Why is there something it is like to be you?
Science can explain what the brain does. The hard problem asks why any of that doing is accompanied by experience at all.
- Reading time
- 6 min
- Difficulty
- Intermediate
- Branch
- Mind
- First posed
- Named by David Chalmers, 1994; rooted in René Descartes and Gottfried Wilhelm Leibniz
The question
Look at something red. Light of a certain wavelength enters your eye, cone cells fire, signals travel along the optic nerve, and regions of your visual cortex become active. Neuroscience can trace much of this chain, and in principle all of it.
But something else is going on too. There is the redness of the red: the vivid, felt quality of seeing it. You are not merely processing information about the colour; you are experiencing it. Philosophers call these felt qualities qualia, and the fact that there is 'something it is like' to be in a state is what they mean by consciousness.
In 1994 the philosopher David Chalmers drew a distinction that has organised the debate ever since. The 'easy problems' of consciousness are explaining functions: how the brain discriminates stimuli, integrates information, controls behaviour, reports its own states. They are easy only in comparison, since they may take centuries. But they are the kind of problem science knows how to solve: find the mechanism that performs the function.
The hard problem of consciousness is different. Even after every function is explained, a question seems to remain: why is all that processing accompanied by experience? Why does it not all go on 'in the dark', as it presumably does in a thermostat or a calculator? Explaining what a system does seems not to explain why it feels like anything to be that system.
“Perception, and that which depends upon it, are inexplicable on mechanical grounds.”
Gottfried Wilhelm Leibniz, Monadology, §17 (1714)
Why it matters
Consciousness is the one thing each of us knows directly. Everything else, including the physical world, we know through it. If our best scientific picture of reality leaves it out, the picture is incomplete at the point that matters most.
The question also has practical edges. Which animals can suffer? Can a patient in a vegetative state feel pain? Could an artificial intelligence ever be a someone rather than a something? Each depends on a theory of when and why experience arises, and we do not have one.
Key terms
- Phenomenal consciousnessThe felt, subjective aspect of experience: what it is like to see red, feel pain or taste coffee.
- QualiaThe qualities of conscious experiences as they feel from the inside, such as the redness of red or the painfulness of pain. Singular: quale.
- Hard problem of consciousnessDavid Chalmers' name for the question of why physical processing in the brain is accompanied by subjective experience at all.
- Explanatory gapJoseph Levine's term for the apparent impossibility of explaining why a given physical process should feel like anything at all from the inside.
- PhysicalismThe view that everything that exists is physical, or is fixed by the physical facts.
- PanpsychismThe view that consciousness, or something like it, is a fundamental and widespread feature of the physical world, present even in very simple things.
The positions
Physicalism: it will be explained
Consciousness is a physical process in the brain. The hard problem reflects the limits of our current concepts, not a gap in nature.
Illusionism: there is no hard problem
Phenomenal consciousness, as philosophers define it, does not exist. What needs explaining is why we are so convinced that it does.
Dualism: mind is something extra
Conscious experience is not physical. It is a further feature of reality, linked to the brain but not identical to it.
Panpsychism: experience goes all the way down
Some form of experience is a basic feature of all matter. Brains do not create consciousness; they organise it.
Mysterianism: we may never know
There is a natural explanation of consciousness, but human minds may be incapable of grasping it.
Arguments and objections
Physicalism: it will be explained
- Best argument
- Every past mystery about life and mind, from heredity to vitalism's 'life force', dissolved as science advanced. We already know that experience changes precisely with brain states: anaesthesia removes it, damage alters it, stimulation produces it. The simplest hypothesis is that experience is certain brain activity, described from the inside. An explanatory gap in our understanding does not imply a gap in the world.
- Strongest objection
- The comparison with vitalism fails. Life was always a matter of functions (metabolism, reproduction), so explaining the functions explained life. Consciousness is not obviously a function. One can imagine all the functions occurring without any experience, which is the point of philosophical zombies.
- The reply
- Physicalists reply that what we can imagine is a poor guide to what is possible, and that the sense of a remaining mystery may itself be explained by how our brains represent their own states.
Illusionism: there is no hard problem
- Best argument
- Keith Frankish and Daniel Dennett argue that our brains represent their own processing in a simplified, misleading way, as if there were ineffable inner qualities. The 'meta-problem' is to explain why we judge that we have such qualities. Solve that, and nothing is left over, because the qualities were never there.
- Strongest objection
- To most people this seems to deny the most obvious fact there is. If I am in pain, the pain is not an illusion; even an illusion of pain would be a painful experience. Illusionism seems to deny the very thing it was meant to explain.
- The reply
- Illusionists accept that pain is real and terrible; what they deny is a particular theory of it, namely that it has intrinsic, private, ineffable qualities over and above its role in the mind.
Dualism: mind is something extra
- Best argument
- No amount of physical description seems to entail facts about experience. Mary in her black and white room knows every physical fact about colour vision, yet learns something new when she sees red. If so, there are facts beyond the physical facts. Chalmers proposes property dualism: experience is a fundamental property, as basic as mass or charge, linked to physical structure by psychophysical laws.
- Strongest objection
- If experience is non-physical, how does it affect the physical world? Your pain makes you say 'ouch', yet physics appears causally closed: every physical event has a sufficient physical cause. Dualism seems to make consciousness either a ghost that breaks physics or an idle spectator.
- The reply
- Some dualists accept that consciousness is causally idle (epiphenomenalism); others argue that physics only describes structure and leaves room for experience to be what fills that structure.
Panpsychism: experience goes all the way down
- Best argument
- Physics tells us what matter does, never what it is in itself. Bertrand Russell and Arthur Eddington suggested that the intrinsic nature behind physical structure might be experiential. Then there is no mystery of how experience emerges from wholly non-experiential stuff, because it never does.
- Strongest objection
- The 'combination problem': how do countless micro-experiences combine into a single unified subject like you? Electrons with flickers of experience do not obviously add up to someone tasting coffee. Many also find the idea that a rock has an inner life simply implausible.
- The reply
- Panpsychists answer that most objects (rocks, chairs) are not subjects at all, only aggregates; only certain organised systems combine experience into a unified mind. The combination problem is real, they grant, but no harder than the hard problem.
Mysterianism: we may never know
- Best argument
- Colin McGinn notes that every species has cognitive limits: a dog cannot understand calculus. It would be surprising if humans had no such limits, and consciousness is exactly where our concepts seem to fail.
- Strongest objection
- It is premature to declare defeat. Many problems once thought permanently beyond us were solved, and mysterianism risks discouraging the research that might solve this one.
Who argued what
- Physicalism: it will be explained Daniel Dennett, Patricia Churchland, Ned Block
- Illusionism: there is no hard problem Daniel Dennett, Keith Frankish
- Dualism: mind is something extra David Chalmers, René Descartes, Frank Jackson (early)
- Panpsychism: experience goes all the way down Philip Goff, Galen Strawson, Bertrand Russell
- Mysterianism: we may never know Colin McGinn
Where you stand
Is there a hard problem of consciousness?
In surveys
Choose one to see how people answer.
Variations
The inverted spectrum
Could your experience of red be like my experience of green, while we both call ripe tomatoes 'red' and behave identically? If that is even coherent, it suggests experience is not fixed by function. This puzzle goes back to John Locke.
The zombie twin
Imagine a being physically identical to you, atom for atom, that behaves exactly like you but has no experience at all. If such a being is conceivable, Chalmers argues, consciousness is not entailed by the physical facts. See philosophical zombies.
Go deeper
Scientific theories of consciousness
Several research programmes try to identify the physical correlates of consciousness. Global workspace theory, developed by Bernard Baars and Stanislas Dehaene, says that information becomes conscious when it is broadcast widely across the brain. Integrated information theory, from Giulio Tononi, says that consciousness corresponds to how much a system's information is unified, a quantity called phi. Higher-order theories say a state is conscious when it is the object of another mental state.
These theories make different predictions, and large collaborative experiments have begun testing them against each other. Whether any of them touches the hard problem, rather than the easy ones, is itself disputed.
Where the phrase came from
Chalmers introduced the term at a conference in Tucson in 1994 and developed it in his book The Conscious Mind (1996). The underlying worry is much older. Gottfried Wilhelm Leibniz imagined walking inside a thinking machine enlarged to the size of a mill: you would see only parts pushing on one another, never a perception. Thomas Nagel's 1974 essay 'What Is It Like to Be a Bat?' gave the problem its modern shape.
Related ideas
Further reading and sources
- EncyclopediaStanford Encyclopedia of Philosophy: Consciousness
- WikipediaHard problem of consciousness
- SurveyPhilPapers Survey, 2020 · question: Hard problem of consciousness; about 1,785 professional philosophers; accept or lean toward
- BookThe Conscious Mind, David Chalmers
- BookConsciousness Explained, Daniel Dennett
- BookGalileo's Error, Philip Goff
- BookBeing You, Anil Seth
Open questions
- Could a complete science of the brain ever tell you what it is like to be someone else?
- If consciousness does nothing, why did evolution give it to us?
- Is the feeling that there is a hard problem itself something the brain produces?