Physicalists are people who equate brain states with mental states. There are people in this category; and yet there are many people who do not hold this view. Such people hold that there is an ontological difference between phenomenological experience and the physical firing of neurons one's brain. Prima facie, this seems to be a reasonable statement; after all, how could the firing of neurons be the same as the taste of an exquisite wine or the beauty of a dazzling sunset? This claim that there is a difference between "mental" states and brain (physical) states seems problematic to me after reflecting on it further.

It occurred to me that in order to make such a claim, one would have to know what both feel like. In other words, I can only distinguish between A and B if I know what A and B are. Just think about that for a moment.

Imagine a person asked you to compare an object, say, a banana, to another object, but he didn't tell you what the second object was. How could you begin to make any claims about the difference between the two objects? You couldn't.

Both sides agree in that all we get in our minds is one thing: phenomenological experience. They differ in that physicalists equate mental states (phenomenological experience) to brain states (physical firing of neurons), whereas proponents of a distinction suggest they are not the same—that there is something intrinsically different between the two. They acknowledge that although mental states may originate in the brain, the end "result" of what appears before our minds is categorically different than the mere firing of neurons; some extra "step" or translation process occurred that changed the mere firing of neurons to the phenomenological experience we receive. However, as I noted above, it doesn't seem possible that someone could make any claim about the inherent qualitative difference between phenomenological experience and the firing of neurons if they've only experienced one of those things. They could only know that the firing of neurons is ontologically distinct from phenomenological experience if they've experienced both, which they don't.

It seems to me that this is a fairly glaring hole in the reasoning of those who believe there is a distinction between the two. Is there some way to remedy this setback? Ideas and/or links to arguments or literature which discusses this would be particularly helpful.

  • So is the question then: what is the difference between neuronal activation and subjective experience of the world? Maybe you could clarify this a bit?
    – Joseph Weissman
    Aug 15, 2011 at 17:02
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    @Joseph - Actually, the nature of the difference is outside the scope of the question. Really, all I'm asking is how someone can claim to know that there is a difference, given that experience occurs through either one or the other (qualia or neuronal firing), but not both. If someone can prove to me that there is a difference, then we'll get to what that difference is. :)
    – stoicfury
    Aug 15, 2011 at 17:36
  • So closer to asking whether the notion of qualia itself is coherent?
    – Joseph Weissman
    Aug 15, 2011 at 18:14
  • Erwin Schrodinger wrote that '[t]he sensation of colour cannot be accounted for by the physicist's objective picture of light-waves. Could the physiologist account for it, if he had fuller knowledge than he has of the processes in the retina and the nervous processes set up by them in the optical nerve bundles and in the brain? I do not think so.'
    – Joseph Weissman
    Aug 15, 2011 at 18:24
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    @Joseph - Yes, I'm concerned with external consistency though as opposed to internal consistency. I.E. whether it's coherent given our understanding of phenomenology and psychology, as opposed to whether it's innately coherent as a concept by itself.
    – stoicfury
    Aug 16, 2011 at 15:03

5 Answers 5


First of all, I have to disagree with your premise. You write:

Proponents of the philosophical concept of qualia {WP}{SEP} suggest, by definition, that brain states do not equal mental states.

That's not strictly speaking true. There is nothing to prevent a physicalist from making use of the notion of qualia; it is just that for the physicalist, qualia are reducible to physical entities. Everyone accepts that there is a phenomenal experience of seeing the color blue; the question is: is this experience reducible to neurons firing?

As you point out, there is no rigorous way to distinguish between the two-- we currently have no way to experience the color blue without neurons firing, nor do we have a way to have those neurons firing without seeing the color blue. But, the fact that the two seem to always occur together (with a Humean regularity) does not permit us to attribute causality; we don't know if the phenomenal experience is epiphenomenal to the neurons firing, or if the neurons firing are epiphenomenal to the phenomenal experience.

So, the problem that you raise is not a problem with qualia (or purely a problem for those who hold that qualia are irreducible to physical states); the same problem faces the physicalist. The reducibility of qualia to physical states likewise depends upon an ability to separate the two and declare one primary and the other epiphenomenal.

  • Well no, maybe I wrote unclearly but I think that everyone accepts that there is something it is like to taste wine or see a sunset. I'm not denying that experience. I'm simply pointing out that trying to suggest that there is a difference between qualia and something we already have evidence of (brains) is irrational. Physicalists don't infer causality because we're not saying A causes B—we're saying A is B. Brains states are mental states, they do not give rise to them.
    – stoicfury
    Aug 16, 2011 at 22:49
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    And the corresponding question for the physicalist is: what makes you think that A is B, when we only experience B? Aug 17, 2011 at 6:50
  • Because physical trauma to the brain alters our phenomenological experience. The question is whether it directly alters our experience, or it alters something which in turn alters our experience. However, parsimony tells us to accept the hypothesis that makes the least assumptions and thus it is only rational to accept the direct relationship, even if it can't necessarily be "proven" true. If you suggest it's OK to accept that trauma affects something which then affects our experience, then you also have to equally accept an infinite chain of possibly affected systems, which is bold...
    – stoicfury
    Aug 18, 2011 at 2:50
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    In retrospect, what I should have said is not that A is B, but rather, there is only A. I.E., "A is A"....
    – stoicfury
    Sep 5, 2012 at 23:55

Your reasoning is assuming that neurons firing have something to do with perception. Dualists reject this, and put forth philsophical zombie arguments as demonstrations that there could, in principle anyway, be a distinction between neuronal firing and conscious perception. (It is an argument from incredulity at its heart, but absent a proof of identity of neuronal firing and conscious perception, it does at least raise the possibility in a way that is not absolutely refutable.)

That said, as we find out more and more about the relationship between neural activity and consciousness, philosophical zombies (thus far) look more and more like Descartes' demon--a possibility, in some sense, but not really worthy of serious consideration given how various mental disorders can have direct, specific, and bizarre impacts on consciousness. Oliver Sacks and V.S. Ramachandran have written particularly accessible books detailing some of these conditions.

So, although there could be a demon generating various entirely virtual sense experiences for us (if we don't worry too much about what we mean by "real" and "virtual"), and there could be a philosophical zombie (if we don't worry too much about how you know whether a zombie does or does not experience something), the evidence isn't consistent with these being likely possibilities. Thus, there are either no demons or possible-zombies, or they are doing an astoundingly good job.


I'm not terribly well versed in challenges to the coherence of qualia, so forgive me if my objection seems obtuse: aren't you constructing a bit of a straw man here? I was always under the impression that everyone agrees that our brain states are at best necessary for qualia to be had at all. The disagreement by dualists has always been that neuronal activity is insufficient.

The kind of objections you mentioned about the taste of wine, etc. is not about the qualitative difference of experiencing one's c-fibres firing and the quale it's processing, but instead derived from the assumption that neural firings in general are a kind of automation. From Cog Sci (Kahneman, D. LaBerge) we know that automaticity is the opposite of attention. Attentive experience is precisely the kind of notion most dualists appear to have in mind when they're seeking to explain qualia-laden consciousness, so it seems uncharitable to think that they'd make such an incoherent statement as "the quality of this activity which can provide experience and the quality of the contents of experience are ontologically different because they give rise to different experiences."

To take your example above, the dualist doesn't need to provide any difference between the banana and the unkowm object, because there's less of a likelihood that the unknown object is identical with the banana than that it's different - and all the more so when you want to discuss their ontological equivalence! A person proposing that they're the same is the one who has the untenable position here.

So I don't have much to supply in additional materials, other than Giulio Tononi's account of qualia as arising from the difference in information entropy which neural states can provide. If nothing else, it should prove an interesting read.

  • I phrased the question in a way which may have caused some confusion. I think you properly answered my question as I meant it though, although I disagree. I don't see how mounds of empirical evidence that changes in the brain causes changes in mental states (and thus why we say they brain states are mental states) is on an even footing with the claim that they are not the same. If you rely on statistics (See your 2nd to last paragraph) then the physicalist wins hands down...
    – stoicfury
    Sep 6, 2012 at 0:04

We can support the idea of qualia being distinct from neuronal firing due to the differences in the descriptions of each. When we use the term "qualia", we are referring to subjectively experienced phenomena; however when we use the phrase "neuronal firing" we are referring to a concept with certain known qualities, foremost being that it is a facet of objective reality and not anything that requires subjective experience.

Your example with the banana is flawed simply because we have been told what the "second object" is: some objective process. Because the conceptual construction of each thing being discussed is different - subjective for one, objective for the other - and more so are described specifically as having opposite natures of a duality (subjective/objective), they are distinct by definition.

Now it may very well be the case that both concepts are flawed, and that neither truly exists ontologically speaking. However the question as stated presents two concepts which are fairly well understood, and which distinguish themselves from the other inherently.


We may start broadly with the appearance versus reality distinction. In the case of the Solar Eclipse it appears that the moon covers the sun. Through empirical science we have discovered the reality, which is that the sun is 400 times the size of the moon and 400 times as far away, thus we have the appearance of equal size. Scientific reduction seems to follow this pattern of taking the appearance and reducing it to the reality.

However this assumes that the appearance is different than the reality. The problem for qualia now become apparent. If science reduces appearances(or we may call them qualia) to something in reality, how can that reality be the very appearance. It seems like a category mistake.

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    I'm confused about this answer. Could you elaborate on the last part? I think I understand your analogy, although the math is way off (the Sun is 160,248.74 times bigger than the Moon!) so I presume you were just plugging in random numbers and emphasizing the relationship difference. But then I get confused at the second to last sentence. Thanks.
    – stoicfury
    Aug 16, 2011 at 23:06
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    400x400 = 160,000 - one number compares surface area, the other compares diameter/radius
    – Lucas
    May 12, 2014 at 3:52

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