Denis Noble
University Laboratory of Physiology, Oxford, UK

https://doi.org/10.36866/pn.55.32

Since writing the Foreword to Philosophical Foundations of Neuroscience (Bennett & Hacker, 2003), I have been asked to explain the ‘private language argument’ in terms more familiar to scientists than the dense tomes of Wittgensteinian philosophy.

The argument lies at the core of a set of philosophical puzzles, so one can encounter it in various guises. Let’s take an example of such a puzzle. The protagonists in my story are called ME and YOU for convenience and all you need to know about them is that they have the same mother.

While I am writing this document, I look closely at the print. I note that it is black and the page is white. So, I tell you that I am currently writing this with a black font on a white background. You reply that, yes, you understand what I have told you, but you nevertheless have a nagging doubt.

You express this by saying ‘How do you know that I see black, or white, as you do? Perhaps, what I see when I receive your email is what you would see as blue on pink, or green on ultramarine, or any one of millions of possible combinations, including colours that perhaps you have never seen! The only restriction is that the form of the relations between my perceived colours and yours must be such that we always agree on what to call what we see. We use the same names, but we may see differently.’

Naively, I respond initially by saying ‘don’t be silly, we both learnt what it means to refer to black and white at our mother’s knee!’ (*1)

*1 Actually, this move is not as naïve as it may initially appear – see the denouement of this story.

YOU: Oh yes, of course, but that is not what I mean. When we learnt at our mother’s knee, I thought we were all looking at the same things and must see them in the same way. Since then I’ve read some philosophy and neuroscience and I can’t for the life of me see how anyone else, even our mother, could know what I am seeing when I look at a black font. My experiences are inside me, inside my head, in my brain, and no-one else can see them. I may see the world completely differently from the way you see it.

ME: Oh dear, you’ve become quite a solipsist recently. I also feel like that sometimes. Don’t worry, it will pass. Let’s have a curry together.

YOU: No, no, it won’t pass, you really don’t understand. I am serious. I am me. You are you. You can’t know what I experience in my own private world.

ME: Where on earth is that?

YOU: Don’t play games with me. You can’t see inside my head.

ME: Well, actually, I can. We can record from your neurons, scan your brain for blood flow changes, and many other things. We would find inside your head much the same stuff that you would find in mine.

YOU: Yes, I know that. I don’t think I am different because I am made differently – though equally obviously we are not physically identical. It’s just that … well, I am me, and you are you. Don’t you see?

ME: Yes, I certainly see that, but I don’t see why that entitles you to say that you have a private world that I can’t know about.

YOU: Look, this is getting exasperating. Obviously I am not referring to my neurons, or my blood flow changes, or anything else of a physical nature. I am referring to these sensory experiences that I have. You know, they even have a name now. People call them ‘qualia’. (*2) You must also have them. Just look at one of those letters on the page. There is a black on white quale there!

*2: This term was originally introduced by 20th century philosophers to refer to the ‘qualitative character of experience’. The singular is ‘quale’.

ME: So you have become a dualist? You think there is something there that is not physical?

YOU: Oh no, not at all! These things are created by my neuronal processes, perhaps in a sense they are my neuronal processes – or at least what it feels like to have them. We are not going back to Cartesian dualism. I am not supposing a soul that interacts with my brain. In fact I just think that I am my brain. And my brain creates these experiences that I see, feel, hear. (*3)

*3: This stage of the argument could have been the departure point for another version of the private language puzzle. The protagonist, ME, could have asked what on earth the ‘I’ was doing in this sentence. It would take another version of the dialogue to explore the problems created by this way of speaking about the relationship between the self and the brain. This illustrates the point that there is a set of puzzles here that are all inter-related by various versions of the private language argument.

ME: I thought that these experiences were created in the same world that both you and I live in, which is why I was puzzled about reference to ‘your private world’.

YOU: Well, yes, that’s sort of true. But I am not referring to the things in the world itself. I am referring to the quality of the sensations I have when I see the world. That’s why they are called qualia.

ME: So, wait a minute. When you look at a black font, you think that there is not only the black font itself but also something else that is inside your head?

YOU: Yes, you’ve got it. I wish I could have put it that way myself.

ME: But that’s just another form of dualism. Why do you need to suppose that there is anything inside your head other than the neuronal processes that occur when you see a black font?

YOU: No, wait a minute. I don’t think these qualia are a different sort of substance, something ethereal and ghostly.

ME: But that’s just what it sounds like to me! Tell me this. You are a scientist. You think that your brain is a material thing, though fiendishly complex. What possible experiment can we perform that will confirm whether or not these things that you call qualia exist?

……… long silence …….

ME: Well?

YOU: Well, it’s not like that. As I said before, you can’t know what I experience, so I can’t tell you.
ME: ‘So, what do you do? Do you, as it were, tell yourself – perform a kind of self-talk? How do you compare your own experiences?

YOU: Of course, that’s easy. I know what I mean when I refer to black and I can remember what it was like. So, in a sense, I can tell myself ‘this is black’.

ME: But you can’t tell me?! You must have a private language.

YOU: Well, if you want to put it that way, I suppose I do. But everyone does.

……… different long silence …….

YOU: Don’t you?

ME: Well, I am not sure about this. Tell me, where did you learn this ‘private language’? Does it have the same words as our language?

YOU: Well, I hadn’t thought much about that. Yes, I suppose it does. At least, when I tell myself that I see black, I don’t invent a new word. I don’t refer to it as ‘kcalb’ for example. Actually, (Oh dear, this is getting muddling!), I don’t think I use any words at all – I certainly don’t need to.

ME: So, this language is neither a different language and, possibly, it isn’t even a language at all?

YOU: Well it’s certainly not a language as we learnt at our mother’s knee. But, look, it’s very simple really. I see black. I know I see black. I remind myself that this is the same kind of quale that I have experienced before. If I must put it into words, I suppose I would tell myself ‘I am seeing black’.

ME: And when you say that to yourself you also tell yourself that you are communicating something different from what you would communicate to me when you say to me ‘I see black?’

YOU: Yes.

ME: So what is it that is different?

YOU: I’ve already told you. It is the description of the quale, not the font itself – it’s how I see it.

ME: But we don’t know that they exist. We have no way of conducting an experiment to see whether they exist. So why do you need to refer to qualia? Why not go back to when we learnt language at our mother’s knee? When we saw black, mother said ‘that is black’, so we both got to know that that is what it is called. Isn’t that simple? Moreover, we could only do that because all three of us looked at the same pictures in the same book. That’s how we came to use the same language. If we had been French we would have called it ‘noir’, if we were Japanese we would have learnt to say ‘kuroi’, but we would still have ended up being able to do all that anyone ever can do to communicate what they see when they see black. Mother didn’t ask us whether we could see any strange qualia!

YOU: No, but she didn’t know any science.

ME: Hey wait a minute. This is not science! We seem to have agreed that what you are talking about is something – qualia – for which we can have no experimental evidence; that you communicate with yourself about seeing these qualia in a language that is either not a language, or just the same language you use to tell me ‘I see black’; that we are not talking about there being anything inside your head other than material substances (neurons, blood vessels) of the same kind that I have in my head; so where is the science in this ‘private language’ stuff?

YOU: OK. I agree that I am expressing a particular philosophical view of the world. But I also think that there are some kinds of philosophical beliefs that are necessary for us to conduct scientific investigation. How could I possibly study the brain-mind problem if I didn’t think there were qualia formed as a result of neuronal processes of a certain kind? Goodness me, this is the greatest challenge for neuroscience! You can’t convince me that this is all a wild goose chase!

ME: Maybe not, but if I am right then you don’t even have a problem. In the sense we are talking about here, there is no mind-brain problem.

YOU: What?!

ME: Well, it’s up to you. If you think there is a problem, then there is a problem, but perhaps the problem is the way you are thinking, not a problem for science. You are proposing to investigate a phenomenon for which we can have no experimental evidence; that requires a language that is private – which is a contradiction in terms; languages are for communication – and which leads to a modern form of dualism which I would suggest is alien to what science can seek to know about us as human beings.

YOU: I think we had better have that curry. You will have to tell me what you see as the relation between mental and physical events!

Reference

Bennett MR. & Hacker PMS (2003). Philosophical Foundations of Neuroscience. Blackwell Publishing, Oxford.