To: Walter F.
From: Geoffrey Klempner
Subject: Defending the idea of sense data
Date: 19 April 2006 08:14

Dear Walter,

Thank you for your email of 4 April, with your first essay for the Metaphysics program, in response to the question, 'What are the attractions of the idea of a 'sense datum'? Can the theory of sense data be defended against criticisms based on the reality principle?'

This short piece is pregnant with ideas, the most important (for me) being the question whether in fact I have merely adopted the term 'the reality principle' for a concept which bears some resemblance to the way this term is used in developmental psychology, or whether there is in fact (as I believed when I wrote these units) a closer, logical connection - that in fact the logical/ metaphysical reading is the foundational one.

Let's consider a case of abnormal development, where an individual acquires some ability with language (maybe restricted) but has failed for whatever reasons to failed to cotton on to the idea of a public world, public knowledge, or, equivalently the idea of a gap between 'the truth' as such and 'what I believe'.

Two candidates for such a condition would be the psychopath and someone with autism. (I would be interested in your comments on this.)

Such an individual 'thinks', makes 'judgements' which in some sense fail to conform to the reality principle. Does that mean that these are not really thoughts or judgements? What would that mean? Consider the train of thought, 'I want an orange, that's an orange, I will take it and eat it.' Here we have an expression of desire, an judgement, and an expression of intention. Applying the reality principle (as I understand it) strictly would have the consequence that the words I have just used do not express a meaningful content for the desire, the judgement or the expression of intention.

Yet clearly these do have a 'meaning', and I am not sure how I want to account for this. In the philosophy of language program, there was a discussion of the question of the psychological states of non-human animals. It was argued there that our attribution of states with content which can be expressed in words is a 'heuristic' device. It is not and cannot be literally true that the 'dog wants a bone', because there is no way to identify the dog's recognitional capacity for bones or 'bone behaviour' with the concept of a 'bone'. (I believe this is what Wittgenstein was onto when he remarked, 'If a lion could talk, we could not understand him' Philosophical Investigations p. 223.)

How would this apply to the psychopath or someone who is autistic? It looks like I have to say that they use the word 'orange', but this utterance is not sufficient for attributing the concept of an orange. There is no 'word' for the 'concept' that such an individual has.

So far as the question of sense data is concerned, we are dealing with something more cut and dried. The sense datum theory is incoherent from a logical point of view, and the reality principle demonstrates this. There cannot be a 'sense datum' as posited by the theory. It would be absurd to say, 'He is unable to recognize objects in the outside world but he has sense data.' What we mean is that he has sensations. Sense data are sensations which have been given additional attributes in order to enable them to bear the weight of an incoherent (Cartesian) theory of knowledge. This happens, e.g. as soon as we call them 'qualia'.

Wittgenstein calls these curious hybrid entities 'private objects'. 'Always get rid of the idea of the private object in this way: assume that it constantly changes, but that you do not notice the change because your memory constantly deceives you' (Philosophical Investigations p. 207).

I like the term, 'conversational approach to knowledge'. Wittgenstein talks of 'agreement in judgements' and 'forms of life' as the basis for truth. It is interesting that the most 'scientific' of twentieth century philosophers - like Carnap - were totally sold on the idea of an epistemology based on sense data. As soon as you move out of the private theatre of the mind into a public arena where we encounter objects there arises the possibility of disagreement and endless debate. Whereas the private linguist has no such obstacles. But then it turns out that the latter strategy is based on an incoherent premise. Dialogue is the only game in town.

Whether or not this lends support to Kuhn's view of science is a moot point. Opponents of Kuhn would point out that he has placed undue emphasis on the irrational elements in science. Then again, there are some, like Feyerabend who think that Kuhn has not gone far enough. But now we are no longer doing metaphysics but philosophy of science.

All the best,

Geoffrey