From Private Sense Data to a Public Material World

How can we get from private sense data to a public material world?

My experiences of sense data don’t overlap at all with yours, and indeed, for all I know, they may be so unlike yours that you cannot conceive what my experiences are like. On the other hand, our experiences of material things had better be a lot alike in important respects: we all need to stop at red lights, and so we all need to agree on what counts as circumstances in which the light is red.

We are trying to see how to bridge the gap between our sense data and material things, and this huge difference seems to make the gap unbridgeable. Indeed, Ayer thinks that that is why Carnap, for example, mistakenly analyzed protocol sentences as being about things in the material world—Carnap thought that otherwise the problem would be hopeless.

If our idea of a material thing is in some sense built out of our sense data of that thing, then, since material things are public, a material thing must be built out of sense data had by many people. But there is no place to stand to know that there are such things. Desperate measures seem called for, and God was often invoked to do the job. Carnap avoided the problem by giving a “public interpretation of sense data” in the first place.

It seems, according to the philosophical tradition, that Ayer has painted himself into a corner. In fact, Ayer has a plausible way out, that does not involve taking material things to be built out of sense data: I have no idea what your red sense data are like and vice versa, but I know that you act as if you have sense data that you call red, just as I do. I also have reason to believe that the interrelationships you seem to experience between your sense data obey rules similar to the ones of my experience.

There are rules and patterns to my experience of sense data. Some of those rules and patterns are what enable me to draw conclusions about the material objects around me. I can explore the general features of my rules that make it useful for me to believe that there are various material things. You will find my explorations interesting if it turns out that your experience of the relation between sense data and material things obeys similar rules.

We can each play solitaire. We can each play solitaire with different decks. There is no common action in your playing solitaire and my playing it. There is no common material object between the two games. Nonetheless, they have something common: they are both games of solitaire, which means in part that they are played in conformance to the same rules. I can write down the rules of solitaire and even advice about solitaire strategy, if many people play the game, but I can also do it if I am the only one who plays the game.

Similarly, my project in the philosophy of perception is to codify the rules and strategies of my sense data to material object transitions. That task will be more worthwhile if it turns out that you play much the same game. But I don’t need to know that to perform the task. My experience of sense data and of the sensory qualities of material things are private. The material things are public precisely to the extent that we have common rules.

-- ShaughanLavine - 21 Feb 2003 - 15 Feb 2007