Structural Disjunctivism, Indistinguishability and Introspection

Perceptual disjunctivism, as I regard it in this paper, is the view that veridical perceptions and hallucinations, while indistinguishable via introspection, are states of fundamentally different kinds. This fundamental difference can be spelled out in various ways. According to the view I will be concerned with, it is a fundamental difference in the personal-level structure of both states. Against this version of disjunctivism, I will raise a new challenge. It is a variant of what can be seen as the standard challenge against disjunctivism: how to do justice to the indistinguishability of veridical perceptions and hallucinations. It differs, however, from common versions of this challenge in where it locates the potential incompatibility of disjunctivism with the relevant fact of indistinguishability. Commonly, it is the disjunctivist assumption of a fundamental difference between both kinds of states which is regarded as incompatible with the indistinguishability of these states. In contrast, I will suggest that if hallucinations and veridical perceptions differed in the way proposed by structural disjunctivism, this difference would induce a corresponding difference in the psychological processes of their introspection and that the assumption of such a difference in the manner of introspection is most likely incompatible with a properly formulated indistinguishability claim.