Bella asked:

What is meant by a ‘disjunctivist’ account of perception? What is the case for disjunctivism?

Answer by Danny Krämer

The interesting point of the philosophy of perception is: “How do we gain knowledge by perception?” Therefore there are three different kinds of perceptual experiences, that are often listed: veridical experience, illusions and hallucinations. The case for a veridical experience is pretty straight forward. If you look at a red tomato and you see indeed a red tomato, then you have a veridical experience of the tomato. An illusion is, for example, when you look at a red tomato but you see it as green, for whatever reason.  And a hallucination is when you see a red tomato but there is just no red tomato to see. Classical philosophy of perception maintains that all three cases have something in common (for example a sense-datum, a representation). Disjunctivists deny this point. A veridical experience and a hallucination of a red tomato have nothing in common. There is nothing like a red tomato representation in my mind, that is the same when I see a red tomato and when I hallucinate a red tomato.

There are many different arguments for the disjunctivist view of perception. The most popular origins from John McDowell and is an epistemological one. First, we recognize that it could be possible that we think we have a veridical experience tomato but in fact we only hallucinate one. Our claim that there is a tomato is therefore not really justified. But the factor that turns the veridical case into a hallucination is not epistemically accessible to us. We believe that there is a red tomato, because we saw it but in fact there is none. That means our epistemic reasons for perceptual judgements are not better in the veridical case as in the hallucinatory case. And this yields scepticism. McDowell takes a disjunctivist stance to block these sceptical arguments. If there is no common factor in the veridical case and the hallucinatory case, then we have different epistemic factors that play into our perceptual judgements. In the veridical case it is the thing itself and our perception of it. In the hallucinatory case it is something different in kind that creates the wrong judgement.