David Chalmers

The easy problems of consciousness are those that seem directly susceptible to the standard methods of cognitive science, whereby a phenomenon is explained in terms of computational or neural mechanisms. The hard problems are those that seem to resist those methods. The easy problems are easy precisely because they concern the explanation of cognitive abilities and functions. Once we have specified the neural or computational mechanism that performs the function of verbal report, for example, the bulk of our work in explaining reportability is over. Baars theory of cognitive accessibility addresses many aspects of human cognition and shows promise as a theory of awareness, the functional correlate of conscious experience, but an explanation of experience itself is not on offer. The key is the conceptual point that the explanation of functions does not suffice for the explanation of experience.

In my book _The Conscious Mind_, I deny a number of claims that John Searle finds "obvious", and I make some claims that he finds "absurd". But if the mind/body problem has taught us anything, it is that nothing about consciousness is obvious, and that one person's obvious truth is another person's absurdity. So instead of throwing around this sort of language, it is best to examine the claims themselves and the arguments that I give for them, to see whether Searle says anything of substance that touches them.

Chapter 1: Two Concepts of Mind. I distinguish the phenomenal and psychological concepts of mind. I argue that every mental state is a phenomenal state, a psychological state, or a hybrid of the two. I discuss the two mind-body problems corresponding to the two concepts of mind, and discuss the various senses of the term “consciousness”. Chapter 2: Supervenience and Explanation. I distinguish varieties of supervenience, especially logical and natural supervenience, where supervening properties covary with base properties across either logically possible or naturally possible worlds. Materialism is the thesis that all positive properties globally metaphysically supervene on microphysical properties. A property is reductively explainable in terms of physical properties if it globally logically supervenes on those properties.

This work is a study of the place of conscious experience in the natural order. In the first part, I examine the prospects for a reductive explanation of consciousness of the kind that has proved successful for other natural phenomena. I develop a systematic framework centered on the notion of supervenience for dealing with the metaphysical and explanatory issues involved, and apply this framework to consciousness. I give a number of arguments to the conclusion that consciousness is not logically supervenient on the physical, and therefore cannot be reductively explained. I illustrate this with a critique of potential explanations using the methods of cognitive modeling, neuroscience, and evolutionary biology. I further argue for a form of dualism, on which consciousness is seen as a non-physical property that supervenes on the physical by a lawful connection. In the second part, I move toward a positive theory of consciousness, focusing on the nature of the laws that connect consciousness and the physical. I deal at length with the relation between consciousness and judgments about consciousness; this provides a nexus between consciousness and cognition that can be exploited to strongly constrain a theory. In addition, I provide and analyze thought-experiments in arguing for the conclusion that any two systems with the same abstract functional organization will have the same conscious experience, and so arguing against what have been called the "absent qualia" and "inverted qualia" hypotheses. Finally, I briefly outline some further work: a double-aspect theory of consciousness based on the notion of information, an investigation of the relationship between computation and consciousness, and an application to some problems in quantum mechanics.

What is the mind? Is consciousness a process in the brain? How do our minds represent the world? Philosophy of Mind: Classical and Contemporary Readings is a grand tour of writings on these and other perplexing questions about the nature of the mind. The most comprehensive collection of its kind, the book includes sixty-three selections that range from the classical contributions of Descartes to the leading edge of contemporary debates. Extensive sections cover foundational issues, the nature of consciousness, and the nature of mental content. Three of the selections are published here for the first time, while many other articles have been revised especially for this volume. Each section opens with an introduction by the editor. Philosophy of Mind is suitable for students at all levels and also for general readers.

Cartesian arguments for global skepticism about the external world start from the premise that we cannot know that we are not in a Cartesian scenario such as an evil-demon scenario, and infer that because most of our empirical beliefs are false in such a scenario, these beliefs do not constitute knowledge. Veridicalist responses to global skepticism respond that arguments fail because in Cartesian scenarios, many or most of our empirical beliefs are true. Some veridicalist responses have been motivated using verificationism, externalism, and coherentism. I argue that a more powerful veridicalist response to global skepticism can be motivated by structuralism, on which physical entities are understood as those that play a certain structural role. I develop the structuralist response and address objections.

*[[This paper appears in _Toward a Science of Consciousness II: The Second Tucson Discussions and Debates_ (S. Hameroff, A. Kaszniak, and A.Scott, eds), published with MIT Press in 1998. It is a transcript of my talk at the second Tucson conference in April 1996, lightly edited to include the contents of overheads and to exclude some diversions with a consciousness meter. A more in-depth argument for some of the claims in this paper can be found in Chapter 6 of my book _The Conscious Mind_ (Chalmers, 1996). ]].

This appeared in Philosophy and Phenomenological Research 59:473-93, as a response to four papers in a symposium on my book The Conscious Mind. Most of it should be comprehensible without having read the papers in question. This paper is for an audience of philosophers and so is relatively technical. It will probably also help to have read some of the book. The papers I’m responding to are: Chris Hill & Brian McLaughlin, There are fewer things in reality than are dreamt of in Chalmers’ philosophy Brian Loar, David Chalmers’ The Conscious Mind Sydney Shoemaker, On David Chalmers’ The Conscious Mind Stephen Yablo, Concepts and consciousness Contents.

I would like to thank the authors of the 26 contributions to this symposium on my article “The Singularity: A Philosophical Analysis”. I learned a great deal from the reading their commentaries. Some of the commentaries engaged my article in detail, while others developed ideas about the singularity in other directions. In this reply I will concentrate mainly on those in the first group, with occasional comments on those in the second. A singularity (or an intelligence explosion) is a rapid increase in intelligence to superintelligence (intelligence of far greater than human levels), as each generation of intelligent systems creates more intelligent systems in turn. The target article argues that we should take the possibility of a singularity seriously, and argues that there will be superintelligent systems within centuries unless certain specific defeating conditions obtain.

This is just a beginning categorization. I claim no 'objective correctness' for it. And of course the categories can be fluid, and the same joke can be a member of more than one category (and perhaps it will be funnier if it is). But thinking about the jokes which I can recall from the Humour Weekend, most seem to fall squarely into one or another category, indicating that perhaps this is a useful way of dividing jokes. It seems to me that the "causes of humour" in all 4 classes are different, coming from different parts of the brain.

What are the philosophical views of contemporary professional philosophers? We surveyed many professional philosophers in order to help determine their views on 30 central philosophical issues. This article documents the results. It also reveals correlations among philosophical views and between these views and factors such as age, gender, and nationality. A factor analysis suggests that an individual's views on these issues factor into a few underlying components that predict much of the variation in those views. The results of a metasurvey also suggest that many of the results of the survey are surprising: philosophers as a whole have quite inaccurate beliefs about the distribution of philosophical views in the profession.

William of Ockham's semantic theory was founded on the idea that thought takes place in a language not unlike the languages in which spoken and written communication occur. This mental language was held to have a number of features in common with everyday languages. For example, mental language has simple terms, not unlike words, out of which complex expressions can be constructed. As with words, each of these terms has some meaning, or signification; in fact Ockham held that the signification of everyday words derives precisely from the signification of mental terms. Furthermore, the meaning of a mental expression depends directly on the meaning of its constituent terms, as is the case with expressions in more familiar languages.

Scott Soames’ Reference and Description contains arguments against a number of different versions of two-dimensional semantics. After early chapters on descriptivism and on Kripke’s anti-descriptivist arguments, a chapter each is devoted to the roots of twodimensionalism in “slips, errors, or misleading suggestions” by Kripke and Kaplan, and to the two-dimensional approaches developed by Stalnaker (1978) and by Davies and Humberstone (1981). The bulk of the book (about 200 pages) is devoted to “ambitious twodimensionalism”, attributed to Frank Jackson, David Lewis, and me. After a quick overview of two-dimensional approaches, I will focus on Soames’ discussion of ambitious twodimensionalism. I will then turn to a system advocated by Soames that is itself strikingly reminiscent of a two-dimensional approach. Two-dimensional semantic theories are varieties of possible-worlds semantics on which linguistic items can be evaluated relative to possibilities in two different ways, yielding two sorts of intensional semantic values, which can be seen as two “dimensions” of meaning. The second dimension is the familiar sort of Kripkean evaluation in metaphysically possible worlds, so that necessarily coextensive terms (such as ‘Hesperus’ and ‘Phosphorus’ or ‘water’ and ‘H2O’) always have the same semantic value. The first dimension behaves differently, so that there are typically at least some cases where necessarily coextensive terms have different semantic values on the first dimension. For this reason, the two-dimensional framework is sometimes seen as a way of granting many of the insights of a Kripkean approach to meaning (on the second dimension), while retaining elements of a Fregean approach to meaning (on the first dimension)