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This essay is a long one. It is not meant to be read in a single sitting. Its structure is as follows. In section I, I explicate perceptual anti-individualism. Section II centers on the two aspects of the representational content of perceptual states. Sections III and IV concern the nature of the empirical psychology of vision, and its bearing on the individuation of perceptual states. Section V shows how what is known from empirical psychology undermines disjunctivism and hence certain further views that entail it, including naive realism. In Section VI, I raise a further point against disjunctivism. Section VII indicates how general reflection on perceptual perspective and epistemic ability supports the constraints from empirical psychology. It also explains how reflection on veridicality conditions, psychological explanation, and cognitive ability conspire to force recognition of the two kinds of representation mentioned in the preceding paragraph. In the Appendix, I criticize attempts to support disjunctivism.

Disjunctivism, as a theory of visual experience, claims that the mental states involved in a “good case” experience of veridical perception and a “bad case” experience of hallucination differ, even in those cases in which the two experiences are indistinguishable for their subject. Consider the veridical perception of a bar stool and an indistinguishable hallucination; both of these experiences might be classed together as experiences (as) of a bar stool or experiences of seeming to see a bar stool. This might lead us to think that the experiences we undergo in the two cases must be of the same kind, the difference being that the former, but not the latter, is connected to the world in the right kind of way. Such a conjecture has been called a “highest common factor” or “common kind” assumption. At heart, disjunctivism consists in the rejection of this assumption. According the disjunctivist, veridical experiences and hallucinations do not share a common component. There are a host of interesting questions surrounding disjunctivism including: What is involved in the claims that good case and bad case experiences differ? Why might one might want to be a disjunctivist? What kinds of claims can the disjunctivist make about hallucination and illusion? These questions, and problems for the thesis, will be discussed as we proceed.

Many philosophers are skeptical about disjunctivism—a theory of perceptual experience which holds roughly that a situation in which I see a banana that is as it appears to me to be (the good case) and one in which I have a hallucination as of a banana (a certain kind of bad case) are mentally completely different. Often this skepticism is rooted in the suspicion that such a view cannot adequately account for the bad case—in particular, (i) that such a view cannot explain why what it’s like to have a hallucination can be exactly like what it’s like to have a veridical experience, (ii) that it cannot explain why the hallucination I have in the bad case is subjectively indistinguishable from the kind of experience I have in the good case, and (iii) that it cannot offer a viable account of the nature of hallucination.

In this paper, I argue that a proper formulation of disjunctivism can avoid these objections. Disjunctivism should be formulated as the weakest claim required to preserve its primary motivation, viz., Naïve Realism—the view that veridical experience fundamentally consists in the subject perceiving entities in her environment. And the weakest claim required to preserve Naïve Realism allows for many sorts of commonalities across the good and hallucinatory cases, commonalities that can be marshaled in responding to the objections. Most importantly, disjunctivism properly formulated is compatible with “positive” accounts of the nature of hallucination (as against M.G.F. Martin’s widely accepted argument to the contrary).

In this paper I argue that McDowell’s brand of disjunctivism about perceptual knowledge is ill-motivated. First, I present a reconstruction of one main motivation for disjunctivism, in the form of an argument that theories that posit a “highest common factor” between veridical and non-veridical experiences must be wrong. Then I show that the argument owes its plausibility to a failure to distinguish between justification and warrant (where “warrant” is understood as whatever has to be added to true belief to yield knowledge).

This essay surveys the varieties of disjunctivism about perceptual experience. Disjunctivism comes in two main flavours, metaphysical and epistemological.

Inspired by the writings of J. M. Hinton (1967a, 1967b, 1973), but ushered into the mainstream by Paul Snowdon (1980–1, 1990–1), John McDowell (1982, 1986), and M. G. F. Martin (2002, 2004, 2006), disjunctivism is currently discussed, advocated, and opposed in the philosophy of perception, the theory of knowledge, the theory of practical reason, and the philosophy of action. But what is disjunctivism?

Early formulations of disjunctivism about perception refused to give any positive account of the nature of hallucination, beyond the uncontroversial fact that they can in some sense seem to the same to the subject as veridical perceptions. Recently, some disjunctivists have attempt to account for hallucination in purely epistemic terms, by developing detailed account of what it is for a hallucinaton to be indiscriminable from a veridical perception. In this paper I argue that the prospects for purely epistemic treatments of hallucinations are dim, and that this undermines the case for disjunctivism.

John McDowell’s original motivation of disjunctivism occurs in the context of a problem regarding other minds. Recent commentators have insisted that McDowell’s disjunctivism should be classed as an epistemological disjunctivism about epistemic warrant, and distinguished from the perceptual disjunctivism of Hinton, Snowdon and others. In this paper I investigate the relation between the problem of other minds and disjunctivism, and raise some questions for this interpretation of McDowell.

Disjunctivism is the view that perceptual experience is either constituted by fact in the world or mere appearance. This view is said to be able to guarantee our cognitive contact with the world, and thus remove a crucial “prop” upon which skepticism depends. This paper has two aims. First, it aims to show that disjunctivism is a solution to Cartesian skepticism. Cartesian skepticism is an epistemological thesis, not an ontological one. Therefore, if there is an external world, we may well undergo a veridical experience, and thus we can take advantage of disjunctivism to adopt an anti-evidential-skepticism strategy to counter Cartesian skepticism. Second, this paper argues that disjunctivism fails to solve Pyrrhonian skepticism. To counter Pyrrhonian skepticism, one has to give reasons both for his belief and for his believing. But disjunctivism can only account the former, that is, the reason for the content of perceptual belief. Given that one’s experience in good case and bad case is subjectively indistinguishable, one cannot just use his experience to justify his believing. This shows that disjunctivism cannot meet the requirement to provide an adequate account for reflective knowledge.