In Colin McGinn's "The Mysterious Flame," McGinn argues against the materialistic response to the hard problem of consciousness with the following argument:

Suppose I know everything about your brain of a neural kind: I know its anatomy, its chemical ingredients, the pattern of electrical activity in its various segments. I even know that position of every atom and its subatomic structure. I know everything that the materialist says your mind is. Do I thereby know everything about your mind? It certainly seems not. On the contrary, I know nothing about your mind. I know nothing about which conscious states you are in -- whether you are morose or manic, for example -- and what these states feel like to you. So knowledge of your brain does not give me knowledge of your mind. How then can the two said to be identical?

Is the premise of this argument, the proposed fact that knowing every physical aspect of one's brain does not reveal its subjective experience, true? Is this argument good?

This at least cannot be entirely true. Shouldn't one be able to deduce whether a brain is conscious and the extent of said consciousness, if any, via knowledge of its physical factors? Shouldn't there be some physical thing, or collection of things, on which the formation and storage of memories rely upon? Shouldn't the investigation these physical things at least give some information of one's subjective experience?

What can we not know about one's subjective experience regardless of what we know about one's brain in a physical aspect?

  • McGinn overreaches with his rhetoric, but the core of his argument refers to "what these states feel like to you" as to what is unknowable. It does seem plausible that we can find physical correlates to say "manic" but on reflection these correlates correlate neural patterns to overt behavior, not to "what it feels like". Indeed, since we have no access to "what it feels like" other than, well, feeling it, and the feeling can only be done in the first person, it is by design impossible to correlate it to anything physical. We know not if what we both call "red" "feels the same" to both of us.
    – Conifold
    Aug 20, 2018 at 21:17
  • @Conifold, eye receptors are connected to neurons and the fact that in all humans the same receptors are activated by the same (or almost the same) wavelength is yet undisputed. Further science shoild investigate if neurons connected to them are similar. If so, assuming physicalism we are done: humans perceive colors in similar ways. However, given that different colors also have different secondary effects (grey sky makes people more sad, for example) it is already plausible these experiences are similar for all people (I don't assume blind and colorblind).
    – rus9384
    Aug 21, 2018 at 0:00
  • @Conifold, there are differences, however, exactly as people can have different taste for food they probably can perceive it differently. But I still think if so, there are physical differences in brains causing that.
    – rus9384
    Aug 21, 2018 at 0:03
  • @rus9384 McGinn does not assume physicalism, and indeed argues for its implausibility, so such an assumption begs the question. And physicalist's position is not that "humans perceive colors in similar ways" in the relevant sense of "what it feels like", it is that asking if something feels different or the same to different subjects is a meaningless question that twists the language.
    – Conifold
    Aug 21, 2018 at 0:07

5 Answers 5


You are asking one of the outstanding unknown questions in philosophy: do mental states supervene on brain states or not?

"Supervene" is a really great word. If A supervenes on B, it means that if you know everything about B, you automatically can deduce everything about A. For example, the value of a pile of $1 bills supervenes on the list of serial numbers of those bills. If I know the serial numbers, I can trivially find the value of the pile by counting how many serial numbers I know and then multiplying by $1.

There are those that argue that our mental states supervene on our brain states, that is to say that if we knew everything about someone's brain, we would have all the information needed to deduce the mental state of that person. Indeed, modern science has done an extraordinary job of saying remarkable things about someone's mental state by studying their brain.

Then there are those that argue that mental states do not supervene on brain states. They argue that there are things like qualia. Qualia is the mental concept of sensation, like "redness." Indeed many argue that there is no physical representation for our concept of "redness."

However, neither side has a complete "winning" argument. If you look at McGinn here, he basically leaves the proof up to the reader: "Do I thereby know everything about your mind? It certainly seems not." He is assuming that you will agree with his claim despite a severe lack of evidence provided.

Indeed both sides do this. I know few who argue that mental states supervene on brain states that are willing to postulate how to go from brain states to mental states. It's just assumed it must be true because... well... they leave the proof up to the reader as well.

  • This is a sort of okay explanation of supervenience, but what it gets wrong is important to the matter at hand. Supervenience comes in different modal strengths. Even the most rabid dualist believes some version of the claim that the mental supervenes on the physical. The materialist's supervenience claim and the dualist's supervenience claim differ in their modal strengths.... so supervenience per se is not what is at issue. See section 3.1 in the SEP article on supervenience, and then reread Frank Jackson etc. Took a Princeton grad course on this lol. Aug 21, 2018 at 2:37
  • @windlessqhickory Interesting. For the purposes of this answer, I only use a binary approach to supervenience. Either mental states are completely defined by brain states, or they aren't. It would be reasonable to talk the subtleties you mention in a more subtle environment, such as one where the author is not using words like "identical" and "know everything" and pinning the materialist to one particular argument.
    – Cort Ammon
    Aug 21, 2018 at 2:46
  • My point is that supervenience isn't what matters here. What matters is whether zombies are possible. Aug 21, 2018 at 18:42
  • @windlessqhickory I may get to learn something here. I always thought of zombies as a purely material thing whose properties give the appearance of conscious thought.
    – Cort Ammon
    Aug 21, 2018 at 18:49
  • That's correct. The zombie question is: Could there be a replica of my body that is materially identical to me but is unconscious, i.e. does not experience the feely side of consciousness? It is more or less agreed that this question is what the materialism-dualism debate comes down to. As I said, everyone agrees that mental properties supervene on natural facts. The question is whether they are metaphysically entailed by natural facts. As a comparison, everyone agrees that moral facts supervene on natural facts. But a minority of philosophers believe they are entailed by natural facts. Aug 22, 2018 at 17:28

When McGinn states that knowing everything about your brain tells us nothing about your mind, he is overstating the case: an advanced cognitive neuroscience should indeed be able to say something about your memories ... and possibly other mental capacities and cognitive capabilities. But that's all about abstract functional causal organizations, something clearly within the realm of normal science. Subjective experience (and that's what McGinn is really talking about) is something different, and many other philosophers have pointed out the difficulty in explaining why the conscious experiences we have are the way they are (why, for example, would brain activity of a certain kind lead to a 'red' experience, but other brain activity to a 'blue' experience?) .. or why there even are subjective conscious experiences at all (why, for example, we would not be 'philosophical zombies')


In fact today it seems entirely plausible that from the neural activity you would be able to predict whether someone is in a manic state or not. (The first hit on a single Google search is this paper which concerns differences between manic bipolar and healthy subjects in fMRI data.)

However, it still seems possible to argue that there's something this leaves out. The knowledge argument comes to mind here, in which scientist Mary has been locked in a black and white room since birth, but otherwise knows everything there is to know about the physics and neuroscience of color. The argument is that when Mary goes outside for the first time and experiences seeing red, there is still something new that she learns.

Similarly, in the case above, it seems that even knowing everything there is to know about your brain, I may not know what you experience phenomenally. In a strong version of the inverted spectrum scenario, two subjects may have the exact same brain state when perceiving a blue sky, but the phenomenal experience of the one is the same as what would have been the phenomenal experience of the other perceiving a green sky. But they'll never know, because they have learned to call the same things in the world "blue".

  • That brains are different between manic bipolar and healthy is quite some distance away from everything.
    – virmaior
    Aug 22, 2018 at 1:24
  • Agreed, this was just referring to the problem of detecting a manic state mentioned in the quote in the question.
    – present
    Aug 22, 2018 at 2:10

The argument quoted presumes that we cannot know things that we surely do know. We can tell if you are manic from an fMRI. And we have a good idea what mania of a given level feels like. We have many accounts of it that can readily evoke an understanding in a wide range of people. Moving forward, we will have even more fine-tuned information about what your brain means about your mind.

The brain state may correctly reflect the mind state. The author's conclusion is just not proved. So this is not the direction that makes sense. The argument is too facile.

At the same time you could have a full and compelling description of every facet of the mind state, and you would still never have access to my subjective reality. Knowing things objectively is not knowing them subjectively. I can know everything about bat neurology and about any given bat and we will still never be able to answer Nagle's question "What is it like to be a bat?"

Nagel's argument is much more reasonable. There is an insurmountable gap between any objective description and any subjective experience that simply cannot be resolved. One can only evoke subjective responses, one can never describe them completely. And I can only evoke similar responses, not identical ones, because different people's experience are not identical, and their reactions are conditions by those experiences.

One does not have to reject materialism to see the mind as an irreducibly emergent phenomenon that cannot be duplicated, shared or fully controlled.


This is a highly speculative question, implying that all people share the underlying assumptions of the author. This is like asking "am I a democrat if my dog votes to democrats?" First, dogs don't vote. Second, even if they would vote, such conclusion is still not possible to be reached. Check the equivalence:

Suppose I know everything about your brain of a neural kind [...] I even know that position of every atom and its subatomic structure. [...]

There's the first fallacy on such affirmation: knowledge does not work such way.

It is enough to answer "can a human know everything about a physical thing?", and the answer is a categorical no.

In order to know a river, a person would need to know not only everything about every atom and quark of the river, which implies the knowledge of the chain of causal processes that leaded all the parts of a river to become such thing (such chain is precisely Hawking's information); it implies a perfect delimitation of all the "parts" of the river excluding the rest of nature, or else, the entire universe in all its possible states would be required to be known. Now, think about knowing not a river, but a tiny piece of sand. The problem comes to be exactly the same.

The universe (or a brain) can be defined for this issue as a massive and fuzzy, huge, humongous energetic interaction, while knowledge is a tiny set of pictures of some states of some insignificant sections of it.

[...] Do I thereby know everything about your mind? It certainly seems not. On the contrary, I know nothing about your mind [...]

After assessing the meaning of knowledge, and assuming that such kind of knowledge would be possible (implying we're kind of gods), there's a second fallacy: the author is denying the possibility of knowing the mind after knowing the brain. The right answer is still unknown. We don't know if it's possible. Even assuming that such kind of knowledge is possible, the answer could be yes or no.

Even if my dog would have voted Trump, you cannot conclude whether I'm a democrat or not. We don't share several political views.

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