I am not a mathematician, but I do enjoy math and numbers, and can't resist playing around a little. One of my "toys" has been Fermat's Last Theorem. For a broader explanation of this theorem and the proof of it, see https://en.wikipedia.org/wiki/Fermat's_Last_Theorem, which I will summarize here with the first paragraph:
"In number theory, Fermat's Last Theorem (sometimes called Fermat's conjecture, especially in older texts) states that no three positiveintegersa, b, and c satisfy the equation an + bn = cn for any integer value of n greater than 2. The cases n = 1 and n = 2 have been known to have infinitely many solutions since antiquity."
As you might know, the proof of this theorem was, and still is, an historic mystery. Fermat claimed to have proved it himself around 1637, but never provided the proof, only a claim "in the margin of a copy of Arithmetica where he claimed he had a proof that was too large to fit in the margin." Yet if Fermat truly did have a valid proof, he never wrote it out, even until his death in 1665.
It was only in 1994. 357 years later after Fermat's cryptic and unproved claim that the mathematician Andrew Wiles finally presented the first proof of the theorem which was accepted by the mathematical community as correct and flawless (please don't ask me to explain it, however!). This in itself is astonishing enough, but what is more astonishing is the fact that Wiles used mathematical techniques which did not exist in Fermat's time. Thus, if Fermat really did supply a proof, he did so using techniques much simpler -- techniques which have evaded the most brilliant math minds for over three hundred years! One can only conclude that either Fermat erred in his claim, or a straightforward proof has been eluding such minds to this day.
Again, I warn I am no mathematician, but since Andrew Wiles' proof I have wondered if Fermat's theorem can be expanded upon. The theorem may follow a pattern, in which the number of integers being added must equal the exponent itself. For example, for 32 + 42 = 52, the simplest example of the theorem, that number is two.
What about three? It turns out there is an example here, one that I stumbled upon quite accidentally: 33 + 43 + 53 = 63. Now I suspect there are more examples for three, just as there are for two, although I have not tried to find any of them. Nor have I attempted to find examples for integers greater than three, though I suspect they exist.
You probably see where I'm going with this. Is it a reasonable conjecture that, for all (positive?) integers n, there are sums of n integers raised to the n'th power which will yield another integer raised to n? Furthermore, is it an iff (if and only if) condition for all integers greater than one?
Of course, I've no idea. I certainly unable to prove or disprove such a conjecture. But it does seem worthy to make the attempt (if no one has done so yet). Perhaps one of you can do so, or at least has some logical input on the question. I'll leave it at that.
The measurement problem in quantum mechanics is the problem of how (or whether) wave function collapse occurs. The inability to observe this process directly has given rise to different interpretations of quantum mechanics, and poses a key set of questions that each interpretation must answer. The wave function in quantum mechanics evolves deterministically according to the Schrödinger equation as a linear superposition
of different states, but actual measurements always find the physical
system in a definite state. Any future evolution is based on the state
the system was discovered to be in when the measurement was made,
meaning that the measurement "did something" to the system that is not
obviously a consequence of Schrödinger evolution.
To express matters differently (to paraphrase Steven Weinberg[1][2]),
the Schrödinger wave equation determines the wave function at any later
time. If observers and their measuring apparatus are themselves
described by a deterministic wave function, why can we not predict
precise results for measurements, but only probabilities? As a general
question: How can one establish a correspondence between quantum and
classical reality?[3]
Schrödinger's cat
The best known example is the "paradox" of the Schrödinger's cat.
A mechanism is arranged to kill a cat if a quantum event, such as the
decay of a radioactive atom, occurs. Thus the fate of a large scale
object, the cat, is entangled
with the fate of a quantum object, the atom. Prior to observation,
according to the Schrödinger equation, the cat is apparently evolving
into a linear combination
of states that can be characterized as an "alive cat" and states that
can be characterized as a "dead cat". Each of these possibilities is
associated with a specific nonzero probability amplitude; the cat seems to be in some kind of "combination" state called a "quantum superposition". However, a single, particular observation
of the cat does not measure the probabilities: it always finds either a
living cat, or a dead cat. After the measurement the cat is
definitively alive or dead. The question is: How are the probabilities converted into an actual, sharply well-defined outcome?
Interpretations
The Copenhagen interpretation is the oldest and probably still the most widely held interpretation of quantum mechanics.[4][5][6] Most generally it posits something in the act of observation which results in the collapse of the wave function. According to the von Neumann–Wigner interpretation the causative agent in this collapse is consciousness.[7] How this could happen is widely disputed.
Hugh Everett's many-worlds interpretation
attempts to solve the problem by suggesting there is only one wave
function, the superposition of the entire universe, and it never
collapses—so there is no measurement problem. Instead, the act of
measurement is simply an interaction between quantum entities, e.g.
observer, measuring instrument, electron/positron etc., which entangle
to form a single larger entity, for instance living cat/happy scientist. Everett also attempted to demonstrate the way that in measurements the probabilistic nature of quantum mechanics would appear; work later extended by Bryce DeWitt.
De Broglie–Bohm theory
tries to solve the measurement problem very differently: the
information describing the system contains not only the wave function,
but also supplementary data (a trajectory) giving the position of the
particle(s). The role of the wave function is to generate the velocity
field for the particles. These velocities are such that the probability
distribution for the particle remains consistent with the predictions of
the orthodox quantum mechanics. According to de Broglie–Bohm theory,
interaction with the environment during a measurement procedure
separates the wave packets in configuration space which is where
apparent wave function collapse comes from even though there is no actual collapse.
The Ghirardi–Rimini–Weber (GRW) theory
differs from other collapse theories by proposing that wave function
collapse happens spontaneously. Particles have a non-zero probability of
undergoing a "hit", or spontaneous collapse of the wave function, on
the order of once every hundred million years.[8]
Though collapse is extremely rare, the sheer number of particles in a
measurement system means that the probability of a collapse occurring
somewhere in the system is high. Since the entire measurement system is
entangled (via quantum entanglement), the collapse of a single particle
initiates the collapse of the entire measurement apparatus.
Erich Joos and Heinz-Dieter Zeh claim that the phenomenon of quantum decoherence, which was put on firm ground in the 1980s, resolves the problem.[9]
The idea is that the environment causes the classical appearance of
macroscopic objects. Zeh further claims that decoherence makes it
possible to identify the fuzzy boundary between the quantum microworld
and the world where the classical intuition is applicable.[10][11] Quantum decoherence was proposed in the context of the many-worlds interpretation[citation needed], but it has also become an important part of some modern updates of the Copenhagen interpretation based on consistent histories.[12][13]
Quantum decoherence does not describe the actual process of the wave
function collapse, but it explains the conversion of the quantum
probabilities (that exhibit interference effects) to the ordinary classical probabilities. See, for example, Zurek,[3] Zeh[10] and Schlosshauer.[14]
The present situation is slowly clarifying, as described in a recent paper by Schlosshauer as follows:[15]
Several decoherence-unrelated proposals have been put forward in
the past to elucidate the meaning of probabilities and arrive at the
Born rule ... It is fair to say that no decisive conclusion appears to
have been reached as to the success of these derivations. ...
As it is well known, [many papers by Bohr insist upon] the
fundamental role of classical concepts. The experimental evidence for
superpositions of macroscopically distinct states on increasingly large
length scales counters such a dictum. Superpositions appear to be novel
and individually existing states, often without any classical
counterparts. Only the physical interactions between systems then
determine a particular decomposition into classical states from the view
of each particular system. Thus classical concepts are to be understood
as locally emergent in a relative-state sense and should no longer
claim a fundamental role in the physical theory.
A fourth approach is given by objective collapse models. In such models, the Schrödinger equation is modified and obtains nonlinear terms. These nonlinear modifications are of stochastic
nature and lead to a behaviour which for microscopic quantum objects,
e.g. electrons or atoms, is unmeasurably close to that given by the
usual Schrödinger equation. For macroscopic objects, however, the
nonlinear modification becomes important and induces the collapse of the
wave function. Objective collapse models are effective theories.
The stochastic modification is thought of to stem from some external
non-quantum field, but the nature of this field is unknown. One possible
candidate is the gravitational interaction as in the models of Diósi
and Penrose. The main difference of objective collapse models compared to the other approaches is that they make falsifiable
predictions that differ from standard quantum mechanics. Experiments
are already getting close to the parameter regime where these
predictions can be tested.[16]
An interesting solution to the measurement problem is also provided by the hidden-measurements interpretation
of quantum mechanics. The hypothesis at the basis of this approach is
that in a typical quantum measurement there is a condition of lack of
knowledge about which interaction between the measured entity and the
measuring apparatus is actualized at each run of the experiment. One can
then show that the Born rule can be derived by considering a uniform average over all these possible measurement-interactions.
Fluctuating solar and wind
power require lots of energy storage, and lithium-ion batteries seem
like the obvious choice—but they are far too expensive to play a major
role.
A pair of 500-foot smokestacks rise
from a natural-gas power plant on the harbor of Moss Landing,
California, casting an industrial pall over the pretty seaside town.
If state regulators sign off, however, it could be the site of the world’s largest lithium-ion battery project by late 2020, helping to balance fluctuating wind and solar energy on the California grid.
The 300-megawatt facility is one of four giant lithium-ion storage
projects that Pacific Gas and Electric, California’s largest utility, asked
the California Public Utilities Commission to approve in late June.
Collectively, they would add enough storage capacity to the grid to
supply about 2,700 homes for a month (or to store about .0009 percent of
the electricity the state uses each year).
The California projects are among a growing number of efforts
around the world, including Tesla’s 100-megawatt battery array in South
Australia, to build ever larger lithium-ion storage systems as prices
decline and renewable generation increases. They’re fueling growing
optimism that these giant batteries will allow wind and solar power to
displace a growing share of fossil-fuel plants.
But there’s a problem with this rosy scenario. These batteries are
far too expensive and don’t last nearly long enough, limiting the role
they can play on the grid, experts say. If we plan to rely on them for
massive amounts of storage as more renewables come online—rather than
turning to a broader mix of low-carbon sources like nuclear and natural gas with carbon capture technology—we could be headed down a dangerously unaffordable path.
Small doses
Today’s battery storage technology works best in a limited role, as
a substitute for “peaking” power plants, according to a 2016 analysis
by researchers at MIT and Argonne National Lab. These are smaller
facilities, frequently fueled by natural gas today, that can afford to
operate infrequently, firing up quickly when prices and demand are high.
Lithium-ion batteries could compete economically with these
natural-gas peakers within the next five years, says Marco Ferrara, a
cofounder of Form Energy, an MIT spinout developing grid storage
batteries.
“The gas peaker business is pretty close to ending, and lithium-ion is a great replacement,” he says.
This peaker role is precisely the one that most of the new and
forthcoming lithium-ion battery projects are designed to fill. Indeed,
the California storage projects could eventually replace three
natural-gas facilities in the region, two of which are peaker plants.
But much beyond this role, batteries run into real problems. The
authors of the 2016 study found steeply diminishing returns when a lot
of battery storage is added to the grid. They concluded that coupling
battery storage with renewable plants is a “weak substitute” for large,
flexible coal or natural-gas combined-cycle plants, the type that can be
tapped at any time, run continuously, and vary output levels to meet
shifting demand throughout the day.
Not only is lithium-ion technology too expensive for this role, but
limited battery life means it’s not well suited to filling gaps during
the days, weeks, and even months when wind and solar generation flags.
This problem is particularly acute in California, where both wind
and solar fall off precipitously during the fall and winter months.
Here’s what the seasonal pattern looks like:
If renewables provided 80 percent of California electricity – half
wind, half solar – generation would fall precipitously beginning in the
late summer.
Clean Air Task Force analysis of CAISO data
This leads to a critical problem: when renewables reach high levels
on the grid, you need far, far more wind and solar plants to crank out
enough excess power during peak times to keep the grid operating through
those long seasonal dips, says Jesse Jenkins, a coauthor of the study
and an energy systems researcher. That, in turn, requires banks upon
banks of batteries that can store it all away until it’s needed.
And that ends up being astronomically expensive.
California dreaming
There are issues California can’t afford to ignore for long. The state is already on track to get 50 percent of its electricity from clean sources by 2020, and the legislature is once again considering a bill that would require it to reach 100 percent by 2045. To complicate things, regulators voted in January to close the state’s last nuclear plant, a carbon-free source that provides 24 percent of PG&E’s energy. That will leave California heavily reliant on renewable sources to meet its goals.
The Clean Air Task Force, a Boston-based energy policy think tank,
recently found that reaching the 80 percent mark for renewables in
California would mean massive amounts of surplus generation during the
summer months, requiring 9.6 million megawatt-hours of energy storage.
Achieving 100 percent would require 36.3 million.
The state currently has 150,000 megawatt-hours of energy storage in
total. (That’s mainly pumped hydroelectric storage, with a small share
of batteries.)
If renewables supplied 80 percent of California electricity, more
than eight million megawatt-hours of surplus energy would be generated
during summer peaks.
Clean Air Task Force analysis of CAISO data.
Building the level of renewable generation and storage necessary to
reach the state’s goals would drive up costs exponentially, from $49
per megawatt-hour of generation at 50 percent to $1,612 at 100 percent.
And that's assuming lithium-ion batteries will cost roughly a third what they do now.
California’s power system costs rise exponentially if renewables generate the bulk of electricity.
Clean Air Task Force analysis of CAISO data.
“The system becomes completely dominated by the cost of storage,”
says Steve Brick, a senior advisor for the Clean Air Task Force. “You
build this enormous storage machine that you fill up by midyear and then
just dissipate it. It’s a massive capital investment that gets utilized
very little.”
These forces would dramatically increase electricity costs for consumers.
“You have to pause and ask yourself: ‘Is there any way the public would stand for that?’” Brick says.
Similarly, a study earlier this year in Energy & Environmental Science
found that meeting 80 percent of US electricity demand with wind and
solar would require either a nationwide high-speed transmission system,
which can balance renewable generation over hundreds of miles, or 12
hours of electricity storage for the whole system (see “Relying on renewables alone significantly inflates the cost of overhauling energy”).
At current prices, a battery storage system of that size would cost more than $2.5 trillion.
A scary price tag
Of course, cheaper and better grid storage is possible, and researchers and startups are exploring various possibilities. Form Energy, which recently secured funding
from Bill Gates’s Breakthrough Energy Ventures, is trying to develop
aqueous sulfur flow batteries with far longer duration, at a fifth the
cost where lithium-ion batteries are likely to land.
Ferrara’s modeling has found that such a battery could make it
possible for renewables to provide 90 percent of electricity needs for
most grids, for just marginally higher costs than today’s.
But it’s dangerous to bank on those kinds of battery
breakthroughs—and even if Form Energy or some other company does pull it
off, costs would still rise exponentially beyond the 90 percent
threshold, Ferrara says.
“The risk,” Jenkins says, “is we drive up the cost of deep
decarbonization in the power sector to the point where the public
decides it’s simply unaffordable to continue toward zero carbon.”
The hard problem of consciousness is the problem of explaining how and why we have qualia or phenomenal experiences—how sensations acquire characteristics, such as colors and tastes. The philosopher David Chalmers, who introduced the term "hard problem" of consciousness,
contrasts this with the "easy problems" of explaining the ability to
discriminate, integrate information, report mental states, focus
attention, etc. Easy problems are easy because all that is required for
their solution is to specify a mechanism that can perform the function.
That is, their proposed solutions, regardless of how complex or poorly
understood they may be, can be entirely consistent with the modern materialistic
conception of natural phenomena. Chalmers claims that the problem of
experience is distinct from this set, and he argues that the problem of
experience will "persist even when the performance of all the relevant functions is explained".
In Facing Up to the Problem of Consciousness (1995), Chalmers wrote:[3]
It is undeniable that some organisms are subjects of
experience. But the question of how it is that these systems are
subjects of experience is perplexing. Why is it that when our cognitive
systems engage in visual and auditory information-processing, we have
visual or auditory experience: the quality of deep blue, the sensation
of middle C? How can we explain why there is something it is like to
entertain a mental image, or to experience an emotion? It is widely
agreed that experience arises from a physical basis, but we have no good
explanation of why and how it so arises. Why should physical processing
give rise to a rich inner life at all? It seems objectively
unreasonable that it should, and yet it does.
In the same paper, he also wrote:
The really hard problem of consciousness is the problem
of experience. When we think and perceive there is a whir of information
processing, but there is also a subjective aspect.
The philosopher Raamy Majeed noted in 2016 that the hard problem is, in fact, associated with two "explanatory targets":[7]
[PQ] Physical processing gives rise to experiences with a phenomenal character.
[Q] Our phenomenal qualities are thus-and-so.
The first fact concerns the relationship between the physical and the
phenomenal, whereas the second concerns the very nature of the
phenomenal itself. Most responses to the hard problem are aimed at
explaining either one of these facts or both.
Easy problems
Chalmers
contrasts the hard problem with a number of (relatively) easy problems
that consciousness presents. He emphasizes that what the easy problems
have in common is that they all represent some ability, or the
performance of some function or behavior. Examples of easy problems
include:[8]
the ability to discriminate, categorize, and react to environmental stimuli;
the integration of information by a cognitive system;
the reportability of mental states;
the ability of a system to access its own internal states;
the focus of attention;
the deliberate control of behavior;
the difference between wakefulness and sleep.
Other formulations
Other formulations of the "hard problem" include:
"How is it that some organisms are subjects of experience?"
"Why does awareness of sensory information exist at all?"
Divide matter into as minute parts as you will (which we
are apt to imagine a sort of spiritualizing or making a thinking thing
of it) vary the figure and motion of it as much as you please—a globe,
cube, cone, prism, cylinder, etc., whose diameters are but 1,000,000th
part of a gry, will operate not otherwise upon other bodies of
proportionable bulk than those of an inch or foot diameter—and you may
as rationally expect to produce sense, thought, and knowledge, by
putting together, in a certain figure and motion, gross particles of
matter, as by those that are the very minutest that do anywhere exist.
They knock, impel, and resist one another, just as the greater do; and
that is all they can do... [I]t is impossible to conceive that matter,
either with or without motion, could have originally in and from itself
sense, perception, and knowledge; as is evident from hence that then
sense, perception, and knowledge must be a property eternally
inseparable from matter and every particle of it.[11]
Moreover, it must be confessed that perception and that
which depends upon it are inexplicable on mechanical grounds, that is to
say, by means of figures and motions. And supposing there were a
machine, so constructed as to think, feel, and have perception, it might
be conceived as increased in size, while keeping the same proportions,
so that one might go into it as into a mill. That being so, we should,
on examining its interior, find only parts which work one upon another,
and never anything by which to explain a perception.[12]
The philosopher and political economist J.S. Mill wrote in A System of Logic (1843), Book V, Chapter V, section 3:
Now I am far from pretending that it may not be capable
of proof, or that it is not an important addition to our knowledge if
proved, that certain motions in the particles of bodies are the
conditions of the production of heat or light; that certain assignable
physical modifications of the nerves may be the conditions not only of
our sensations or emotions, but even of our thoughts; that certain
mechanical and chemical conditions may, in the order of nature, be
sufficient to determine to action the physiological laws of life. All I
insist upon, in common with every thinker who entertains any clear idea
of the logic of science, is, that it shall not be supposed that by
proving these things one step would be made towards a real explanation
of heat, light, or sensation; or that the generic peculiarity of those
phenomena can be in the least degree evaded by any such discoveries,
however well established. Let it be shown, for instance, that the most
complex series of physical causes and effects succeed one another in the
eye and in the brain to produce a sensation of colour; rays falling on
the eye, refracted, converging, crossing one another, making an inverted
image on the retina, and after this a motion—let it be a vibration, or a
rush of nervous fluid, or whatever else you are pleased to suppose,
along the optic nerve—a propagation of this motion to the brain itself,
and as many more different motions as you choose; still, at the end of
these motions, there is something which is not motion, there is a
feeling or sensation of colour. Whatever number of motions we may be
able to interpolate, and whether they be real or imaginary, we shall
still find, at the end of the series, a motion antecedent and a colour
consequent. The mode in which any one of the motions produces the next,
may possibly be susceptible of explanation by some general law of
motion: but the mode in which the last motion produces the sensation of
colour, cannot be explained by any law of motion; it is the law of
colour: which is, and must always remain, a peculiar thing. Where our
consciousness recognises between two phenomena an inherent distinction;
where we are sensible of a difference which is not merely of degree, and
feel that no adding one of the phenomena to itself would produce the
other; any theory which attempts to bring either under the laws of the
other must be false; though a theory which merely treats the one as a
cause or condition of the other, may possibly be true.
But what consciousness is, we know not; and how it is
that anything so remarkable as a state of consciousness comes about as
the result of irritating nervous tissue, is just as unaccountable as the
appearance of the Djin when Aladdin rubbed his lamp in the story, or as
any other ultimate fact of nature.[13]
If physicalism is to be defended, the phenomenological
features must themselves be given a physical account. But when we
examine their subjective character it seems that such a result is
impossible. The reason is that every subjective phenomenon is
essentially connected with a single point of view, and it seems
inevitable that an objective, physical theory will abandon that point of
view.[14]
Relationship to scientific frameworks
Neural correlates of consciousness
Since 1990, researchers including the molecular biologist Francis Crick and the neuroscientist Christof Koch
have made significant progress toward identifying which neurobiological
events occur concurrently to the experience of subjective
consciousness.[15] These postulated events are referred to as neural correlates of consciousness or NCCs. However, this research arguably addresses the question of which neurobiological mechanisms are linked to consciousness but not the question of why
they should give rise to consciousness at all, the latter being the
hard problem of consciousness as Chalmers formulated it. In "On the
Search for the Neural Correlate of Consciousness", Chalmers said he is
confident that, granting the principle that something such as what he
terms global availability can be used as an indicator of consciousness,
the neural correlates will be discovered "in a century or two".[16] Nevertheless, he stated regarding their relationship to the hard problem of consciousness:
One can always ask why these processes of availability
should give rise to consciousness in the first place. As yet we cannot
explain why they do so, and it may well be that full details about the
processes of availability will still fail to answer this question.
Certainly, nothing in the standard methodology I have outlined answers
the question; that methodology assumes a relation between availability
and consciousness, and therefore does nothing to explain it. [...] So
the hard problem remains. But who knows: Somewhere along the line we may
be led to the relevant insights that show why the link is there, and
the hard problem may then be solved.[16]
The neuroscientist and Nobel laureate Eric Kandel
wrote that locating the NCCs would not solve the hard problem, but
rather one of the so-called easy problems to which the hard problem is
contrasted.[17] Kandel went on to note Crick and Koch's suggestion that once the binding problem—understanding what accounts for the unity of experience—is solved, it will be possible to solve the hard problem empirically.[17] However, neuroscientist Anil Seth
argued that emphasis on the so-called hard problem is a distraction
from what he calls the "real problem": understanding the neurobiology
underlying consciousness, namely the neural correlates of various
conscious processes.[18] This more modest goal is the focus of most scientists working on consciousness.[17] Psychologist Susan Blackmore
believes, by contrast, that the search for the neural correlates of
consciousness is futile and itself predicated on an erroneous belief in
the hard problem of consciousness.[19]
Integrated information theory
Integrated information theory (IIT), developed by the neuroscientist and psychiatrist Giulio Tononi
in 2004 and more recently also advocated by Koch, is one of the most
discussed models of consciousness in neuroscience and elsewhere.[20][21] The theory proposes an identity
between consciousness and integrated information, with the latter item
(denoted as Φ) defined mathematically and thus in principle measurable.[21][22] The hard problem of consciousness, write Tononi and Koch, may indeed be intractable when working from matter to consciousness.[23]
However, because IIT inverts this relationship and works from
phenomenological axioms to matter, they say it could be able to solve
the hard problem.[23]
In this vein, proponents have said the theory goes beyond identifying
human neural correlates and can be extrapolated to all physical systems.
Tononi wrote (along with two colleagues):
While identifying the “neural correlates of
consciousness” is undoubtedly important, it is hard to see how it could
ever lead to a satisfactory explanation of what consciousness is and how
it comes about. As will be illustrated below, IIT offers a way to
analyze systems of mechanisms to determine if they are properly
structured to give rise to consciousness, how much of it, and of which
kind.[24]
As part of a broader critique of IIT, Michael Cerullo suggested that
the theory's proposed explanation is in fact for what he dubs (following
Scott Aaronson)
the "Pretty Hard Problem" of methodically inferring which physical
systems are conscious—but would not solve Chalmers' hard problem.[21] "Even if IIT is correct," he argues, "it does not explain why integrated information generates (or is) consciousness."[21]
Responses
Consciousness is fundamental or elusive
Some philosophers, including David Chalmers in the late 20th century and Alfred North Whitehead earlier in the 1900s, argued that conscious experience is a fundamental constituent of the universe, a form of panpsychism sometimes referred to as panexperientialism.
Chalmers argued that a "rich inner life" is not logically reducible to
the functional properties of physical processes. He states that
consciousness must be described using nonphysical means. This
description involves a fundamental ingredient capable of clarifying
phenomena that have not been explained using physical means. Use of this
fundamental property, Chalmers argues, is necessary to explain certain
functions of the world, much like other fundamental features, such as
mass and time, and to explain significant principles in nature.
The philosopher Thomas Nagel
posited in 1974 that experiences are essentially subjective (accessible
only to the individual undergoing them), while physical states are
essentially objective (accessible to multiple individuals). So at this
stage, he argued, we have no idea what it could even mean to claim that
an essentially subjective state just is an essentially non-subjective state. In other words, we have no idea of what reductivism really amounts to.[14]
New mysterianism, such as that of the philosopher Colin McGinn, proposes that the human mind, in its current form, will not be able to explain consciousness.[25]
Deflationary accounts
Some philosophers, such as Daniel Dennett[4] and Peter Hacker[26]
oppose the idea that there is a hard problem. These theorists have
argued that once we really come to understand what consciousness is, we
will realize that the hard problem is unreal. For instance, Dennett
asserts that the so-called hard problem will be solved in the process of
answering the "easy" ones (which, as he has clarified, he does not
consider "easy" at all).[4]
In contrast with Chalmers, he argues that consciousness is not a
fundamental feature of the universe and instead will eventually be fully
explained by natural phenomena. Instead of involving the nonphysical,
he says, consciousness merely plays tricks on people so that it appears
nonphysical—in other words, it simply seems like it requires nonphysical
features to account for its powers. In this way, Dennett compares
consciousness to stage magic and its capability to create extraordinary
illusions out of ordinary things.[27]
To show how people might be commonly fooled into overstating the
powers of consciousness, Dennett describes a normal phenomenon called change blindness, a visual process that involves failure to detect scenery changes in a series of alternating images.[28]
He uses this concept to argue that the overestimation of the brain's
visual processing implies that the conception of our consciousness is
likely not as pervasive as we make it out to be. He claims that this
error of making consciousness more mysterious than it is could be a
misstep in any developments toward an effective explanatory theory.
Critics such as Galen Strawson
reply that, in the case of consciousness, even a mistaken experience
retains the essential face of experience that needs to be explained,
contra Dennett.
To address the question of the hard problem, or how and why
physical processes give rise to experience, Dennett states that the
phenomenon of having experience is nothing more than the performance of
functions or the production of behavior, which can also be referred to
as the easy problems of consciousness.[4]
He states that consciousness itself is driven simply by these
functions, and to strip them away would wipe out any ability to identify
thoughts, feelings, and consciousness altogether. So, unlike Chalmers
and other dualists, Dennett says that the easy problems and the hard
problem cannot be separated from each other. To him, the hard problem of
experience is included among—not separate from—the easy problems, and
therefore they can only be explained together as a cohesive unit.[27]
Like Dennett, Hacker argues that the hard problem is
fundamentally incoherent and that "consciousness studies", as it exists
today, is "literally a total waste of time":[26]
The whole endeavour of the consciousness studies
community is absurd—they are in pursuit of a chimera. They misunderstand
the nature of consciousness. The conception of consciousness which they
have is incoherent. The questions they are asking don't make sense.
They have to go back to the drawing board and start all over again.
Critics of Dennett's approach, such as Chalmers and Nagel, argue that
Dennett's argument misses the point of the inquiry by merely
re-defining consciousness as an external property and ignoring the
subjective aspect completely. This has led detractors to refer to
Dennett's book Consciousness Explained as Consciousness Ignored or Consciousness Explained Away.[4] Dennett discussed this at the end of his book with a section entitled Consciousness Explained or Explained Away?[28]
Though the most common arguments against deflationary accounts and eliminative materialism
are the argument from qualia and the argument that conscious
experiences are irreducible to physical states—or that current popular
definitions of "physical" are incomplete—the objection follows that the
one and same reality can appear in different ways, and that the
numerical difference of these ways is consistent with a unitary mode of
existence of the reality.[citation needed]
Critics of the deflationary approach object that qualia are a case
where a single reality cannot have multiple appearances. For example,
the philosopher John Searle pointed out: "where consciousness is concerned, the existence of the appearance is the reality".[29]
A notable deflationary account is the higher-order theories of consciousness.[30] In 2005, the philosopher Peter Carruthers
wrote about "recognitional concepts of experience", that is, "a
capacity to recognize [a] type of experience when it occurs in one's own
mental life", and suggested that such a capacity does not depend upon
qualia.[31]
The philosophers Glenn Carruthers and Elizabeth Schier said in 2012 that the main arguments for the existence of a hard problem—philosophical zombies, Mary's room, and Nagel's bats—are
only persuasive if one already assumes that "consciousness must be
independent of the structure and function of mental states, i.e. that
there is a hard problem". Hence, the arguments beg the question.
The authors suggest that "instead of letting our conclusions on the
thought experiments guide our theories of consciousness, we should let
our theories of consciousness guide our conclusions from the thought
experiments".[32]
In 2013, the philosopher Elizabeth Irvine pointed out that both science and folk psychology do not treat mental states
as having phenomenal properties, and therefore "the hard problem of
consciousness may not be a genuine problem for non-philosophers (despite
its overwhelming obviousness to philosophers), and questions about
consciousness may well 'shatter' into more specific questions about
particular capacities".[33]
The philosopher Massimo Pigliucci
distances himself from eliminativism, but he said in 2013 that the hard
problem is still misguided, resulting from a "category mistake":[34]
Of course an explanation isn't the same as an experience,
but that's because the two are completely independent categories, like
colors and triangles. It is obvious that I cannot experience what it is
like to be you, but I can potentially have a complete explanation of how
and why it is possible to be you.
The source of illusion
A complete reductionistic or mechanistic theory of consciousness must include the description of a mechanism
by which the subjective aspect of consciousness is perceived and
reported by people. Philosophers such as Chalmers or Nagel have rejected
reductionist theories of consciousness because they believe that the
reports of subjective experience constitute a vast and important body of
empirical evidence which is ignored by modern reductionist theories of
consciousness.[9]
Dennett argued that solving the easy problem of consciousness,
that is finding out how the brain works, will eventually lead to the
solution of the hard problem of consciousness.[4]
In particular, the solution can be achieved by identifying the stimuli
and neurological pathways whose operation generates evidence of
subjective experience.
Neuroscientist Michael Graziano, in his book Consciousness and the Social Brain, advocates what he calls attention schema theory,
in which our perception of being conscious is merely an error in
perception, held by brains which evolved to hold erroneous and
incomplete models of their own internal workings, just as they hold
erroneous and incomplete models of their own bodies and of the external
world.[35][36]
Cognitive neuroscientist Stanislas Dehaene, in his 2014 book Consciousness and the Brain,
summarized the previous decades of experimental consciousness research
involving reports of subjective experience, and argued that Chalmers'
"easy problems" of consciousness are actually the hard problems and the
"hard problems" are based only upon ill-defined intuitions that,
according to Dehaene, are continually shifting as understanding evolves:[5]
Once our intuitions are educated by cognitive
neuroscience and computer simulations, Chalmers' hard problem will
evaporate. The hypothetical concept of qualia, pure mental experience,
detached from any information-processing role, will be viewed as a
peculiar idea of the prescientific era, much like vitalism...
[Just as science dispatched vitalism] the science of consciousness will
keep eating away at the hard problem of consciousness until it
vanishes.
A phrenological mapping[1] of the brain – phrenology
was among the first attempts to correlate mental functions with
specific parts of the brain although it is now largely discredited.
Philosophy of mind is a branch of philosophy that studies the nature of the mind. The mind–body problem is a paradigm issue in philosophy of mind, although other issues are addressed, such as the hard problem of consciousness, and the nature of particular mental states. Aspects of the mind that are studied include mental events, mental functions, mental properties, consciousness, the ontology of the mind, the nature of thought, and the relationship of the mind to the body.
Dualism and monism are the two central schools of thought
on the mind–body problem, although nuanced views have arisen that do
not fit one or the other category neatly. Dualism is seen even in the
Eastern tradition, in the Sankhya and Yoga schools of Hindu philosophy,[5] and Plato,[6] but its entry into Western philosophy was thanks to René Descartes in the 17th century.[7] Substance dualists like Descartes argue that the mind is an independently existing substance, whereas property dualists maintain that the mind is a group of independent properties that emerge from and cannot be reduced to the brain, but that it is not a distinct substance.[8]
Monism is the position that mind and body are not ontologically distinct entities (independent substances). This view was first advocated in Western philosophy by Parmenides in the 5th century BCE and was later espoused by the 17th century rationalistBaruch Spinoza.[9]Physicalists
argue that only entities postulated by physical theory exist, and that
mental processes will eventually be explained in terms of these entities
as physical theory continues to evolve. Physicalists maintain various
positions on the prospects of reducing mental properties to physical
properties (many of whom adopt compatible forms of property dualism),[10][11][12][13][14][15] and the ontological status of such mental properties remains unclear.[14][16][17]Idealists
maintain that the mind is all that exists and that the external world
is either mental itself, or an illusion created by the mind. Neutral monists such as Ernst Mach and William James
argue that events in the world can be thought of as either mental
(psychological) or physical depending on the network of relationships
into which they enter, and dual-aspect monists such as Spinoza
adhere to the position that there is some other, neutral substance, and
that both matter and mind are properties of this unknown substance. The
most common monisms in the 20th and 21st centuries have all been
variations of physicalism; these positions include behaviorism, the type identity theory, anomalous monism and functionalism.[18]
Most modern philosophers of mind adopt either a reductive or
non-reductive physicalist position, maintaining in their different ways
that the mind is not something separate from the body.[18] These approaches have been particularly influential in the sciences, especially in the fields of sociobiology, computer science (specifically, artificial intelligence), evolutionary psychology and the various neurosciences.[19][20][21][22]
Reductive physicalists assert that all mental states and properties
will eventually be explained by scientific accounts of physiological
processes and states.[23][24][25] Non-reductive physicalists argue that although the mind is not a separate substance, mental properties supervene
on physical properties, or that the predicates and vocabulary used in
mental descriptions and explanations are indispensable, and cannot be
reduced to the language and lower-level explanations of physical
science.[26][27] Continued neuroscientific
progress has helped to clarify some of these issues; however, they are
far from being resolved. Modern philosophers of mind continue to ask
how the subjective qualities and the intentionality of mental states and properties can be explained in naturalistic terms.[28][29]
Mind–body problem
The mind–body problem concerns the explanation of the relationship that exists between minds, or mental processes, and bodily states or processes.[2]
The main aim of philosophers working in this area is to determine the
nature of the mind and mental states/processes, and how—or even if—minds
are affected by and can affect the body.
Our perceptual experiences depend on stimuli that arrive at our various sensory organs
from the external world, and these stimuli cause changes in our mental
states, ultimately causing us to feel a sensation, which may be pleasant
or unpleasant. Someone's desire for a slice of pizza, for example, will
tend to cause that person to move his or her body in a specific manner
and in a specific direction to obtain what he or she wants. The
question, then, is how it can be possible for conscious experiences to
arise out of a lump of gray matter endowed with nothing but
electrochemical properties.[18]
A related problem is how someone's propositional attitudes (e.g. beliefs and desires) cause that individual's neurons to fire and muscles to contract. These comprise some of the puzzles that have confronted epistemologists and philosophers of mind from at least the time of René Descartes.[7]
Dualist solutions to the mind–body problem
Dualism is a set of views about the relationship between mind and matter (or body). It begins with the claim that mental phenomena are, in some respects, non-physical.[8] One of the earliest known formulations of mind–body dualism was expressed in the eastern Sankhya and Yoga schools of Hindu philosophy (c. 650 BCE), which divided the world into purusha (mind/spirit) and prakriti (material substance).[5] Specifically, the Yoga Sutra of Patanjali presents an analytical approach to the nature of the mind.
In Western Philosophy, the earliest discussions of dualist ideas are in the writings of Plato
who maintained that humans' "intelligence" (a faculty of the mind or
soul) could not be identified with, or explained in terms of, their
physical body.[6][30] However, the best-known version of dualism is due to René Descartes (1641), and holds that the mind is a non-extended, non-physical substance, a "res cogitans".[7] Descartes was the first to clearly identify the mind with consciousness and self-awareness,
and to distinguish this from the brain, which was the seat of
intelligence. He was therefore the first to formulate the mind–body
problem in the form in which it still exists today.[7]
Arguments for dualism
The
most frequently used argument in favor of dualism appeals to the
common-sense intuition that conscious experience is distinct from
inanimate matter. If asked what the mind is, the average person would
usually respond by identifying it with their self, their personality, their soul,
or some other such entity. They would almost certainly deny that the
mind simply is the brain, or vice versa, finding the idea that there is
just one ontological entity at play to be too mechanistic, or simply unintelligible.[8]
Many modern philosophers of mind think that these intuitions are
misleading and that we should use our critical faculties, along with empirical evidence from the sciences, to examine these assumptions to determine whether there is any real basis to them.[8]
Another important argument in favor of dualism is that the mental
and the physical seem to have quite different, and perhaps
irreconcilable, properties.[31]
Mental events have a subjective quality, whereas physical events do
not. So, for example, one can reasonably ask what a burnt finger feels
like, or what a blue sky looks like, or what nice music sounds like to a
person. But it is meaningless, or at least odd, to ask what a surge in
the uptake of glutamate in the dorsolateral portion of the hippocampus feels like.
Philosophers of mind call the subjective aspects of mental events "qualia" or "raw feels".[31]
There is something that it is like to feel pain, to see a familiar
shade of blue, and so on. There are qualia involved in these mental
events that seem particularly difficult to reduce to anything physical.
David Chalmers explains this argument by stating that we could
conceivably know all the objective information about something, such as
the brain states and wavelengths of light involved with seeing the color
red, but still not know something fundamental about the situation –
what it is like to see the color red.[32]
If consciousness (the mind) can exist independently of physical
reality (the brain), one must explain how physical memories are created
concerning consciousness. Dualism must therefore explain how
consciousness affects physical reality. One possible explanation is that
of a miracle, proposed by Arnold Geulincx and Nicolas Malebranche, where all mind–body interactions require the direct intervention of God.
Another possible argument that has been proposed by C. S. Lewis[33] is the Argument from Reason:
if, as monism implies, all of our thoughts are the effects of physical
causes, then we have no reason for assuming that they are also the consequent
of a reasonable ground. Knowledge, however, is apprehended by reasoning
from ground to consequent. Therefore, if monism is correct, there would
be no way of knowing this—or anything else—we could not even suppose
it, except by a fluke.
The zombie argument is based on a thought experiment proposed by Todd Moody, and developed by David Chalmers in his book The Conscious Mind.
The basic idea is that one can imagine one's body, and therefore
conceive the existence of one's body, without any conscious states being
associated with this body. Chalmers' argument is that it seems possible
that such a being could exist because all that is needed is that all
and only the things that the physical sciences describe about a zombie
must be true of it. Since none of the concepts involved in these
sciences make reference to consciousness or other mental phenomena, and
any physical entity can be by definition described scientifically via physics, the move from conceivability to possibility is not such a large one.[34] Others such as Dennett have argued that the notion of a philosophical zombie is an incoherent,[35] or unlikely,[36]
concept. It has been argued under physicalism that one must either
believe that anyone including oneself might be a zombie, or that no one
can be a zombie—following from the assertion that one's own conviction
about being (or not being) a zombie is a product of the physical world
and is therefore no different from anyone else's. This argument has been
expressed by Dennett who argues that "Zombies think they are conscious,
think they have qualia, think they suffer pains—they are just 'wrong'
(according to this lamentable tradition) in ways that neither they nor
we could ever discover!"[35]
See also the problem of other minds.
Interactionist dualism, or simply interactionism, is the particular form of dualism first espoused by Descartes in the Meditations.[7] In the 20th century, its major defenders have been Karl Popper and John Carew Eccles.[37] It is the view that mental states, such as beliefs and desires, causally interact with physical states.[8]
Descartes' famous argument for this position can be summarized as
follows: Seth has a clear and distinct idea of his mind as a thinking
thing that has no spatial extension (i.e., it cannot be measured in
terms of length, weight, height, and so on). He also has a clear and
distinct idea of his body as something that is spatially extended,
subject to quantification and not able to think. It follows that mind
and body are not identical because they have radically different
properties.[7]
At the same time, however, it is clear that Seth's mental states (desires, beliefs, etc.) have causal
effects on his body and vice versa: A child touches a hot stove
(physical event) which causes pain (mental event) and makes her yell
(physical event), this in turn provokes a sense of fear and
protectiveness in the caregiver (mental event), and so on.
Descartes' argument crucially depends on the premise that what Seth believes to be "clear and distinct" ideas in his mind are necessarily true. Many contemporary philosophers doubt this. For example, Joseph Agassi
suggests that several scientific discoveries made since the early 20th
century have undermined the idea of privileged access to one's own
ideas. Freud
claimed that a psychologically-trained observer can understand a
person's unconscious motivations better than the person himself does. Duhem has shown that a philosopher of science can know a person's methods of discovery better than that person herself does, while Malinowski
has shown that an anthropologist can know a person's customs and habits
better than the person whose customs and habits they are. He also
asserts that modern psychological experiments that cause people to see
things that are not there provide grounds for rejecting Descartes'
argument, because scientists can describe a person's perceptions better
than the person herself can.[41][42]
Other forms of dualism
Four varieties of dualism. The arrows indicate the direction of the causal interactions. Occasionalism is not shown.
Psychophysical parallelism
Psychophysical parallelism, or simply parallelism,
is the view that mind and body, while having distinct ontological
statuses, do not causally influence one another. Instead, they run along
parallel paths (mind events causally interact with mind events and
brain events causally interact with brain events) and only seem to
influence each other.[43] This view was most prominently defended by Gottfried Leibniz. Although Leibniz was an ontological monist who believed that only one type of substance, the monad,
exists in the universe, and that everything is reducible to it, he
nonetheless maintained that there was an important distinction between
"the mental" and "the physical" in terms of causation. He held that God
had arranged things in advance so that minds and bodies would be in
harmony with each other. This is known as the doctrine of pre-established harmony.[44]
Occasionalism
Occasionalism is the view espoused by Nicholas Malebranche as well as Islamic philosophers such as Abu Hamid Muhammad ibn Muhammad al-Ghazali
that asserts that all supposedly causal relations between physical
events, or between physical and mental events, are not really causal at
all. While body and mind are different substances, causes (whether
mental or physical) are related to their effects by an act of God's
intervention on each specific occasion.[45]
Property dualism
Property dualism is the view that the world is constituted of just one kind of substance – the physical kind – and there exist two distinct kinds of properties: physical properties and mental properties.
In other words, it is the view that non-physical, mental properties
(such as beliefs, desires and emotions) inhere in some physical bodies
(at least, brains). How mental and physical properties relate causally
depends on the variety of property dualism in question, and is not
always a clear issue. Sub-varieties of property dualism include:
Strong emergentism
asserts that when matter is organized in the appropriate way (i.e. in
the way that living human bodies are organized), mental properties
emerge in a way not fully accountable for by physical laws. Hence, it
is a form of emergent materialism.[8]
These emergent properties have an independent ontological status and
cannot be reduced to, or explained in terms of, the physical substrate
from which they emerge. They are dependent on the physical properties
from which they emerge, but opinions vary as to the coherence of top–down causation, i.e. the causal effectiveness of such properties. A form of property dualism has been espoused by David Chalmers and the concept has undergone something of a renaissance in recent years,[46] but was already suggested in the 19th century by William James.
Epiphenomenalism is a doctrine first formulated by Thomas Henry Huxley.[47]
It consists of the view that mental phenomena are causally ineffectual,
where one or more mental states do not have any influence on physical
states or mental phenomena are the effects, but not the causes, of
physical phenomena. Physical events can cause other physical events and
physical events can cause mental events, but mental events cannot cause
anything, since they are just causally inert by-products (i.e.
epiphenomena) of the physical world.[43] This view has been defended most strongly in recent times by Frank Jackson.[48]
Non-reductive Physicalism
is the view that mental properties form a separate ontological class to
physical properties: mental states (such as qualia) are not reducible
to physical states. The ontological stance towards qualia in the case of
non-reductive physicalism does not imply that qualia are causally
inert; this is what distinguishes it from epiphenomenalism.
Panpsychism
is the view that all matter has a mental aspect, or, alternatively, all
objects have a unified center of experience or point of view.
Superficially, it seems to be a form of property dualism, since it
regards everything as having both mental and physical properties.
However, some panpsychists say mechanical behaviour is derived from
primitive mentality of atoms and molecules—as are sophisticated
mentality and organic behaviour, the difference being attributed to the
presence or absence of complex structure in a compound object. So long as the reduction of non-mental properties to mental ones is in place, panpsychism is not a (strong) form of property dualism; otherwise it is.
Dual aspect theory
Dual aspect theory or dual-aspect monism is the view that the mental and the physical
are two aspects of, or perspectives on, the same substance. (Thus it
is a mixed position, which is monistic in some respects). In modern
philosophical writings, the theory's relationship to neutral monism
has become somewhat ill-defined, but one proffered distinction says
that whereas neutral monism allows the context of a given group of
neutral elements and the relationships into which they enter to
determine whether the group can be thought of as mental, physical, both,
or neither, dual-aspect theory suggests that the mental and the
physical are manifestations (or aspects) of some underlying substance,
entity or process that is itself neither mental nor physical as normally
understood. Various formulations of dual-aspect monism also require the
mental and the physical to be complementary, mutually irreducible and
perhaps inseparable (though distinct).
Experiential dualism
This
is a philosophy of mind that regards the degrees of freedom between
mental and physical well-being as not necessarily synonymous thus
implying an experiential dualism between body and mind. An example of
these disparate degrees of freedom is given by Allan Wallace
who notes that it is "experientially apparent that one may be
physically uncomfortable—for instance, while engaging in a strenuous
physical workout—while mentally cheerful; conversely, one may be
mentally distraught while experiencing physical comfort".[52]
Experiential dualism notes that our subjective experience of merely
seeing something in the physical world seems qualitatively different
than mental processes like grief that comes from losing a loved one.
This philosophy also is a proponent of causal dualism which is defined
as the dual ability for mental states and physical states to affect one
another. Mental states can cause changes in physical states and vice
versa.
However, unlike cartesian dualism or some other systems,
experiential dualism does not posit two fundamental substances in
reality: mind and matter. Rather, experiential dualism is to be
understood as a conceptual framework that gives credence to the
qualitative difference between the experience of mental and physical
states. Experiential dualism is accepted as the conceptual framework of
Madhyamaka Buddhism.
Madhayamaka Buddhism goes even further, finding fault with the monist
view of physicalist philosophies of mind as well in that these generally
posit matter and energy as the fundamental substance of reality.
Nonetheless, this does not imply that the cartesian dualist view is
correct, rather Madhyamaka regards as error any affirming view of a
fundamental substance to reality.
In denying the
independent self-existence of all the phenomena that make up the world
of our experience, the Madhyamaka view departs from both the substance
dualism of Descartes and the substance monism—namely, physicalism—that
is characteristic of modern science. The physicalism propounded by many
contemporary scientists seems to assert that the real world is composed
of physical things-in-themselves, while all mental phenomena are
regarded as mere appearances, devoid of any reality in and of
themselves. Much is made of this difference between appearances and
reality.[52]
Indeed, physicalism, or the idea that matter is the only fundamental substance of reality, is explicitly rejected by Buddhism.
In
the Madhyamaka view, mental events are no more or less real than
physical events. In terms of our common-sense experience, differences of
kind do exist between physical and mental phenomena. While the former
commonly have mass, location, velocity, shape, size, and numerous other
physical attributes, these are not generally characteristic of mental
phenomena. For example, we do not commonly conceive of the feeling of
affection for another person as having mass or location. These physical
attributes are no more appropriate to other mental events such as
sadness, a recalled image from one's childhood, the visual perception of
a rose, or consciousness of any sort. Mental phenomena are, therefore,
not regarded as being physical, for the simple reason that they lack
many of the attributes that are uniquely characteristic of physical
phenomena. Thus, Buddhism has never adopted the physicalist principle
that regards only physical things as real.[52]
Hylomorphism
Hylomorphism is a theory that originates with Aristotelian philosophy, which conceives being as a compound of matter and form. "Hylomorphism" is a 19th-century term formed from the Greek words ὕλη hyle, "wood, matter", and μορφή, morphē, "form".
Monist solutions to the mind–body problem
In contrast to dualism, monism
does not accept any fundamental divisions. The fundamentally disparate
nature of reality has been central to forms of eastern philosophies for
over two millennia. In Indian and Chinese philosophy, monism is integral to how experience is understood. Today, the most common forms of monism in Western philosophy are physicalist.[18]
Physicalistic monism asserts that the only existing substance is
physical, in some sense of that term to be clarified by our best
science.[53] However, a variety of formulations (see below) are possible. Another form of monism, idealism, states that the only existing substance is mental. Although pure idealism, such as that of George Berkeley, is uncommon in contemporary Western philosophy, a more sophisticated variant called panpsychism,
according to which mental experience and properties may be at the
foundation of physical experience and properties, has been espoused by
some philosophers such as Alfred North Whitehead[54] and David Ray Griffin.[46]
Phenomenalism is the theory that representations (or sense data) of external objects are all that exist. Such a view was briefly adopted by Bertrand Russell and many of the logical positivists during the early 20th century.[55]
A third possibility is to accept the existence of a basic substance
that is neither physical nor mental. The mental and physical would then
both be properties of this neutral substance. Such a position was
adopted by Baruch Spinoza[9] and was popularized by Ernst Mach[56] in the 19th century. This neutral monism, as it is called, resembles property dualism.
Physicalistic monisms
Behaviorism
Behaviorism dominated philosophy of mind for much of the 20th century, especially the first half.[18] In psychology, behaviorism developed as a reaction to the inadequacies of introspectionism.[53]
Introspective reports on one's own interior mental life are not subject
to careful examination for accuracy and cannot be used to form
predictive generalizations. Without generalizability and the possibility
of third-person examination, the behaviorists argued, psychology cannot
be scientific.[53]
The way out, therefore, was to eliminate the idea of an interior mental
life (and hence an ontologically independent mind) altogether and focus
instead on the description of observable behavior.[57]
Parallel to these developments in psychology, a philosophical behaviorism (sometimes called logical behaviorism) was developed.[53] This is characterized by a strong verificationism,
which generally considers unverifiable statements about interior mental
life pointless. For the behaviorist, mental states are not interior
states on which one can make introspective reports. They are just
descriptions of behavior or dispositions to behave in certain ways, made by third parties to explain and predict another's behavior.[58]
Philosophical behaviorism has fallen out of favor since the latter half of the 20th century, coinciding with the rise of cognitivism.[2] Cognitivists reject behaviorism due to several perceived problems. For example, behaviorism could be said to be counterintuitive when it maintains that someone is talking about behavior in the event that a person is experiencing a painful headache.
Identity theory
Type physicalism (or type-identity theory) was developed by John Smart[25] and Ullin Place[59]
as a direct reaction to the failure of behaviorism. These philosophers
reasoned that, if mental states are something material, but not
behavioral, then mental states are probably identical to internal states
of the brain. In very simplified terms: a mental state M is nothing other than brain state B.
The mental state "desire for a cup of coffee" would thus be nothing
more than the "firing of certain neurons in certain brain regions".[25]
The
classic Identity theory and Anomalous Monism in contrast. For the
Identity theory, every token instantiation of a single mental type
corresponds (as indicated by the arrows) to a physical token of a single
physical type. For anomalous monism, the token–token correspondences
can fall outside of the type–type correspondences. The result is token
identity.
Despite its initial plausibility, the identity theory faces a strong challenge in the form of the thesis of multiple realizability, first formulated by Hilary Putnam.[27]
It is obvious that not only humans, but many different species of
animals can, for example, experience pain. However, it seems highly
unlikely that all of these diverse organisms with the same pain
experience are in the identical brain state. And if this is the case,
then pain cannot be identical to a specific brain state. The identity
theory is thus empirically unfounded.[27]
On the other hand, even granted the above, it does not follow
that identity theories of all types must be abandoned. According to
token identity theories, the fact that a certain brain state is
connected with only one mental state of a person does not have to mean
that there is an absolute correlation between types of mental state and
types of brain state. The type–token distinction can be illustrated by a
simple example: the word "green" contains four types of letters (g, r,
e, n) with two tokens (occurrences) of the letter e along with
one each of the others.
The idea of token identity is that only particular occurrences of mental
events are identical with particular occurrences or tokenings of
physical events.[60] Anomalous monism (see below) and most other non-reductive physicalisms are token-identity theories.[61] Despite these problems, there is a renewed interest in the type identity theory today, primarily due to the influence of Jaegwon Kim.[25]
Functionalism
Functionalism was formulated by Hilary Putnam and Jerry Fodor as a reaction to the inadequacies of the identity theory.[27] Putnam and Fodor saw mental states in terms of an empirical computational theory of the mind.[62] At about the same time or slightly after, D.M. Armstrong and David Kellogg Lewis formulated a version of functionalism that analyzed the mental concepts of folk psychology in terms of functional roles.[63] Finally, Wittgenstein's idea of meaning as use led to a version of functionalism as a theory of meaning, further developed by Wilfrid Sellars and Gilbert Harman. Another one, psychofunctionalism, is an approach adopted by the naturalistic philosophy of mind associated with Jerry Fodor and Zenon Pylyshyn.
What all these different varieties of functionalism share in
common is the thesis that mental states are characterized by their
causal relations with other mental states and with sensory inputs and
behavioral outputs. That is, functionalism abstracts away from the
details of the physical implementation of a mental state by
characterizing it in terms of non-mental functional properties. For
example, a kidney is characterized scientifically by its functional role
in filtering blood and maintaining certain chemical balances. From this
point of view, it does not really matter whether the kidney be made up
of organic tissue, plastic nanotubes or silicon chips: it is the role
that it plays and its relations to other organs that define it as a
kidney.[62]
Non-reductive physicalism
Non-reductionist philosophers hold firmly to two essential
convictions with regard to mind–body relations: 1) Physicalism is true
and mental states must be physical states, but 2) All reductionist
proposals are unsatisfactory: mental states cannot be reduced to
behavior, brain states or functional states.[53] Hence, the question arises whether there can still be a non-reductive physicalism. Donald Davidson's anomalous monism[26]
is an attempt to formulate such a physicalism. He "thinks that when one
runs across what are traditionally seen as absurdities of Reason, such
as akrasia or self-deception, the personal psychology framework is not
to be given up in favor of the subpersonal one, but rather must be
enlarged or extended so that the rationality set out by the principle of
charity can be found elsewhere."[64]
Davidson uses the thesis of supervenience:
mental states supervene on physical states, but are not reducible to
them. "Supervenience" therefore describes a functional dependence: there
can be no change in the mental without some change in the
physical–causal reducibility between the mental and physical without
ontological reducibility.[65]
Because non-reductive physicalist theories attempt to both retain
the ontological distinction between mind and body and to try to solve
the "surfeit of explanations puzzle" in some way; critics often see this
as a paradox and point out the similarities to epiphenomenalism, in that it is the brain that is seen as the root "cause" not the mind, and the mind seems to be rendered inert.
Epiphenomenalism regards one or more mental states as the
byproduct of physical brain states, having no influence on physical
states. The interaction is one-way (solving the "surfeit of explanations
puzzle") but leaving us with non-reducible mental states (as a
byproduct of brain states) – causally reducible, but ontologically
irreducible to physical states. Pain would be seen by epiphenomenaliasts
as being caused by the brain state but as not having effects on other
brain states, though it might have effects on other mental states (i.e.
cause distress).
Weak emergentism
Weak emergentism is a form of "non-reductive physicalism" that
involves a layered view of nature, with the layers arranged in terms of
increasing complexity and each corresponding to its own special science.
Some philosophers hold that emergent properties causally interact with
more fundamental levels, while others maintain that higher-order
properties simply supervene over lower levels without direct causal
interaction. The latter group therefore holds a less strict, or
"weaker", definition of emergentism, which can be rigorously stated as
follows: a property P of composite object O is emergent if it is
metaphysically impossible for another object to lack property P if that
object is composed of parts with intrinsic properties identical to those
in O and has those parts in an identical configuration.
Sometimes emergentists use the example of water having a new property when Hydrogen H and Oxygen O combine to form H2O
(water). In this example there "emerges" a new property of a
transparent liquid that would not have been predicted by understanding
hydrogen and oxygen as gases. This is analogous to physical properties
of the brain giving rise to a mental state. Emergentists try to solve
the notorious mind–body gap this way. One problem for emergentism is the
idea of "causal closure" in the world that does not allow for a
mind-to-body causation.[66]
Eliminative materialism
If one is a materialist and believes that all aspects of our common-sense psychology will find reduction to a mature cognitive neuroscience, and that non-reductive materialism is mistaken, then one can adopt a final, more radical position: eliminative materialism.
There are several varieties of eliminative materialism, but all maintain that our common-sense "folk psychology" badly misrepresents the nature of some aspect of cognition. Eliminativists such as Patricia and Paul Churchland
argue that while folk psychology treats cognition as fundamentally
sentence-like, the non-linguistic vector/matrix model of neural network
theory or connectionism will prove to be a much more accurate account of how the brain works.[23]
The Churchlands often invoke the fate of other, erroneous popular theories and ontologies that have arisen in the course of history.[23][24]
For example, Ptolemaic astronomy served to explain and roughly predict
the motions of the planets for centuries, but eventually this model of
the solar system was eliminated in favor of the Copernican model. The
Churchlands believe the same eliminative fate awaits the
"sentence-cruncher" model of the mind in which thought and behavior are
the result of manipulating sentence-like states called "propositional attitudes".
Non-physicalist monisms
Idealism
Idealism
is the form of monism that sees the world as consisting of minds,
mental contents and or consciousness.
Idealists are not faced with explaining how minds arise from bodies:
rather, the world, bodies and objects are regarded as mere appearances
held by minds. However, accounting for the mind–body problem is not
usually the main motivation for idealism; rather, idealists tend to be
motivated by skepticism,
intentionality, and the unique nature of ideas.
Idealism is prominent in Eastern religious and philosophical thought. It
has gone through several cycles of popularity and neglect in the
history of Western philosophy.
Different varieties of idealism may hold that there are
Neutral monism, in philosophy, is the metaphysical
view that the mental and the physical are two ways of organizing or
describing the same elements, which are themselves "neutral", that is,
neither physical nor mental. This view denies that the mental and the
physical are two fundamentally different things. Rather, neutral monism
claims the universe consists of only one kind of stuff, in the form of
neutral elements that are in themselves neither mental nor physical.
These neutral elements might have the properties of color and shape,
just as we experience those properties. But these shaped and colored
elements do not exist in a mind (considered as a substantial entity,
whether dualistically or physicalistically); they exist on their own.
Mysterianism
Some philosophers take an epistemic approach and argue that the
mind–body problem is currently unsolvable, and perhaps will always
remain unsolvable to human beings. This is usually termed New mysterianism. Colin McGinn holds that human beings are cognitively closed
in regards to their own minds. According to McGinn human minds lack the
concept-forming procedures to fully grasp how mental properties such as
consciousness arise from their causal basis.[67] An example would be how an elephant is cognitively closed in regards to particle physics.
A more moderate conception has been expounded by Thomas Nagel,
which holds that the mind–body problem is currently unsolvable at the
present stage of scientific development and that it might take a future
scientific paradigm shift or revolution to bridge the explanatory gap. Nagel posits that in the future a sort of "objective phenomenology" might be able to bridge the gap between subjective conscious experience and its physical basis.[68]
Linguistic criticism of the mind–body problem
Each
attempt to answer the mind–body problem encounters substantial
problems. Some philosophers argue that this is because there is an
underlying conceptual confusion.[69] These philosophers, such as Ludwig Wittgenstein and his followers in the tradition of linguistic criticism, therefore reject the problem as illusory.[70]
They argue that it is an error to ask how mental and biological states
fit together. Rather it should simply be accepted that human experience
can be described in different ways—for instance, in a mental and in a
biological vocabulary. Illusory problems arise if one tries to describe
the one in terms of the other's vocabulary or if the mental vocabulary
is used in the wrong contexts.[70]
This is the case, for instance, if one searches for mental states of
the brain. The brain is simply the wrong context for the use of mental
vocabulary—the search for mental states of the brain is therefore a category error or a sort of fallacy of reasoning.[70]
Today, such a position is often adopted by interpreters of Wittgenstein such as Peter Hacker.[69] However, Hilary Putnam,
the originator of functionalism, has also adopted the position that the
mind–body problem is an illusory problem which should be dissolved
according to the manner of Wittgenstein.[71]
Externalism and internalism
Where
is the mind located? If the mind is a physical phenomenon of some kind,
it has to be located somewhere. According to some, there are two
possible options: either the mind is internal to the body (internalism) or the mind is external to it (externalism).
More generally, either the mind depends only on events and properties
taking place inside the subject's body or it depends also on factors
external to it.
Proponents of internalism are committed to the view that neural activity is sufficient to produce the mind.
Proponents of externalism maintain that the surrounding world is in some sense constitutive of the mind.
Externalism differentiates into several versions. The main ones are semantic externalism, cognitive externalism and phenomenal externalism.
Each of these versions of externalism can further be divided into
whether they refer only to the content or to the vehicles of the mind.
Semantic externalism holds that the semantic content of the mind
is totally or partially defined by a state of affairs external to the
body of the subject. Hilary Putnam's Twin Earth thought experiment is a good example.
Cognitive externalism is a very broad collection of views that
suggests the role of the environment, of tools, of development, and of
the body in fleshing out cognition. Embodied cognition, the extended mind, and enactivism are good examples.
Phenomenal externalism suggests that the phenomenal aspects of
the mind are external to the body. Authors who addressed this
possibility are Ted Honderich, Edwin Holt, Francois Tonneau, Kevin
O'Regan, Riccardo Manzotti, Teed Rockwell and Max Velmans.
Naturalism and its problems
The
thesis of physicalism is that the mind is part of the material (or
physical) world. Such a position faces the problem that the mind has
certain properties that no other material thing seems to possess.
Physicalism must therefore explain how it is possible that these
properties can nonetheless emerge from a material thing. The project of
providing such an explanation is often referred to as the "naturalization of the mental".[53]
Some of the crucial problems that this project attempts to resolve
include the existence of qualia and the nature of intentionality.[53]
Qualia
Many mental states seem to be experienced subjectively in different ways by different individuals.[32] And it is characteristic of a mental state that it has some experiential quality,
e.g. of pain, that it hurts. However, the sensation of pain between two
individuals may not be identical, since no one has a perfect way to
measure how much something hurts or of describing exactly how it feels
to hurt. Philosophers and scientists therefore ask where these
experiences come from. The existence of cerebral events, in and of
themselves, cannot explain why they are accompanied by these
corresponding qualitative experiences. The puzzle of why many cerebral
processes occur with an accompanying experiential aspect in
consciousness seems impossible to explain.[31]
Yet it also seems to many that science will eventually have to explain such experiences.[53] This follows from an assumption about the possibility of reductive explanations.
According to this view, if an attempt can be successfully made to
explain a phenomenon reductively (e.g., water), then it can be explained
why the phenomenon has all of its properties (e.g., fluidity,
transparency).[53]
In the case of mental states, this means that there needs to be an
explanation of why they have the property of being experienced in a
certain way.
The 20th-century German philosopher Martin Heidegger criticized the ontological
assumptions underpinning such a reductive model, and claimed that it
was impossible to make sense of experience in these terms. This is
because, according to Heidegger, the nature of our subjective experience
and its qualities is impossible to understand in terms of Cartesian
"substances" that bear "properties". Another way to put this is that
the very concept of qualitative experience is incoherent in terms of—or
is semantically incommensurable with the concept of—substances that bear properties.[72]
This problem of explaining introspective first-person aspects of
mental states and consciousness in general in terms of third-person
quantitative neuroscience is called the explanatory gap.[73] There are several different views of the nature of this gap among contemporary philosophers of mind. David Chalmers and the early Frank Jackson interpret the gap as ontological in nature; that is, they maintain that qualia can never be explained by science because physicalism is false. There are two separate categories involved and one cannot be reduced to the other.[74] An alternative view is taken by philosophers such as Thomas Nagel and Colin McGinn. According to them, the gap is epistemological
in nature. For Nagel, science is not yet able to explain subjective
experience because it has not yet arrived at the level or kind of
knowledge that is required. We are not even able to formulate the
problem coherently.[32]
For McGinn, on other hand, the problem is one of permanent and inherent
biological limitations. We are not able to resolve the explanatory gap
because the realm of subjective experiences is cognitively closed to us
in the same manner that quantum physics is cognitively closed to
elephants.[75] Other philosophers liquidate the gap as purely a semantic problem. This semantic problem, of course, led to the famous "Qualia Question", which is: Does Red cause Redness?
Intentionality is the capacity of mental states to be directed towards (about) or be in relation with something in the external world.[29] This property of mental states entails that they have contents and semantic referents and can therefore be assigned truth values.
When one tries to reduce these states to natural processes there arises
a problem: natural processes are not true or false, they simply happen.[76]
It would not make any sense to say that a natural process is true or
false. But mental ideas or judgments are true or false, so how then can
mental states (ideas or judgments) be natural processes? The possibility
of assigning semantic value to ideas must mean that such ideas are
about facts. Thus, for example, the idea that Herodotus
was a historian refers to Herodotus and to the fact that he was a
historian. If the fact is true, then the idea is true; otherwise, it is
false. But where does this relation come from? In the brain, there are
only electrochemical processes and these seem not to have anything to do
with Herodotus.[28]
Humans
are corporeal beings and, as such, they are subject to examination and
description by the natural sciences. Since mental processes are
intimately related to bodily processes, the descriptions that the
natural sciences furnish of human beings play an important role in the
philosophy of mind.[2] There are many scientific disciplines that study processes related to the mental. The list of such sciences includes: biology, computer science, cognitive science, cybernetics, linguistics, medicine, pharmacology, and psychology.[78]
Neurobiology
The theoretical background of biology, as is the case with modern natural sciences
in general, is fundamentally materialistic. The objects of study are,
in the first place, physical processes, which are considered to be the
foundations of mental activity and behavior.[79]
The increasing success of biology in the explanation of mental
phenomena can be seen by the absence of any empirical refutation of its
fundamental presupposition: "there can be no change in the mental states
of a person without a change in brain states."[78]
Within the field of neurobiology, there are many subdisciplines
that are concerned with the relations between mental and physical states
and processes:[79]Sensory neurophysiology investigates the relation between the processes of perception and stimulation.[80]Cognitive neuroscience studies the correlations between mental processes and neural processes.[80]Neuropsychology describes the dependence of mental faculties on specific anatomical regions of the brain.[80] Lastly, evolutionary biology
studies the origins and development of the human nervous system and, in
as much as this is the basis of the mind, also describes the ontogenetic and phylogenetic development of mental phenomena beginning from their most primitive stages.[78] Evolutionary biology furthermore places tight constraints on any philosophical theory of the mind, as the gene-based mechanism of natural selection
does not allow any giant leaps in the development of neural complexity
or neural software but only incremental steps over long time periods.[81]
Since the 1980s, sophisticated neuroimaging procedures, such as fMRI
(above), have furnished increasing knowledge about the workings of the
human brain, shedding light on ancient philosophical problems.
The methodological
breakthroughs of the neurosciences, in particular the introduction of
high-tech neuroimaging procedures, has propelled scientists toward the
elaboration of increasingly ambitious research programs: one of the main
goals is to describe and comprehend the neural processes which
correspond to mental functions (see: neural correlate).[79] Several groups are inspired by these advances.
Computer science
Computer science concerns itself with the automatic processing of information (or at least with physical systems of symbols to which information is assigned) by means of such things as computers.[82] From the beginning, computer programmers
have been able to develop programs that permit computers to carry out
tasks for which organic beings need a mind. A simple example is
multiplication. It is not clear whether computers could be said to have a
mind. Could they, someday, come to have what we call a mind? This
question has been propelled into the forefront of much philosophical
debate because of investigations in the field of artificial intelligence (AI).
Within AI, it is common to distinguish between a modest research
program and a more ambitious one: this distinction was coined by John Searle in terms of a weak AI and strong AI.
The exclusive objective of "weak AI", according to Searle, is the
successful simulation of mental states, with no attempt to make
computers become conscious or aware, etc. The objective of strong AI, on
the contrary, is a computer with consciousness similar to that of human
beings.[83] The program of strong AI goes back to one of the pioneers of computation Alan Turing. As an answer to the question "Can computers think?", he formulated the famous Turing test.[84]
Turing believed that a computer could be said to "think" when, if
placed in a room by itself next to another room that contained a human
being and with the same questions being asked of both the computer and
the human being by a third party human being, the computer's responses
turned out to be indistinguishable from those of the human. Essentially,
Turing's view of machine intelligence followed the behaviourist model
of the mind—intelligence is as intelligence does. The Turing test has
received many criticisms, among which the most famous is probably the Chinese roomthought experiment formulated by Searle.[83]
The question about the possible sensitivity (qualia)
of computers or robots still remains open. Some computer scientists
believe that the specialty of AI can still make new contributions to the
resolution of the "mind–body problem". They suggest that based on the
reciprocal influences between software and hardware that takes place in
all computers, it is possible that someday theories can be discovered
that help us to understand the reciprocal influences between the human
mind and the brain (wetware).[85]
Psychology
Psychology is the science that investigates mental states directly.
It uses generally empirical methods to investigate concrete mental
states like joy, fear or obsessions. Psychology investigates the laws that bind these mental states to each other or with inputs and outputs to the human organism.[86]
An example of this is the psychology of perception. Scientists working in this field have discovered general principles of the perception of forms. A law of the psychology of forms says that objects that move in the same direction are perceived as related to each other.[78]
This law describes a relation between visual input and mental
perceptual states. However, it does not suggest anything about the
nature of perceptual states. The laws discovered by psychology are
compatible with all the answers to the mind–body problem already
described.
Cognitive science
Cognitive science is the interdisciplinary scientific study of the mind and its processes. It examines what cognition
is, what it does, and how it works. It includes research on
intelligence and behavior, especially focusing on how information is
represented, processed, and transformed (in faculties such as
perception, language, memory, reasoning, and emotion) within nervous
systems (human or other animal) and machines (e.g. computers). Cognitive
science consists of multiple research disciplines, including psychology, artificial intelligence, philosophy, neuroscience, linguistics, anthropology, sociology, and education.[87]
It spans many levels of analysis, from low-level learning and decision
mechanisms to high-level logic and planning; from neural circuitry to
modular brain organisation. Rowlands
argues that cognition is enactive, embodied, embedded, affective and
(potentially) extended. The position is taken that the "classical
sandwich" of cognition sandwiched between perception and action is
artificial; cognition has to be seen as a product of a strongly coupled
interaction that cannot be divided this way.[88][89]
Philosophy of mind in the continental tradition
Most
of the discussion in this article has focused on one style or tradition
of philosophy in modern Western culture, usually called analytic philosophy (sometimes described as Anglo-American philosophy).[90] Many other schools of thought exist, however, which are sometimes subsumed under the broad (and vague) label of continental philosophy.[90]
In any case, though topics and methods here are numerous, in relation
to the philosophy of mind the various schools that fall under this label
(phenomenology, existentialism,
etc.) can globally be seen to differ from the analytic school in that
they focus less on language and logical analysis alone but also take in
other forms of understanding human existence and experience. With
reference specifically to the discussion of the mind, this tends to
translate into attempts to grasp the concepts of thought and perceptual experience in some sense that does not merely involve the analysis of linguistic forms.[90]
Immanuel Kant's Critique of Pure Reason,
first published in 1781 and presented again with major revisions in
1787, represents a significant intervention into what will later become
known as the philosophy of mind. Kant's first critique is generally recognized as among the most significant works of modern philosophy in the West. Kant is a figure whose influence is marked in both continental and analytic/Anglo-American philosophy. Kant's work develops an in-depth study of transcendental consciousness, or the life of the mind as conceived through universal categories of consciousness.
In Georg Wilhelm Friedrich Hegel's Philosophy of Mind (frequently translated as Philosophy of Spirit or Geist),[91] the third part of his Encyclopedia of the Philosophical Sciences,
Hegel discusses three distinct types of mind: the "subjective
mind/spirit", the mind of an individual; the "objective mind/spirit",
the mind of society and of the State; and the "Absolute mind/spirit",
the position of religion, art, and philosophy. See also Hegel's The Phenomenology of Spirit. Nonetheless, Hegel's work differs radically from the style of Anglo-American philosophy of mind.
In 1896, Henri Bergson made in Matter and Memory
"Essay on the relation of body and spirit" a forceful case for the
ontological difference of body and mind by reducing the problem to the
more definite one of memory, thus allowing for a solution built on the empirical test case of aphasia.
In modern times, the two main schools that have developed in
response or opposition to this Hegelian tradition are phenomenology and
existentialism. Phenomenology, founded by Edmund Husserl, focuses on the contents of the human mind (see noema) and how processes shape our experiences.[92] Existentialism, a school of thought founded upon the work of Søren Kierkegaard,
focuses on Human predicament and how people deal with the situation of
being alive. Existential-phenomenology represents a major branch of
continental philosophy (they are not contradictory), rooted in the work
of Husserl but expressed in its fullest forms in the work of Martin Heidegger, Jean-Paul Sartre, Simone de Beauvoir and Maurice Merleau-Ponty. See Heidegger's Being and Time, Merleau-Ponty's Phenomenology of Perception, Sartre's Being and Nothingness, and Simone de Beauvoir's The Second Sex.
Mind in Eastern philosophy
Mind in Hindu philosophy
Dualism
Substance Dualism is a common feature of several orthodox Hindu schools including the Sāṅkhya, Nyāya, Yoga and Dvaita Vedanta. In these schools a clear difference is drawn between matter and a non-material soul, which is eternal and undergoes samsara, a cycle of death and rebirth. The Nyāya
school argued that qualities such as cognition and desire are inherent
qualities which are not possessed by anything solely material, and
therefore by process of elimination must belong to a non-material self,
the atman.[93] Many of these schools see their spiritual goal as moksha, liberation from the cycle of reincarnation.
Vedanta monistic idealism
Śaṅkara
In the Advaita Vedanta of the 8th century Indian philosopher Śaṅkara, the mind, body and world are all held to be the same unchanging eternal conscious entity called Brahman. Advaita, which means non-dualism, holds the view that all that exists is pure absolute consciousness. The fact that the world seems to be made up of changing entities is an illusion, or Maya. The only thing that exists is Brahman, which is described as Satchitananda
(Being, consciousness and bliss). Advaita Vedanta is best described by a
verse which states "Brahman is alone True, and this world of plurality
is an error; the individual self is not different from Brahman."[94]
Another form of monistic Vedanta is Vishishtadvaita (qualified non-dualism) as posited by the eleventh century philosopher Ramanuja. Ramanuja criticized Advaita Vedanta by arguing that consciousness is always intentional
and that it is also always a property of something. Ramanuja's Brahman
is defined by a multiplicity of qualities and properties in a single
monistic entity. This doctrine is called "samanadhikaranya" (several things in a common substrate).[95]
Materialism
Arguably the first exposition of empiricalmaterialism in the history of philosophy is in the Cārvāka
school (also called Lokāyata). The Cārvāka school rejected the
existence of anything but matter (which they defined as being made up of
the four elements),
including God and the soul. Therefore, they held that even
consciousness was nothing but a construct made up of atoms. A section of
the Cārvāka school believed in a material soul made up of air or
breath, but since this also was a form of matter, it was not said to
survive death.[96]
Buddhist teachings describe that the mind manifests moment-to-moment
as sense impressions and mental phenomena that are continuously
changing.[97]
The moment-by-moment manifestation of the mind-stream has been
described as happening in every person all the time, even in a scientist
who analyses various phenomena in the world, or analyses the material
body including the organ brain.[97]
The manifestation of the mind-stream is also described as being
influenced by physical laws, biological laws, psychological laws,
volitional laws, and universal laws.[97]
A salient feature of Buddhist philosophy which sets it apart from Indian orthodoxy is the centrality of the doctrine of not-self (Pāli.
anatta, Skt. anātman). The Buddha's not-self doctrine sees humans as an
impermanent composite of five psychological and physical aspects
instead of a single fixed self. In this sense, what is called ego or the
self is merely a convenient fiction, an illusion that does not apply to
anything real but to an erroneous way of looking at the ever-changing
stream of five interconnected aggregate factors.[98] The relationship between these aggregates is said to be one of dependent-arising (pratītyasamutpāda).
This means that all things, including mental events, arise
co-dependently from a plurality of other causes and conditions. This
seems to reject both causal determinist and epiphenomenalist conceptions of mind.[98]
Abhidharma theories of mind
Three centuries after the death of the Buddha (c. 150 BCE) saw the growth of a large body of literature called the Abhidharma in several contending Buddhist schools. In the Abhidharmic analysis of mind, the ordinary thought is defined as prapañca
('conceptual proliferation'). According to this theory, perceptual
experience is bound up in multiple conceptualizations (expectations,
judgments and desires). This proliferation of conceptualizations form
our illusory superimposition of concepts like self and other upon an ever-changing stream of aggregate phenomena.[98]
In this conception of mind no strict distinction is made between the
conscious faculty and the actual sense perception of various phenomena.
Consciousness is instead said to be divided into six sense modalities,
five for the five senses and sixth for perception of mental phenomena.[98]
The arising of cognitive awareness is said to depend on sense
perception, awareness of the mental faculty itself which is termed
mental or 'introspective awareness' (manovijñāna) and attention (āvartana), the picking out of objects out of the constantly changing stream of sensory impressions.
Rejection of a permanent agent eventually led to the
philosophical problems of the seeming continuity of mind and also of
explaining how rebirth and karma continue to be relevant doctrines without an eternal mind. This challenge was met by the Theravāda school by introducing the concept of mind as a factor of existence. This "life-stream" (Bhavanga-sota)
is an undercurrent forming the condition of being. The continuity of a
karmic "person" is therefore assured in the form of a mindstream (citta-santana), a series of flowing mental moments arising from the subliminal life-continuum mind (Bhavanga-citta), mental content, and attention.[98]
Indian Mahayana
The Sautrāntika school held a form of phenomenalism
that saw the world as imperceptible. It held that external objects
exist only as a support for cognition, which can only apprehend mental
representations. This influenced the later Yogācāra school of Mahayana Buddhism. The Yogācāra school is often called the mind-only school because of its internalist stance that consciousness is the ultimate existing reality. The works of Vasubandhu have often been interpreted as arguing for some form of Idealism. Vasubandhu uses the dream argument and a mereological refutation of atomism to attack the reality of external objects as anything other than mental entities.[99] Scholarly interpretations of Vasubandhu's philosophy vary widely, and include phenomenalism, neutral monism and realist phenomenology.
The Indian Mahayana schools were divided on the issue of the possibility of reflexive awareness (svasaṃvedana). Dharmakīrti
accepted the idea of reflexive awareness as expounded by the Yogācāra
school, comparing it to a lamp that illuminates itself while also
illuminating other objects. This was strictly rejected by Mādhyamika scholars like Candrakīrti. Since in the philosophy of the Mādhyamika all things and mental events are characterized by emptiness,
they argued that consciousness could not be an inherently reflexive
ultimate reality since that would mean it was self-validating and
therefore not characterized by emptiness.[98] These views were ultimately reconciled by the 8th century thinker Śāntarakṣita.
In Śāntarakṣita's synthesis he adopts the idealist Yogācāra views of
reflexive awareness as a conventional truth into the structure of the two truths doctrine.
Thus he states: "By relying on the Mind-Only system, know that external
entities do not exist. And by relying on this Middle Way system, know
that no self exists at all, even in that [mind]." [100]
The Yogācāra school also developed the theory of the repository consciousness (ālayavijñāna) to explain continuity of mind in rebirth and accumulation of karma. This repository consciousness acts as a storehouse for karmic seeds (bija) when all other senses are absent during the process of death and rebirth as well as being the causal potentiality of dharmic phenomena.[98] Thus according to B. Alan Wallace:
No constituents of the body—in the brain or
elsewhere—transform into mental states and processes. Such subjective
experiences do not emerge from the body, but neither do they emerge from
nothing. Rather, all objective mental appearances arise from the
substrate, and all subjective mental states and processes arise from the
substrate consciousness.[101]
Tibetan Buddhism
Tibetan Buddhist theories of mind evolved directly from the Indian Mahayana views. Thus the founder of the Gelug school, Je Tsongkhapa discusses the Yogācāra system of the Eight Consciousnesses in his Explanation of the Difficult Points.[102] He would later come to repudiate Śāntarakṣita's pragmatic idealism.
According to the 14th Dalai Lama
the mind can be defined "as an entity that has the nature of mere
experience, that is, 'clarity and knowing'. It is the knowing nature, or
agency, that is called mind, and this is non-material."[103] The simultaneously dual nature of mind is as follows:
1. Clarity (gsal) – The mental activity which produces cognitive phenomena (snang-ba).
2. Knowing (rig) – The mental activity of perceiving cognitive phenomena.
The 14th Dalai Lama has also explicitly laid out his theory of mind as experiential dualism which is described above under the different types of dualism.[52]
Because Tibetan philosophy of mind is ultimately soteriological, it focuses on meditative practices such as Dzogchen and Mahamudra
that allow a practitioner to experience the true reflexive nature of
their mind directly. This unobstructed knowledge of one's primordial,
empty and non-dual Buddha nature is called rigpa. The mind's innermost nature is described among various schools as pure luminosity or "clear light" ('od gsal) and is often compared to a crystal ball or a mirror. Sogyal Rinpoche
speaks of mind thus:
"Imagine a sky, empty, spacious, and pure from the beginning; its
essence is like this. Imagine a sun, luminous, clear, unobstructed, and
spontaneously present; its nature is like this."
Zen Buddhism
The
central issue in Chinese Zen philosophy of mind is in the difference
between the pure and awakened mind and the defiled mind. Chinese Chan
master Huangpo
described the mind as without beginning and without form or limit while
the defiled mind was that which was obscured by attachment to form and
concepts.[104] The pure Buddha-mind is thus able to see things "as they truly are", as absolute and non-dual "thusness" (Tathatā).
This non-conceptual seeing also includes the paradoxical fact that
there is no difference between a defiled and a pure mind, as well as no
difference between samsara and nirvana.[104]
In the Shobogenzo, the Japanese philosopher Dogen argued that body and mind are neither ontologically nor phenomenologically distinct but are characterized by a oneness called shin jin (bodymind). According to Dogen, "casting off body and mind" (Shinjin datsuraku) in zazen will allow one to experience things-as-they-are (genjokoan) which is the nature of original enlightenment (hongaku).[105]
Topics related to philosophy of mind
There
are countless subjects that are affected by the ideas developed in the
philosophy of mind. Clear examples of this are the nature of death and its definitive character, the nature of emotion, of perception and of memory. Questions about what a person is and what his or her identity
consists of also have much to do with the philosophy of mind. There are
two subjects that, in connection with the philosophy of the mind, have
aroused special attention: free will and the self.[2]
Free will
In the context of philosophy of mind, the problem of free will takes
on renewed intensity. This is certainly the case, at least, for
materialistic determinists.[2]
According to this position, natural laws completely determine the
course of the material world. Mental states, and therefore the will as
well, would be material states, which means human behavior and decisions
would be completely determined by natural laws. Some take this
reasoning a step further: people cannot determine by themselves what
they want and what they do. Consequently, they are not free.[106]
This argumentation is rejected, on the one hand, by the compatibilists.
Those who adopt this position suggest that the question "Are we free?"
can only be answered once we have determined what the term "free" means.
The opposite of "free" is not "caused" but "compelled" or "coerced". It
is not appropriate to identify freedom with indetermination. A free act
is one where the agent could have done otherwise if it had chosen
otherwise. In this sense a person can be free even though determinism is
true.[106] The most important compatibilist in the history of the philosophy was David Hume.[107] More recently, this position is defended, for example, by Daniel Dennett.[108]
On the other hand, there are also many incompatibilists who reject the argument because they believe that the will is free in a stronger sense called libertarianism.[106]
These philosophers affirm the course of the world is either a) not
completely determined by natural law where natural law is intercepted by
physically independent agency,[109]
b) determined by indeterministic natural law only, or c) determined by
indeterministic natural law in line with the subjective effort of
physically non-reducible agency.[110]
Under Libertarianism, the will does not have to be deterministic and,
therefore, it is potentially free. Critics of the second proposition (b)
accuse the incompatibilists of using an incoherent concept of freedom.
They argue as follows: if our will is not determined by anything, then
we desire what we desire by pure chance. And if what we desire is purely
accidental, we are not free. So if our will is not determined by
anything, we are not free.[106]
Self
The philosophy of mind also has important consequences for the
concept of "self". If by "self" or "I" one refers to an essential,
immutable nucleus of the person, some modern philosophers of mind, such as Daniel Dennett believe that no such thing exists. According to Dennett and other contemporaries, the self is considered an illusion.[111] The idea of a self as an immutable essential nucleus derives from the idea of an immaterial soul.
Such an idea is unacceptable to modern philosophers with physicalist
orientations and their general skepticism of the concept of "self" as
postulated by David Hume, who could never catch himself not doing, thinking or feeling anything.[112] However, in the light of empirical results from developmental psychology, developmental biology and neuroscience,
the idea of an essential inconstant, material nucleus—an integrated
representational system distributed over changing patterns of synaptic
connections—seems reasonable.
