To: David U.
From: Geoffrey Klempner
Subject: Visual experience and the argument from illusion
Date: 1 March 2006 13:39

Dear David,

Thank you for your email of 18 February, with your University of London essay in response to the question, 'What is the argument from illusion? What if anything does it imply about visual experience?'

For the most part I agreed with what you wrote. Most of the necessary ingredients for an answer to the question are there. However, I found your exposition a little bit difficult to follow. You need to make the reader more aware of the structure of your argument. In an examination, a good answer can lose marks simply because the structure of the argument is unclear. One thing that can help improve this aspect is writing a plan. Even when you have only one hour to write, it is worth taking a few minute to work out what you are going to say first.

One point that needs to be stressed is that the argument from illusion does not depend on any sceptical assumptions. My impression from your opening paragraph is that the argument from illusion is a part of, or a consequence of scepticism regarding the external world. In fact, things are the other way round. The argument from illusion, when used to justify a representative theory of perception, leads to scepticism.

(I raised my eyebrows at your statement, 'In many instances we see what is simply not there.' I think 'some' would be more appropriate in the context.)

The main issue is the clash between the sense datum account and the disjunctivist account, and whether, as some philosophers have claimed (see Scott Sturgeon, Matters of Mind. Consciousness, Reason and Nature, Routledge, London and New York, 2000) there is room for a third view in between the sense datum theory and disjunctivism, which does not draw such a sharp distinction between the account of veridical and non-veridical experience.

Consider the statement, 'I see a elephant' as an example of veridical perception, and also as an example of a hallucination.

On the sense data theory, in both cases it is true that 'I see X' for some X. In both cases, I see a elephant-shaped sense datum. But in the first case the sense datum is caused by, and also more or less correctly 'represents' the elephant, while in the second case the sense datum is caused by something entirely different, say, the state of my intoxicated brain.

On the disjunctivist theory, it is simply false that in both cases I see X for some X. If my perception is veridical, then I see an elephant. If I am undergoing a hallucination, on the other hand, then I only *seem to see* an elephant. End of story.

On the disjunctivist view, 'It seems to A that A sees X' does not contain a component, 'A sees Y, for some Y'. That is how the disjunctivist avoids the argument from illusion.

You say, 'The disjunctivist's argument doesn't seem to have that much solidity, because it doesn't really do much but simply deny the mental veil.' Then you go on to observe that this is not as 'weak' as the sense datum theorist's assumption. So how is this argument going to be resolved? We have a choice between a not very solid theory and a weaker theory? Can you see a third alternative? Surely, this is the crucial issue.

The stuff about Berkeley, idealism and quantum physics is not really relevant to this essay because it concerns the consequences of first accepting the sense datum view, then retreating to an idealist position which attempts to replace the external world altogether by means of something constructed out of mental materials.

I am sceptical about claims that there is a third possibility in between disjunctivism and sense data. I would argue that the point of disjunctivism is not simply to 'deny the mental veil' but rather in its positive claim, which invokes the use of Occam's Razor, that extra 'objects' are not *needed* in order to give a complete and satisfactory account of illusions and hallucinations.

Consider the statement, 'I seem to see a pink elephant.' This would be analysed as a propositional attitude, 'It seems to me that I see a pink elephant.' Another example of a proposition attitude would be, 'I believe that there is a pink elephant at London Zoo.' It turns out that my belief is false. There are plenty of grey elephants at London Zoo but no pink ones. Perhaps I glanced at something in a newspaper and got hold of the wrong end of the stick. The latest show at London Circus, just a few miles down the road, includes some elephants which were painted pink.

The philosophical question is what the terms 'pink elephant' and 'London Zoo' are doing in the statement of my belief. One plausible account is that the terms are not functioning as names which refer to 'objects' but rather as general descriptions. I believe that there is something which satisfies the description, 'pink elephant' and a location that satisfies the description, 'London Zoo' and that the thing can be found at that location. But my belief is false. There is a location which satisfies the description, 'London Zoo' but there is nothing which satisfies the description, 'pink elephant' located there.

No additional mental object called a 'mental representation of a pink elephant' is needed in order to describe my state of belief. If you think that there is a pink elephant in my mind, ask me how big the elephant is, whether it is an African elephant or an Indian elephant. The fact is, it never occurred to me to consider that question. Does that mean that my mental pink elephant is indistinct or fuzzy? how does that explain the lack of determinate size?

In explaining, 'It seems to me that I see a pink elephant,' there is no need to posit an elephant shaped sense datum, in addition to the disposition to form false beliefs concerning a pink elephant.

All the best,

Geoffrey