philosophy is for everyone
and not just philosophers

philosophers should know lots
of things besides philosophy

Philosophical Connections

Electronic Philosopher

Feature Articles

University of London BA

Philosophy Lovers Gallery

PhiloSophos Home

International Society for Philosophers

Hallucination and the disjunctive analysis of perception


To: Scott B.
From: Geoffrey Klempner
Subject: Hallucination and the disjunctive analysis of perception
Date: 7th January 2010 14:33

Dear Scott,

Thank you for your email of 17 December, with your second attempt at the question for the University of London Epistemology module, 'You cannot distinguish between a case in which you see the exam paper before you and a case in which you undergo a perfectly matching hallucination. Therefore the difference between seeing and hallucinating is not an experiential difference.' Discuss.

Your revised essay is a model answer to this question. It is actually quite difficult for me to find any faults with it (a pretty unusual occurrence).

Obviously, given the constrictions of time you would not be expected to go into the whys and wherefores of cognitive externalism. But apart from questioning the wider theoretical basis for the disjunctivist view, is there any plausible objection which one might mount against disjunctivism about perception?

You hint at a possible objection when you say, 'The difficulty with the idea of disjunctivism though is that I would not be able to tell which particular disjunct I am experiencing. Should I be hallucinating or subject to an illusion, it would appear to me as if I actually perceived the actual state of the world. I would therefore [not] be in the same perceptual state that I would be in if the world was exactly how I perceive it to be. As a result, I would be deluded not only about the state of the world but also about the state of my own mind.'

The objection is that if I were to be subject to a hallucination that there is an exam paper in front of me, then not only would I be wrong about there being an exam paper, but I would also be wrong about the kind of *mental* state I was in. I thought that mental state was 'enjoying a perception' but I was wrong. But how can I be wrong about the mental state that I am in? Aren't I the best authority?

Wouldn't the disjunctivist reply, 'Well, yes, that is exactly what I am saying. You are not an infalliable authority about the mental state you are in. So where's the objection?'

The knowledge or belief that I am in a given mental state is not itself a datum. It involves an act of reflection, what one might term a 'theory'. I see the exam paper, and, reflecting on this experience, I form the judgement, 'I am currently in a perceptual state whose content is, There is an exam paper in front of me'.' According to the disjunctivist, therefore, if in fact I am not perceiving an exam paper but undergoing a hallucination, then my judgement that I am in such-and-such a perceptual state is false. That is to say, it is a false theory. That's what the disjunctivist has to say, in order to be consistent.

I liked the thought experiment of removing the exam paper and instantaneously commencing brain stimulation causing a hallucination of the exam paper which segues seamlessly with the original perception. Here, the potential objection seems to be that a mental state cannot transform into an entirely different mental state without the subject's knowledge. Again, that is simply what the disjunctivist has to say to be consistent. Strange as it may seem, your mental state can unknowingly transform in this way given suitably bizarre circumstances. ('So what? do you have a problem with that?', the disjunctivist would say.)

But what about doing the same thought experiment in reverse? Suppose we start with the hallucination then seamlessly transform this into veridical perception. If you don't know that you were previously hallucinating, then you can't tell when the hallucination has ended. In that case there does seem to be a (mildly) stronger intuition that there is something 'wrong' with talking about perception. Things are very far from 'normal'. Yes, there is an exam paper, and, yes, technically, you are now perceiving it. But in this case the whole setup seems a bit too fragile to call 'perception'.

I don't know where to take that thought -- maybe you can do something with it.

That's pretty much all I have to say. As for further improvements, there are probably more marks to be got if you put in a few more references -- e.g. to back up what you say about the intentional view, or the disjunctivist view. But that's just icing on the cake.

I am pleased to see that your efforts have paid off. Well done!

All the best for 2010,