The Meaning of ‘Red’ (and Wittgenstein’s Private Language Argument)

I recently posted a question on my Facebook page (Marianne Talbot Philosophy – come and join us!) which triggered a lot of discussion. This was the question:

Pillar box

Pillar box

Pillar boxes in the UK are red. So are strawberries and tomatoes. We can all agree on this. So we agree on what the word ‘red’ applies to.

But it is possible (logically at least) that when you and I look at UK pillar boxes, strawberries and tomatoes we have experiences with different quale. What does this tell us about the meaning of ‘red’?

I was immediately asked what ‘quale’ means. Good question.

‘Quale’ is the singular of ‘qualia’. Qualia are the ‘raw feels’ of experiential states. Experiential states are states of the sort that there is something it is like to have them. So having toothache, experiencing red, being in love or feeling jealous are all experiential states; there is something it is like to experience all of them.

Experiential states are distinguished from propositional attitudes.

Marmite Jar

Marmite Jar

Propositional attitudes are all attitudes to contents constituted of propositions (very roughly – meaningful sentences). So believing the chair is comfortable, intending to make a cup of coffee, or wanting to eat a marmite sandwich are all attitudes (of, respectively belief, intention and desire) to propositional contents (respectively ‘the chair is comfortable’, ‘I will make a cup of coffee’ and ‘I eat a marmite sandwich’)

All mental states involve some combination (or at least one) of these two state-types.

Experiential states are individuated by qualia – by what it is like to have them. (To ‘individuate’ a state is to classify it and distinguish it from other state-types.) Unless we are colour-blind we all know that what it is like to experience red differs markedly from what it is like to experience green. If we have ever been in love we know that it is common simultaneously to feel jealous. We also know that the former is a wonderful feeling, the latter is awful, and the combination is excruciating.

Qualia are central to the notion of consciousness. (So are propositional attitudes but perhaps not so obviously).

So my question was a way of asking whether the word ‘red’ refers to the quale we experience when we call pillar boxes, strawberries and tomatoes ‘red’.



The fact that we use the same colour-word for pillar boxes, strawberries and tomatoes suggests we believe them to be the same colour. (This is a rough classification – we all know that red shades into other colours – in answering philosophical questions we must resist red herrings).

The fact we recognize that we might all experience different qualia when looking at pillar boxes, strawberries and tomatoes tells us that the word ‘red’ cannot refer to the quale we experience when we look at pillar boxes, strawberries and tomatoes.

Green tomatoes

Green tomatoes

Think about it: we accept that these things are the same colour, and linguistically we act on this by applying to these things the same colour word – ‘red’. Yet we also accept that we might not experience the same quale when we look at these things. Perhaps when YOU look at pillar boxes, strawberries and tomatoes YOU experience what I experience when I look at grass, summer leaves and unripe tomatoes? (This may not be an empirical possibility, but it is certainly a logical possibility – it is another red herring to suggest this isn’t really possible).

So the colour word ‘red’ cannot apply to the quale.



Wittgenstein’s ‘private language argument’ deals with this problem. A quale is something intrinsically private. You cannot, even in principle, share your private conscious experiences with other people. I know what you are experiencing only through your language (or your other behavior). How can the word ‘red’, or indeed any other word, apply to something that cannot, even in principle, be known?

If ‘red’ applied to a quale it could not, even in principle, be taught. The teacher would never be able to tell whether or not the pupil was learning (because the pupil wouldn’t know for which quale the teacher was using the word, and the teacher couldn’t check the pupil was using it for the right quale).

If ‘red’ applied to a quale we could not, even in principle, communicate by means of it (because communication requires knowledge of same meaning and if ‘red referred to a quale we couldn’t know whether we meant the same by ‘red’).

So by ‘red’ we do not mean the experience we have when we look at pillar boxes, strawberries and tomatoes.

But we also don’t mean the wavelength of light reflected by an object – in the case of ‘red’ 650 nanometres. Can anyone tell me why?

About Marianne

Marianne is Director of Studies in Philosophy at Oxford University's Department for Continuing Education
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37 Responses to The Meaning of ‘Red’ (and Wittgenstein’s Private Language Argument)

  1. The argument seems to be valid so long as you know nothing about biological, genetic, and cognitive science – but the more that you do know, the smaller becomes the area in which distinctive (personal) experiences might hide. There are some colours (esp in the blue/green area) where we know of genetic and biological differences – and it’s in this same area that we find disagreements about the colour of objects.
    Now there are qualia that aren’t (or are only badly) communicated because our language is impoverished without an external reference. Offer an external reference* and the communication can commence and the private language becomes public.

    *eg control over the ‘lie detector’ response given sight of the electronic readings.

    • Marianne says:

      The private language does indeed become public once there is an external reference. Without an external reference it is essentially private and cannot, therefore, be a language.

      The argument does not turn at all on empirical findings. Or are you suggesting that science will discover that we do not have qualia? there are some philosophers (Michael The for example)who think precisely this. I’m not unsympathetic to this view, but also sympathise with Russell who said no-one could convince him that qualia don’t exist.

  2. Mark Matchen says:

    I don’t follow. First, if something is logically possible but empirically impossible, what is gained by pursuing it, other than philosophical gamesmanship?

    More critically, when you say the colour ‘red’ CANNOT apply to the quale, it doesn’t seem to me you’ve proven that. If we all are receiving the 650 nm wavelength, and we all (barring colour blindness, etc.) are processing it in the same way (such that most everyone feels the same effect of colour pairings) then it’s entirely possible that the quale of red is the same for all. And the way we can know what the other means by that quale is that the other says, “I see red”. (I don’t think I’m being circular.) More subjectively, if redness tends to inspire alarm or excitement (though not universally) then we can understand the other’s quale when he says so.

    I grant that some qualia may not be communicable, but I don’t think we can say none are, especially when they are so tightly coupled with physiological responses.

    • Marianne says:

      We have (roughly) two ways of acquiring knowledge. Science acquires knowledge by empirical means. Mathematics and philosophy acquire knowledge by logical means. If you think the laws of nature could have been other than they are (you might not) then you admit that there are logical laws that differ from (and given) the laws of nature. once you admit logical laws, then you admit logical possibility and impossibility.

      What is gained by pursuing it? Knowledge!

      The point is that we CANNOT know the quale is the same for each of us. But we do know the meaning is the same for each of us. Therefore the meaning cannot be the quake. It is indeed possible the quake is the same for each of us. But that isn’t enough. It is also possible it differs for each of us. That’s what makes its intrinsic nature irrelevant – we must HAVE a quale, but which quale we have doesn’t matter.

      • Ruben says:

        in Philisophical Investigation how can we connect in paragraph 378 language and the color red? and what does this paragraph signify?

      • Marianne says:

        Dear Ruben,

        The passage is an extension of the famous ‘Private Language argument’. Wittgenstein is arguing that the meaning of the word ‘red’ cannot be the subjective experience each of us has when looking at (e.g.) a ripe strawberry. This is because such a meaning cannot be taught, and cannot be communicated. You have no idea whatsoever what my subjective experience is when I look at a ripe strawberry, nor do you have any idea whether my experience is the same as yours. I cannot teach you the meaning of the word ‘red’ by pointing to my private experience because this experience is essentially private, nor could I possibly be sure, if you use the word ‘red’ to mean your subjective experience, and I do the same, that we mean the same by the word ‘red’ – because neither of us has any idea whether our experiences are the same.

        The meaning of the word ‘red’ must therefore be public – so long as we both classify ripe strawberries together with ripe tomatoes and British postboxes as the same colour, we know we mean the same by our word.

        Hope that helps.


  3. Bob Stone says:

    When I say ‘red’, it may be that I DO mean the colour that I experience as red. Not, that is, the experience in itself, or some characteristic of it, just the colour of the object that appears to be causing the experience. If I were teaching a child to name the colours, I suppose I would be teaching her to call ‘red’ the colour that I call ‘red’ – regardless of what experience she is having. (I would just hope that she did in fact have the same experience, whatever it was, every time she looked at what appears to me the same colour.)

    If I had to teach a machine what to call ‘red’, then I might define it according to the wavelength.

    Thought experiment. I have a strange experience when eating strawberries and watching cricket on TV at the same time. I can’t describe it, and so can’t communicate its nature to anyone else. But I recognise it when it occurs, have my own word for it (which I do not divulge), and use that word in my head when thinking about it. I could invent many such words for strange experiences, and they would constitute a private language. Well, more accurately, a private vocabulary. Wouldn’t they?

    • Marianne says:

      Hi Bob,

      Yes, if we communicate with ‘red’ as we clearly do, it must be the colour of an object we refer to, not the quality of our experience of the object. You are right to say that if you were teaching a child to name the colours, you would be teaching her to call ‘red’ the colour that you call ‘red’ – regardless of what experience she is having. The experience she is having is irrelevant.

      A private language is a language that COULDN’T even in principle be shared. Not one that isn’t in fact shared.


  4. Kris says:

    I may have a quick answer to this… Maybe it’s all a matter of agreement, just as a language itself is. We can know for instance that ‘red’ (light) has a wavelenght between these and these values and that it is just a matter of measuring it, to know. This sounds a bit mechanical or reductionistic perhaps… but isn’t it the way Wittgenstein refers to this (‘use’ vs. ‘meaning’)?
    Also Descartes tells us how we can doubt our senses and how other methods can reassure us again. Do we have to doubt our eyes if we’re thinking about ‘red’ or do we have to doubt even more and let the demon be the one that’s making us believe we’re seeing red?..But in doubting, I can reassure myself (and asking a scientist perhaps).

    • Marianne says:

      Yes, we do indeed know that we call an object ‘red’ when it reflects light at 650 nanometers.It is unlikely though that this is the meaning of ‘red’ unless the meaning of ‘red’ changed when science discovered this (and we might prefer to think of this as learning something about redness, rather than as changing the meaning of ‘red’).

      But you are right to think that ‘use’ comes into the meaning of the word ‘red’.

      If you are engaging in Cartesian doubt scientists can’t help you. Neither can anyone else. Not if you are engaged properly in doubt.

  5. Nick Whitsun-Jones says:

    Q. But we also don’t mean the wavelength of light reflected by an object – in the case of ‘red’ 650 nanometres. Can anyone tell me why?
    A. Presumably because the wavelength of light is a physical state independent from and external to the human body and it is the latter that is experiencing the particular quale.

    • Marianne says:

      You are quite right that the answer to my question is to do with the fact that the wavelength of light reflected is independent of human beings. Colour seems essentially to involve an experiential state. Colour may not be the wholly subjective state that is the quake. But nor is it the wholly objective state that is the wavelength. Colour has to be a combination of the two. In fact the accepted account of the meaning of the word ‘red’ is: an object is red if and only if it appears red to normal human beings in normal circumstances.

      ‘Normal human beings’ rules out people who are blind or colour blind (no object appears unproblematically red to either)
      ‘Normal circumstances’ rules out lights behind red cellophane
      ‘appears red’ makes the definition sound circular, but the circle is benign – because to appear red and to be red are different things, and the ‘appears’ introduces the inescapably subjective element.
      That it is an object that appears red to normal human beings under normal circa,stances brings in the wavelength of light reflected from the object (and the objective element).

      How is that?

      • Nick Whitsun-Jones says:

        So the quale in seeing red (whether it be a pillar box or a tomato) is part of the experiential state that the individual ‘seeing’ is experiencing, but the light wavelength is not part of that state and a constituent part of the quale until the light is received and internalised in the body by the eye?

      • Marianne says:

        The quale of an experiential state is the experience you consciously have. So there is one quale when you experience redness and another when you experience green.The light wavelength causes the experience the subject is having.

      • nickwhitsunjones says:

        Thanks for a clear answer Marianne. So if I take, say, LSD and see many colours when viewing a red object, the LSD would be causative as well as and independent from the light wavelength but there would be one quale of seeing red as corrupted by the LSD drug? Or is the LSD experiential state a quale in its own right distinct from that of seeing red uncorrupted? As lawyers say, the LSD being a novus actus interveniens (new act coming in between) between the cause and the result of the chain of events that started with the light wavelength emanating from the red source? Or perhaps the LSD would offend the “normal circumstances” bit of the accepted definition of red that you mentioned earlier,so that what the individual was seeing after taking LSD could not be described as properly ‘red’?

      • Marianne says:

        You can quite easily experience redness without there being a red object that is causing your experience. Any sort of hallucination will do. Or you might be seeing something white by a light that is covered in red cellophane.

        Think about the definition: ‘an object is red if it appear red to a normal person in normal circumstances’. This allows for an object’s appearing, but not being red, and for an object’s being red, but not appearing red.

      • Nick Whitsun-Jones says:

        Sorry Marianne, I should have said thank you for your reply and also what a great site this is, a real brain teaser! I will be listening to your lectures soon. The problem now is finding the time to seriously study both history and philosophy. But better than being bored!

      • Marianne says:

        Glad you like the site Nick. Far better to be busy than bored!

  6. Shamus Mac says:

    Your difficulty arises in the attempt to define experience in specific terms. A quale is being considered precisely this: A quanta of qualia. That’s a strange concept, in practice.

    The meaning of “red” is … an approximation of a quale.

    In fact, your true encounter of a quale is not able to be neatly sliced, even to 653 subjective nanometers for you and 657 subjective nanometers for me, on the same surface and from the same angle, twice. Except, of course, under the sorts of extremely controlled conditions in which too many pretend reality occurs.

    Splitting perception into phases of (subjectively measurable) quanta is not the most productive method of inquiry. Applying reductionism to the study of subjective experience should only have been attempted if it had not proven self-contradictory elsewhere (yes, the first mover chestnut ;).

    • Marianne says:

      My difficulty?! You don’t see a difficulty? A quanta of quake? not sure what you mean. There are types of qualia (the experience we assume we both have when we have a toothache). then there is a token quake – the quake you have, and that I have.

      What is an approximation of a quake? Something LIKE a quake?

      I was not reducing subjective experience, in fact my argument was that we cannot reduce subjective experience to wavelength.

  7. Jörgen Tang Larsen says:

    I triggered at this: “You cannot, even in principle, share your private conscious experiences with other people.”.
    It seems to me that ones private experience of 650 nm electromagnetic wave-emitting objects (for example a red light at a roadcrossing) may in principle not be possible to relate to others by direct speech or other communication. But it will not be a very long lived communication problem unless we all in a fairly quick manner by darwinianesque biological responses ( for example by depressing the brake pedal) agree on a common interpretation.
    I am saying that we by “red” mean not the experience but the phyical/biological effect of our experience.
    I see red.
    I stop.
    I stopped and my genes and memes go on and on and on…

    …I may be wrong, eventually.

    • Marianne says:

      Hi Jörgen,

      it is clear that we can communicate the fact that we have seen the red light at the road crossing. But you are not quite (I think) understanding the problem. When you see the red light, you have an experience of a certain kind – it is the experience you have that prompts you to say that the experience is that of a red light. But you cannot communicate the quality of the experience you have. It is possible that when I see the same red light, my experience is quite different from yours (perhaps I see what you see when you look at objects you would call ‘yellow’).

      It’s the inability to communicate this that makes a bit of a mystery as to the meaning of ‘red’ – so many of us would say ‘red’ refers to that essentially private experience.


    • Marianne says:

      Jörgen, I think I might have got you wrong. Yes, when we say ‘red object’ we mean that the object will appear red to normal observers under normal circumstances. But I can’t see what you think the problem is. Or perhaps you don’t think there is a problem?

      • Jörgen Tang Larsen says:

        Interestingly, you ask: “what do you think the problem is” ( I paraphrase you). I was perversely not accepting that there is a problem, or less acutely; not recognizing that there is one.
        I restate your question (singularily for my own fulcrumitudelessness)

        “So by ‘red’ we do not mean the experience we have when we look at pillar boxes, strawberries and tomatoes.

        But we also don’t mean the wavelength of light reflected by an object – in the case of ‘red’ 650 nanometres. Can anyone tell me why?”

        Maybe it has something to do with that “red” is a Word, part of language, therefore part of our common interpretation of experience. Experience is not common but always private.So the Word “red” is not part of of our precommunicate brains but more a part our interpretation of our “biological” response to 650 nm light hitting our individual retinas.
        Thus it is impossible to name things experienced, because the Word has to be born out of experience before it can be used to name the experience…hey maybe it’s all a bit of Strange Loop?(Hofstadter).

        But, hey, somewhere around the Circuit I don’t really see a problem. Things work, eh?

      • Marianne says:

        “fulcrumitudelessness” Wow!

        I agree with you that the problem is dissolved once we see that we use language to refer to the common objects (etc.) around us. It is only a problem when we insist either that ‘red’ refers to the private experience we have when we look at red objects, or to the wavelength of light reflected by red objects.

        The former is a problem for all the reasons to do with ‘private’ languages – ie. i.e. ‘languages that are supposedly essentially private and therefore not possible.

        The latter is a problem because colour concepts link essentially too subjective experiences.

        But language, as you say, are able to negotiate the schylla and Charybdis of these problems and come out triumphant: with proper understanding problems are dissolved!

  8. Jörgen Tang Larsen says:

    one where to substitute the word “red” with the word “God” in the present argumentation it would yield some fascinating products, I venture..
    It is, on the one side, the quale-side, very recognisable, that the experiential state of “God”, is, of course, entirely personal and utterly impossible to explain to anyone outside the experiencing brain.
    On the other side, the “650 nm -side”, or perhaps the “Dawkins-side”, (sorry, Richard), we would find something, …ehm, maybe a green teapot zipping around the globe at a million miles an hour? But this green tea-pot is certainly NOT what one would mean by the Word “God”.

    … we invented the word “red” because we needed it for our common use as shurely as we invented the word “God” for the same reason. Neither word is less valid. They’re part of OUR language.(this, however, doesn’t necessarily mean that we will eventually discover the equivalent of the green tea-pot as we have at one time discovered wavelengths of light).


    • Marianne says:

      I am not sure that an experience of God is a simple qualitative experience in a way the experience of ‘red’ is. For a start a huge number of beliefs must be involved. I think that most people who believe in God would not claim to have an experience of God that could be captured in images.

      We invent many words the meaning of which cannot be explained by ostensive definition (by pointing). We need the words, but have to explain their meanings in terms of other words.

      ‘God’ is like this, but ‘red’ isn’t.

      But perhaps you disagree?


      • Jörgen says:

        I may have had a wrong turn, on the way to the forum, in that I decided that all words have qualia in the sense that we experience something as reactions to them. That’s probably a bit too inclusive.

      • Marianne says:

        It IS too inclusive. There are many words that we wouldn’t normally associate with qualia. A quale is a ‘raw feel’, an experience with a certain distinctive quality. Mental states fall into two categories: qualitative states (those with qualia), and propositional attitudes (attitudes like belief, desire, intention, to propositional contents. So my belief [my computer is in front of me], my desire [the day be sunny], my intention [that a cup of coffee be made] are all propositional attitudes that may or may not be associated with qualia).


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  10. Karel Konečný says:

    If I remember correctly from school, my concept for red was the wavelength of light that the object absorbs. So I can’t know for sure if some people see the object in the same color as me. So when someone says that an object is red, I can’t be sure that I will have the same perception. So I have no experience looking at pillar boxes for the word red.

    • Marianne says:

      You were told, probably, that red is the wavelength of light. But actually it can’t be because there is also an irreducibly subjective element – an experience that is an ineliminable part of redness (as I have argued in my blog on this subject – did you see it?).

      • Karel says:

        Thank you for the right direction, I hope. I believe that the word red can evoke an experience in a person that is emotionally very strong. I am thinking, for example, of the blushing of a person in an embarrassing situation, which happened repeatedly even in different situations at school or in society. This is probably quite unpleasant for the person concerned, because the word red can be an impulse to repeat the experience.

      • Marianne says:

        It is not so much that the WORD ‘red’ evokes an experience as that a red object does.

  11. Karel says:

    I apologize for returning to your question. You teach about relative and representative causality. During a school exam, I had a question from a professor about red, so my thought of the word red is a wavelength number. It’s almost like a joke.

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