Editing Hard problem of consciousness (section)

==Overview==
Cognitive scientist [[David Chalmers]] first formulated the hard problem in his paper "Facing up to the problem of consciousness" (1995)<ref name="Chalmers" /> and expanded upon it in ''[[The Conscious Mind]]'' (1996). His works provoked comment. Some, such as philosopher [[David Lewis (philosopher)|David Lewis]] and Steven Pinker, have praised Chalmers for his argumentative rigour and "impeccable clarity".<ref name=":0" /> Pinker later said, in 2018, "In the end I still think that the hard problem is a meaningful conceptual problem, but agree with Dennett that it is not a meaningful scientific problem. No one will ever get a grant to study whether you are a zombie or whether the same Captain Kirk walks on the deck of the Enterprise and the surface of Zakdorn. And I agree with several other philosophers that it may be futile to hope for a solution at all, precisely because it is a conceptual problem, or, more accurately, a problem with our concepts."<ref>{{cite book|first1=Steven|last1=Pinker|date=2018|title=Enlightenment Now|page=481|isbn=9780525427575|publisher=Viking}}</ref> [[Daniel Dennett]] and [[Patricia Churchland]], among others, believe that the hard problem is best seen as a collection of easy problems that will be solved through further analysis of the brain and behaviour.<ref name=":1" /><ref>{{cite book|doi=10.1016/S0079-6123(05)49020-2|chapter=A neurophilosophical slant on consciousness research|title=Cortical Function: A View from the Thalamus|series=Progress in Brain Research|year=2005|last1=Churchland|first1=Patricia Smith|volume=149|pages=285–293|pmid=16226591|isbn=9780444516794}}</ref>

Consciousness is an ambiguous term. It can be used to mean self consciousness, awareness, the state of being awake, and so on. Chalmers uses [[Thomas Nagel]]'s definition of consciousness: "''the feeling of what it is like to be something."'' Consciousness, in this sense, is synonymous with ''experience.''<ref name="Bat" /><ref name=":0" />

=== Chalmers' formulation ===
{{Quote|text=. . .even when we have explained the performance of all the cognitive and behavioral functions in the vicinity of experience—perceptual discrimination, categorization, internal access, verbal report—there may still remain a further unanswered question: ''Why is the performance of these functions accompanied by experience?''|author=David Chalmers|title=Facing up to the problem of consciousness|source=}}The problems of consciousness, Chalmers argues, are of two kinds: the ''easy problems'' and the ''hard problem''.

==== Easy problems ====
The easy problems are amenable to reductive enquiry. They are a [[logical consequence]] of lower-level facts about the world, similar to how a clock's ability to tell time is a logical consequence of its clockwork and structure, or a hurricane being a logical consequence of the structures and functions of certain weather patterns. A clock, a hurricane, and the easy problems, are all the sum of their parts (as are most things).<ref name=":0" />

The easy problems relevant to consciousness concern mechanistic analysis of the neural processes that accompany behaviour. Examples of these include how sensory systems work, how sensory data is processed in the brain, how that data influences behaviour or verbal reports, the neural basis of thought and emotion, and so on. They are problems that can be analysed through "structures and functions".<ref name=":0" />

==== Hard problem ====
The hard problem, in contrast, is the problem of ''why'' and ''how'' those processes are accompanied by experience.<ref name="Chalmers" /> It may further include the question of why these processes are accompanied by this or that particular experience, rather than some other kind of experience. In other words, the hard problem is the problem of explaining why certain mechanisms are accompanied by conscious experience.<ref name=":0">{{Cite book|last=Chalmers|first=David|title=The Conscious Mind|publisher=Oxford University Press|year=1996|location=New York|pages=xii–xiii, 95–106, backcover}}</ref> For example, why should neural processing in the brain lead to the felt sensations of, say, feelings of hunger? And why should those neural firings lead to feelings of hunger rather than some other feeling (such as, for example, feelings of thirst)?

Chalmers argues that it is conceivable that the relevant behaviours associated with hunger, or any other feeling, could occur even in the absence of that feeling. This suggests that experience is [[Irreducibility|irreducible]] to physical systems such as the brain. This is the topic of the next section.

==== How the easy and hard problems are related ====
Chalmers believes that the hard problem is irreducible to the easy problems: solving the easy problems will not lead to a solution to the hard problems. This is because the easy problems pertain to the causal structure of the world while the hard problem pertains to consciousness, and facts about consciousness include facts that go beyond mere causal or structural description.<ref name=":2">{{Cite web |title=Hard Problem of Consciousness |url=https://iep.utm.edu/hard-problem-of-conciousness/ |access-date=2024-10-09 |website=Internet Encyclopedia of Philosophy |language=en-US}}</ref>

For example, suppose someone were to stub their foot and yelp. In this scenario, the easy problems are mechanistic explanations that involve the activity of the nervous system and brain and its relation to the environment (such as the propagation of nerve signals from the toe to the brain, the processing of that information and how it leads to yelping, and so on). The hard problem is the question of why these mechanisms are accompanied by ''the feeling of pain'', or why these feelings of pain feel the particular way that they do. Chalmers argues that facts about the neural mechanisms of pain, and pain behaviours, do not lead to facts about conscious experience. Facts about conscious experience are, instead, [[further facts]], not derivable from facts about the brain.<ref name=":0" /><ref name=":2" />[[File:Inverted_qualia_of_colour_strawberry.jpg|thumb|The hard problem is often illustrated by appealing to the logical possibility of inverted visible spectra. If there is no logical contradiction in supposing that one's colour vision could be inverted, it follows that mechanistic explanations of visual processing do not determine facts about what it is like to see colours.|280x280px]] An explanation for all of the relevant physical facts about neural processing would leave unexplained facts about what it is like to feel pain. This is in part because functions and physical structures of any sort could conceivably exist in the absence of experience. Alternatively, they could exist alongside a different set of experiences. For example, it is [[Logical possibility|logically possible]] for a perfect replica of Chalmers to have no experience at all, or for it to have a different set of experiences (such as an inverted visible spectrum, so that the blue-yellow red-green axes of its visual field are flipped).<ref name=":2" />

The same cannot be said about clocks, hurricanes, or other physical things. In those cases, a structural or functional description is a complete description. A perfect replica of a clock is a clock, a perfect replica of a hurricane is a hurricane, and so on. The difference is that physical things are nothing more than their physical constituents. For example, water is nothing more than H<sub>2</sub>O molecules, and understanding everything about H<sub>2</sub>O molecules is to understand everything there is to know about water. But consciousness is not like this. Knowing everything there is to know about the brain, or any physical system, is not to know everything there is to know about consciousness. Consciousness, then, must not be purely physical.<ref name=":0" />

==== Implications for physicalism ====
{{See also|Physicalism}}
[[File:Sturnus vulgaris -Rotterdam, South Holland, Netherlands -flock-8.ogv|thumb|right|A swarm of birds showing high order structure emerging from simpler physical constituents]]

Chalmers's idea contradicts [[physicalism]], sometimes labelled [[materialism]]. This is the view that everything that exists is a physical or material thing, so everything can be reduced to microphysical things. For example, the rings of Saturn are a physical thing because they are nothing more than a complex arrangement of a large number of subatomic particles interacting in a certain way. According to physicalism, everything, including consciousness, can be explained by appeal to its microphysical constituents. Chalmers's ''hard problem'' presents a [[counterexample]] to this view and to other phenomena like swarms of birds, since it suggests that consciousness, like swarms of birds, cannot be reductively explained by appealing to their physical constituents. Thus, if the hard problem is a real problem then physicalism must be false, and if physicalism is true then the hard problem must not be a real problem.{{cn|date=September 2022}}

Though Chalmers rejects physicalism, he is still a [[Naturalism (philosophy)|naturalist]].<ref name=":0" />{{importance inline|date=April 2023}}

[[Christian List]] argues that the existence of first-person perspectives and the inability for physicalism to answer Hellie's vertiginous question is evidence against physicalism, since first-personal facts cannot supervene on physical third-personal facts.<ref>{{cite web |url=https://philpapers.org/rec/LISTFA |title=The first-personal argument against physicalism |last=List |first=Christian |date=2023 |website= |publisher= |access-date=4 March 2025 |quote=}}</ref> List also claims that there exists a "quadrilemma" for metaphysical theories of consciousness, and that for the metaphysical claims of first-person realism, non-solipsism, non-fragmentation, and one-world, at least one of these must be false.<ref>{{cite web |url=https://philarchive.org/rec/LISAQF |title=A quadrilemma for theories of consciousness |last=List |first=Christian |date=2023 |website= |publisher=The Philosophical Quarterly |access-date=4 March 2025 |quote=}}</ref> List has proposed a model he calls the "many-worlds theory of consciousness" in order to reconcile the subjective nature of consciousness without lapsing into solipsism.<ref>{{cite web |url=https://philarchive.org/rec/LISTMT-2 |title=The many-worlds theory of consciousness |last=List |first=Christian |date=2023 |website= |publisher=The Philosophical Quarterly |access-date=4 March 2025 |quote=}}</ref>

=== Historical precedents ===
{{Wikiquote}}
The hard problem of consciousness has scholarly antecedents considerably earlier than Chalmers. Chalmers himself notes that "a number of thinkers in the recent and distant past" have "recognised the particular difficulties of explaining consciousness."<ref name="Moving forward">{{cite journal
| last=Chalmers
| first=David
| author-link=David Chalmers
| date=January 1997
| title=Moving forward on the problem of consciousness| journal=[[Journal of Consciousness Studies]]
| volume=4
| issue=1
| pages=3–46 
| url=https://philpapers.org/rec/CHAMFO}}</ref> He states that all his original 1996 paper contributed to the discussion was "a catchy name, a minor reformulation of philosophically familiar points".<ref name="Moving forward" />

Among others, thinkers who have made arguments similar to Chalmers' formulation of the hard problem include [[Isaac Newton]],<ref name="chalmers-2020">{{cite journal|last1=Chalmers|first1=David|title=Is the hard problem of consciousness universal?|journal=Journal of Consciousness Studies|date=2020|volume=27|issue=5–6|pages=227–257|url=http://consc.net/papers/universal.pdf|access-date=22 February 2022}}</ref> [[John Locke]],<ref>{{cite book|last=Locke|first=John|author-link=John Locke|date=1722|title=The works of John Locke: in three volumes|location=London|publisher=Printed for A. Churchill, and A. Manship, and sold by W. Taylor in Pater-noster-Row|volume=1|page=[https://books.google.com/books?id=0BfmAAAAMAAJ&pg=PA293 293]}}</ref> [[Gottfried Wilhelm Leibniz]],<ref name="Aranyosi" /><ref name="chalmers-2020"/> [[John Stuart Mill]],<ref>Mill, John Stuart. ''A System of Logic'' (1843), Book V, Chapter V, section 3</ref> and [[Thomas Henry Huxley]].<ref>{{cite book|last1=Huxley|first1=Thomas Henry|author-link1=Thomas Henry Huxley|last2=Youmans|first2=William Jay|author-link2=William Jay Youmans|date=1868|title=The elements of physiology and hygiene: a text-book for educational institutions|location=New York|publisher=D. Appleton and company|page=[https://books.google.com/books?id=aVUAAAAAYAAJ&pg=PA178 178]}}</ref><ref name="chalmers-2020"/> Likewise, Asian philosophers like [[Dharmakirti]] and [[Guifeng Zongmi]] discussed the problem of how consciousness arises from unconscious matter.<ref name="chalmers-2020"/><ref name="arnold-2021">{{cite book|last1=Arnold|first1=Dan|editor1-last=Emmanuel|editor1-first=Steven M.|title=Philosophy's Big Questions: Comparing Buddhist and Western Approaches|date=2021|publisher=Columbia University Press|location=New York|isbn=978-0231174879|pages=97–128|chapter=Philosophy of Mind’s “Hard Problem” in Light of Buddhist Idealism}}</ref><ref>Bryan Van Norden, {{Citation|title=Buddhism Comes to China| date=17 March 2021 |url=https://www.youtube.com/watch?v=Q1xv3HmUddY|language=en|access-date=2021-12-29}}</ref><ref>Tiwald, Justin; Van Norden, Bryan W. eds. (2005), ''Readings in Later Chinese Philosophy,'' p. 101. Hackett Publishing.</ref> The Tattva Bodha, an eighth century text attributed to [[Adi Shankara]] from the [[Advaita Vedanta]] school of [[Hinduism]], describes consciousness being ''anubhati'', or self-revealing, illuminating all objects of knowledge without itself being a material object.<ref>{{Cite book |last=Shankara |first=Adi |title=Tattva Bodha |last2=Chaturvedi |first2=Shraddhesh |publisher=Vedic Scriptures Publishing |year=2019 |isbn=9781701001374 |location=Amroha, Uttar Pradesh, India |trans-title=Understanding Reality}}</ref><ref>{{Cite web |last=Vas |first=Andre |date=29 October 2023 |title=23 – Tattva Bodha: Existence-Consciousness Alone Is (Satchit Meaning) |url=https://www.yesvedanta.com/tattva-bodha-discourses/discourse-23/ |url-status=live |access-date=19 January 2025 |website=Yes Vedanta |archive-url=https://web.archive.org/web/20250122101033/https://www.yesvedanta.com/tattva-bodha-discourses/discourse-23/ |archive-date=Jan 22, 2025 }}</ref>

=== Related concepts ===

==== The mind–body problem ====
{{Main|Mind–body problem}}
The mind–body problem is the problem of how the mind and the body relate. The mind-body problem is more general than the hard problem of consciousness, since it is the problem of discovering how the mind and body relate in general, thereby implicating any theoretical framework that broaches the topic. The hard problem, in contrast, is often construed as a problem uniquely faced by physicalist or materialist theories of mind.

==== "What Is It Like to Be a Bat?" ====
{{Main|What Is It Like to Be a Bat?}}
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 he argued we have no idea what it could mean to claim that an essentially subjective state just ''is'' an essentially non-subjective state (i.e., that a felt state is nothing but a functional state). In other words, we have no idea of what reductivism amounts to.<ref name="Bat"/> He believes "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."<ref name="Bat">{{cite journal|last=Nagel|first=Thomas|author-link=Thomas Nagel|date=October 1974|title=What is it like to be a bat?|journal=[[The Philosophical Review]]|volume=83|issue=4|pages=435–450|doi=10.2307/2183914|jstor=2183914|s2cid=49125889}}</ref>

==== Explanatory gap ====
{{Main|Explanatory gap}}
{{see also|Reductionism}}
In 1983, the philosopher [[Joseph Levine (philosopher)|Joseph Levine]] proposed that there is an ''explanatory gap'' between our understanding of the physical world and our understanding of consciousness.<ref name=Levine1983>Levine, J. 1983. “Materialism and qualia: the explanatory gap”. ''Pacific Philosophical Quarterly'', 64: 354–361.</ref>

Levine's disputes that conscious states are reducible to neuronal or brain states. He uses the example of pain (as an example of a conscious state) and its reduction to the firing of [[Group C nerve fiber|c-fibers]] (a kind of nerve cell). The difficulty is as follows: even if consciousness is physical, it is not clear which physical states correspond to which conscious states. The bridges between the two levels of description will be [[Contingency (philosophy)|contingent]], rather than [[Necessity and sufficiency|necessary]]. This is significant because in most contexts, relating two scientific levels of descriptions (such as physics and chemistry) is done with the assurance of necessary connections between the two theories (for example, chemistry follows with necessity from physics).<ref name="jw-iep">{{cite web|last1=Weisberg|first1=Josh|title=The Hard Problem of Consciousness|url=https://www.iep.utm.edu/hard-con/|website=Internet Encyclopedia of Philosophy}}</ref>

Levine illustrates this with a thought experiment: Suppose that humanity were to encounter an alien species, and suppose it is known that the aliens do not have any c-fiber. Even if one knows this, it is not obvious that the aliens do not feel pain: that would remain an open question. This is because the fact that aliens do not have c-fibers does not entail that they do not feel pain (in other words, feelings of pain do not follow with logical necessity from the firing of c-fibers). Levine thinks such thought experiments demonstrate an explanatory gap between consciousness and the physical world: even if consciousness is reducible to physical things, consciousness cannot be explained in terms of physical things, because the link between physical things and consciousness is a contingent link.<ref name="jw-iep" />

Levine does not think that the explanatory gap means that consciousness is not physical; he is open to the idea that the explanatory gap is only an [[Epistemology|epistemological]] problem for physicalism.<ref name="jw-iep" /> In contrast, Chalmers thinks that the hard problem of consciousness does show that consciousness is not physical.<ref name=":0" />

==== Philosophical zombies ====
{{Main|Philosophical zombie}}
Philosophical zombies are a thought experiment commonly used in discussions of the hard problem.<ref>{{Cite web|last=Seager|first=William|title=Are Zombies Logically Possible?|url=https://www.utsc.utoronto.ca/~seager/zombie.html|access-date=2020-09-03|website=www.utsc.utoronto.ca}}</ref><ref>{{Cite journal|last1=Kaszniak|first1=Alfred W.|last2=Scott|first2=Andrew C.|date=2007|title=Zombie Killer|s2cid=14891432|journal=Association of Scientific Studies of Consciousness}}</ref> They are hypothetical beings physically identical to humans but that lack conscious experience.<ref>{{Cite web|last=Polger|first=Tom|title=Zombies: Entry|url=https://host.uniroma3.it/progetti/kant/field/zombies.htm|access-date=2020-09-03|website=host.uniroma3.it|archive-date=2020-06-15|archive-url=https://web.archive.org/web/20200615155145/http://host.uniroma3.it/progetti/kant/field/zombies.htm|url-status=dead}}</ref> Philosophers such as Chalmers, Joseph Levine, and Francis Kripke take zombies as impossible within the bounds of nature but possible within the bounds of logic.<ref>{{Citation|last=Kirk|first=Robert|title=Zombies|date=2019|url=https://plato.stanford.edu/archives/spr2019/entries/zombies/|encyclopedia=The Stanford Encyclopedia of Philosophy|editor-last=Zalta|editor-first=Edward N.|edition=Spring 2019|publisher=Metaphysics Research Lab, Stanford University|access-date=2020-09-03}}</ref> This would imply that facts about experience are not logically entailed by the "physical" facts. Therefore, consciousness is irreducible. In Chalmers' words, "after God (hypothetically) created the world, he had more work to do."<ref name=":3">[[David Chalmers]] (1996) ''The Conscious Mind: In Search of a Fundamental Theory'', pp. 153–56. Oxford University Press, New York, {{ISBN|0-19-511789-1}} (Pbk.)</ref> Daniel Dennett, a philosopher of mind, criticised the field's use of "the zombie hunch" which he deems an "embarrassment"<ref>Dennett, Daniel (1999), [https://www.nyu.edu/gsas/dept/philo/courses/consciousness/papers/DD-zombie.html "The Zombie Hunch: Extinction of an Intuition?"],{{dead link|date=January 2025}} ''Royal Institute of Philosophy Millennial Lecture''</ref> that ought to "be dropped like a hot potato".<ref name=":1">Dennett, Daniel; commentary on T. Moody, O. Flanagan and T. Polger. "[https://ase.tufts.edu/cogstud/dennett/papers/unzombie.htm The Unimagined Preposterous of Zombies]", ''Journal of Consciousness Studies'' vol. 2, no. 4, 1995, pp. 322–326.</ref>

==== Knowledge argument ====
{{Main|Knowledge argument}}
The knowledge argument, also known as ''Mary's Room'', is another common thought experiment: A hypothetical neuroscientist named Mary has lived her whole life in a black-and-white room and has never seen colour before. She also happens to know everything there is to know about the brain and colour perception.<ref name="Nida-Rümelin2019">{{cite encyclopedia|author1=Martine Nida-Rümelin|author2=Donnchadh O Conaill|title=Qualia: The Knowledge Argument|date=2019|encyclopedia=The Stanford Encyclopedia of Philosophy|editor=Edward N. Zalta|edition=Winter 2019|publisher=Metaphysics Research Lab, Stanford University|url=https://plato.stanford.edu/archives/win2019/entries/qualia-knowledge/|access-date=2020-09-03}}</ref> Chalmers believes<ref name=":3" />{{Page needed|date=September 2020}} that when Mary sees the colour red for the first time, she gains new knowledge — the knowledge of "what red looks like" — which is distinct from, and irreducible to, her prior physical knowledge of the brain or visual system. A stronger form of the knowledge argument<ref name="Nida-Rümelin2019"/> claims not merely that Mary would lack subjective ''knowledge'' of "what red looks like," but that she would lack knowledge of an objective ''fact'' about the world: namely, "what red looks like," a non-physical fact that can be learned only through direct experience (qualia). Others, such as Thomas Nagel, take a "[[physicalism|physicalist]]" position, disagree with the argument in its stronger and/or weaker forms.<ref name="Nida-Rümelin2019"/> For example, [[Thomas Nagel|Nagel]] put forward a "speculative proposal" of devising a language that could "explain to a person blind from birth what it is like to see."<ref name="Bat"/> The knowledge argument implies that such a language could not exist.