Hard problem of consciousness

In the philosophy of mind, the hard problem of consciousness asks how and why living things have feelings and experiences. This question is different from other, easier problems about how the brain works, like how we see, hear, or speak. Even if we understand all the brain’s functions, some thinkers say we still need to explain why these functions feel like something to us.

The idea of the hard problem was introduced by the philosopher David Chalmers in 1994. He argued that explaining why our experiences exist is a special challenge that cannot be solved just by studying the brain’s mechanics. Some experts agree with this view, while others believe it is not a real problem at all.

Many philosophers and scientists have debated this issue, with no clear answer yet. Some think there are even harder questions about consciousness, such as why we experience the world in our own unique way. This mystery continues to inspire research in both philosophy and science.

Overview

The hard problem of consciousness is a big question in philosophy. It asks why and how we have feelings and experiences. For example, why does seeing red feel like something, instead of just processing information?

David Chalmers first talked about this problem in 1995. He said that some things about consciousness are easy to explain, like how our brains process information. But the hard part is explaining why these brain processes feel like something to us. Even if we understand all the brain activity, we still wonder why it comes with feelings and experiences. This question is tricky because feelings don’t seem to come from just the physical parts of the brain alone.

Philosophical responses

David Chalmers' formulation of the hard problem of consciousness led to much discussion in the field of philosophy of mind and also influenced scientific research. The hard problem is mainly a challenge for physicalist views, which suggest that the mind is a physical object or process. Because of this, some physicalists argue that the hard problem disappears when examined closely. Others accept the problem and try to develop a theory of consciousness that solves it, either by changing physicalism or by adopting a different ontology (such as panpsychism or dualism). A third group accepts the problem but believes human minds cannot solve it. According to a 2020 survey by PhilPapers, most philosophers (62.42%) think the hard problem is real, while a smaller group (29.76%) disagrees.

Views on physicalism also vary. In a 2009 survey, 56.5% of philosophers supported physicalism, 27.1% did not, and 16.4% were unsure. By 2020, 51.93% accepted or leaned toward physicalism, 32.08% rejected it, and 6.23% were agnostic or undecided. Different solutions to the hard problem have been suggested. These responses were first organized by Chalmers in a 2003 review, and this way of grouping them has become common in philosophy.

Type-A materialism

Further information: Reductive materialism and A priori physicalism

Type-A materialism, also called reductive materialism or a priori physicalism, is a view that fully supports physicalism and rejects the hard problem. It argues that the hard problem either does not exist or is just another easy problem, because every fact about the mind relates to functions or behaviors. Once all functions and behaviors are explained, there will be no additional facts left to explain. Supporters of this view include Paul and Patricia Churchland, Daniel Dennett, Keith Frankish, and Thomas Metzinger. Some believe conscious experience exists but is just another function or behavior. Others argue that conscious experience does not exist at all.

Strong reductionism

Many philosophers argue there is no hard problem of consciousness separate from what Chalmers calls the easy problems. Some, called strong reductionists, believe phenomenal consciousness (i.e., conscious experience) exists but can be fully understood as a result of brain activity. They reject ideas that support the hard problem (like the idea that the same brain activity could happen without consciousness) as mistakes.

One group of strong reductionists supports higher-order theories of consciousness. In 2005, philosopher Peter Carruthers suggested that the ability to recognize different types of experiences could explain conscious experience without needing special qualities. On this view, since consciousness is a representation, and representations can be fully explained by functions, there is no hard problem.

Philosophers Glenn Carruthers and Elizabeth Schier argued in 2012 that main reasons for the hard problem—philosophical zombies, Mary's room, and Nagel's bats—only seem convincing if one already assumes consciousness is separate from brain activity. They suggest letting theories of consciousness guide conclusions from these thought experiments instead. Philosopher Massimo Pigliucci argued in 2013 that the hard problem is misplaced, stemming from a "category mistake." He said explaining something is not the same as experiencing it, comparing them to colors and triangles.

In 2017, philosopher Marco Stango noted that John Dewey's approach to consciousness, which predates Chalmers, would see the hard problem as a mistake in assuming feelings and behaviors are not the same physical process. Philosopher Thomas Metzinger compares the hard problem to vitalism, an old idea in biology that was abandoned. Philosopher Peter Hacker argues the hard problem misasks how consciousness comes from matter, when it actually comes from the evolution of living organisms.

Eliminative materialism and illusionism

Main article: Eliminative materialism

Eliminative materialism or eliminativism is the idea that many or all mental states from everyday talk about the mind do not match real brain mechanisms. According to the 2020 PhilPapers survey, 4.51% of philosophers support eliminativism. Figures like Patricia Churchland and Paul Churchland have applied this to beliefs, while Daniel Dennett, Georges Rey, and Keith Frankish have applied it to conscious experience. They argue not only that there is no hard problem, but that conscious experience does not exist.

In the 2010s, this idea became known as illusionism: the view that conscious experience is an illusion. The term was popularized by philosopher Keith Frankish. He argues illusionism is better than realism about conscious experience. He states: "Theories of consciousness usually try to explain how conscious experience exists. Another approach says conscious experience is an illusion and tries to explain why it seems to exist." Frankish concludes that illusionism "replaces the hard problem with the illusion problem—explaining how the illusion of conscious experience arises and why it is strong."

Philosopher Daniel Dennett is another key figure in illusionism. After Frankish published a paper titled Illusionism as a Theory of Consciousness, Dennett responded with Illusionism as the Obvious Default Theory of Consciousness. Dennett has argued for the illusory nature of consciousness since early in his career. For instance, in 1979 he published a paper titled On the Absence of Phenomenology (where he argues against the existence of conscious experience). He also discussed these ideas in his 1991 book Consciousness Explained. Dennett argues the hard problem will be solved by solving the easy problems of consciousness. He compares consciousness to magic, which creates illusions from ordinary things. He mentions change blindness, where people fail to notice changes in scenes, to show how introspection can be unreliable. He argues that having experience is just performing functions or producing behavior, which are the easy problems. Therefore, the hard problem is part of the easy problems and can be explained together.

Eliminativists differ on the role of intuitive judgment in creating the apparent reality of consciousness. Philosopher Jacy Reese Anthis believes this issue comes from too much reliance on intuition, calling discussions about consciousness "intuition jousting." But when examined with "formal argumentation" and "precise semantics," the hard problem disappears. Philosopher Elizabeth Irvine, however, argues that properties of consciousness do not exist in everyday views of the world. She states that "the hard problem of consciousness may not be a real problem for non-philosophers, even though it seems obvious to philosophers."

An illusionist theory of consciousness must describe a mechanism for how the illusion of subjective experience is created and reported. For example, neuroscientist Michael Graziano proposes attention schema theory in his book Consciousness and the Social Brain, suggesting our sense of being conscious is an error in perception, like brains that evolved to hold incomplete models of themselves and the world.

Criticisms

The main criticisms of eliminative materialism and illusionism focus on how unlikely they seem. These arguments are called Moorean Arguments. They aim to show that denying the conclusion of an argument is more certain than the argument's premises. The roots of Moorean Arguments against illusionism go back to Augustine of Hippo, who said he could not be deceived about his own existence because being deceived requires a mind to be deceived.

In 2002, David Chalmers published a Moorean argument against illusionism. He argues that the reality of consciousness is more certain than any theory (like physicalism) that might deny it. This is because we know consciousness directly, but we do not know anything else directly. Chalmers concludes that "there is little doubt that something like the Moorean argument is why most people reject illusionism and many find it strange."

Eliminative materialism and illusionism have also been criticized in popular writing. Philosopher Galen Strawson called illusionism "the silliest claim ever made" in an article for the New York Review of Books. Neuroscientist Christof Koch, in his book The Feeling of Life Itself, compares eliminativism to Cotard's syndrome, where patients deny being alive, calling it evidence that "much of twentieth-century analytic philosophy has gone to the dogs."

Frankish has responded to such criticisms by saying that "qualia realists" must see qualia as either observational or theoretical. If seen as observational, illusionists are not leaving anything out. If seen as theoretical, illusionists are denying theoretical parts but not the fact that they exist, which they are trying to explain.

Type-B materialism

Further information: Phenomenal concept strategy and A posteriori physicalism

Type-B materialism, also known as weak reductionism or a posteriori physicalism, argues that the hard problem comes from human psychology and does not show a real gap between consciousness and the physical world. Like Type-A Materialists, Type-B Materialists believe in physicalism. But unlike Type-A Materialists, Type-B Materialists accept arguments for the hard problem but say they only show gaps in how we understand, not in reality.

Type-B Materialists differ on whether our intuitions about the hard problem are innate or learned. This is called the "hard-wired/soft-wired distinction." The "hard-wired view" says these intuitions are innate and shared by all humans. The "soft-wired view" says they are learned through culture. Unless specified, "Type-B Materialism" refers to the hard-wired view. Supporters include David Papineau, Joseph Levine, and Janet Levine.

"Hard-wired view"

Joseph Levine, who introduced the explanatory gap, states: "The explanatory gap argument does not show a gap in nature, but a gap in our understanding of nature." He argues that full scientific understanding will not close this gap, and that similar gaps do not exist for other identities in nature, like water and H₂O. Philosophers Ned Block and Robert Stalnaker agree that facts about what an experience feels like cannot be deduced from knowing all facts about the brain's activity. However, they argue such gaps exist in many other cases in nature, like the difference between water and H₂O.

To explain why scientific observation and personal experience give different understandings of consciousness, weak reductionists often use the phenomenal concepts strategy. This argues the difference comes from our inaccurate ideas about consciousness, not from consciousness itself. On this view, the hard problem comes from a conflict in concepts, not properties or substances.

"Soft-wired view"

Some researchers argue the hard problem is a cultural feature, unique to modern Western culture. This is similar to Type-B Materialism but adds that the psychological facts causing us to sense the hard problem are not innate but learned. Supporters include Anna Wierzbicka, Hakwan Lau, and Matthias Michel. Wierzbicka, a linguist, argues that words used in consciousness research (like experience and consciousness) are not translatable across all languages and are specific to English. She criticizes David Chalmers for using these words, saying if philosophers used universally translatable concepts (like know, think, or feel), the hard problem would disappear. David Chalmers responded that he uses technical terms for efficient communication in academic writing.

Type-C materialism

Type-C materialists see a difference between knowledge and experience but do not fully explain the experiential side. They admit there is an explanatory gap with no current solution but believe it will eventually be filled, like other scientific questions such as mass-energy equivalence, abiogenesis, or a future theory of everything. They think the consciousness question is a result of our current ignorance but will be solved like other neuroscience issues.

Type-C materialism does not assume consciousness exists in non-living things. It is based on the strong link between consciousness and living brain tissue, rejecting panpsychism without explaining how physical processes cause consciousness. It also denies the existence of philosophical zombies, as there is no evidence for them and no way to test for them. This contradiction shows the consciousness problem is not truly hard.

Type-C materialism can align with several views depending on future scientific discoveries. With evidence of emergence, it may become strong reductionism (Type A). With a new cultural understanding of consciousness, it may become Type-B materialism. If explained by quantum mind theories, it may become property dualism (Type D). If physics includes intrinsic properties beyond structure, it may become Type-F monism.

Richard Brown supports a unique form of Type-C materialism stating the hard problem cannot be decided in advance and both physicalism and dualism can only be proven through science. He uses "reverse zombie" and "reverse knowledge" experiments to show that a priori arguments depend on personal views and are only useful for showing intuitions. He argues these thought experiments seem convincing because they are conceivable but not ideally conceivable, meaning with full scientific knowledge, their conclusions could change.

Type-D and Type-E dualism

Main articles: Dualism (philosophy of mind), Interactionism (philosophy of mind), and Epiphenomenalism

Dualism sees consciousness as either a non-physical substance separate from the brain or a non-physical property of the brain. Dualism argues the mind cannot be reduced to the physical body. There are multiple dualist views on how the mental and physical interact, with interactionism and epiphenomenalism being common today. Interactionism says the mental and physical affect each other, linked to René Descartes (1596–1650). Epiphenomenalism says the mental depends on the physical but does not affect it.

In modern philosophy, interactionism has been supported by philosophers like Martine Nida-Rümelin, while epiphenomenalism has been supported by Frank Jackson, though Jackson later switched to physicalism. Chalmers has defended both views as possible. Traditional dualists like Descartes believed the mental and physical were two separate substances, but modern dualists accept one physical substance with both mental and physical properties.

Type-F monism

Main articles: Panpsychism and Neutral monism

Meanwhile, panpsychism and neutral monism see consciousness as basic to matter. In simple terms, panpsychism says all physical things have minds, while neutral monism says things are made of a substance with both mental and physical aspects. These views were supported in the early 20th century by psychologist William James, philosopher Alfred North Whitehead, physicist Arthur Eddington, and philosopher Bertrand Russell. Interest in these ideas has grown recently, with support from philosophers like Thomas Nagel, Galen Strawson, Philip Goff, and David Chalmers. Chalmers calls his view "naturalistic dualism" but says panpsychism is a type of physicalism. Supporters argue it solves the hard problem simply by making consciousness a basic feature of reality.

Idealism and cosmopsychism

Main article: Idealism

A traditional answer to the hard problem is idealism, which says consciousness is basic and not just a result of matter. This avoids the hard problem entirely. Objective idealism and cosmopsychism say mind or consciousness is the basic substance of the universe. Supporters say this avoids issues with the materialist view of the mind as a result of the brain. Critics say it leads to a decombination problem: how can one universal conscious experience split into many separate experiences? In response, Bernardo Kastrup suggests dissociation, as seen in dissociative identity disorder, could be a natural example of how multiple minds develop from one universal mind.

Cognitive psychologist Donald D. Hoffman uses a mathematical model based on conscious agents in a fundamentally conscious universe to support conscious realism as a description of nature—this falls under objective idealism. David Chalmers calls this form of idealism one of "the handful of promising approaches to the mind–body problem."

New mysterianism

Main article: New mysterianism

New mysterianism, mainly linked to philosopher Colin McGinn, argues that the human mind, as it is now, cannot explain consciousness. McGinn uses Noam Chomsky's idea that some problems are solvable while others are mysteries we cannot understand. He places the mind–body problem in the latter group. He says a naturalistic explanation exists but our minds are cognitively closed to it due to limited abilities. He references Jerry Fodor's idea of the modularity of mind to support cognitive closure.

In McGinn's strong form, new mysterianism says the link between consciousness and the material world can never be understood by humans. Weaker forms say it cannot be understood in current theories but future science or philosophy might find solutions. Philosophers Thomas Nagel and Joseph Levine fall into this category. Steven Pinker supports this weaker view, summarizing it as follows:

And then there is the theory put forward by philosopher Colin McGinn that our dizziness when thinking about the Hard Problem is a quirk of our brains. The brain is a product of evolution, and just as animal brains have limits, ours do too. We can't remember a hundred numbers, can't visualize seven-dimensional space, and perhaps can't intuitively understand why outer neural processing should give inner subjective experience. This is where I place my bet, though I admit the theory could be proven wrong when an unborn genius—a Darwin or Einstein of consciousness—comes up with a surprising new idea that suddenly makes it all clear.

Commentary on the problem's explanatory targets

Philosopher Raamy Majeed argued in 2016 that the hard problem involves two "explanatory targets":

1. [PQ] Physical processing leads to experiences with a specific nature.
2. [Q] Our experiences have particular qualities.

The first fact is about the link between physical and experienced states. The second is about what these experienced states are like. Wolfgang Fasching argues the hard problem is not about qualities but about the nature of experience itself—the way things are given to us subjectively. He says philosophy often focuses too much on the contents of experience (the qualities) and not enough on consciousness itself—the act of experiencing.

Relationship to scientific frameworks

Most scientists believe that the big question about why we have feelings and experiences might be answered when we learn more about how our brains work. They think this big question is really just part of smaller, easier questions about how the brain processes information.

Researchers have made progress in finding which brain activities happen when we are aware. However, this work helps us understand which brain parts are involved but not why these parts create feelings and experiences. Some scientists think solving these easier problems will also solve the big question, while others disagree.

One idea is that the mind works like a computer, processing information. Another idea, called integrated information theory, suggests that a measure called Φ could explain consciousness. However, some believe this still doesn’t explain why these processes create feelings. Another theory, called global workspace theory, compares the mind to a theatre where information is shared across the brain, but it also doesn’t explain why this leads to experiences. Finally, representationalism suggests our experiences are based on mental representations of the world, trying to connect ideas from philosophy with brain science.

Meta-problem

In 2018, a thinker named Chalmers talked about something called the "meta-problem of consciousness." This problem is about why we think there is a hard problem of consciousness.

He explained that even though this meta-problem seems easy to solve, it is very important because it is closely linked to the harder question about consciousness. Some believe that solving the meta-problem might actually help us understand or even solve the bigger hard problem of consciousness. Others think it won’t fully solve the hard problem but will still give us useful clues.

In popular culture

The playwright Tom Stoppard wrote a play called The Hard Problem in 2015. The title of the play comes from a big question in philosophy: how can we explain why we have our own special feelings and thoughts, instead of just acting like machines? Stoppard describes this as having "subjective First Person experiences."