ThinkBlog

On Consciousness and Its Place in Nature, by David J. Chalmers

1.
“Russell pointed out that physics characterizes physical entities and properties by their relations to one another and to us. […] At the same time, physics says nothing about the intrinsic nature of these entities and properties. […] So this is one metaphysical problem: what are the intrinsic properties of fundamental physical systems?”

2.
In the eleventh section of his paper, Chalmers reintroduces one of the fundamental problems with a materialistic view of consciousness in a way that sets the stage for an answer in what he calls type-F monism. This passage is particularly interesting because of this question regarding the intrinsic nature of that which is functionally described by physics. It is usually taken for granted in the empirical sciences, including psychology, that physics is complete where we can accurately measure data, infer conclusions, and test hypotheses. But, taking a cue from Bertrand Russell’s The Analysis of Matter (1927), Chalmers points out what’s missing in physicalism as a viable theory of consciousness—and the viability of something more than reductive materialistic explanations of the mind—by pointing out the deficiencies of physics itself. He does this by pointing out, what physics does describe, viz. the relations of entities within physical systems. We know what a quark is by the way it relates to other physical entities; likewise with all the elements of atoms. We know how to define mass in terms of resistance to acceleration (from another entity having mass), but we do not have a substantive explanation of the “intrinsic properties associated with mass,” or of the intrinsic physical constituency of a quark itself. If we cannot deduce or observe the intrinsic properties of fundamental physical systems, then there is a gap precisely there in the explanation of consciousness which, claims Chalmers (with Russell), provides enough ontological gap for there to exist something intrinsic to the nature of the physical for which relational, dispositional physics cannot account.

3.
In order to understand how Chalmers reaches this conclusion and somewhat strange hypothesis for the nature of consciousness, it is necessary to evaluate his project in this article. He gives a sweeping overview of the problems that have traditionally beset discussions of the metaphysics of consciousness from an admittedly anti-materialist viewpoint. Distinguishing between the “hard” and “easy” problems of consciousness, Chalmers claims that problems of empirical investigation, those things readily accounted for in a physicalist system, are “easy”—we can see how there can be eventual neurobiological explanations of the “easy” problems of consciousness. Stimulus discrimination, internal state monitoring, and information report are examples of these problems. The so-called “hard” problem of consciousness, as Chalmers continues, is that of experience. There is something that it is to be like a human being, to have a conscious experience, which (Chalmers argues, though disputable to some materialists) is unaccounted for by a purely physicalist view of consciousness. Even if we are able to explain cognitive functions and systems in terms of structure and dynamics, we will nevertheless not have explained the subjective experience that is tied inextricably to consciousness. In the third section of his paper, Chalmers sets forth three arguments against materialism to which he refers in later sections. Specifically, the “explanatory argument” is tied explicitly to the distinction of the hard and easy problems of consciousness: physical theories of consciousness can account for structure and function and no more; but this is insufficient to explain consciousness; therefore, physical theories of consciousness are inadequate. This is a part of what Chalmers seeks to answer in his proposal of type-F monism, or what he calls panprotopsychism, by offering a theory that postulates precisely that “the natural world contains more than the physical world.” The second broad argument against materialism is the “conceivability argument,” involving the thought experiment of zombies—that is, beings with the exact and comprehensive physical constitution of human beings which nevertheless have no conscious experience—to provide the hinge of the debate. Specifically, since it is conceivable that zombies exist, it is metaphysically possible that they do exist; hence, consciousness is nonphysical. Finally, there is the “knowledge argument,” which states that there are facts about conscious experience that cannot be deduced from physical facts. This argument is favored by epiphenomenalist Frank Jackson, as exemplified in Mary the neuroscientist who from a black and white room learns everything there is to know about the workings of the human brain and all the physical facts about what constitutes the structure and function of consciousness—only to learn something genuinely new when she actually leaves the room and experiences “red” (and so forth) for herself. Again, this is the proposal of Chalmers’ panprotopsychism, that there are intrinsic properties of which physical entities are constituted that account for phenomenal, subjective experience in a way that purely physical science cannot. All of these arguments amount to one crucial underlying argument against materialism: that there is an epistemic gap between physical and phenomenal truths, which implies the existence of an ontological gap—and therefore, materialism is false.

Chalmers goes on to explain the positions of what he sees as the three broad views that materialists tend to take in arguments about consciousness. The first are whom he calls type-A materialists, who deny that there is an epistemic gap between physical and phenomenal truths. For the type-A materialist, either consciousness does not exist as such, or by explaining fine neurobiological detail along with the functional state and the environmental position, we have thereby accounted for phenomenal truths and conscious states. For Chalmers, this denies the obvious, and I am inclined to agree; there is something to phenomenal, subjective experience—and in the light of a lack of extraordinary evidence, type-A materialism does not seem to be adequate. This is a different problem than that of “vitalism” to account for life, or the reduction of chemistry from physics: there is conscious experience that remains unexplained by the explanation of neurobiology, &c. The second type of materialism holds that while there is an epistemic gap, there is no ontological gap: type-B materialists, then, deny that from the premise that there is an epistemic gap between physical and phenomenal truths it follows that phenomenal reality is somehow greater than or removed from a full explanation of physical reality. In the same way that water and H2O are identical, but are different concepts, so for the type-B materialist are physical states identical with conscious experiences. Chalmers argues at length against the type-B materialists, claiming that this epistemic gap is different than the epistemic gap that has existed in other, hard sciences, and that a type-B materialist essentially gives up a reductive explanation of consciousness.

Eventually, through a nuanced argument in section six, Chalmers reaches the conclusion that materialism is false—or that type-F monism, panprotopsychism, is true. This will be revisited momentarily. Type-C materialism concedes that there is presently an epistemic gap between physical and phenomenal truths, but that it will be closed eventually. According to Chalmers, this position is either untenable or collapses into one of the other forms of materialism, or into a kind of Cartesian dualism, or again, into type-F monism. The basic argument against type-C materialism that makes it untenable for Chalmers is as follows: “physical descriptions of the world characterize the world in terms of structure and dynamics”; from these descriptive truths one can only deduce more truths about structure and dynamics; those sorts of truths are not truths about conscious experience.

Having dispensed with reductive materialism, Chalmers argues that we must expand our conception of what constitutes natural reality, to either take consciousness as a fundamental aspect of universal constitution or as necessitated by something fundamental—hence the proto- in panprotopsychism, which holds to the first position. Essentially, if arguments against materialism are substantial enough to knock them down, physics cannnot fully explain consciousness, and we must look to the most viable alternatives, viz. dualism (types D and E) and type-F. Type-D dualism is the position that microphysics is not causally closed, that “[p]sychophysical principles specifying the effect of phenomenal states on physical states will also play an irreducible role” alongside physical principles. This view of consciousness includes Descartes’ substance dualism, in which there are two distinct substances working on one another, as well as property dualism, which holds that there is a fundamental substance which includes physical as well as phenomenal properties. Answering the strongest objection to this theory of consciousness, viz. that it flies in the face of Newtonian physics, Chalmers counters that in fact, quantum mechanics suggests a kind of type-D dualism itself, and that the objection from contemporary knowledge of physics is only a kind of appeal to authority. On the other hand, Chalmers says, we can accept the causal closure of microphysics such that no phenomenal properties play any kind of role whatsoever in determining the nature of physical reality as such. On this view, referred to as epiphenomenalism, especially according to Frank Jackson, consciousness is an evolutionary appendage having no effect on the natural order but simply arising from it. This means that there is no causative mental process working on the physical body in any circumstance; the flow of causation is one-way. Jerking away from a flame would then not be due to the pain, but merely concurrent with it; seemingly rational decisions that end in physical actions are actually not causing those actions, and so forth. Chalmers is more willing than I to concede that while it is counterintuitive, it is still a contender for an explanation of reality. The sixth and final option that Chalmers is willing to consider as a viable explanation of consciousness is the aforementioned panprotopsychism. With this type-F monism, Chalmers draws deeply on scientific ignorance of the intrinsic nature of physical entities to propose a system in which phenomenal characteristics are intertwined with the physical by nature, instead of relationally or structural-dynamically in the conception of contemporary physics. Phenomenal properties, then, play a causal role along with physical properties in a causally closed microphysical schema, but would constitute the intrinsic nature of physical properties instead of being defined relationally. This is what Chalmers is doing in the above quote, challenging notions that physics alone as we know it today is able to explain consciousness. Chalmers claims that it is reasonable to expect that there are neutral protophenomenal elements of the natural world which by their relation with one another constitute what we understand as the physical world, while each of the has phenomenal properties in itself because of its intrinsic nature. Objections to this, other than the obvious about physics not constituting the basest understanding of the natural world, include that of counter-intuition and what is called the combination problem for panpsychism itself. The combination problem is that, if there are phenomenal properties intrinsic to some protophenomenal properties, then it still must be shown how these various phenomenal elements combine in each human being to make one coherent, rich, differentiated structure. Resorting to higher-level processing arguments to answer the combination problem, says Chalmers, turns type-F monism into type-D dualism. In conclusion, Chalmers briefly mentions Berkeleyan idealism (type-I monism) and overdetermination (type-O dualism), but does not treat them as the most rational or coherent alternatives to materialism.

4.
Type-F monism is an attractive alternative to materialism if for no other reason than it seems so strange yet coherent. Invoking Russell is perhaps not the best course of action for Chalmers, though, in introducing panprotopsychism: for all the respect he deserves as a critical thinker, Russell could not have known certain things about the nature of science. On the other hand, physics has not given us any more knowledge about the intrinsic nature of things, so there is no direct evidence contradicting type-F monism in the same way that Chalmers says occurs with all three broad types of materialism. The idea that each particle, each of the underlying intrinsic properties of natural reality has its own “what it is like to be,” its own conscious experience in a sense, its own phenomenal actuality—this seems very close to animism, the idea that all things have spirit, and are alive. This seems untenable, but only because it is so counterintuitive in light of modern philosophy. Brentano (1995) and Chisholm (1957), for example, held that intentionality was the mark of conscious experience—but nowhere in their systems does one find metaphysics of consciousness explained in terms of intrinsic phenomenal properties. Still, this seems a much better alternative to Jackson’s (1982) epiphenomenalism, which I see as untenable because it makes us simply conscious observers of the deterministic march of reality. We could have held to this perhaps in pre-Socratic Greece, before we knew how rich and complex the psyche was, before we were able to infer relationships between cognitive, neurobiological processes and physiological, bodily actions. But today it seems ridiculous, a step backward from materialism itself for no other reason than to try to have the metaphysical schema both ways: a causally closed microphysics along with qualitative experience. The idea that physics does not provide a fully comprehensive explanation of reality, however, is compelling. Cartesian dualism has been largely rejected these days for what I think should be similar reasons to reject epiphenomenalism; but the spirit of Descartes may be preserved in panprotopsychism. Certainly Ryle (1949) and Putnam (1968) would dismiss it outright as mysticism in relation to a clear-cut explanation of cognition in terms of behavior. But it seems that nevertheless there remains a gaping hole in the behavioristic account of consciousness, viz. the existence of qualia, especially Nagel’s (1974) “what it is like to be” problem—there is no account of what it is like to be a human being in describing “psychology in physical language” (Carnap, 1932). Panprotopsychism should prove a fascinating jumping-off point for research as advancements are made in quantum physics; there is still hope for a non-materialistic account of consciousness if it ultimately fails, but overall panprotopsychism seems the most compelling and, in a sense, most cutting edge option to philosophers of mind today.

References

Brentano, F. (1995). “The distinction between mental and physical phenomena.” In Psychology from an empirical standpoint. D. Terrell, A. Rancurello, & L. McAlister, Trans; L. McAlister, Ed. New York: Routledge.

Carnap, R. (1932). “Psychology in physical language.” In Erkenntnis, 3:107-42. Norwell: Kluwer Academic Publishers.

Chalmers, D. J. (2002). “Consciousness and its place in nature.” From Blackwell guide to the philosophy of mind. S. Stich & T. Warfield, Eds.

Chisholm, R. (1957). “Intentional inexistence.” From Perceiving: A philosophical study. New York: Cornell UP.

Jackson, F. (1982). “Epiphenomenal qualia.” From Philosophical quarterly 32:127-136.

Nagel, T. (1974). “What is it like to be a bat?” From Philosophical review 83:435-50. New York: Cornell UP.

Putnam, H. (1968). “Brains and behavior.” From Analytical philosophy: Second series,
in Blackwell, 1968.

Russell, B. (1927). The analysis of matter. London: Kegan Paul.

Ryle, G. (1949). “Descartes’ myth.” From The concept of mind. In Hutchinson, 1949. Oxford: Oxford UP.

All citations taken from:

Chalmers, D. J., Ed. (2002). Philosophy of mind: Classical and contemporary readings.
New York: Oxford UP.

On Consciousness and Its Place in Nature, by David J. Chalmers

1.
“Russell pointed out that physics characterizes physical entities and properties by their relations to one another and to us. […] At the same time, physics says nothing about the intrinsic nature of these entities and properties. […] So this is one metaphysical problem: what are the intrinsic properties of fundamental physical systems?”

2.
In the eleventh section of his paper, Chalmers reintroduces one of the fundamental problems with a materialistic view of consciousness in a way that sets the stage for an answer in what he calls type-F monism. This passage is particularly interesting because of this question regarding the intrinsic nature of that which is functionally described by physics. It is usually taken for granted in the empirical sciences, including psychology, that physics is complete where we can accurately measure data, infer conclusions, and test hypotheses. But, taking a cue from Bertrand Russell’s The Analysis of Matter (1927), Chalmers points out what’s missing in physicalism as a viable theory of consciousness—and the viability of something more than reductive materialistic explanations of the mind—by pointing out the deficiencies of physics itself. He does this by pointing out, what physics does describe, viz. the relations of entities within physical systems. We know what a quark is by the way it relates to other physical entities; likewise with all the elements of atoms. We know how to define mass in terms of resistance to acceleration (from another entity having mass), but we do not have a substantive explanation of the “intrinsic properties associated with mass,” or of the intrinsic physical constituency of a quark itself. If we cannot deduce or observe the intrinsic properties of fundamental physical systems, then there is a gap precisely there in the explanation of consciousness which, claims Chalmers (with Russell), provides enough ontological gap for there to exist something intrinsic to the nature of the physical for which relational, dispositional physics cannot account.

3.
In order to understand how Chalmers reaches this conclusion and somewhat strange hypothesis for the nature of consciousness, it is necessary to evaluate his project in this article. He gives a sweeping overview of the problems that have traditionally beset discussions of the metaphysics of consciousness from an admittedly anti-materialist viewpoint. Distinguishing between the “hard” and “easy” problems of consciousness, Chalmers claims that problems of empirical investigation, those things readily accounted for in a physicalist system, are “easy”—we can see how there can be eventual neurobiological explanations of the “easy” problems of consciousness. Stimulus discrimination, internal state monitoring, and information report are examples of these problems. The so-called “hard” problem of consciousness, as Chalmers continues, is that of experience. There is something that it is to be like a human being, to have a conscious experience, which (Chalmers argues, though disputable to some materialists) is unaccounted for by a purely physicalist view of consciousness. Even if we are able to explain cognitive functions and systems in terms of structure and dynamics, we will nevertheless not have explained the subjective experience that is tied inextricably to consciousness. In the third section of his paper, Chalmers sets forth three arguments against materialism to which he refers in later sections. Specifically, the “explanatory argument” is tied explicitly to the distinction of the hard and easy problems of consciousness: physical theories of consciousness can account for structure and function and no more; but this is insufficient to explain consciousness; therefore, physical theories of consciousness are inadequate. This is a part of what Chalmers seeks to answer in his proposal of type-F monism, or what he calls panprotopsychism, by offering a theory that postulates precisely that “the natural world contains more than the physical world.” The second broad argument against materialism is the “conceivability argument,” involving the thought experiment of zombies—that is, beings with the exact and comprehensive physical constitution of human beings which nevertheless have no conscious experience—to provide the hinge of the debate. Specifically, since it is conceivable that zombies exist, it is metaphysically possible that they do exist; hence, consciousness is nonphysical. Finally, there is the “knowledge argument,” which states that there are facts about conscious experience that cannot be deduced from physical facts. This argument is favored by epiphenomenalist Frank Jackson, as exemplified in Mary the neuroscientist who from a black and white room learns everything there is to know about the workings of the human brain and all the physical facts about what constitutes the structure and function of consciousness—only to learn something genuinely new when she actually leaves the room and experiences “red” (and so forth) for herself. Again, this is the proposal of Chalmers’ panprotopsychism, that there are intrinsic properties of which physical entities are constituted that account for phenomenal, subjective experience in a way that purely physical science cannot. All of these arguments amount to one crucial underlying argument against materialism: that there is an epistemic gap between physical and phenomenal truths, which implies the existence of an ontological gap—and therefore, materialism is false.

Chalmers goes on to explain the positions of what he sees as the three broad views that materialists tend to take in arguments about consciousness. The first are whom he calls type-A materialists, who deny that there is an epistemic gap between physical and phenomenal truths. For the type-A materialist, either consciousness does not exist as such, or by explaining fine neurobiological detail along with the functional state and the environmental position, we have thereby accounted for phenomenal truths and conscious states. For Chalmers, this denies the obvious, and I am inclined to agree; there is something to phenomenal, subjective experience—and in the light of a lack of extraordinary evidence, type-A materialism does not seem to be adequate. This is a different problem than that of “vitalism” to account for life, or the reduction of chemistry from physics: there is conscious experience that remains unexplained by the explanation of neurobiology, &c. The second type of materialism holds that while there is an epistemic gap, there is no ontological gap: type-B materialists, then, deny that from the premise that there is an epistemic gap between physical and phenomenal truths it follows that phenomenal reality is somehow greater than or removed from a full explanation of physical reality. In the same way that water and H2O are identical, but are different concepts, so for the type-B materialist are physical states identical with conscious experiences. Chalmers argues at length against the type-B materialists, claiming that this epistemic gap is different than the epistemic gap that has existed in other, hard sciences, and that a type-B materialist essentially gives up a reductive explanation of consciousness.

Eventually, through a nuanced argument in section six, Chalmers reaches the conclusion that materialism is false—or that type-F monism, panprotopsychism, is true. This will be revisited momentarily. Type-C materialism concedes that there is presently an epistemic gap between physical and phenomenal truths, but that it will be closed eventually. According to Chalmers, this position is either untenable or collapses into one of the other forms of materialism, or into a kind of Cartesian dualism, or again, into type-F monism. The basic argument against type-C materialism that makes it untenable for Chalmers is as follows: “physical descriptions of the world characterize the world in terms of structure and dynamics”; from these descriptive truths one can only deduce more truths about structure and dynamics; those sorts of truths are not truths about conscious experience.

Having dispensed with reductive materialism, Chalmers argues that we must expand our conception of what constitutes natural reality, to either take consciousness as a fundamental aspect of universal constitution or as necessitated by something fundamental—hence the proto- in panprotopsychism, which holds to the first position. Essentially, if arguments against materialism are substantial enough to knock them down, physics cannnot fully explain consciousness, and we must look to the most viable alternatives, viz. dualism (types D and E) and type-F. Type-D dualism is the position that microphysics is not causally closed, that “[p]sychophysical principles specifying the effect of phenomenal states on physical states will also play an irreducible role” alongside physical principles. This view of consciousness includes Descartes’ substance dualism, in which there are two distinct substances working on one another, as well as property dualism, which holds that there is a fundamental substance which includes physical as well as phenomenal properties. Answering the strongest objection to this theory of consciousness, viz. that it flies in the face of Newtonian physics, Chalmers counters that in fact, quantum mechanics suggests a kind of type-D dualism itself, and that the objection from contemporary knowledge of physics is only a kind of appeal to authority. On the other hand, Chalmers says, we can accept the causal closure of microphysics such that no phenomenal properties play any kind of role whatsoever in determining the nature of physical reality as such. On this view, referred to as epiphenomenalism, especially according to Frank Jackson, consciousness is an evolutionary appendage having no effect on the natural order but simply arising from it. This means that there is no causative mental process working on the physical body in any circumstance; the flow of causation is one-way. Jerking away from a flame would then not be due to the pain, but merely concurrent with it; seemingly rational decisions that end in physical actions are actually not causing those actions, and so forth. Chalmers is more willing than I to concede that while it is counterintuitive, it is still a contender for an explanation of reality. The sixth and final option that Chalmers is willing to consider as a viable explanation of consciousness is the aforementioned panprotopsychism. With this type-F monism, Chalmers draws deeply on scientific ignorance of the intrinsic nature of physical entities to propose a system in which phenomenal characteristics are intertwined with the physical by nature, instead of relationally or structural-dynamically in the conception of contemporary physics. Phenomenal properties, then, play a causal role along with physical properties in a causally closed microphysical schema, but would constitute the intrinsic nature of physical properties instead of being defined relationally. This is what Chalmers is doing in the above quote, challenging notions that physics alone as we know it today is able to explain consciousness. Chalmers claims that it is reasonable to expect that there are neutral protophenomenal elements of the natural world which by their relation with one another constitute what we understand as the physical world, while each of the has phenomenal properties in itself because of its intrinsic nature. Objections to this, other than the obvious about physics not constituting the basest understanding of the natural world, include that of counter-intuition and what is called the combination problem for panpsychism itself. The combination problem is that, if there are phenomenal properties intrinsic to some protophenomenal properties, then it still must be shown how these various phenomenal elements combine in each human being to make one coherent, rich, differentiated structure. Resorting to higher-level processing arguments to answer the combination problem, says Chalmers, turns type-F monism into type-D dualism. In conclusion, Chalmers briefly mentions Berkeleyan idealism (type-I monism) and overdetermination (type-O dualism), but does not treat them as the most rational or coherent alternatives to materialism.

4.
Type-F monism is an attractive alternative to materialism if for no other reason than it seems so strange yet coherent. Invoking Russell is perhaps not the best course of action for Chalmers, though, in introducing panprotopsychism: for all the respect he deserves as a critical thinker, Russell could not have known certain things about the nature of science. On the other hand, physics has not given us any more knowledge about the intrinsic nature of things, so there is no direct evidence contradicting type-F monism in the same way that Chalmers says occurs with all three broad types of materialism. The idea that each particle, each of the underlying intrinsic properties of natural reality has its own “what it is like to be,” its own conscious experience in a sense, its own phenomenal actuality—this seems very close to animism, the idea that all things have spirit, and are alive. This seems untenable, but only because it is so counterintuitive in light of modern philosophy. Brentano (1995) and Chisholm (1957), for example, held that intentionality was the mark of conscious experience—but nowhere in their systems does one find metaphysics of consciousness explained in terms of intrinsic phenomenal properties. Still, this seems a much better alternative to Jackson’s (1982) epiphenomenalism, which I see as untenable because it makes us simply conscious observers of the deterministic march of reality. We could have held to this perhaps in pre-Socratic Greece, before we knew how rich and complex the psyche was, before we were able to infer relationships between cognitive, neurobiological processes and physiological, bodily actions. But today it seems ridiculous, a step backward from materialism itself for no other reason than to try to have the metaphysical schema both ways: a causally closed microphysics along with qualitative experience. The idea that physics does not provide a fully comprehensive explanation of reality, however, is compelling. Cartesian dualism has been largely rejected these days for what I think should be similar reasons to reject epiphenomenalism; but the spirit of Descartes may be preserved in panprotopsychism. Certainly Ryle (1949) and Putnam (1968) would dismiss it outright as mysticism in relation to a clear-cut explanation of cognition in terms of behavior. But it seems that nevertheless there remains a gaping hole in the behavioristic account of consciousness, viz. the existence of qualia, especially Nagel’s (1974) “what it is like to be” problem—there is no account of what it is like to be a human being in describing “psychology in physical language” (Carnap, 1932). Panprotopsychism should prove a fascinating jumping-off point for research as advancements are made in quantum physics; there is still hope for a non-materialistic account of consciousness if it ultimately fails, but overall panprotopsychism seems the most compelling and, in a sense, most cutting edge option to philosophers of mind today.

References

Brentano, F. (1995). “The distinction between mental and physical phenomena.” In Psychology from an empirical standpoint. D. Terrell, A. Rancurello, & L. McAlister, Trans; L. McAlister, Ed. New York: Routledge.

Carnap, R. (1932). “Psychology in physical language.” In Erkenntnis, 3:107-42. Norwell: Kluwer Academic Publishers.

Chalmers, D. J. (2002). “Consciousness and its place in nature.” From Blackwell guide to the philosophy of mind. S. Stich & T. Warfield, Eds.

Chisholm, R. (1957). “Intentional inexistence.” From Perceiving: A philosophical study. New York: Cornell UP.

Jackson, F. (1982). “Epiphenomenal qualia.” From Philosophical quarterly 32:127-136.

Nagel, T. (1974). “What is it like to be a bat?” From Philosophical review 83:435-50. New York: Cornell UP.

Putnam, H. (1968). “Brains and behavior.” From Analytical philosophy: Second series,
in Blackwell, 1968.

Russell, B. (1927). The analysis of matter. London: Kegan Paul.

Ryle, G. (1949). “Descartes’ myth.” From The concept of mind. In Hutchinson, 1949. Oxford: Oxford UP.

All citations taken from:

Chalmers, D. J., Ed. (2002). Philosophy of mind: Classical and contemporary readings.
New York: Oxford UP.