  Can the disjunctivist respond by saying that there is a non-causal constitutive condition necessary for the kind experience that occurs when one hallucinates—namely the absence of an appropriate candidate object of perception in the subject’s environment? A problem with this response is that it relies on characterising the kind of psychological effect involved in hallucination in terms of what it is not, namely a veridical perception, and it is plausible to demand that it should be possible to provide some positive account of the kind of psychological effect involved when one hallucinates.