This question is similar to (and following on from) but significantly different from this question: Who, if anyone did say it, was the first to say that because no qualia exist it is meaningless to say what I call "red" could be what you call "blue"?.

There's a famous question that asks whether two people who agree that they are seeing a red object might be seeing (in their respective subjective experiences) different colors. For example, one is seeing the object as red in his private experience and the other is seeing it as blue in his private experience. The idea is that the one who is seeing what the other would call "blue", calls what he sees "red", because he always has done, having been told all his life that this color is called "red". And vice versa: I don't think the idea/question assumes that there is one correct blue or red. It's just that the subjective experiences could be completely different while the stimulus and the utterances are identical. It's a very widely known question/idea even among nonphilosophers.

If I understand Keith Frankish and his consciousness illusionism correctly, he is saying or implying that it doesn't mean anything to ask that, because there is no such thing as a quale. And I am under the impression that Dan Dennett and his heterophenomenology (HP) said or implied something similar, decades before Frankish did.

If I understand HP correctly, it says that subjective impressions are not data, but hypotheseses. Thus qualia do not exist and/or are incoherent concepts, say Dennett and Frankish. The difference in the "experience of color" is a difference between qualia in the example given above, and therefore is meaningless or incoherent according to HP.

But I am not sure whether I have understood Frankish ("An Illusionist Manifesto" https://www.keithfrankish.com/presentations/an-illusionist-manifesto/ and "Lecture 1: The Illusionist Option" https://www.youtube.com/watch?v=Y2n-s6C1iYQ&list=PLhgvALi0LQGXIA7cKNmGNTiQ7dpS-7dLw) and Dennett ("The illusion of consciousness | Dan Dennett" https://www.youtube.com/watch?v=fjbWr3ODbAo and "Daniel Dennett - Consciousness, Qualia and the "Hard Problem": https://www.youtube.com/watch?v=eSaEjLZIDqc&t=101s) correctly.

So my question is whether it is true that if qualia don't exist,this subjective color question is meaningless. In other words, does it logically follow that it's meaningless to ask whether the red you see is different from the red I see, if qualia don't exist?

In very valuable comments on the question that this question follows on from Conifold wrote, "A common view is that the question does not make sense even if qualia do exist. The whole point of them is that they are accessible to the subject only, but to ask the question one needs to "objectify" them so that different subject can "import" other's qualia to compare and contrast them with theirs, as if they were just another object. The conception behind the question is thereby incoherent. The idea that things have strictly non-relational "qualities", which, by definition, cannot be shared and hence compared, goes back at least to Kant, if not scholastics. There is a version of the question which is more meaningful, it involves the same subject experiencing inversion of the spectrum (so the color qualia of tomatoes and cucumbers swap places, for example). That one goes back to Malebranche and Locke, but logical positivists (e.g. Schlick in 1932) once dismissed it as meaningless [...] based on their verificationism, see SEP, Inverted Qualia. However, verificationism is out of fashion nowadays."

Reading up on Schlick I found out that Schlick was murdered by a former student just four years after he made this claim, and possibly as a result of making it: the student claimed he murdered Schlick because of what the latter had taught him.

Marxos also made a comment that I suspect would be very useful to anyone with access to a library: "Look at Daniel Dennett in Consciousness Explained. He goes into the issue in detail."

To clarify, in light of the comment by sdenham: "I feel that adding ‘alleged’ to the question makes it almost meaningless (the answer is, trivially, ‘no’.) If it is merely alleged that a person has committed a murder, we cannot conclude they have killed someone." the question is saying that it has been alleged that qualia don't exist, and asking whether, if the allegation is correct, that would imply that it is meaningless to say that what I call "red" could be what you call "blue".

  • 2
    At the beginning you need to answer following key questions: identify what is qualia? how do you understand what is qualia? why you need qualia? and how does qualia work? When you ll able to give this definitions all other questions will be clear. Apr 28, 2023 at 15:53
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    Knowledge is a model of the world, and it is essentially a structure of qualia, ERGO-1: qualia do exist subjectively... what would not? Everything exists subjectively before becoming objective; ERGO-2: since qualia is loaded with meaning, signification, indication of, qualia is meaningful (not meaningless).
    – RodolfoAP
    Apr 30, 2023 at 3:20
  • the colors of the visible spectrum - red, blue, etc., has been proven by science to be perceived the same by all humans. Apr 30, 2023 at 9:00
  • @SwamiVishwananda Really? I didn't know that. Do you have a citation? May 1, 2023 at 0:13
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    @RodolfoAP I added "alleged" to the title to make the meaning of the question clearer. The OP does not say qualia don't exist. It asks about what if they didn't exist. By the way, what makes you so sure qualia exist? May 1, 2023 at 0:35

2 Answers 2


No, regardless of what theories any philosopher might put forward to explain our sense impressions- whether you consider them to be illusions, hypotheses, qualia, incoherent concepts etc- the fact remains that we experience them, and my experience of them might differ from yours, in that what I experience as 'red' is what you experience as 'blue'. If someone thinks they are illusions, the the question becomes 'might my illusion of red be your illusion of blue?'. If someone consider them to be incoherent conceptual hypotheses, the question becomes 'might my incoherent conceptual hypothesis of red be your incoherent conceptual hypothesis of blue?'. And so on.

What you cannot expect, yet, is a definitive answer to such questions, as we have no way of comparing our respective sense experiences first hand- I cannot see your blue, for example. Arguments can be made that sense experiences should be broadly similar. Humans have evolved as a species and are biologically similar, so you might expect that a function- such as the interpretation of colour- works in one human pretty much as it does in another. Some theories of evolution suggest that plants have evolved to have flowers of certain colours because those colours attract certain insects- that might be hard to explain if insects did not process colours in a reasonably standard way.

If someone dismisses that famous question as meaningless because it cannot be answered, then to be consistent they should write off much of philosophy as meaningless on the same basis.

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    I definitely agree with your last sentence.
    – Scott Rowe
    Apr 29, 2023 at 21:49
  • Solipsism solves the problem in the first paragraph (there is no “your”), but no one believes in Solipsism anyway. May 31, 2023 at 5:38
  • I suggest you add "think" to your first sentence, reading "the fact remains we think we experience them". Dennett and the delusionists deny that we actually experience, but they agree that we THINK we experience.
    – Dcleve
    May 31, 2023 at 16:47
  • Even if we accept the proposition that hypotheses not containing qualia must nevertheless have some component that is subject to the same arguments for qualia-inversion as are made under the assumption that there are qualia, it remains an open question whether it makes sense to speak of qualia-inverting scenarios even under the assumption that there are qualia... The points made by @conifold (as quoted in the question) raise considerable doubts as to whether this is so, especially in the case of inter-personal qualia inversion, which is the sort being asked about here.
    – A Raybould
    May 31, 2023 at 18:39
  • @Dcleve I defy you to define a meaningful difference between experiencing qualia and thinking you experience qualia. (In the best possible spirit!) May 31, 2023 at 21:21

Since I don't understand what qualia are and have found myself unable to carry out the thought-experiment that is supposed to establish their existence, I can only comment on this:- "The idea is that the one who is seeing what the other would call "blue", calls what he sees "red", because he always has done, having been told all his life that this colour is called "red"."

The account of this possibility presents the problem as if it were "What if I am introduced to Bill and told that his name is Fred and introduced to Fred and told that his name is Bill, I will call Bill Fred and Fred Bill." Clearly, it would not be long before someone put me right.

The idea you are talking about treat the colours as if they were independently existing entities, in the way that Fred and Bill are independently existing entities. But the colours are inter-related. So if I were to learn to apply "blue" where everyone else applies "red", it could be discovered in the way that colour-blindness or that the fact that dogs do not see the colour spectrum in the same way that humans do is discovered.

The colour wheel (and the tests for colour blindness) show that the colours are inter-related in systematic ways. It simply isn't credible to suppose that two colours could be swopped (or the prism inverted) without disturbing those inter-relationships. To describe a credible example, you would have to describe it in such a way that those inter-relationships were not disturbed. I very much doubt that that's possible.

See Colour vision deficiency (colour blindness) - NHS (www.nhs.uk)

I'm tempted to suggest an example of the test so that you can see what's involved. But there are health issues involved, so I must leave you to a search and your own judgement.

For a systematic representation of the inter-relationships of the colours see Color wheel - Wikipedia

For colour vision in dogs, see Are Dogs Color Blind? Examples of Dog Color Vision | PetMD

  • "I'm tempted to suggest an example of the test so that you can see what's involved. But there are health issues involved, so I must leave you to a search and your own judgement." I'm afraid I don't follow. May 31, 2023 at 16:06
  • I'm sorry I wasn't clear. I mean the test for colour vision deficiency.
    – Ludwig V
    May 31, 2023 at 16:10
  • This answer presumes direct realism, that the sensation detected by the light sensors of the eyes (which is what is tested for in the color testing) is identical to the qualia experience in the mind. This direct realism is thoroughly refuted by consciousness testing, which shows that our mind experiences manufactured hypotheses assembled by our subconscious. The best single summary I have seen of this data is in Incognito: goodreads.com/book/show/9827912-incognito Dennett and the delusionists take this data further, to DENY we have a mind or self.
    – Dcleve
    May 31, 2023 at 16:44
  • @LudwigV What do you mean by "health issues" and how does your conclusion follow from their existence? May 31, 2023 at 19:27
  • @Matthew Christopher Bartsh. I'm sorry if I seem obscure. Colour blindness is a health issue and testing for it is the diagnosis of a health condition. The internet is so unreliable that I think it would be foolish for someone unqualified to recommend a test. That's all. My conclusion is that the colours are systematically inter-related and the hypothesis that two of them can be swopped without it showing up in some way is simplistic.
    – Ludwig V
    May 31, 2023 at 20:13

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