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Perceptual realism and the argument from hallucination


To: Emelie G.
From: Geoffrey Klempner
Subject: Perceptual realism and the argument from hallucination
Date: 24th February 2011 12:09

Dear Emelie,

Thank you for your email of 14 February, with your essay for the University of London BA Epistemology module, in response to the question, 'Is there a compelling argument from the possibility of hallucination to the impossibility of our experience being partly constituted by the ordinary objects that we seem to experience?'

In your essay you offer a competent and clear summary of four positions which have been taken up with regard to the question of whether or not our experience is 'partly constituted by the ordinary objects that we seem to perceive': The sense datum theory, the intentional theory of perception, naive realism, and disjunctivism.

Although you allude to the arguments in favour of each of these views, I didn't get a strong feeling of being 'compelled' in any direction. But then, right at the end in the last paragraph, you throw in what seems to be a new argument which you haven't considered above, 'The naive realist and the disjunctivist both claim to see the ordinary objects of our world as they really are, but they cannot give a satisfactory answer to the skeptic's basic arguments like why the grass is green in daylight, grey in twilight, how tepid water feels warm to a cold hand and cool to a hot hand.'

I think that this line deserves to be explored further.

Suppose that it's late evening and I look out at the lawn and notice that it 'looks grey'. There are two possibilities. The more likely possibility is that I don't think anything of it, because I know 'how green grass looks' at dusk. I see the grass 'as' green even though the actual content of my experience, the colour of my visual field, would be more accurately described as grey. It is also possible, however, that I didn't notice how late in the evening it is and for a few moments the panicked thought strikes me, 'What's happened to the grass? The weed killer I sprayed on it earlier must have turned it grey!'

In both cases, the disjunctivist would say, the grass itself partly constitutes my experience. Moreover, as a competent perceiver I know that things 'look' different in different circumstances. In the first case, there is no sense of surprise, I don't think that the colour of the grass has been changed by the weed killer I sprayed on it, I see exactly what I expected to see. In the second case, I am surprised. This leads me to form the false hypothesis that the weed killer has turned the grass grey.

Initially, there doesn't seem to be any problem here for the disjunctivist theory.

Analysing your example of the grey grass from the point of view of the disjunctivist theory, there are two aspects which we can distinguish in perception: the idea that perception puts us into some kind of direct cognitive relation with an object in the world, and the idea that perception furnishes with information about that object. Prima facie, if I am in a direct cognitive relation with an object, then I am in the appropriate state to gather reliable information or facts about that object. However, it is also part of our ordinary understanding of perception that the way objects look depends on the circumstances, and this is something that it is possible to have a false belief about. The result is that I form a false belief about the grass, namely that it has turned grey.

But now it occurs to me that one could 'ratchet up' up this example. The typical case of hallucination that sense datum theorists consider is the case where, e.g., I see a pink elephant in the bar when in fact no object is there at all, just empty space. The 'pink elephant' is just something created by my own mind. However, it is more often the case that we *see an object* as something totally different from what it actually is. The 'huge tarantula spider' about to jump on me is just a ball of tangled thread. The 'object' itself, the tangled thread, plays a minimal part in my experience. My fear of spiders has the tendency to turn completely innocent items into objects that terrify me. Or let's say I have just taken LSD and see a dragon walk into the room. The 'dragon' is only my mother-in-law, but the drug has combined with my negative feelings to turn my experience into the vivid experience of seeing a fire-breathing dragon. (My mother-in-law as she 'truly' is.)

This does look like a challenge for the disjunctivist. We were originally told that experiences are 'either...or...'. Either I am having a veridical experience, an experience of seeing an object, which is in fact there (one doesn't normally talk of a 'veridical object'), or I am undergoing a hallucination produced by my own mind, 'seeming to see' an object which isn't in fact there. But in the examples of the spider and the dragon, neither of these alternatives apply. Are we going to admit a third disjunction into the theory? Or maybe more?

Is this compelling? No, but it looks like a problem for the disjunctive theory which should at least cause some degree of discomfort.

All the best,