Hard problem of consciousness

The hard problem of consciousness is the problem of explaining why and how sentient organisms have qualia[note 1] or phenomenal experiences—how and why it is that some internal states are felt states, such as heat or pain, rather than unfelt states, as in a thermostat or a toaster.[2] The philosopher David Chalmers, who introduced the term "hard problem" of consciousness,[3] contrasts this with the "easy problems" of explaining the ability to discriminate, integrate information, report mental states, focus attention, and so forth.[4] Easy problems are (relatively) easy because all that is required for their solution is to specify a mechanism that can perform the function.[4] That is, regardless of how complex or poorly understood the phenomena of the easy problems may be, they can eventually be understood by relying entirely on standard scientific methodologies.[4] Chalmers claims that the problem of experience is distinct from this set and will "persist even when the performance of all the relevant functions is explained".[4]

The existence of a "hard problem" is controversial. It has been accepted by philosophers of mind such as Joseph Levine,[5] Colin McGinn,[6] and Ned Block[7] and cognitive neuroscientists such as Francisco Varela,[8] Giulio Tononi,[9][10] and Christof Koch,[9][10] but disputed by philosophers of mind such as Daniel Dennett,[11] Massimo Pigliucci,[12] and Keith Frankish[13] and cognitive neuroscientists such as Stanislas Dehaene,[14] Bernard Baars,[15] and Antonio Damasio.[16]

Chalmers' formulation

The hard problem

In "Facing Up to the Problem of Consciousness" (1995), Chalmers wrote:[4]

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.

Easy problems

Chalmers contrasts the hard problem with a number of easy problems that consciousness presents. He acknowledges that these "easy problems" will require much "difficult empirical work" and calls them easy only in the sense that they are methodologically amenable to standard scientific methods. 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. Chalmers provides the following list of easy problems:[4]

  • 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 of consciousness include:

  • "How is it that some organisms are subjects of experience?"
  • "Why does awareness of sensory information exist at all?"
  • "Why do qualia exist?"
  • "Why is there a subjective component to experience?"
  • "Why aren't we philosophical zombies?"

The philosopher Raamy Majeed argued in 2016 that the hard problem is, in fact, associated with two "explanatory targets":[17]

  1. [PQ] Physical processing gives rise to experiences with a phenomenal character.
  2. [Q] Our phenomenal qualities are thus-and-so.

The first fact concerns the relationship between the physical and the phenomenal (i.e., how and why are some physical states felt states), whereas the second concerns the very nature of the phenomenal itself (i.e., what does the felt state feel like?).

Historical predecessors

The hard problem has scholarly antecedents considerably earlier than Chalmers, as Chalmers himself has pointed out.[18][note 2]

The physicist and mathematician Isaac Newton wrote in a 1672 letter to Henry Oldenburg:

to determine by what modes or actions light produceth in our minds the phantasm of colour is not so easie.[19]

In An Essay Concerning Human Understanding (1690), the philosopher and physician John Locke argued:

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.[20]

The polymath and philosopher Gottfried Leibniz wrote in 1714, as an example also known as Leibniz's gap:

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.[21]

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.

The biologist T.H. Huxley wrote in 1868:

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.[22]

Similar recent arguments

The philosopher Thomas Nagel posited in his 1974 paper "What is it like to be a bat?" that experiences are essentially subjective (accessible only to the individual undergoing them—i.e., felt only by the one feeling 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 (i.e., how and why a felt state is just a functional state). In other words, we have no idea of what reductivism really amounts to.[23] He argued:

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.[23]

In 1983, the philosopher Joseph Levine proposed that there is an explanatory gap between our understanding of the physical world and our understanding of consciousness.[24] He contended that a full explanation of a phenomenon should deductively entail it; that is, the conclusion (the phenomenon) must follow necessarily from the premises (the specifications of the explanation).[25] By contrast, he said, no matter how complete a physical explanation was, it would not entail subjective consciousness.[25]

Relationship to scientific frameworks

Most neuroscientists and cognitive scientists believe that Chalmers' alleged hard problem will be solved in the course of solving what he terms the easy problems, although a significant minority disagrees.[26][27]

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.[28] 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".[29] 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.[29]

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.[30] 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.[30] 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.[31] This more modest goal is the focus of most scientists working on consciousness.[30] 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.[32]

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.[33][34] The theory proposes an identity between consciousness and integrated information, with the latter item (denoted as Φ) defined mathematically and thus in principle measurable.[34][35] The hard problem of consciousness, write Tononi and Koch, may indeed be intractable when working from matter to consciousness.[10] However, because IIT inverts this relationship and works from phenomenological axioms to matter, they say it could be able to solve the hard problem.[10] 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.[36]

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.[34] "Even if IIT is correct," he argues, "it does not explain why integrated information generates (or is) consciousness."[34] Chalmers on the other hand has expressed some enthusiasm for IIT.[37]

Global workspace theory

Global workspace theory (GWT) is a cognitive architecture and theory of consciousness proposed by the cognitive psychologist Bernard Baars in 1988.[38] Baars explains the theory with the metaphor of a theater, with conscious processes represented by an illuminated stage.[38] This theater integrates inputs from a variety of unconscious and otherwise autonomous networks in the brain and then broadcasts them to unconscious networks (represented in the metaphor by a broad, unlit "audience").[38] The theory has since been expanded upon by other scientists including cognitive neuroscientist Stanislas Dehaene.[39]

In his original paper outlining the hard problem of consciousness, Chalmers discussed GWT as a theory that only targets one of the "easy problems" of consciousness.[4] In particular, he said GWT provided a promising account of how information in the brain could become globally accessible, but argued that "now the question arises in a different form: why should global accessibility give rise to conscious experience? As always, this bridging question is unanswered."[4] J. W. Dalton similarly criticized GWT on the grounds that it provides, at best, an account of the cognitive function of consciousness, and fails to explain its experiential aspect.[40] By contrast, A. C. Elitzur argued: "While [GWT] does not address the 'hard problem', namely, the very nature of consciousness, it constrains any theory that attempts to do so and provides important insights into the relation between consciousness and cognition."[41]

For his part, Baars writes (along with two colleagues) that there is no hard problem of explaining qualia over and above the problem of explaining causal functions, because qualia are entailed by neural activity and themselves causal.[15] Dehaene, in his 2014 book Consciousness and the Brain, rejected the concept of qualia and argued that Chalmers' "easy problems" of consciousness are actually the hard problems.[14] He further stated that the "hard problem" is based only upon ill-defined intuitions that are continually shifting as understanding evolves:[14]

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.


Chalmers' formulation of the hard problem of consciousness has provoked considerable debate within philosophy of mind as well as scientific research.[25] Some responses accept the problem as real and seek to develop a theory of consciousness' place in the world that can solve it, while others seek to show that the apparent hard problem as distinct from the easy problems dissolves upon analysis. A third response has been to accept the hard problem as real but deny human cognitive faculties can solve it.

Proposed solutions

Different solutions have been proposed to the hard problem of consciousness. One of these, weak reductionism, is the view that while there is an epistemic hard problem of consciousness that will not be solved directly by scientific progress, this is due to our conceptualization not an ontological gap.[25] Other proposed solutions suggest consciousness is in fact fundamental and not simply an emergent physical property like other aspects of life. Dualism views consciousness as either a non-physical substance separate from the brain or a non-physical property of the physical brain.[42] Meanwhile, panpsychism and neutral monism, broadly speaking, view consciousness as intrinsic to matter.[43] Chalmers considers the correct solution to be an open question, but favors a solution falling under either property dualism or what he calls "type-F monism" (which includes panpsychism and neutral monism), whereas he has argued against weak reductionism.[43]

Weak reductionism

There is a split among those subscribing to reductive materialism between those who hold there is no hard problem of consciousness—"strong reductionists" (see below)—and those who, while remaining ontologically committed to physicalism, accept an epistemic hard problem of consciousness—"weak reductionists" or "type-B materialists."[25][43] Put differently, weak reductionists believe there is a gap between two ways of knowing (introspection and neuroscience) that will not be resolved by understanding all the underlying neurobiology, but still believe that consciousness and neurobiology are one and the same in reality.[25] For example, Joseph Levine, who formulated the notion of the explanatory gap (see above), states: "The explanatory gap argument doesn't demonstrate a gap in nature, but a gap in our understanding of nature."[44] He nevertheless contends that a full scientific understanding will not close the gap,[25] and that analogous gaps do not exist for other identities in nature, such as that between water and H2O.[45] The philosophers Ned Block and Robert Stalnaker agree that facts about what a conscious experience is like to the one experiencing it cannot be deduced from knowing all the facts about the underlying physiology, but by contrast argue that such gaps of knowledge are also present in many other cases in nature, such as the distinction between water and H2O.[46][7]

To explain why these two ways of knowing (i.e. third-person scientific observation and first-person introspection) yield such different understandings of consciousness, weak reductionists often invoke the phenomenal concepts strategy, which argues the difference stems from our inaccurate phenomenal concepts (i.e., how we think about consciousness), not the nature of consciousness itself.[25][47] Thus, the hard problem of consciousness stems only from a dualism of concepts, not a dualism of properties or substances (see next section).[25] Chalmers argues that phenomenal concepts are ultimately characterized either in a manner too weak to bridge the explanatory gap or too strong to themselves yield to physical explanation, and therefore rejects weak reductionism.[47][43]


Dualism is the view that the mind is irreducible to the physical body.[42] There are multiple dualist accounts of the causal relationship between the mental and the physical, of which interactionism and epiphenomenalism are the most common today. Interactionism posits that the mental and physical causally impact one another, and is associated with the thought of René Descartes (1596–1650).[43] Since Descartes' time, it has been criticized for failing to suggest a plausible mechanism by which a non-physical mind could impact the physical world.[48] One alternative is epiphenomenalism, the view that the mental is causally dependent on the physical, but does not in turn causally impact it.[43] This raises the question of why our conscious intentions, sensations, and so forth appear to clearly influence our physical actions.[42] In contemporary philosophy, interactionism has been defended by philosophers including Martine Nida-Rümelin,[49] while epiphenomenalism has been defended by philosophers including Frank Jackson[50][51] (although Jackson later changed his stance to physicalism).[52] Chalmers has also defended versions of both positions as plausible and offered responses to objections.[43] Traditional dualists such as Descartes believed the mental and the physical to be two separate substances, or fundamental types of entities (hence "substance dualism"); some more recent dualists (such as Chalmers[43]), however, accept only one substance, the physical, but state it has both mental and physical properties (hence "property dualism").[42]

Panpsychism and neutral monism

In its most basic form, panpsychism holds that all physical entities have minds (though its proponents in fact take more qualified positions),[53] while neutral monism, in at least some variations, holds that entities are composed of a substance with mental and physical aspects—and is thus sometimes described as a type of panpsychism.[54] Forms of panpsychism and neutral monism were defended in the early twentieth century by the psychologist William James,[55][56][note 3] the philosopher Alfred North Whitehead,[56] the physicist Arthur Eddington,[57][58] and the philosopher Bertrand Russell,[53][54] and interest in these views has been revived in recent decades by philosophers including Thomas Nagel,[56] Galen Strawson,[56][59] and David Chalmers.[53] Chalmers describes his overall view as "naturalistic dualism,"[4] but he says panpsychism is in a sense a form of physicalism,[43] as does Strawson.[59] Proponents of panpsychism argue it solves the hard problem of consciousness parsimoniously by making consciousness a fundamental feature of reality;[25][57] they have also offered other arguments in favor, while many critics have dismissed panpsychism on the basis of its highly counter-intuitive nature and other issues such as the combination problem.[56][60]

Rejection of the problem

Many philosophers have disputed that there is a hard problem of consciousness distinct from what Chalmers calls the easy problems of consciousness. Some, termed strong reductionists, hold that phenomenal consciousness (i.e., conscious experience) does exist but that it can be fully understood as reducible to the brain.[25] Others maintain that phenomenal consciousness can be eliminated from the scientific picture of the world, and hence are called eliminative materialists or eliminativists.[25]

Strong reductionism

Broadly, strong reductionists accept that conscious experience is real but argue it can be fully understood in functional terms as an emergent property of the material brain.[25] In contrast to weak reductionists (see above), strong reductionists reject ideas used to support the existence of a hard problem (that the same functional organization could exist without consciousness, or that a blind person who understood vision through a textbook would not know everything about sight) as simply mistaken intuitions.[25][43]

A notable family of strong reductionist accounts are the higher-order theories of consciousness.[61][25] 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 could explain phenomenal consciousness without positing qualia.[62] On the higher-order view, since consciousness is a representation, and representation is fully functionally analyzable, there is no hard problem of consciousness.[25]

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."[63]

The philosopher Massimo Pigliucci argued in 2013 that the hard problem is misguided, resulting from a "category mistake."[12] He said: "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."[12]

In 2017, the philosopher Marco Stango, in a paper on John Dewey's approach to the problem of consciousness (which preceded Chalmers' formulation of the hard problem by over half a century), noted that Dewey's approach would see the hard problem as the consequence of an unjustified assumption that feelings and functional behaviors are not the same physical process: "For the Deweyan philosopher, the 'hard problem' of consciousness is a 'conceptual fact' only in the sense that it is a philosophical mistake: the mistake of failing to see that the physical can be had as an episode of immediate sentiency."[64]

Reductive materialism has been criticized from an eliminativist/illusionist perspective (see below). Keith Frankish argues it is "an unstable position, continually on the verge of collapsing into illusionism. The central problem, of course, is that phenomenal properties seem too weird to yield to physical explanation. They resist functional analysis and float free of whatever physical mechanisms are posited to explain them."[13]

Eliminative materialism

Eliminative materialism or eliminativism is the view that many or all of the mental states used in folk psychology (i.e., common-sense ways of discussing the mind) do not, upon scientific examination, correspond to real brain mechanisms.[65] While Patricia Churchland and Paul Churchland have famously applied eliminative materialism to propositional attitudes, philosophers including Daniel Dennett, Georges Rey, and Keith Frankish have applied it to qualia or phenomenal consciousness (i.e., conscious experience).[65] On their view, it is mistaken not only to believe there is a hard problem of consciousness, but to believe consciousness exists at all (in the sense of phenomenal consciousness).[13][66]

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).[11] 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.[67]

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.[68] 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.

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.[11] 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. Thus, 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.[67]

The philosopher John Searle replied to Dennett, saying "where the existence of conscious states is concerned, you can’t make the distinction between appearance and reality, because the existence of the appearance is the reality in question. If it consciously seems to me that I am conscious, then I am conscious."[69] In this vein, 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 experiential aspect completely. This has led detractors to refer to Dennett's book Consciousness Explained as Consciousness Ignored or Consciousness Explained Away.[11] Dennett discussed this at the end of his book with a section entitled "Consciousness Explained or Explained Away?".[68]

In 2013, the philosopher Elizabeth Irvine argued 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."[70]

In 2016, Frankish proposed the term "illusionism" as superior to "eliminativism" for describing the position that phenomenal consciousness is an illusion. In the introduction to his paper, he states: "Theories of consciousness typically address the hard problem. They accept that phenomenal consciousness is real and aim to explain how it comes to exist. There is, however, another approach, which holds that phenomenal consciousness is an illusion and aims to explain why it seems to exist."[13] After offering arguments in favor and responding to objections, Frankish concludes that illusionism "replaces the hard problem with the illusion problem — the problem of explaining how the illusion of phenomenality arises and why it is so powerful."[13]

A complete illusionist theory of consciousness must include the description of a mechanism by which the apparently subjective aspect of consciousness is perceived and reported by people. Various philosophers and scientists have proposed possible theories.[71] For example, in his book Consciousness and the Social Brain neuroscientist Michael Graziano 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.[72][73]

Illusionists generally hold that once it is explained why people believe and say they are conscious, the hard problem of consciousness will have been dissolved. Chalmers agrees that a mechanism for these beliefs and reports can and should be identified using the standard methods of physical science, but disagrees that this would support illusionism, stating that the datum illusionism fails to account for is not reports of consciousness but rather first-person consciousness itself.[71] While he separates consciousness from beliefs and reports about consciousness, he holds that a fully satisfactory theory of consciousness should explain how the two are "inextricably intertwined" so that their alignment does not require an inexplicable coincidence.[71]

Eliminativism has also been criticized by philosophers including Galen Strawson,[74] Jesse Prinz,[75] and Massimo Pigliucci.[12]

Other views

The philosopher Peter Hacker argues that the hard problem is misguided in that it asks how consciousness can emerge from matter, whereas in fact sentience emerges from the evolution of living organisms.[76] He states: "The hard problem isn’t a hard problem at all. The really hard problems are the problems the scientists are dealing with. [...] The philosophical problem, like all philosophical problems, is a confusion in the conceptual scheme."[76] Hacker's critique extends beyond Chalmers and the hard problem and is directed against contemporary philosophy of mind and neuroscience more broadly. Along with the neuroscientist Max Bennett, he has argued that most of contemporary neuroscience remains implicitly dualistic in its conceptualizations and is predicated on the mereological fallacy of ascribing psychological concepts to the brain that can properly be ascribed only to the person as a whole.[77] Hacker further states that "consciousness studies," as it exists today, is "literally a total waste of time":[76]

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.

New mysterianism

New mysterianism, most significantly associated with the philosopher Colin McGinn, proposes that the human mind, in its current form, will not be able to explain consciousness.[78][6] McGinn draws on Noam Chomsky's distinction between problems, which are in principle soluble, and mysteries, which human cognitive faculties are unequipped to ever understand, and places the mind-body problem in the latter category.[78] His position is that a naturalistic explanation does exist but that the human mind is cognitively closed to it due to its limited range of intellectual abilities.[78] He cites Jerry Fodor's concept of the modularity of mind in support of cognitive closure.[78]

While in McGinn's strong form, new mysterianism states that the relationship between consciousness and the material world can never be understood by the human mind, there are also weaker forms that argue it cannot be understood within existing paradigms but that advances in science or philosophy may open the way to other solutions (see above).[25] The ideas of Thomas Nagel and Joseph Levine fall into the second category.[25] The cognitive scientist Steven Pinker has also endorsed this weaker version of the view, summarizing it as follows:[26]

And then there is the theory put forward by philosopher Colin McGinn that our vertigo when pondering the Hard Problem is itself a quirk of our brains. The brain is a product of evolution, and just as animal brains have their limitations, we have ours. Our brains can't hold a hundred numbers in memory, can't visualize seven-dimensional space and perhaps can't intuitively grasp why neural information processing observed from the outside should give rise to subjective experience on the inside. This is where I place my bet, though I admit that the theory could be demolished when an unborn genius—a Darwin or Einstein of consciousness—comes up with a flabbergasting new idea that suddenly makes it all clear to us.

The meta-problem

In 2018, Chalmers highlighted what he calls the "meta-problem of consciousness", another problem related to the hard problem of consciousness:[71]

The meta-problem of consciousness is (to a first approximation) the problem of explaining why we think that there is a [hard] problem of consciousness.

In his "second approximation", he says it is the problem of explaining the behavior of "phenomenal reports", and the behavior of expressing a belief that there is a hard problem of consciousness.[71]

Explaining its significance, he says:[71]

Although the meta-problem is strictly speaking an easy problem, it is deeply connected to the hard problem. We can reasonably hope that a solution to the meta-problem will shed significant light on the hard problem. A particularly strong line holds that a solution to the meta-problem will solve or dissolve the hard problem. A weaker line holds that it will not remove the hard problem, but it will constrain the form of a solution.

British playwright Sir Tom Stoppard's play The Hard Problem, first produced in 2015, is named after the hard problem of consciousness, which Stoppard defines as having "subjective First Person experiences."[79]

See also


  1. The term qualia is used in at least two different senses by different authors. Keith Frankish (2012) distinguishes between "classic qualia," which are "introspectable qualitative properties of experience that are intrinsic, ineffable, and subjective"(close to the original definition of C. I. Lewis), and "diet qualia," which are conceptualized more modestly as "what it is like" to have subjective experience (close to the definition of, for example, Ned Block).[1] The latter is synonymous with phenomenal experiences.[1]
  2. Chalmers (1997) states: "Any number of thinkers in the recent and distant past - including a number of contributors to this symposium – have recognized the particular difficulties of explaining consciousness and have tried to face up to them in various ways. All my paper really contributes is a catchy name, a minor reformulation of philosophically familiar points, and a specific approach to dealing with them."
  3. There has been debate over how best to characterize James' position. The Stanford Encyclopedia of Philosophy states: "James’s commitment to panpsychism remains somewhat controversial, since he also advanced a cogent set of objections against a version of the view, which he labelled the 'mind dust' theory, in chapter six of The Principles of Psychology ([1890] 1981). These objections are the inspiration for the so-called 'combination problem', around which much of the twenty first century literature on panpsychism focuses. But in the end James’s commitment is quite clear (see James 1909, 1911; Lamberth 1997; and for an excellent analysis of James’s views on mind see Cooper 1990 or chapters 2–4 of Cooper 2002)."


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  3. See Cooney's foreword to the reprint of Chalmers' paper: Brian Cooney, ed. (1999). "Chapter 27: Facing up to the problem of consciousness". The place of mind. Cengage Learning. pp. 382 ff. ISBN 978-0534528256.
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