Communicating about Sense Data

Sense Data are Private

My experiences, including my experiences of sense data, are my own, your experiences are your own, anre can be no overlap: I never experience what you do, and vice versa. One way of making that clear, which Ayer doesn’t mention is the “inverted spectrum problem”: suppose when you see something red you experience what I do when I see something green, and vice versa. How could we ever know? It seems we could have no way to know, which is one way to emphasize the point that experience is private. Nonetheless, we each somehow manage to constitute a public, intersubjective and even objective world on the basis of private experience alone. How can that be? Ayer has to give some answer at least concerning material things and experience of sense data.

We all see many of the same material things, but none of us has ever seen the sense data of another. What reason can I have to think that anyone other than me even has sense data, or experiences of any kind?

We often say things like, I know how you feel, I feel your pain, that color was just the one you told me you saw. But, we never mean that your experience and mine are numerically identical, at best we mean that they are of the same type. How we could even know that is worth talking about, but first we need to be clear on the minimal fact that we never have literally shared experience, and indeed we never have the same experience twice. This seems obvious enough, and indeed it is just a matter of stipulation. I could have decided to use sense data terminology in such a way that I could be aware of the same sense data twice. When I say that I used the same word twice I can still make sense of the idea that the two used involved different utterances of the same type, namely the word. We could have used sense data language to name types (like words) instead of tokens (like the individual utterances of a word), but once we have agreed to talk about the tokens, the claim that we never share awareness of the same sense data, and, by extension, that we never have the same experience, is just a trivial fact about conventions of language. Note that the idea that no two experiences are experiences of the same sense data is critical to Ayer’s explanation of incorrigibility.

Question: what about when we have a single experience of significant duration, can’t we then be said to be having the same experience at different times? Ayer doesn’t deal with such cases. He hasn’t freed himself from the grip of the idea that experience somehow has a physical basis, that visual sense data have something to do with stimulation to the visual cortex, and the like, an idea he criticizes in others. However, I don’t think that such examples cause a serious problem for him: he should just say that there is single experience not two, and not worry about physical time, only conscious time.

Sense Data and Personal Identity

Why do we use such language to describe experiences? Is it merely a convention? Well, like any convention, it is only appropriate to use it given that a certain empirical situation makes it convenient. If I literally felt your pain or saw what you saw, so that I could know when you were injured even in my absence, and what you were looking at even when my eyes were closed, we might want to adopt a different way of talking.

Question: What about cases of twins who feel pain when the other one gets hurt far away? If, when you are injured, we both wince, then my wincing is separate from yours, and so it is still reasonable to say that we experience different pains, though perhaps from the same cause. It would only be if I literally experience what was happening to you in your body, not in mine, that we would be forced to say that the experiences would be the same.

Personal identity: How is it that certain experiences are experiences of the same person? We so far seem to have described experiences (at least experiences of awareness of sense data) as each being separate.

There are two standard kinds of criteria of personal identity:

Psychological criteria

Bodily criteria

The Egocentric Predicament

Private Data, Private Language

This section says pretty much what the previous one did but in a different way. In that section, Ayer criticizes Carnap’s notion of physical language vs. protocol languages (which are Carnap’s analog of sense-data language). Here he presents the problem that sense data are private in Carnap’s terms. The main new thing is that he presents and criticizes Carnap’s view that protocol language must be taken to refer to physical things: I see red means something about my dispositions to behave (which are publically observable) or else something about the state of, presumably, my nervous system.

Why does Carnap think that? Because otherwise, according to Carnap, there could be no public protocol language, since you couldn’t possibly know what I was talking about when I spoke my protocol language. If that were correct, Carnap believes, there just would be no way to constitute public physical language out of our various private protocol languages. Thus, he needs an alternative, and proposes the ones mentioned.

Ayer says that this is just a mistake. A private language would be one that only its user used {150). That has nothing to do with whether a language is a physical or a protocol language. I do in fact say, I see what appears to me to be something red or, I see red sense data, and you in fact do in some sense that needs to clarified in subsequent chapters, hear and understand me. When I say such things, I do not intend to communicate anything about my dispositions to behave or my brain states, and you do not understand me to be communicating about dispositions or brain states. Carnap has the plainly evident facts wrong. How we are to make sense of those facts is problematic, since you have no idea what my red sense data are like. Ayer doesn’t say anything about that until later, except that it is quite common to have only partial understanding. Physicists tell us that charmed quarks have properties called beauty and truth, and I, at least, have no more idea what beauty and truth are like than I have what your sense data are like. That doesn’t stop me from being able to read Scientific American.

-- ShaughanLavine - 17 Feb 2003 - 19 Feb 2003 - 13 Feb 2007