounts, but think the account itself is considered fairly neutral.

This chapter addresses a related form of opposition to the anti-materialist arguments. Some type-B materialists allow that a unique epistemic gap exists between physics and consciousness: truths about consciousness are not deducible from physical truths, but truths about water, life, and other high-level phenomena are deducible from physical truths. Others argue that these epistemic gaps arise in many high-level domains. It is argued that there are in fact a priori entailments from a nearly physical base to truths about water, life, and so on. The base needs to be expanded a little to allow indexicals, a “that's all” truth, and of course truths about consciousness. But from this base, other ordinary macroscopic truths can be deduced by a priori reasoning. The argument here turns on some general observations about concepts and conceptual analysis. One of the key points is that there can be a priori entailments even in the absence of definitions or explicit analyses.

This chapter is mainly devoted to the conceivability argument against materialism, viewed through the lens of the two-dimensional semantic framework. The key issue is whether conceivability entails metaphysical possibility. The key opponent is the type-B materialist, who denies the entailment. Many objections and putative counterexamples to the conceivability-possibility thesis have been mooted: the chapter discusses fifteen or so putative counterexamples, along with ten or so objections of other sorts to the conceivability argument. It also sketches a positive grounding for the sort of modal rationalism that drives the conceivability argument.

This chapter starts by presenting the central arguments against materialism, which involve establishing an epistemic gap between the physical and the phenomenal, and moves from there to an ontological gap. It then distinguishes between the three most important sorts of materialist opposition to these arguments: type-A materialism (which denies the epistemic gap), type-B materialism (which accepts the epistemic gap but denies the ontological gap), and type-C materialism (which holds that there is a deep epistemic gap but one that will be closed in the limit). It argues that each of these three views should be rejected. The second half of the chapter investigates the most important nonreductive views that result: type-D dualism (or interactionism), type-E dualism (or epiphenomenalism), and type-F monism (Russellian monism, or panprotopsychism). It discusses the pros and cons of each, suggesting that all three have significant attractions and that none has fatal flaws.

This chapter addresses the question: how can we isolate the neural correlate of consciousness (NCC) in the absence of a “consciousness meter,” which measures consciousness directly? The obvious answer is that we rely on verbal reports and other behavioral indicators of consciousness. Importantly, the use of these indicators tacitly relies on pre-experimental principles that connect these behavioral indicators to consciousness. The use of these principles is unavoidable, and this has a number of interesting consequences for the science. After drawing out some of the key principles, the chapter presents some conclusions that bear directly on the practical methodology of the scientific work in this area.

The cornerstone of recent work in the neuroscience of consciousness has been the search for the “neural correlate of consciousness” (NCC). This phrase refers to the neural system or systems primarily associated with conscious experience. This chapter addresses conceptual issues about what it is to be an NCC. The question generates all sorts of interesting puzzles: Must there be one neural correlate of consciousness, or might there be many? How strong a correlation is required? Over what range of cases? The chapter addresses these questions and a number of others, and puts forward a proposal for understanding the notion of an NCC.

Consciousness poses the most baffling problems in the science of the mind. There is nothing that we know more intimately than conscious experience, but there is nothing that is harder to explain. All sorts of mental phenomena have yielded to scientific investigation in recent years, but consciousness has stubbornly resisted. This chapter first isolates the truly hard part of the problem of consciousness, separating it from more tractable parts and giving an account of why it is so difficult to explain. It critiques some recent work that uses reductive methods to address consciousness and argues that these methods inevitably fail to come to grips with the hardest part of the problem. Once this failure is recognized, the door to further progress is opened. The second half of the chapter argues that, if we move to a new kind of nonreductive explanation, a naturalistic account of consciousness can be given.

Philosophers have reacted in different ways to the apparent explanatory gap between physical processes and consciousness. Some deny that any explanatory gap exists at all. Some hold that there is an explanatory gap for now, but that it will eventually be closed. Some hold that the explanatory gap corresponds to an ontological gap in nature. This chapter explores another reaction to the explanatory gap — those who react in this way agree that there is an explanatory gap, but they hold that it stems from the way we _think_ about consciousness. In particular, this view locates the gap in the relationship between our concepts of physical processes and our concepts of consciousness, rather than in the relationship between physical processes and consciousness themselves.

A number of popular arguments for dualism start from a premise about an epistemic gap between physical truths about truths about consciousness, and infer an ontological gap between physical processes and consciousness. Arguments of this sort include the conceivability argument, the knowledge argument, the explanatory-gap argument, and the property dualism argument. Such arguments are often resisted on the grounds that epistemic premises do not entail ontological conclusion. My view is that one can legitimately infer ontological conclusions from epistemic premises, if one is very careful about how one reasons. To do so, the best way is to reason first from epistemic premises to modal conclusions, and from there to ontological conclusions. Here, the crucial issue is the link between the epistemic and modal domains. How can one reason from theses about what is knowable or conceivable to theses about what is necessary or possible? To bridge the epistemic and modal domains, the framework of two-dimensional semantics can play a central role. I have used this framework in earlier work to mount an argument against materialism. Here, I want to revisit the argument, laying it out in a more explicit and careful form, and responding to a number of objections. In what follows I will concentrate mostly on the conceivability argument. I think that very similar considerations apply to the other arguments mentioned above, however. In the final section of the paper, I show how this analysis might yield a unified treatment of a number of anti-materialist arguments.

This chapter explores the conceptual landscape of the most important, current critique of panpsychism—the combination problem. He sets out from the ‘locus classicus’: William James’s presentation of the combination problem in his 1890 _The Principles of Psychology_. He discerns three ways of formulating the problem, which evolve around three distinct characteristics of phenomenal states: the subject combination problem, the quality combination problem, and the structural combination problem. Chalmers then turns to seven subversions of these three versions. The first four are connected to the subject combination problem. Subversion five and six are connected to the quality combination problem. And the final explication is connected to the structural combination problem. The chapter closes by presenting various solutions and answers to these explications of the combination problem.