This is a question that aims to clarify Chalmers's "hard problem of consciousness".

Suppose one day neuroscientists figured out how exactly to reproduce all (or virtually all) human experiences through stimulating neurons in different specific patterns.

For instance, you want to hear Beethoven's 9th symphony? No problem. Scientists will stimulate your neurons in a particular way so you exactly hear the symphony in all its richness (tones, timbre, rhythm, etc.). And suppose it feels so real that you cannot differentiate between scientists manipulating your neurons or you really hearing the symphony.

additional clarification: Many people state that they think that subjective feeling is a fundamentally different thing from neurons firing. In my hypothetical example, this can also be manipulated by scientists. That is, with the flip of a switch, scientists can decide whether you think subjective feeling (“consciousness”) is the same, or different, from mechanical firing of neurons.

Would this resolve the "hard problem"?

I'm not claiming that this is realistic (although this is certainly something neuroscientists are striving for in the end, and they believe this can be done in principle). Again, this is a clarifying question, aiming at clarifying what exactly is referred to by the "hard problem".

  • No, this will not resolve the hard problem, as its proponents understand it. Figuring out the inputs to get desired responses out of a black box does not explain why the responses, "what it is likes" in this case, are thus and so, or why they are there at all. To get into the black box the explanation has to be of a different nature than matching descriptions, it has to mediate between descriptions and something not of a kind with them.
    – Conifold
    Commented Nov 20, 2020 at 6:18
  • Reproducing experiences is not the issue. The question is why are certain physical systems like 'brains' conscious, and other things not conscious. We need a chain of explanation from the basic laws of the universe=> brains are conscious, toasters are not conscious. Commented Nov 20, 2020 at 7:45
  • @AmeetSharma: let me change the subject here. Suppose we are dealing with X = horses. Suppose scientists can perfectly generate all possible horse subjective experiences. Do we have a "hard problem of horse consciousness"? (Us not knowing their consciousness isn't a reason to say they are not conscious; strictly speaking, you also don't know if I am conscious because you are not me). If your answer is yes, then replace horses with cockroaches; if still yes, then with one cell amoeba, or with the COVID-19 virus, or with a rock.
    – J Li
    Commented Nov 20, 2020 at 8:50
  • 1
    @Conifold As far as I can tell, this assertion of "different nature" is only justified by "we perceive them to be different". Human perception can be wrong. For instance, people intuitively feel that the morning star and evening star are different stars, when in fact they are the same planet. If scientists can reproduce all human experiences with neuron manipulation, then perhaps we should be open to the idea that our perception of "differentness" may not be so meaningful after all.
    – J Li
    Commented Nov 20, 2020 at 8:53
  • 1
    It sounds to me like you don't quite understand Chalmer's objection. I would suggest opening another question and picking out claims that he makes to back up his response to your question so that we might better see why his answer doesn't seem to click with your intuition. My sense of it is that you're not clear on what 'experience' means in regards to the mind-body duality and how SEP: qualia play an important role in differentiating experience (which is 'sensory') from knowledge (which tends towards being more 'linguistic').
    – J D
    Commented Nov 20, 2020 at 12:36

5 Answers 5


Q: What exactly is referred to by the "hard problem".

A: The hard problem of consciousness, according to Chalmers and the majority of philosophers that use this term, is the problem of how and why there is conscious experience occurring in a physical process. (1-5) Again, let’s examine Chalmers’ frequently quoted words:

“The hard problem, as I understand it, is that of explaining how and why consciousness arises from physical processes in the brain.” Chalrmers 1997(1)

The hard problem of consciousness is the problem of experience. …There is no question that experience is closely associated with physical processes in systems such as brains. … But how and why do physical processes give rise to experience? Why do not these processes take place "in the dark," without any accompanying states of experience? This is the central mystery of consciousness.” Charlmers 2002(2)

And by the term experience or subjective experience, he means “Humans beings have subjective experience: there is something it is like to be them. … There is something it is like to see a vivid green, to feel a sharp pain, to feel a deep regret, .... Each of these states has a phenomenal character, with phenomenal properties (or qualia) characterizing what it is like to be in the state.” Charlmers 2002(2)

For example, our digestive system, our endocrine system, our cerebellar system, and all other unconscious systems in the brain are all complex physical processes that manage a lot of complex information, yet there are no conscious experiences (e.g. no what it is like to sense protein or fat in the stomach, no what is like to sense plasma testosterone at various levels, no what it is like to sense various signals from spinocerebellar tract, etc.) occurring in these systems. They all operate purely mechanically – in the dark – just like computers, and all their operations are completely explicable by existing physical laws.

On the other hand, the consciousness system operates with additional phenomena occurring – the conscious experiences: what it is like to see the red color in our mind, to hear in the sound of a song in our mind, to smell the sweetness of a rose in our mind, to feel happy in our mind, to relive past events in our mind, etc. Why does not the consciousness system just operate in the dark like all subconscious processes above – how and why do these conscious experiences occur in this particular physical process? So far, no known physical laws can explain their occurring. This is the essence of the problem.

So, the hard problem of consciousness is not the problem of whether we can replicate the consciousness system (its complex neural circuits and their orderly firing) in another system so that conscious experience occurs in the physical process of the latter system. If we can do that but still cannot answer the problem of how and why there is conscious experience occurring in such a physical process, the hard problem is still not resolved. Even if we cannot replicate such a feat because of some technical obstacles but know exactly what neural circuits and their firing that create conscious experience are, we still do not solve the hard problem if we cannot explain how and why there is conscious experience occurring in such a physical process.

On the contrary, even if we cannot replicate neural circuits and their firing in a physical process so that conscious experience occurs (because of some technical obstacles or any other things) but we can explain how and why a certain physical process has conscious experience occurring, we will have the done the task of solving the hard problem of consciousness.

Q: Does Chalmers believe that the hard problem can never be solved?

No, Chalmers does not espouse Mysterianism (which holds that the hard problem of consciousness cannot be resolved). In fact, he has a hope that the solution will be found and that some of the ideas needed for this are already present but only need to be developed:

“It is often held that even though it is hard to see how materialism could be true, materialism must be true, since the alternatives are unacceptable. As I see it, there are at least three prima facie acceptable alternatives to materialism on the table, each of which is compatible with a broadly naturalistic (even if not materialistic) worldview, and none of which has fatal problems. So given the clear arguments against materialism, it seems to me that we should at least tentatively embrace the conclusion that one of these views is correct. ...” Chalmers 2002(2)

Q: Does Chalmers believe that neuroscience cannot solve this hard problem?

I’ve never seen Chalmers concluded anywhere that neuroscience will not be able to do that. For him, to solve the hard problem requires some natural principles, which are not known at present:

“A solution to the hard problem would involve an account of the relation between physical processes and consciousness, explaining on the basis of natural principles how and why it is that physical processes are associated with states of experience.” Chalmers 2002(2)

And, as far as I know, he did not assert that this cannot come from neuroscience.

P.S. The following is not one of the questions directly asked in this thread, but it is an interesting and exciting question: Chalmers’ ideas and beliefs put aside, “Has the hard problem of consciousness actually been solved?” I believe the consensus at present among the majority of philosophers is “no”. But, to neuroscientists, quite some of them believe that they have solved it. Of course, their theories have not been accepted widely as correct, and the solution to the hard problem remains controversial and is still being widely discussed, debated, and researched. But, for those who are interested in exploring these new ideas, please try browsing references 6-10. At least, you’ll get some ideas of how neuroscientists are currently trying to solve this hard problem.


  1. Chalmers DJ. Moving forward on the problem of consciousness. J Conscious Stud. 1997;4(1):3-46. http://consc.net/papers/moving.html

  2. Chalmers DJ. Consciousness and its place in nature. In: Chalmers DJ, editor. Philosophy of mind: Classical and contemporary readings. Oxford: Oxford University Press; 2002. ISBN-13: 978-0195145816 ISBN-10: 019514581X. http://consc.net/papers/nature.html

  3. Weisberg J. The hard problem of consciousness. The Internet Encyclopedia of Philosophy. https://www.iep.utm.edu/hard-con/

  4. Gennaro RJ. Consciousness. Internet Encyclopedia of Philosophy. Retrieved 2017 Apr 18 from http://www.iep.utm.edu/consciou/

  5. Van Gulick R. Consciousness. In: Zalta EN, editor. The Stanford Encyclopedia of Philosophy (Summer 2017 Edition). Retrieved 2017 Sep 8 from https://plato.stanford.edu/archives/sum2017/entries/consciousness/

  6. Grossberg S. Towards solving the hard problem of consciousness: The varieties of brain resonances and the conscious experiences that they support. Neural Netw. 2017 Mar;87:38-95.

  7. Loorits K. Structural qualia: A solution to the hard problem of consciousness. Front Psychol. 2014;5:237.

  8. McFadden J. The Conscious Electromagnetic Information (Cemi) Field Theory. The hard problem made easy? J Conscious Stud. 2001;9(8):45–60.

  9. Tononi G, Koch C. Consciousness: Here, there and everywhere? Philos Trans R Soc Lond B Biol Sci. 2015 May 19;370(1668):20140167.

  10. Ukachoke C. The Basic Theory of the Mind. 1st ed. Bangkok, Thailand; Charansanitwong Printing Co. 2018.


Short Answer

In his paper, Chalmers answers you directly himself, p.10:

We have seen that there are systematic reasons why the usual methods of cognitive science and neuroscience fail to account for conscious experience. These are simply the wrong sort of methods: nothing that they give us can yield an explanation. To account for conscious experience, we need an extra ingredient in explanation.

Long Answer

The Hard Problem of Consciousness was originally put forth by Chalmers in Facing Up to the Problem of Consciousness. It behooves us to quote him directly to ensure we are on the same page with his characterization. From page 3:

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. As Nagel (1974) has put it, there is something it is like to be a conscious organism. This subjective aspect is experience... What unites all of these states is that there is something it is like to be in them. All of them are states of experience... Why is it that when our cognitive systems engage in visual and auditory information-processing, we have visual or auditory experience?

What Chalmers is after is a scientific explanation to this question. This is an important point, because the notion of 'explanation' is itself a philosophical problem. In Blackwell's Companion to the Philosophy of Science, the editor makes the following claim:

The current situation [regarding an explanation of explanation] is an embarrassment for the philosophy of science. Indeed, one might go so far as to say that it is the sort of scandal to philosophy of science that Kant thought skepticism was to epistemology. While we have insightful studies of explanation, we are a very long way from having this single unifying theory of explanation.

So here is the state of affairs when you come to this forum and ask for clarification about the hard problem: one philosopher who claims and is met with a polarized response in the literature that there is no good explanation for 'experience' does so when there also seems to be no universal consensus on what constitutes what the experience necessary to define 'explanation'. Bit of a chicken and egg scenario, no? Perhaps we should proceed by evaluating Chalmers's own proposed explanation to seek additional clarity on his proposed problem.

First, note that Chalmers's draws from Nagel's What Is It Like to Be a Bat? which an old philosophical problem that goes back to trying to peer into someone else's mind (if you don't reject it fully like a solipsist). These issues fall into a series of frameworks familiar to those who are familiar with the topic of dualism, perhaps most famous in the Cartesian form. So, right away your question, like all philosophical questions seems falls to questions of metaphysical presupposition or what Quine might refer to as first-philosophy questions. Of course, Quine according to the IEP sought to place those questions firmly within the realm of science instead:

The basic conception of philosophy and philosophical practice that informs his discussion of science is commonly known as naturalism, a view that recommends the “abandonment of the goal of a first philosophy prior to natural science” (1981, 67), which further involves a “readiness to see philosophy as natural science trained upon itself and permitted free use of scientific findings” (1981, 85) and lastly, recognizes that “…it is within science itself, and not in some prior philosophy, that reality is to be identified and described” (1981, 21).

So, it bears asking, is the explanation we are seeking fundamentally scientific or metaphysical or both? Let's examine Chalmers's first proposal to get insight into your question which fundamentally reduces to:

Is turning on and off the mechanisms of experience helpful in explaining experience?

This, of course, is an astute question to ask, and maybe not one so easy to answer!

Chalmers and His Functional and Non-Reductive Explanation Dichotomy

Now, since you are astute, let's notice that Chalmers embraces a duality of sorts in his taxonomy of explanation. In his paper, he attempts to characterize both and review some of his questions that arise.


Why is the performance of [neurological] functions accompanied by experience?


Why doesn't [our brain's] information-processing go on "in the dark" free of any feel?


A... promising approach [to analyzing experience] appeals to... methods to explain the structure of experience?

[Another] reasonable strategy is to isolate the substrate of experience.


I suggest that a theory of consciousness should take experience as fundamental.


So now we are in a position to answer your question:

Would [having the ability to manipulate states of consciousness externally] resolve the "hard problem"?

To which, the answer according to Chalmers is no. Why?

According to how Chalmers himself frames the problem, the question is not one of understanding functionality or even awareness, but building a theory that takes 'experience' as a conceptual primitive and then integrating materialist and mentalist doctrines. Let's take a simpler example to explain.

It is known to neurologists that when electricity is applied to regions of the brain, one can cause a patient to laugh without reason. Now, does that technique or the atomic and evolutionary theory that explain the mechanism explain why it usually feels good to laugh and why we smile while doing so? Absolutely not. To explain in causal terms why we laugh when electrically triggered is not the same as explaining what it feels like to laugh. Since Socrates, people have been experiencing laughter, but how is triggering a laugh with an electrode any different than telling a joke to trigger it to explaining the experience of laughter? What does the method add to our knowledge fundamentally? Does it answer why it feels good to laugh or explain why I might laugh at the following joke?

Knock, knock. Who's there? Interrupting cow. Interrupting co... MOOOOOOOO!

He clarifies why function is not good enough on p.6:

There is an explanatory gap... between the functions and experience and we need an explanatory bridge to cross it. A mere account of the functions stays on one side of the gap, so the materials for the bridge must be found elsewhere.

This is not a new issue. Behaviorists, like Dennett's response from his position of eliminative materialism, recognized the problem a long time ago and opted to just deny the existence of experience as opposed to create a theory to bridge the objective functions and the subjective qualia of consciousness. But much like those epistemologists who reject "belief" only to fall back on "schmelief" as a psychological operation, so too does the attempt to replace experience purely in functional terms find itself embarrassed by the need to use explanation based on subjective experience. This, of course, isn't an easy problem. The logical positivists and their kin ran smack dab into the same problem. How do you reduce phenomenological experience to purely objective language?

  • 1
    "How do you reduce phenomenological experience to purely objective language?" -- Would this do? Commented Nov 20, 2020 at 18:23
  • @YuriAlexandrovich: What do you think of this answer? JD also philosophy.stackexchange.com/questions/77555/…
    – CriglCragl
    Commented Nov 21, 2020 at 1:56
  • @CriglCragl -- that's a Neural Net's take. And that of any person whose rational Self gave up the control of their thought process, and their agency, leaving the neural net of their subconsciousness to do the thinking for them, pretending to be them. Except the Neural Net's outlook is very different from that of the rational Self. NN must rely on its own experiences, making it 100% subjective. Having no concept of the "outside", the objective reality makes no sense to it. Along with everything that depends on the OR -- the concepts of truth, knowledge.... Commented Nov 21, 2020 at 21:52
  • .... of understanding (of ourselves, our lives, everything), of consciousness, compassion, ethics, the ability to tell right from wrong and good from evil. To explain our apparent interactions it comes, for our sins, with the idea of "intersubjectivity." It speaks in its private language because lacking the concept of the truth, it can only offer its own perspective, with no way of understanding those of others or reconciling the differences -- leaving the power struggle as the only way to function together.... all that is contrary to the human nature of being your conscious, rational Self. Commented Nov 21, 2020 at 22:02
  • Thank you so much for the answer. I need more time digest and think it through. Without more deliberation, at present, my perspective is closer to Dennett - I’m simply denying the existence of a purely subjective notion of “experience”, which, it seems to me, to be the core of what I disagree with Chalmers on. But I need to think more.
    – J Li
    Commented Nov 23, 2020 at 8:39

The Wikipedia page states (emphasis mine):

The philosopher David Chalmers, who introduced the term "hard problem of consciousness,"[3] contrasts this with the "easy problems" of explaining the physical systems that give us and other animals the ability to discriminate, integrate information [...].

It seems to me what you describe would explain how we hear the symphony, but not why we feel it, as opposed to, say, a microphone, which has access to the same sensory input and can even capture it with better accuracy than we can, but does not feel anything.

  • Thank you for the answer, but I think there is a key difference between my description and microphones. I am literally referring to a scenario where all human feelings can be generated and induced by neural stimulation. Feeling, not just the recording of sound waves. (microphones don't have neurons)
    – J Li
    Commented Nov 20, 2020 at 8:56
  • Indeed, but this induction will, IMHO, give you insight only about the mechanical part of the process, which David Chalmers does not consider to be the "hard problem of consciousness". I'll see how I can express it better in.my answer.
    – armand
    Commented Nov 20, 2020 at 9:22
  • I just amended my question above. Note that “you” in the question can also refer to David Chalmers himself. Scientists can flip a switch, and then he will deny there is a hard problem of consciousness. (Just for clarification purposes, no office to Mr Chalmers here)
    – J Li
    Commented Nov 20, 2020 at 9:27
  • @JLi Why use electrodes rather than headphones? What does neural stimulation to generate a symphony bring to the problem that listening to a record doesn't? Aren't both apparatus of a similar kind? Setting up pressure waves to stimulate neurons in the inner ear is how hearing works. Listening to the symphony brings mere ordinary insight into the experience, and neurally stimulating is the same kind of experiment.
    – Dan
    Commented Feb 18, 2023 at 3:46


Neuroscience can only solve the easy problem. Once we have consciousness, we can trace out some correlations. You feel sadness, neuron A fires, you feel happy, neuron B fires etc. That not at all what the hard problem is about.

The hard problem is about how consciousness arose in the first place.

At the most basic level, you are bunch of atoms. Consciousness is a product of the brain, and the brain is billions of atoms.

For example, let's look at a chemical reaction. What happens if we mix atom A + atom b. 2 possibilities, either nothing happens, or a spontaneous chemical reaction happens that produces some new substance (kind of like hydrogen and oxygen produce water).

Do we get consciousness if we mix 2 atoms? No. 3 atoms, nothing. We add a billion more, and we spontaneously get consciousness. How in the world? That is the hard problem and it is not clear if science will ever solve it, or even solve 0.001% of this problem. The mind cannot be derived from a pile of atoms.

Neuroscience has no explanation for a chemical reaction atom 1 + atom 2 + billion more = consciousness.

If you ask me, this problem will never be solved.


I suggest you consider one aspect of consciousness, such as colour perception. Take the colour red, for example. The quality of the mental experience you have of the colour red has no explanation in physics or neuroscience. In physics, it is possible to show that our mental picture of red is triggered by electromagnetic fields with a certain spread of frequencies. In neuroscience our mental picture of red is associated with certain chemical processes in specific parts of the brain. Suppose, in principle, that these could be modelled very exactly, so that we know for certain precisely which combinations of physical processes triggered the experience of red- we would still not know how or why the quality of that experience arises from those processes.

In physics, there is an important principle of dimensional consistency. When you model phenomena, you use equations, and it is in the nature of an equation that the quantity on one side of the equals signs is the same as the quantity on the other. That extends to the two quantities having the same dimensions, by which I mean length, time, mass, charge and so on. So an equation can never equate a length with a mass, for example, because the quantities are inherently different. I remember in my late teens (a long time ago!) discussing consciousness with friends at school not long after we had been introduced to dimensional analysis in physics, and it struck me then, as it still does now, that framing consciousness as a physical phenomenon would require consciousness to be reduced to a set of known units, or that one or more an entirely new physical units would need to be introduced to account for it.

Given the above, I am currently disinclined to imagine that we will find a purely physical explanation for consciousness using existing concepts of physics. I am also disinclined to imagine that the answer will be found in the field of information processing. Some have suggested that consciousness- say the experience of the colour red, for example- might arise when we have sufficiently powerful computers running sufficiently powerful processes. My answer to that is a thought experiment in which the computer and the process which it performs is modelled by trillions of people, each passing bits of information to each other in exactly the same sequence as the processing of bits by the electronic computer. How, collectively, would the billions of people experience the colour red?

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