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13 Externalism and the Gappy Content of Hallucination Susanna Schellenberg When we suffer a nonveridical hallucination, our environment seems to be a way that it is not. Because we are not perceptually related to the objects that we seem to be perceiving, we fail to refer to particulars in our environment. How should we understand the effects of this failure of reference? Although our hallucinatory experiences do not yield knowledge, we are arguably justified in believing that our environment is the way that it seems to us to be. How should we understand the nature of hallucinations to explain that hallucinations can be subjectively indistinguishable from perceptions and that hallucinations justify beliefs? This chapter aims to present an answer to these questions. There are powerful reasons to think of perceptual content as determined at least in part by the environment of the perceiving subject: insofar as the subject is perceptually related to, say, a white cup, she is in a mental state that is of that white cup and determined in part by that very white cup.1 A view on which the content of a veridical perceptual experience is determined at least in part by the environment of the perceiving subject is committed to externalism about the content of experience. Now, such externalist views are often rejected on grounds that they do not give a good account of hallucinations. I will show that this reason for rejecting content externalism is not well founded if we embrace a moderate externalism about content, that is, an externalist view on which content is only in part dependent on the experiencing subject’s environment. In section 1, I motivate content externalism. In section 2, I argue that hallucinations are best understood in terms of a deficiency of veridical perceptual experiences. I discuss the consequences of this thesis by developing a view of hallucinations that is committed to externalism about content. 1. For a defense of this view, see Schellenberg (2010, 2011a). 292 S. Schellenberg 1 Content Externalism about Perceptual Experience When a subject perceives a white coffee cup on her desk, she is in a conscious mental state: it seems to her that there is a white coffee cup on her desk. When a subject hallucinates that there is a white coffee cup on her desk, her experience can be subjectively indistinguishable from a perception: it seems to her that there is a white coffee cup on her desk. If perceptions and hallucinations can be subjectively indistinguishable , what is the connection between the sensory character of experience (that is, the way the environment seems to the experiencing subject) and the subject’s perceptual or causal relations to objects in the world? There are two traditional approaches to answering this question. (1) Conjunctive accounts posit that subjectively indistinguishable hallucinations and perceptions share a common element. A subject perceives an object if and only if she is in a mental state that is characterized by this common element, and some additional conditions obtain. Typically the additional condition is considered to be a causal relation between the experiencing subject and the perceived objects (see Byrne, 2001; Crane, 2003). This approach is analogous to the view that knowledge can be factorized into true belief and some additional element, such as justification. (2) Disjunctive and naive realist accounts characterize hallucinations in terms of a deficiency of an accurate perceptual experience and argue that perceptions and hallucinations do not share a common element (see Hinton, 1973; Snowdon, 1981; McDowell, 1982; Campbell, 2002; Martin, 2004; Brewer, 2006).2 This approach is analogous to the view that mere belief is to be analyzed as deficient of knowledge. We do not need to choose between these two options. With conjunctivists, I will argue that subjectively indistinguishable perceptions and hallucinations share a common factor that grounds their sensory character. But with disjunctivists, I will argue that hallucinations can only be understood in terms of a deficiency of perceptions. I will argue that subjectively indistinguishable perceptions and hallucinations share an element that grounds their sensory character, while exhibiting fundamental differences in their content. Why should we think of hallucinations in terms of a deficiency of an accurate perceptual experience? The reasons are the same as the reasons motivating content externalism about experience. We have three main reasons for holding that the content of perceptual experience is at least in part environment-dependent: to give a 2. Naive realism is a newfangled version of disjunctivism. By contrast to most traditional disjunctivists , naive realists not only...

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