  Disjunctivists and their opponents agree that veridical perceptions, illusions and hallucinations have something in common, in so far as they agree that such mental events should be grouped together as being perceptual experiences. They also agree that there are differences to be marked between them, hence the different labels for them. However, they disagree when it comes to specifying what these commonalities and differences consist in. What distinguishes the disjunctivist theory is its rejection of a ‘common kind claim’—the claim that the conscious perceptual experiences that are involved in cases of veridical perception, illusion and hallucination have the same nature. If one accepts that the same kind of conscious experience occurs in all three cases, then this imposes a constraint on the account one can give of the kind of conscious event that occurs when one veridically perceives the world.  Disjunctivists deny that our accounts of veridical perception should be constrained in this way. So the disjunctivist view of perceptual experience can be regarded as a negative thesis—the rejection of a common kind claim—that is adopted in defence of a positive view of veridical perception.