QuestionsIs the mind the brain?The hard problem of consciousness and zombies
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The hard problem of consciousness and zombies

The philosophical zombie argument (the "hard problem")

David Chalmers born 1966The 'hard problem': why is information processing accompanied by lived experience?
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What it claims

Consciousness is not physical: materialism, which says that everything, consciousness included, is physical, is false.

Why

We can conceive a being physically identical to us but without consciousness, so consciousness is something beyond the physical.

The same idea through history
René Descartes1641Descartes argues that he can conceive his mind without his body, so they are distinct. Chalmers lists him among the predecessors of the argument.Gottfried Wilhelm Leibniz1714Leibniz's "mill": walking through a machine we would see only parts, never a perception. Chalmers also lists it as a predecessor.
Saul Kripke1980In Naming and Necessity, Saul Kripke says that God, after creating the physical processes of our world, would have had to do more work to put consciousness in it.
David Chalmers1995Chalmers separates the "easy problems" (explaining attention, memory, speech) from the "hard problem": why is all this information processing accompanied by lived experience?
David Chalmers1996In The Conscious Mind, Chalmers develops the zombie argument; he restates it in short form in his 2003 paper, which we quote.
In short

"The hard problem of consciousness and zombies" is an argument by David Chalmers ("Facing Up to the Problem of Consciousness", 1995; The Conscious Mind, 1996, 1995) on the question "Is the mind the brain?" (answer: the mind is not matter). Its claim: Consciousness is not physical: materialism, which says that everything, consciousness included, is physical, is false. According to AskPhilosophy's logic check (Z3 solver), the conclusion does follow from its 3 premises. AskPhilosophy presents 5 objections, 5 of them with a documented reply, and the original text behind each premise, checked word for word.

"Facing Up to the Problem of Consciousness", 1995; The Conscious Mind, 1996
Valid

Explaining how the brain pays attention, remembers, speaks or reacts: these are "easy problems", hard for researchers but we can see how to solve them. David Chalmers (1995) calls "hard problem" another question: why is all this information processing accompanied by lived experience? To show that the question does not go away, he uses zombies. A philosophical zombie is a being identical to us, atom for atom, behaving as we do and saying "I am in pain", but for whom there is nothing it is like to feel anything. Chalmers says such a being can be conceived without contradiction. If it is possible, consciousness does not follow from the physical: it is something more. The argument shows that the mind cannot be reduced to physics. Chalmers himself defends a form of dualism (he speaks of "naturalistic dualism"), but he also says another way out is possible: panpsychism.

P1A zombie can be conceived without contradiction: a being physically identical to a conscious being (same brain, same behaviour) but with no consciousness. The idea does not contradict itself, even on reflection.
P2What is conceivable in this way (with no hidden contradiction) is metaphysically possible: a zombie could have existed, perhaps in a universe with laws different from ours.
P3If a universe physically identical to ours but without consciousness is possible, then consciousness is something over and above the physical in our universe.
So consciousness is not physical: materialism, which says that everything, consciousness included, is physical, is false.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
The argument is valid: it is a three-step chain. Conceivable, hence possible (P1 and P2); possible, hence consciousness is non-physical (P3). There is no hidden premise. The whole debate is about P1 (can we really conceive a zombie?) and P2 (is the conceivable always possible?).
Analogy. If we can imagine, without contradiction, two houses with exactly the same bricks and plan, one inhabited and one empty, then living in it is not one more brick. What remains is whether we really imagine it without contradiction.

Objections

5

Each objection is a conversation: click to see who replies and where the debate stands.

"Type-B" materialists (Block and Stalnaker, Loar, Papineau, Tye...), following Kripke 1990 · attacks premise 2

The conceivable is not always possible. We can conceive that water is not H2O, and yet water is necessarily H2O: we discovered that truth by experience, not by thought alone. In the same way, the link between brain states and consciousness could be necessary without our being able to see it by thinking. Zombies seem possible to us, but they are not.

Chalmers replies
David Chalmers 2003
Chalmers answers that water and H2O are a bad model. The link between water and H2O can be deduced from the complete physical description of the world; the type-B materialist must instead hold that the link between physical states and consciousness is "epistemically primitive", that is, that it cannot be deduced from the complete physical truth.
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Ned Block and Robert Stalnaker 1999
Block and Stalnaker argue that even truths about water or genes cannot be deduced from the underlying physical truths. So there would be no such sharp difference between consciousness and other cases.
The debate goes on (our summary) The debate goes on. Chalmers and Frank Jackson answered Block and Stalnaker in 2001 ("Conceptual Analysis and Reductive Explanation"), arguing that truths about water can be deduced from the physical if the concepts are properly understood. Type-B materialists find this deduction too demanding. Neither side has won. Note that Kripke himself thought his lesson about water did not apply to pain.
Daniel Dennett 1995 · attacks premise 1

Zombies are not conceivable: we think we conceive them because we imagine them badly. Supposing that one can remove consciousness while keeping all the body's functions is like supposing that one can remove health while keeping all the body's functions intact: one is then wrongly imagining a "module" of health that might be missing. Dennett thinks the tradition of zombies would disappear if philosophers stopped mis-imagining them.

Chalmers replies
David Chalmers 2003
Chalmers answers that this materialist must either deny even the appearance of a further fact to explain, which seems to deny the obvious, or give substantial arguments for why only the functions need to be explained.
The debate goes on (our summary) The debate goes on. Dennett answers that this sense of obviousness is precisely what has to be explained, and that it comes from the way we think about our own inner life. For his opponents, this answers a different question. Neither side has won.
Paul Churchland 1996 · attacks premise 2

A gap between what we can explain and what we feel is not a gap in nature. In Goethe's time, someone could have built arguments of the same kind against the idea that light reduces to waves: light could not be deduced from the rest of physics. Yet the reduction succeeded.

Chalmers replies
David Chalmers 2003
Chalmers answers that, in the case of light, the only further fact that could have caused doubts is the experience of seeing light. The analogy therefore does not help this materialist, since that fact remains unexplained.
K
Keith Frankish (illusionism) 2016 · attacks premise 1

There are no mysterious "phenomenal" properties: the idea that we have them comes from an introspective illusion, that is, from the way we represent our own mental states to ourselves. The "hard problem" therefore rests on a mistake. Frankish proposes replacing the hard problem with the "illusion problem": explaining why we believe we have these properties. Zombies are conceivable only because this illusion is powerful.

Chalmers replies
David Chalmers 2018
Chalmers argues that the illusionist must explain why we have this illusion, and that this "meta-problem" (why do we think there is a hard problem?) is itself hard. In his view, that explanation remains to be given.
The debate goes on (our summary) The debate goes on. Illusionists answer that the meta-problem is precisely their research programme and that it is easier than the hard problem, since it concerns beliefs and behaviour. Their opponents hold that the illusion is itself an experience that remains to be explained. Neither side has won.
David Chalmers then Philip Goff (panpsychism as a way out) 2003 · attacks the conclusion

One can accept the argument without believing in a separate soul. On Chalmers's "type-F" monism, consciousness is constituted by the intrinsic properties of fundamental physical entities: at the deepest level of reality there would be properties that are experience (or nearly so), and physics describes only their relations. It is a form of panpsychism, which Philip Goff defends today. There is only one world, but it contains consciousness at its base.

Chalmers replies
William James (the combination problem), taken up by Chalmers 1890
Chalmers recognises a difficulty: how do a large number of tiny experiences or proto-experiences, one per particle, add up to a single rich consciousness like ours? He sees in it a version of what James called the combination problem.
P
Philip Goff 2017
Philip Goff defends panpsychism in Consciousness and Fundamental Reality (2017) and discusses the combination problem.
The debate goes on (our summary) Panpsychism does not settle every question and remains much debated: its critics say it is hard to test and merely moves the mystery. Its supporters answer that it is the only position that takes both science and experience seriously. Neither side has won.
What today's voices say
Defend it
Sam HarrisIn 2021 he tells Anil Seth he is 'taken in more by the so-called hard problem of consciousness'. Even without zombies, 'the hard problem still stays hard'.
Steven PinkerIn 2023 he says it is "a fallacy to say well it's not intuitive to me therefore it's a miracle"; in 2026 he calls subjective experience "the hardest intellectual problem" because no causal story bridges the objective and the subjective. In 2025 he calls the hard problem 'a head-scratching conceptual enigma' rather than a scientific puzzle, and he sympathizes with Dennett's wish to drop the term. He still says sentience really exists.
David ChalmersHis own argument: zombies are conceivable, so physical facts do not explain experience.
Donald HoffmanHe says he was prompted by how little progress physicalist approaches have made on the hard problem of consciousness, and starts from consciousness instead. He proposes to solve the reverse problem: how conscious agents create what we call brains.
Criticize it
Deepak ChopraHe says the hard problem of consciousness is not a problem at all, because consciousness comes first. Recalling a talk with Chalmers, he says Indian philosophy addresses the hard problem of matter instead.
Daniel DennettHe denied there is a hard problem: he called it vitalism reborn and expected it to dissolve once the many lesser problems are solved. He called the philosophical zombie 'a blatant mistake'.
Sean CarrollOn Mindscape (2018) he says he does not need anything beyond physics to explain consciousness, finds Chalmers's property dualism unconvincing, and doubts that zombies are conceivable.