Anonymous
11th July 2003, 07:56
Philosophical Materialism
Richard C. Vitzthum
[This essay is from a lecture given to the Atheist Students Association at the University of Maryland, College Park, on November 14, 1996.]
http://www.infidels.org/library/modern/ric...aterialism.html (http://www.infidels.org/library/modern/richard_vitzthum/materialism.html)
Materialism is the oldest philosophical tradition in Western civilization. Originated by a series of pre-Socratic Greek philosophers in the 6th and 5th centuries before the Christian era, it reached its full classical form in the atomism of Democritus and Epicurus in the 4th century BCE. Epicurus argued that ultimate reality consisted of invisible and indivisible bits of free-falling matter called atoms randomly colliding in the void. It was on this atomic hypothesis that the Roman poet Lucretius wrote the first masterpiece of materialist literature around 50 BCE, the 7400-line philosophical poem De Rerum Natura, or, as it's usually translated, The Nature of Things.
Already in Lucretius' great poem we can see one of the hallmarks that distinguishes materialism from every other comprehensive philosophy produced by European civilization before the 20th century: its insistence on direct observation of nature and on explaining everything that happens in the world in terms of the laws of nature. In other words, from the beginning materialists have always based their theory on the best scientific evidence at hand, rather than on some putative "first philosophy" waiting to be discovered through abstract philosophical reasoning.
The tendency is clear in the second masterpiece of materialist literature, Baron Paul d'Holbach's anonymously published La Systeme de la Nature (The System of Nature), which appeared in France in 1770 and was promptly condemned by Louis 16th's government. This meant that the official state hangman was authorized to ferret out every copy of the book and have it literally cut to pieces on a beheading block. D'Holbach bases his mechanical determinism on Newtonian physics and Lockeian psychology, arguing that every event in nature, including all human thought and moral action, is the result of an inexorable chain of causation rooted in the flux of atomic motion. Like Lucretius, he insists there is no reality other than matter moving in space, as Newton theorized in his laws of motion and gravity. D'Holbach also attributes all thought to images impressed on the mind's tabula rasa, or blank slate, in wholly mechanical fashion according to these same laws of motion, as Locke had argued.
So too with the third pre-20th-century masterpiece of materialist literature, Ludwig Buechner's 1884 edition of Kraft und Stoff, translated Force and Matter, one of the most widely read and influential German books of the 19th century. Himself trained as a scientist, Buechner, like Lucretius and d'Holbach, saturated Force and Matter with the best science of his day, including cutting-edge theories and discoveries in physics, chemistry, geology, and biology, which of course incorporated Darwin's recently published theory of evolution.
Yet neither Lucretius, d'Holbach, nor Buechner claimed that materialist philosophy was an empirical science. They all realized it rested on assumptions that were ultimately metascientific, though never metaphysical in the Aristotelian sense. That is, the assumptions of materialism reached beyond empirical science, though never beyond physical reality. These metascientific assumptions were, first of all, that material or natural reality formed an unbroken material continuum that was eternal and infinite[1]. Nature had no beginning or end. It was an eternal, self-generating and self-sustaining material fact without any sort of barrier or limit zoning it off from a nonmaterial, non-physical, or supernatural type of being. The only foundational being there was, was material being, and some kind of natural substance underlay all visible phenomena. Lucretius called this endless fact of material being the "All," and with d'Holbach and Buechner concluded it lacked any plan or purpose and consisted of blindly opposing forces locked in an ultimately self-canceling, cosmic equipoise or gridlock.
Of course these assumptions implied, secondly, the lack of any governance or management of the universe by any sort of transcendental intelligence. From the start, materialism has been implicitly atheistic, though its atheistic implications were not fully spelled out before d'Holbach did so in his System. Materialism has always viewed atheism merely as a necessary consequence of its premises, not as a philosophically important end in itself. Supernatural gods, spiritual deities, or immaterial moralizers could obviously not be taken seriously, or for that matter even imagined to exist, in the materialist hypothesis.
Thirdly and last, materialism has always assumed that life is wholly the product of natural processes. All human thought and feeling emerges from the nonliving, inorganic matrix of physical nature and ends at death. Lucretius believed that thoughts and feelings were literally made up of a film of very fine atoms that peeled away from objects and recombined in the brain. D'Holbach believed that thoughts and feelings were the end product of chains of physical causation rooted in atomic motion. Buechner believed that thoughts and feelings were electrical impulses somehow shaped by the human nervous system into coherent patterns. Moreover, though it's not widely known, Lucretius and d'Holbach both theorized that organic life evolved from inorganic matter, though it was not until Buechner's championing of Darwinian theory that materialism could justify the theory scientifically.
So materialism has always inferred its theories from the best empirical evidence at hand and has as a result always had its metascientific hypotheses scientifically confirmed, because the basic assumption of valid science has also always been that nature is governed by coherent, discoverable physical laws. Indeed, the triumphs of science in the 20th century have been so stunning that today a majority of professional philosophers, at least in the English-speaking world, identify themselves as materialists of one kind or another[2]. Because these contemporary materialists disagree on some issues, I'd like to introduce you to modern materialism this evening by explaining some of its main concepts and controversies.
When someone today describes himself or herself as a materialist, they generally mean they stand somewhere in a spectrum defined at one end as reductive materialism[3] and at the other end as eliminative materialism[4]. Reductive and eliminative materialism[5] describe the poles of the process known as intertheoretic reduction. Intertheoretic reduction[6] refers to what happens when a new scientific theory either better explains or else completely invalidates an existing scientific theory. If the new theory better explains the old one, it is said to have reduced it to a fuller, more convincing explanation. A successful reduction of this kind was the incorporation and clarification of Newton's laws of motion in Einstein's theory of relativity, or of Maxwell's laws of electromagnetism in quantum theory.
The other pole of intertheoretic reduction, eliminative materialism, consists of the invalidation or complete displacement of an earlier theory by a new one. Examples of this kind of elimination are: the theory of demonic possession being eliminated by the theory of mental disease, the theory of phlogiston being eliminated by the discovery of oxygen as the cause of combustion, or creationism being eliminated by evolution as an explanation of the earth's history.
Obviously, modern reductive and eliminative materialists are allies in believing, as pre-20th century materialists did, that science has always confirmed and will most probably always continue to confirm the basic hypotheses of materialist philosophy: that is, first, that all reality is essentially a material reality and that therefore, second, no supernatural or immaterial reality can exist; and, third, that all organic life arises from and returns to inorganic matter. Their main disagreement is over the mind-brain problem, which has been the focus of 20th century materialist debate.
The so-called mind-brain problem refers to the question of whether or not human consciousness is reducible in all respects to scientific laws. In the 1960s and 1970s those materialists who said it is, known as identity theorists (i.e. the mind is identical to the brain in all respects), were challenged by other materialists known as property dualists[7], functionalists[8], or supervenience[9] theorists. What all of these challengers had in common was a belief that in some way human consciousness was irreducible to or inexplicable in terms of natural processes[10]. They held, for example, that so-called qualia -- a person's experience of pain or of after-images of color, for example -- were unique to that person and incommunicable and unknowable to any one else. They argued further that such properties of consciousness as qualia could not be translated into the terms of physical science in any meaningful way and hence represented a reality not amenable to the laws of nature.
Moreover, these challengers doubted the reducibility of one person's consciousness to the same series of physical events as that which underlay another person's consciousness, even though both consciousnesses might depend on, or, in current philosophical jargon, be supervenient on, physical events happening in each brain. Two different brains did not have to work exactly the same way, much less intelligences that might be silicon-based rather than biologically-based but capable of sharing thoughts or feelings with biological brains. The fact that the same mental experience might be physically realized in different ways in two different biological or non-biological brains limited the identity of mind and brain to at most a token identity[11] between a specific brain and its unique mental experience. It invalidated broad, "type" identities between mental experiences and brain processes in general.
To these objections, current eliminative and reductive materialists make the following reply. First of all, they argue that qualia, or the private feels of one's own experience, are no more incorrigible -- no more infallibly known by the individual -- than one's experience of the external world[12]. One's body and brain is just as likely to misrepresent internal as external experience. Pain can be anaesthetized and disappear, even though the same knife continues to cut your skin. One can hallucinate colors privately as well as publicly, and in fact the brain's moment-to-moment reconstruction of the external world is arguably just as private an experience as that of one's qualia, yet no one claims one's knowledge of the external world is infallible or incorrigible.
Secondly, a token identity between mental events and brain events is all that is needed for a robust and defensible mind-brain reductionism. No reductive materialist needs to claim that every brain works precisely the same way when it sees a tree, multiplies 2 times 2, or hears a Beethoven symphony. All that is needed is a convincing theory of how brains in general succeed in producing what we call consciousness from their visceral pulps and fluids. Since how the brain actually works is today one of the least-understood and most hotly-debated subjects in science, I'd like to explain briefly the most promising of these theories and in the process finish my discussion of philosophical materialism.
Neuroscience has concluded that the firing, or spiking, of cells in the brain known as neurons is the foundation of all brain functioning. Every brain has billions of these neurons, joined together in billions of networks by tiny filaments called dendrites and axons. Incoming signals, in the form of tiny electrical impulses generated by other neurons, pass down the dendrites to circuit-breaker-like gaps around the neuron known as synapses, which chemically monitor all the incoming signals and, when all the signals have reached the appropriate level, suddenly depolarize the electric differential outside and inside the neuron and cause the neuron to fire, or spike. The neuron's fired or spiked signal is then communicated to other neurons in the network down its axons. It takes roughly a hundredth of a second for a neuron to spike and repolarize for a new spike, which means that a neuron can fire at most a hundred times a second -- far too slow to complete the incredibly complex tasks the brain can do almost instantly, like recognizing someone's face, identifying a note or two or music as part of a song or symphony, or picking up a glass from a table.
This means that the brain is confined to what is known as the "hundred-step rule," or the fact that the maximum number of sequential steps the brain can take in one second is about a hundred. Since high-powered digital computers (computers that do all their computations sequentially, like a herd of sheep passing one by one through a gate) can do millions of steps in a second yet are notoriously poor at doing the perceptual and discriminatory tasks brains do with ease, the brain, it is theorized, is not structured like a linear computer but like a vast number of multi-dimensional computers working in parallel with each other.
In what sense is the brain a "multi-dimensional" computer? At bottom, the brain evidently works on the same on-off, binary principle that governs all linear computers: like them, its basic language is either "on" or "off" -- either spike/fire or not spike/fire. When a neuron spikes or fires, it does so in mechanical, all-or-nothing fashion like a spark plug, entirely as a result of having reached just the level of electrical excitation in its synapses it needs to make it suddenly depolarize. By themselves, neurons are nothing but stupid, mechanically controlled switches.
But when they are joined in networks whose signals parallel those of billions of other networks and interact at critical points, the result is human consciousness. From a countless plethora of dumb, electrical relay switches and settings emerges the amazing phenomenon we call human consciousness and intentionality -- the ability to think about things, to feel a range of emotions, and to realize one's self as a subjective entity distinct from the rest of the world.
How can this happen? How can something oblivious of the world become conscious of the world? Though theoretical neuroscience is still in its infancy, furiously boiling with new ideas, some likely answers are emerging from the steam. One promising theory is that networks of neurons in the brain consist of subsidiary groups of neurons or even individual neurons that serve as the axes of a multi-dimensional system of coordinates that can mathematically translate one kind of value to another kind of value. For example, someone sees an apple hanging from a tree. His brain locates the apple in an abstract visual space calculated in terms of how many degrees above a distant horizon the apple is, how close to him the focusing of his eyes tells him the apple is, and so on. But in order to pick the apple, his brain must translate its abstract visual calculation of the apple's location into an abstract motor-muscular space which will tell the muscles of his arm at which angle they will have to set themselves in order to approach the apple. What happens here, it is theorized, is that an array of neuronal networks transforms the values of his visual space into those of his motor space by means of a mathematical tensor, or formula, that translates the multi-dimensional coordinates, or vectors, of visual space into the vectors of motor space -- all the angles of sight are translated into angles of arm-bending. Although it does not seem so to the person reaching for the apple, his behavior is the result of a vast number of mathematical computations in his brain, which, because of its parallel computing capacity, it is able to carry out almost instantly.
Moreover, one of the brain's most impressive powers is that it is incredibly plastic and capable of learning, especially in infancy and childhood. It may well learn by adjusting the synaptic openings, or weightings, as they are called, of neurons individually and in networks so that the signals reaching them must produce just the right polarity from just the right dendrites to fire. This could explain, for example, why we recognize faces and other hard-to-distinguish sense experiences so quickly. Our brain has so many neuronal networks available for use -- one researcher has calculated them as totaling more than 10 to the 80th power -- that every single thing we learn may have its own network set at just the right synaptic weightings to be activated only by that bit of learning. This means that impulses coming into the brain from the senses are blocked from activating all but the relevant network, which almost instantly verifies that it's granny's face at the door. And synaptic weightings are flexible enough to readjust to changing circumstances if necessary.
The bottom line of this theoretical approach, of course, is that the mind is reducible to natural processes that can be translated into the language of math and physics. Neuronal networks are computing mechanisms that effortlessly transform multi-dimensional vectors of one kind of mathematical value into other vectors of mathematical value. Visual space being changed into motor space has been mentioned, but a great deal of work has already also been done along these lines on how we see and hear. Images from the eyes' retinas are translated into neuronal signals and processed through countless neural networks simultaneously so quickly that it seems to the viewer she is seeing the external world on a mirror in her mind, whereas in fact her brain is recreating and re-representing everything "out there" from, as it were, scratch. So too with sound. Varying air pressures entering the ear are translated into electrical impulses which are then massively and instantly parallel-processed into noises that seem to be coming to us, direct and unmediated, from the external world. But in fact they too, like our vision, are the result of incredibly complex processes of vector transformation among multi-dimensional coordinate systems performed by the countless neural networks of our brain.
Most reductive and eliminative materialists agree that the theory of mathematical transformations just sketched is one of the most promising explanations we have of how our brains work. But the eliminativists hold that the theory is so revolutionary and so much more convincing than current theories of the brain -- for instance, that the brain is basically propositional and language-oriented -- that it will eventually displace and replace the linguistic theory, just as the modern theory of mental disease displaced the medieval theory of demonic possession. Against them stand the reductive materialists, I among them, who share their enthusiasm for the new theory but believe that it will successfully reduce at least portions of the old theory the way Einstein's relativity successfully reduced Newton's laws of motion.
A couple of further comments on reductive materialism are in order. First, what is the status of mathematical concepts like numbers, mythical figures like river nymphs, comic-book characters like Donald Duck, and the like? Non-reductionists argue they are non-material, non-physical entities that are able to influence the physical world yet are inexplicable in terms of natural laws[13]. While granting a fictional, artificially man-made status to such phenomena, reductionists, on the other hand, argue that they do physically exist. Even when they are not physically embodied, say, in maps, epic poems, or comic books, they are actively or passively realized in the brains of intelligences capable of understanding and communicating them. In other words, all such ideas must be created, remembered, and transmitted in the form of appropriately processed neuronal firings by conscious intelligences to have whatever effect they do have outside those intelligences. They are in fact always physically embodied, either in brains or in the artifacts produced as a result of conscious effort. When and if no brain ever again lights up with the concept or memory of them, they have ceased to exist in that form, though most of the atomic elements which have produced them in brains in the past and could again produce them in the future will probably persist in some form as long as our present cosmos persists. To the reductionist, human thought and feeling are most definitely material entities capable of influencing other material entities like mountains, rivers, metal ores, and electric and nuclear energy in huge and spectacular ways.
The reductionist takes a similar approach to a second objection often raised by non-reductionists: Moral concepts, they say, are not reducible to natural process and physical law. In contrast, the reductionist, convinced that all life is the product of natural selection, sees morality as fundamentally the result of evolutionary survival. Social cooperation, love of one's mate, offspring, relatives, or tribe, repugnance to the murder of one's own species, and the like, are the reverse side of the coin of virtues like social competition, hatred of one's enemies, successful prosecution of war and the killing of one's own species, and the like. They are essentially the residue of human experience on the face of the planet, as are the invention of gods, of creation myths, of apocalyptic destructions of the world, and so on. Furthermore, the reductionist equates moral discrimination with sense discrimination. That is, the ability to sense a difference between heat and cold, light and dark, acid and alkaline is indistinguishable from the ability to decide whether this thing or place or experience is better or worse than that thing, place, or experience. Physical sensing and moral judgment have from the start been simultaneous and identical processes, and even the most refined and abstruse moral reasoning is rooted in the slime and grit of earth's natural history. Human beings are moral to the core, not because a deity has commanded them to be or because they've chosen to be but because natural selection has forced them to be[14].
Finally, reductive materialism applauds and identifies itself with the stunning success of the reductive program of 20th century science as a whole. It regards such triumphs of human intelligence as the establishment of the periodic table of elements and of the standard model of elementary particles as surely among humanity's greatest achievements. The periodic table and the standard model are outstanding examples of the relentless effort of scientists in this century to uncover deeper and deeper levels of physical explanation and to reduce their findings to more and more comprehensive and fundamental theories. Equally outstanding has been the effort to unify the four basic forces of nature at greater and greater levels of generalization. Already it has been proven that two of the four forces, electromagnetism and the weak nuclear force, were unified at energy levels that are theorized to have existed until a billionth of a second after the Big Bang had passed, after which they split. At a still earlier moment, it's theorized that the electroweak force was unified with the strong nuclear force, and at a still more primordial moment before that -- the so-called Planck era, when the universe was still less than 10 to the minus 43rd seconds old and seethed with a thousand million billion billion volts of energy -- the electroweak and strong nuclear forces were still unified with the fourth force, gravity. Modern scientific reductionism has succeeded in showing that the manifold phenomena of physical nature -- light, heat, rocks, flora, fauna, consciousness -- are probably manifestations of a single, foundational, material reality, perhaps ultimately describable in the terms of some future human science. Materialism welcomes this success as further confirmation of its 2500-year-old hypotheses.
Richard C. Vitzthum
[This essay is from a lecture given to the Atheist Students Association at the University of Maryland, College Park, on November 14, 1996.]
http://www.infidels.org/library/modern/ric...aterialism.html (http://www.infidels.org/library/modern/richard_vitzthum/materialism.html)
Materialism is the oldest philosophical tradition in Western civilization. Originated by a series of pre-Socratic Greek philosophers in the 6th and 5th centuries before the Christian era, it reached its full classical form in the atomism of Democritus and Epicurus in the 4th century BCE. Epicurus argued that ultimate reality consisted of invisible and indivisible bits of free-falling matter called atoms randomly colliding in the void. It was on this atomic hypothesis that the Roman poet Lucretius wrote the first masterpiece of materialist literature around 50 BCE, the 7400-line philosophical poem De Rerum Natura, or, as it's usually translated, The Nature of Things.
Already in Lucretius' great poem we can see one of the hallmarks that distinguishes materialism from every other comprehensive philosophy produced by European civilization before the 20th century: its insistence on direct observation of nature and on explaining everything that happens in the world in terms of the laws of nature. In other words, from the beginning materialists have always based their theory on the best scientific evidence at hand, rather than on some putative "first philosophy" waiting to be discovered through abstract philosophical reasoning.
The tendency is clear in the second masterpiece of materialist literature, Baron Paul d'Holbach's anonymously published La Systeme de la Nature (The System of Nature), which appeared in France in 1770 and was promptly condemned by Louis 16th's government. This meant that the official state hangman was authorized to ferret out every copy of the book and have it literally cut to pieces on a beheading block. D'Holbach bases his mechanical determinism on Newtonian physics and Lockeian psychology, arguing that every event in nature, including all human thought and moral action, is the result of an inexorable chain of causation rooted in the flux of atomic motion. Like Lucretius, he insists there is no reality other than matter moving in space, as Newton theorized in his laws of motion and gravity. D'Holbach also attributes all thought to images impressed on the mind's tabula rasa, or blank slate, in wholly mechanical fashion according to these same laws of motion, as Locke had argued.
So too with the third pre-20th-century masterpiece of materialist literature, Ludwig Buechner's 1884 edition of Kraft und Stoff, translated Force and Matter, one of the most widely read and influential German books of the 19th century. Himself trained as a scientist, Buechner, like Lucretius and d'Holbach, saturated Force and Matter with the best science of his day, including cutting-edge theories and discoveries in physics, chemistry, geology, and biology, which of course incorporated Darwin's recently published theory of evolution.
Yet neither Lucretius, d'Holbach, nor Buechner claimed that materialist philosophy was an empirical science. They all realized it rested on assumptions that were ultimately metascientific, though never metaphysical in the Aristotelian sense. That is, the assumptions of materialism reached beyond empirical science, though never beyond physical reality. These metascientific assumptions were, first of all, that material or natural reality formed an unbroken material continuum that was eternal and infinite[1]. Nature had no beginning or end. It was an eternal, self-generating and self-sustaining material fact without any sort of barrier or limit zoning it off from a nonmaterial, non-physical, or supernatural type of being. The only foundational being there was, was material being, and some kind of natural substance underlay all visible phenomena. Lucretius called this endless fact of material being the "All," and with d'Holbach and Buechner concluded it lacked any plan or purpose and consisted of blindly opposing forces locked in an ultimately self-canceling, cosmic equipoise or gridlock.
Of course these assumptions implied, secondly, the lack of any governance or management of the universe by any sort of transcendental intelligence. From the start, materialism has been implicitly atheistic, though its atheistic implications were not fully spelled out before d'Holbach did so in his System. Materialism has always viewed atheism merely as a necessary consequence of its premises, not as a philosophically important end in itself. Supernatural gods, spiritual deities, or immaterial moralizers could obviously not be taken seriously, or for that matter even imagined to exist, in the materialist hypothesis.
Thirdly and last, materialism has always assumed that life is wholly the product of natural processes. All human thought and feeling emerges from the nonliving, inorganic matrix of physical nature and ends at death. Lucretius believed that thoughts and feelings were literally made up of a film of very fine atoms that peeled away from objects and recombined in the brain. D'Holbach believed that thoughts and feelings were the end product of chains of physical causation rooted in atomic motion. Buechner believed that thoughts and feelings were electrical impulses somehow shaped by the human nervous system into coherent patterns. Moreover, though it's not widely known, Lucretius and d'Holbach both theorized that organic life evolved from inorganic matter, though it was not until Buechner's championing of Darwinian theory that materialism could justify the theory scientifically.
So materialism has always inferred its theories from the best empirical evidence at hand and has as a result always had its metascientific hypotheses scientifically confirmed, because the basic assumption of valid science has also always been that nature is governed by coherent, discoverable physical laws. Indeed, the triumphs of science in the 20th century have been so stunning that today a majority of professional philosophers, at least in the English-speaking world, identify themselves as materialists of one kind or another[2]. Because these contemporary materialists disagree on some issues, I'd like to introduce you to modern materialism this evening by explaining some of its main concepts and controversies.
When someone today describes himself or herself as a materialist, they generally mean they stand somewhere in a spectrum defined at one end as reductive materialism[3] and at the other end as eliminative materialism[4]. Reductive and eliminative materialism[5] describe the poles of the process known as intertheoretic reduction. Intertheoretic reduction[6] refers to what happens when a new scientific theory either better explains or else completely invalidates an existing scientific theory. If the new theory better explains the old one, it is said to have reduced it to a fuller, more convincing explanation. A successful reduction of this kind was the incorporation and clarification of Newton's laws of motion in Einstein's theory of relativity, or of Maxwell's laws of electromagnetism in quantum theory.
The other pole of intertheoretic reduction, eliminative materialism, consists of the invalidation or complete displacement of an earlier theory by a new one. Examples of this kind of elimination are: the theory of demonic possession being eliminated by the theory of mental disease, the theory of phlogiston being eliminated by the discovery of oxygen as the cause of combustion, or creationism being eliminated by evolution as an explanation of the earth's history.
Obviously, modern reductive and eliminative materialists are allies in believing, as pre-20th century materialists did, that science has always confirmed and will most probably always continue to confirm the basic hypotheses of materialist philosophy: that is, first, that all reality is essentially a material reality and that therefore, second, no supernatural or immaterial reality can exist; and, third, that all organic life arises from and returns to inorganic matter. Their main disagreement is over the mind-brain problem, which has been the focus of 20th century materialist debate.
The so-called mind-brain problem refers to the question of whether or not human consciousness is reducible in all respects to scientific laws. In the 1960s and 1970s those materialists who said it is, known as identity theorists (i.e. the mind is identical to the brain in all respects), were challenged by other materialists known as property dualists[7], functionalists[8], or supervenience[9] theorists. What all of these challengers had in common was a belief that in some way human consciousness was irreducible to or inexplicable in terms of natural processes[10]. They held, for example, that so-called qualia -- a person's experience of pain or of after-images of color, for example -- were unique to that person and incommunicable and unknowable to any one else. They argued further that such properties of consciousness as qualia could not be translated into the terms of physical science in any meaningful way and hence represented a reality not amenable to the laws of nature.
Moreover, these challengers doubted the reducibility of one person's consciousness to the same series of physical events as that which underlay another person's consciousness, even though both consciousnesses might depend on, or, in current philosophical jargon, be supervenient on, physical events happening in each brain. Two different brains did not have to work exactly the same way, much less intelligences that might be silicon-based rather than biologically-based but capable of sharing thoughts or feelings with biological brains. The fact that the same mental experience might be physically realized in different ways in two different biological or non-biological brains limited the identity of mind and brain to at most a token identity[11] between a specific brain and its unique mental experience. It invalidated broad, "type" identities between mental experiences and brain processes in general.
To these objections, current eliminative and reductive materialists make the following reply. First of all, they argue that qualia, or the private feels of one's own experience, are no more incorrigible -- no more infallibly known by the individual -- than one's experience of the external world[12]. One's body and brain is just as likely to misrepresent internal as external experience. Pain can be anaesthetized and disappear, even though the same knife continues to cut your skin. One can hallucinate colors privately as well as publicly, and in fact the brain's moment-to-moment reconstruction of the external world is arguably just as private an experience as that of one's qualia, yet no one claims one's knowledge of the external world is infallible or incorrigible.
Secondly, a token identity between mental events and brain events is all that is needed for a robust and defensible mind-brain reductionism. No reductive materialist needs to claim that every brain works precisely the same way when it sees a tree, multiplies 2 times 2, or hears a Beethoven symphony. All that is needed is a convincing theory of how brains in general succeed in producing what we call consciousness from their visceral pulps and fluids. Since how the brain actually works is today one of the least-understood and most hotly-debated subjects in science, I'd like to explain briefly the most promising of these theories and in the process finish my discussion of philosophical materialism.
Neuroscience has concluded that the firing, or spiking, of cells in the brain known as neurons is the foundation of all brain functioning. Every brain has billions of these neurons, joined together in billions of networks by tiny filaments called dendrites and axons. Incoming signals, in the form of tiny electrical impulses generated by other neurons, pass down the dendrites to circuit-breaker-like gaps around the neuron known as synapses, which chemically monitor all the incoming signals and, when all the signals have reached the appropriate level, suddenly depolarize the electric differential outside and inside the neuron and cause the neuron to fire, or spike. The neuron's fired or spiked signal is then communicated to other neurons in the network down its axons. It takes roughly a hundredth of a second for a neuron to spike and repolarize for a new spike, which means that a neuron can fire at most a hundred times a second -- far too slow to complete the incredibly complex tasks the brain can do almost instantly, like recognizing someone's face, identifying a note or two or music as part of a song or symphony, or picking up a glass from a table.
This means that the brain is confined to what is known as the "hundred-step rule," or the fact that the maximum number of sequential steps the brain can take in one second is about a hundred. Since high-powered digital computers (computers that do all their computations sequentially, like a herd of sheep passing one by one through a gate) can do millions of steps in a second yet are notoriously poor at doing the perceptual and discriminatory tasks brains do with ease, the brain, it is theorized, is not structured like a linear computer but like a vast number of multi-dimensional computers working in parallel with each other.
In what sense is the brain a "multi-dimensional" computer? At bottom, the brain evidently works on the same on-off, binary principle that governs all linear computers: like them, its basic language is either "on" or "off" -- either spike/fire or not spike/fire. When a neuron spikes or fires, it does so in mechanical, all-or-nothing fashion like a spark plug, entirely as a result of having reached just the level of electrical excitation in its synapses it needs to make it suddenly depolarize. By themselves, neurons are nothing but stupid, mechanically controlled switches.
But when they are joined in networks whose signals parallel those of billions of other networks and interact at critical points, the result is human consciousness. From a countless plethora of dumb, electrical relay switches and settings emerges the amazing phenomenon we call human consciousness and intentionality -- the ability to think about things, to feel a range of emotions, and to realize one's self as a subjective entity distinct from the rest of the world.
How can this happen? How can something oblivious of the world become conscious of the world? Though theoretical neuroscience is still in its infancy, furiously boiling with new ideas, some likely answers are emerging from the steam. One promising theory is that networks of neurons in the brain consist of subsidiary groups of neurons or even individual neurons that serve as the axes of a multi-dimensional system of coordinates that can mathematically translate one kind of value to another kind of value. For example, someone sees an apple hanging from a tree. His brain locates the apple in an abstract visual space calculated in terms of how many degrees above a distant horizon the apple is, how close to him the focusing of his eyes tells him the apple is, and so on. But in order to pick the apple, his brain must translate its abstract visual calculation of the apple's location into an abstract motor-muscular space which will tell the muscles of his arm at which angle they will have to set themselves in order to approach the apple. What happens here, it is theorized, is that an array of neuronal networks transforms the values of his visual space into those of his motor space by means of a mathematical tensor, or formula, that translates the multi-dimensional coordinates, or vectors, of visual space into the vectors of motor space -- all the angles of sight are translated into angles of arm-bending. Although it does not seem so to the person reaching for the apple, his behavior is the result of a vast number of mathematical computations in his brain, which, because of its parallel computing capacity, it is able to carry out almost instantly.
Moreover, one of the brain's most impressive powers is that it is incredibly plastic and capable of learning, especially in infancy and childhood. It may well learn by adjusting the synaptic openings, or weightings, as they are called, of neurons individually and in networks so that the signals reaching them must produce just the right polarity from just the right dendrites to fire. This could explain, for example, why we recognize faces and other hard-to-distinguish sense experiences so quickly. Our brain has so many neuronal networks available for use -- one researcher has calculated them as totaling more than 10 to the 80th power -- that every single thing we learn may have its own network set at just the right synaptic weightings to be activated only by that bit of learning. This means that impulses coming into the brain from the senses are blocked from activating all but the relevant network, which almost instantly verifies that it's granny's face at the door. And synaptic weightings are flexible enough to readjust to changing circumstances if necessary.
The bottom line of this theoretical approach, of course, is that the mind is reducible to natural processes that can be translated into the language of math and physics. Neuronal networks are computing mechanisms that effortlessly transform multi-dimensional vectors of one kind of mathematical value into other vectors of mathematical value. Visual space being changed into motor space has been mentioned, but a great deal of work has already also been done along these lines on how we see and hear. Images from the eyes' retinas are translated into neuronal signals and processed through countless neural networks simultaneously so quickly that it seems to the viewer she is seeing the external world on a mirror in her mind, whereas in fact her brain is recreating and re-representing everything "out there" from, as it were, scratch. So too with sound. Varying air pressures entering the ear are translated into electrical impulses which are then massively and instantly parallel-processed into noises that seem to be coming to us, direct and unmediated, from the external world. But in fact they too, like our vision, are the result of incredibly complex processes of vector transformation among multi-dimensional coordinate systems performed by the countless neural networks of our brain.
Most reductive and eliminative materialists agree that the theory of mathematical transformations just sketched is one of the most promising explanations we have of how our brains work. But the eliminativists hold that the theory is so revolutionary and so much more convincing than current theories of the brain -- for instance, that the brain is basically propositional and language-oriented -- that it will eventually displace and replace the linguistic theory, just as the modern theory of mental disease displaced the medieval theory of demonic possession. Against them stand the reductive materialists, I among them, who share their enthusiasm for the new theory but believe that it will successfully reduce at least portions of the old theory the way Einstein's relativity successfully reduced Newton's laws of motion.
A couple of further comments on reductive materialism are in order. First, what is the status of mathematical concepts like numbers, mythical figures like river nymphs, comic-book characters like Donald Duck, and the like? Non-reductionists argue they are non-material, non-physical entities that are able to influence the physical world yet are inexplicable in terms of natural laws[13]. While granting a fictional, artificially man-made status to such phenomena, reductionists, on the other hand, argue that they do physically exist. Even when they are not physically embodied, say, in maps, epic poems, or comic books, they are actively or passively realized in the brains of intelligences capable of understanding and communicating them. In other words, all such ideas must be created, remembered, and transmitted in the form of appropriately processed neuronal firings by conscious intelligences to have whatever effect they do have outside those intelligences. They are in fact always physically embodied, either in brains or in the artifacts produced as a result of conscious effort. When and if no brain ever again lights up with the concept or memory of them, they have ceased to exist in that form, though most of the atomic elements which have produced them in brains in the past and could again produce them in the future will probably persist in some form as long as our present cosmos persists. To the reductionist, human thought and feeling are most definitely material entities capable of influencing other material entities like mountains, rivers, metal ores, and electric and nuclear energy in huge and spectacular ways.
The reductionist takes a similar approach to a second objection often raised by non-reductionists: Moral concepts, they say, are not reducible to natural process and physical law. In contrast, the reductionist, convinced that all life is the product of natural selection, sees morality as fundamentally the result of evolutionary survival. Social cooperation, love of one's mate, offspring, relatives, or tribe, repugnance to the murder of one's own species, and the like, are the reverse side of the coin of virtues like social competition, hatred of one's enemies, successful prosecution of war and the killing of one's own species, and the like. They are essentially the residue of human experience on the face of the planet, as are the invention of gods, of creation myths, of apocalyptic destructions of the world, and so on. Furthermore, the reductionist equates moral discrimination with sense discrimination. That is, the ability to sense a difference between heat and cold, light and dark, acid and alkaline is indistinguishable from the ability to decide whether this thing or place or experience is better or worse than that thing, place, or experience. Physical sensing and moral judgment have from the start been simultaneous and identical processes, and even the most refined and abstruse moral reasoning is rooted in the slime and grit of earth's natural history. Human beings are moral to the core, not because a deity has commanded them to be or because they've chosen to be but because natural selection has forced them to be[14].
Finally, reductive materialism applauds and identifies itself with the stunning success of the reductive program of 20th century science as a whole. It regards such triumphs of human intelligence as the establishment of the periodic table of elements and of the standard model of elementary particles as surely among humanity's greatest achievements. The periodic table and the standard model are outstanding examples of the relentless effort of scientists in this century to uncover deeper and deeper levels of physical explanation and to reduce their findings to more and more comprehensive and fundamental theories. Equally outstanding has been the effort to unify the four basic forces of nature at greater and greater levels of generalization. Already it has been proven that two of the four forces, electromagnetism and the weak nuclear force, were unified at energy levels that are theorized to have existed until a billionth of a second after the Big Bang had passed, after which they split. At a still earlier moment, it's theorized that the electroweak force was unified with the strong nuclear force, and at a still more primordial moment before that -- the so-called Planck era, when the universe was still less than 10 to the minus 43rd seconds old and seethed with a thousand million billion billion volts of energy -- the electroweak and strong nuclear forces were still unified with the fourth force, gravity. Modern scientific reductionism has succeeded in showing that the manifold phenomena of physical nature -- light, heat, rocks, flora, fauna, consciousness -- are probably manifestations of a single, foundational, material reality, perhaps ultimately describable in the terms of some future human science. Materialism welcomes this success as further confirmation of its 2500-year-old hypotheses.