Sense-Data Sara S.
November 15, 2001

Two Voices on Sense-Data

A: It feels like it has been months since we last got together for lunch.

B: That's because it has been.

A: I suppose your right. Why is that?

B: Because you got tired of your coffee getting cold before we were done arguing?

A: Yes, that could be it. You can be rather argumentative.

B: Am not!

A: See?

B: Alright, alright. I'll try not to jump on everything you say.

A: This cafe sure is crowded.

B: I would have chosen to go somewhere else.

A: Of course you would have.

B: There isn't even a place to sit.

A: I see a table over there.

B: No you don't.

A: Yes, I do.

B: No you don't.

A: Yes, I do.

They sit down.

B: I still don't think that you saw a table.

A: Oh, really? And what are we eating at?

B: A table. But you didn't see a table.

A: What, then, did I see? An elephant?

B: No. You saw a dark, round, flat surface on top of some tall, thin cylinders.

A: The table does look as you have described it, but, no, I saw a table.

B: But if I asked you to describe the table, your description would be similar to what I just claimed you saw?

A: Yes, but it seems that what you mean by see is something quite different than what I mean.

B: Seeing to me means the kinds of properties that I would convey if I were to draw this scene, things like shape, size, color, and texture.

A: And what I mean by see is that we see physical objects: tables, chairs, cups ...

B: But you don't! Surely you can't expect me to agree that you see a cup.

A: I do.

B: No, what you see is at most only part of the surface of what we call a cup.

A: I understand what you are saying, but I really see a coffee cup. I know what you want to say, but it is just ridiculous. If I am to follow your line of reasoning, I wouldn't be able to see any opaque objects at all. But I am quite comfortable saying that I see a coffee cup. That's what it is that I'm looking at, and that's what I see.

B: No, it's just what you think you see.

A: I'll grant you that I see, in one sense of the word, a portion of a curved white surface, the curved white surface that is the appearance of a coffee cup. What I see, or perceive if you prefer, is a coffee cup. Ask as many people here as you want; they will all tell you that they see a coffee cup.

B: What you say is interesting, particularly the part about perceiving. It sounds to me like you might be agreeing with me for once. What you are seeing is really the curved white surface; you are merely saying that you see a coffee cup because that is what you have consciously concluded the object you are seeing is.

A: Sorry to disappoint you, but that's not quite what I'm saying. I guess I must be translating from colors and shapes to objects, but none of that is done consciously. All of that happens, as it were, before I see ... it, the coffee cup.

B: And you say I'm the argumentative one. There I was, offering an agreement ...

A: But you were missing my point. Your concept of sight is so technical and tedious. And why stop at shapes and colors? Why not say that you are seeing projections and light waves that you interpret as shapes and colors? I know, you think that is absurd. But so is what you would have me believe sight is. The process of seeing is somewhat mysterious to me. There's a lot of complicated stuff going on between my eyes and my brain, but I don't have to understand it. The very first thing that I see aren't these properties, although I can describe what I see in terms of them, if you would like. I really am seeing an object, a coffee cup. We have names for objects because we think in language. We think in terms of objects because we see in terms of objects.

B: ``In terms of objects?''

A: Yes, as I said earlier, we see appearances. I see the appearance of your coffee cup.

B: It sounds to me like you are saying that seeing is about subjective appearances and is not objective.

A: You could say that. Your eyes are not my eyes and I am not you, so it makes sense that what we see is different.

B: That's a reason why my theory is more epistemologically useful than yours is. We both may see the same surface, of the exact same color and dimensions, but you want to claim that I might be seeing a tea cup while you are seeing a coffee mug. It seems like you are talking about thinking about seeing rather than about seeing itself.

A: That does seem problematic. But that's part of why sight is subjective; we are seeing different things. Your account suffers from a number of the same problems, too.

B: Such as?

A: That guy over there, the one wearing sunglasses. If we see your shapes and colors and whatnot ...

B: Sense-data.

A: If we see sense-data, then he is going to see a beige surface where you see a white one. Which one of you is seeing correctly? There's subjectivity for you. Of course, you are both seeing coffee cups and there's no dispute about that.

B: But we might even both say we are seeing something white. He knows he is wearing tinted glasses, and I'm not. I don't see where there's a problem.

A: How do you know that the cup is really white? The lighting in here may be off. And color isn't the only thing you might be wrong about. There's shape. Or size. Look at your coffee cup and that coffee cup on the table across the room. You see that yours is larger, don't you? But it isn't, of course. That's perspective. I don't think you are in any better epistemological position than I am; in fact, you are in a worse position.

B: Perhaps anything empirical is doubtable, but if you are going to play that game, your seeing is at least as objectionable as mine. There are hundreds of so-called optical illusions where things appear to be otherwise than they really are.

A: Sure. I'm not saying that things are really as they appear. But I do think we can learn something about the reality of objects from their appearance.

B: Oh? I'm eager to hear how you do this. Do tell.

A: Well, I'm not exactly sure what the relation is between the appearance of objects and the physical objects themselves, but it seems there must be one. And clearly appearance and reality are not always one and the same. We have both demonstrated that. But often appearance and reality are very similar. And even when they aren't, there seems to be a predictable correlation. We know that tinted glasses alter the apparent color, that things in the distance seem to be smaller, that certain images will play tricks on us.

B: And you think if we gain a better understanding of this relation, we can get from seeing to knowing?

A: I certainly think we might be able to, and I can think of no other way that we could have any certainty about external objects and their physical properties.

B: Enlighten me. How do we get from subjectivity to objectivity? From appearance to reality? From sensory input to justified true belief?

A: This is still a rough theory, but I'll give it a shot. It's an empirical theory because it starts with what we see, hear, feel, and so forth, but unlike what we were talking about earlier, it does involve conscious intervention - thought. Regardless of whether we see sense-data or objects, we talk about things in ordinary everyday speech as objects. Do you agree?

B: I do.

A: So you should be comfortable with me saying something like ``Whatever it is I am seeing, I say that I am seeing a coffee cup.''

B: You certainly seem to be saying that, yes. And that's a lot easier to say than all of the colors and shapes.

A: I might say ``I think I see a coffee cup'' or ``I think what I see is a coffee cup''.

B: Sure, although those two statements are quite different. The first makes the claim that you are literally seeing the object, whereas the second ...

A: ... implies that I have consciously inferred from what I have seen and my knowledge of coffee cups that what I am seeing is objectively a coffee cup.

B: Yes.

A: And this is what we both want, don't we? To be able to say something justified, something about the cup itself. And we are having trouble finding grounds for certainty about the objective cup starting from our personal, known-deceptive sight.

B: It looks like you have plenty of grounds right in your cup.

A: What?

B: Coffee grounds. You seem to have .... Oh, never mind. Continue.

A: You were on the right track earlier. What did you suggest we do to reconcile your vision with that of the man wearing sunglasses?

B: Compensate for the fact that what he was seeing would be tinted?

A: Right. This is something it seems we do automatically. And I think, with a little work, we can get to a fairly rigorous rational process. Suppose he wasn't convinced that his vision were distorted, if you will. Then what would you do?

B: I might ask him to take off the glasses.

A: What if he couldn't?

B: Then, I might ask a dozen other people what they saw and try to convince him that through an understanding that he was the minority.

A: And if you couldn't do that, you'd probably think of something else. What you are describing is a method of experimentation.

B: But I haven't said anything about knowledge. I'm just trying to convince some random non-philosophic person that the cup is white.

A: It's a start to convincing ourselves though. Knowledge can come from such humble beginnings. Let me flush out some of the details of my process a bit more. First, you saw the cup and had a hypothesis. ``It's white,'' you claim. Why should anyone believe you? They shouldn't. You aren't in any privileged position. Why should you believe yourself? Maybe you shouldn't. Haven't you sometimes seen things differently than you knew they really were? You need to justify your hypothesis.

B: But how can I do that when you are calling everything into doubt?

A: Not everything. I'm assuming that you are a rational being who can think clearly. And that's assuming a lot.

B: Hey!

A: Well it is. You have the ability to attempt to justify your hypothesis. You can design a test of its validity, and if that isn't enough, you can design another test. If your hypothesis fails, you can revise it and test again. These are quite remarkable things that people can do, things that scientists do every day.

B: The scientific method.

A: You are familiar with it?

B: Only vaguely.

A: It's quite simple. First, we have a question and a hypothesis, a belief to justify. Then we devise an experiment that will test our hypothesis. We run the experiment, either a real experiment like measuring the object with a ruler or perhaps a thought-experiment. Finally, we gather our results and analyze them. If there's enough information to come to a conclusion about our hypothesis, we do. If there isn't, we devise another test. If our hypothesis is incorrect or can be shown to be unsupportable, we start all over again and conjecture a different hypothesis that we think is more likely to be true and justifiable.

B: Interesting. But must the process terminate? Or can I be stuck in an infinite loop of experimentation forever, never to get to justified truth? Or, might I think I have discovered knowledge, only to find later that some new piece of evidence ruins my theory, and I was only deceiving myself by believing I was justified?

A: I am not sure. At the very least, you will derive a coherent system of statements about the object. At the very least, you will have extremely probable knowledge.

B: But that's not knowledge. Certainty and probable are very different.

A: Even if we are talking about things which are so highly probable as to be indistinguishable?

B: They can't be indistinguishable. Things which are certain, are known, are indubitable.

A: Hmm ... as for the last part of your question, you are touching on something worth discussing in some detail. Science gives us revisable theories.

B: Exactly, and theories aren't truth. For thousands of years people thought the earth was flat, that atoms were indivisible, and dozens of other things, all of which were wrong.

A: But these theories were revised. Once we have a reason for disproof, we don't continue believing false beliefs. We modify our beliefs. Our body of knowledge isn't fixed; it is dynamic and constantly evolving.

B: So science gives us justified belief. But no truth. How can we know the truth? How do I know that I won't wake up one day and find no gravity, nothing keeping me on the ground? Why should I believe in gravity?

A: Because not doing so would be a tremendous paradigm shift. It would upset nearly all of your beliefs.

B: And heaven forbid that I be a skeptic!

A: In a way, yes. I may not be able to convince you that we can know anything to your satisfaction, but I hope I have given you the idea that if we are to know anything of physical objects it is through objective means and a rational, precise process like the scientific method. And if we are to remain convinced of our body of knowledge, we must constantly be testing and revising. It is with science that our attention should lie, and it is foolish of us if we ignore science and the practices it has to offer.

B: I had no idea it was this late. I must get back to my office. It was good seeing you again. You've given me much to think about.


Moore, G. E. ``Visual Sense-Data''. Perceiving, Sensing, and Knowing. Swartz, Robert. Berkeley: University of California Press, 1965.

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