For similar reasons, Indirect Realists needn't assume that every feature of every sense datum is fully manifest to its subject. For example, a sense datum might have exactly 17 spots, even though the subject perceiving the sense datum isn't aware of the number of spots.
Is there any reason to accept even something as weak as the Phenomenal Exportation Principle? Why should we think that, just because I seem to be perceiving something, that there is anything at all that I am perceiving? Why couldn't my perceptual states sometimes be completely misleading? The most plausible response to this objection would be to appeal to the Principle of Sensory Error Minimization:
PEpist 4.1 Sensory Error Minimization. Other things being equal, prefer a theory that posits the fewest and least severe sensory errors to human subjects.
We have epistemological grounds for adopting such a principle. If we don't, we will have no reason to give the evidence of the senses weight in our choice of scientific or metaphysical theories. The Phenomenal Principle could be defended by an appeal to the Principle of Sensory Error Minimization, although this appeal would be complicated by the fact that we have to concede that our perceptual states are in some kind of error in the case of hallucinations and other illusions. However, there is no such complication in the case of the Phenomenal Exportation Principle. We don't have to concede that our perceptions are completely unreliable in the case of hallucination: only that they are unreliable as guides to the external, physical world. The Phenomenal Exportation Principle enables us to salvage some element of correctness within every case of hallucination, something that Sensory Error Minimization urges us to do. This provides some support for Indirect Realism.
The Perceptual Realist alternative to Indirect Realism is Direct Realism. There are two varieties of Direct Realism, namely, Perceptual Dualism and Unitary Direct Realism. They differ on what happens in hallucination. Perceptual Dualists claim that in a hallucination we perceive some real mental entity, while Unitary Direct Realists deny that we perceive any real thing in a hallucination.
13.3A.1A.1T Perceptual Dualism. It is possible to directly perceive non-mental (physical) objects, as in veridical perception. It is also possible to be in states (hallucinatory states) in which one directly perceives a wholly mental object but perceives no physical object, and some hallucinatory states are introspectively indistinguishable from some veridical perceptions.
13.3A.1A.1A Unitary Direct Realism. Cases in which existing physical things are directly perceived are introspectively indistinguishable from cases in which no existing thing is directly perceived.
Unitary Direct Realism in turn comes in two varieties, Meinongian and Non-Meinongian. The Non-Meinongian version of Unitary Direct Realism is Intentionalism.
13.3A.1A.1A.1T Meinongian Direct Realism. It is possible to directly perceive both existing and non-existing physical objects, and some cases of the former are introspectively indistinguishable from the latter.
13.3A.1A.1A.1T Intentionalism. It is possible to directly perceive existing physical objects, and there are possible states introspectively indistinguishable from these in which one perceives nothing whatsoever (whether mental or physical, existing or non-existing).
Intentionalists suppose that direct, veridical perception of physical objects can be analyzed into two factors. First, the perceiver must be in a sensory state that represents some physical object O's being a certain way. Second, that physical object O must be that way in reality and O's being that way must have caused the sensory state in the appropriate way. Thus, whether or not a given sensory state is a case of veridical perception depends ultimately on the causal connections between that sensory state and the external world.
Some versions of Intentionalism, including the adverbial theory of perception (Ducasse 1942, Chisholm 1957), the belief or propensity-to-believe theory (Anscombe 1965), and especially mental-representation Intentionalism (Tye 2000) became dominant in the last part of the twentieth century. A perceptual state possesses some kind of content, in much the way that a sentence or a map has content, that is, meaning or significance. What are present in the mind, what are introspectible, are symbols or representations of physical objects akin to proper names or mug shots. These internal symbols are ordinarily the representations of some unique physical object, that object whose characteristics cause the representation in the appropriate way. In the case of hallucination, this normal process goes awry, resulting in something like an empty or denotationless proper name. Suppose, for example, that unbeknownst to one there never was anyone named ‘Homer’ (the Greek poet). One could nonetheless use the name ‘Homer’ as though it signified some individual. One is not really referring to anyone in using the name, but it seems to oneself that one is. One can't tell the difference between using an empty and a non-empty name merely by introspecting the psychological processes involved in generating these uses. In the same way, a hallucination corresponds to the occurrence of an empty symbol within the sensory part of one's mind.
13.3.1.1 The solipsistic veil of perception.
The argument from hallucination proceeds by process of elimination. We must first be convinced that we should be unhappy with Indirect Realism, Perceptual Dualism, Meinongian Realism, and Intentionalism. Then we are left with the Solipsistic Veil of Perception, by process of elimination, as the only plausible account of hallucination and non-veridical perception generally.
As we've said, the Solipsistic Veil of Perception runs strongly against common sense, as well as against contemporary science. Consequently, we should embrace the Veil only if there are irrefutable objections to the other four accounts. If any one of the alternatives is defensible, the Veil should be rejected.
13.3.1.2 Indirect realism.
Indirect Realism was most famously defended by John Locke in his Essay Concerning Human Understanding (Locke 1690/1979). Locke's view subsequently came under severe criticism from Idealists like Berkeley. Here we will focus only on those criticisms that build on the problem of hallucination.
The strongest challenge to Indirect Realism in this context involves another appeal to Ockham's Razor. Why suppose that we even indirectly perceive physical objects when we never directly perceive them? The simplest account of perception is one in which all perception is direct. We could simply deny that indirect perception occurs, without any fear that this denial could be contradicted by an act of direct perception. After all, it would seem to be impossible to directly perceive that one is indirectly perceiving something.
There does seem to be some sense in which the fact being perceived is present in the very content of an act of direct perception, in contrast to cases of merely indirect perception. When one directly perceives a red triangle, redness and triangularity are somehow given or present to one, whereas when one indirectly perceives a hawk or electron, all that is given in experience is the thing (the shadow, the cloud trail) perceived directly. It seems at least initially plausible to think that only cases of direct perception license beliefs without the need for further evidential support.
This line of thought has been resisted, most notably by Thomas Reid and those who have followed him in embracing a kind of common-sense philosophy. Reid (1785) argued that any belief that we form naturally is prima facie justified, even if the belief is formed on the basis of indirect perception.
13.3.1.3 Intentionalism.
Intentionalism is somewhat implausible on its face, since there seems to be something before us when we hallucinate. This thing that presents itself to us in hallucination can persist, move, and undergo other changes. Nonetheless, many philosophers have argued that this impression that we are seeing something when we hallucinate is itself illusory. Perhaps we are presented with an incomplete content, something like a sentence or diagram with an element that normally signifies a unique object but which, in abnormal cases like hallucination, fails to signify anything at all.
Critics of Intentionalism, from G.E. Moore (1903b/1993) to Frank Jackson (1977),4 have argued that
the theory overlooks the obvious act-object structure of perceptual experience. When Macbeth hallucinates the knife, there is something that is the object of his sensory awareness, something apparently knife-shaped and blood-red. The hallucinatory experience isn't anything like the experience of unwittingly using a name that happens to lack denotation. Whenever one uses a name, one is well aware of the fact that one's consciousness includes something that merely stands for the absent name-bearer. A hallucinated knife is not some merely hypothetical object supposedly related to a consciously apprehended symbol. Any such mere symbol would be something that is obviously not knife-shaped or blood-red, whereas there is in fact an object of awareness that itself appears to be knife-shaped (not merely to be something that is supposed to represent a knife-shaped object).
When one hallucinates visually, one seems to be perceiving something with a certain color and shape. This gives us good grounds, at least prima facie, for thinking that there really is something with that color and shape, or something close to them, in our environment. We may have good grounds for disbelieving that there is something physical with that color and shape, but this counter-evidence does not undermine our grounds, based on Sensory Error Minimization, for thinking that there is nonetheless something that we are perceiving, unless we assume that we cannot perceive anything non-physical. But hallucinatory and dream experiences give us some reason to think that we do perceive non-physical things.
In addition, it is possible via hallucination to gain real knowledge about perceivable objects, as Adam Pautz (2007) has noted. Suppose that one has never seen anything red or triangular, and that one has a hallucination of a red triangle. On the basis of the hallucination, one could learn that red is more similar to yellow than it is to green or that there is a plane figure with exactly three sides. One can learn that it is possible for something to be both red and triangular, and one can become acquainted with what such an object looks like. If such a case of hallucinatory learning is possible (as it seems it is), then the mere presence in one's mind of a symbol of redness or of triangularity was not in fact the ground of the knowledge one gained from hallucination, since one had such symbols without knowing what one learned about redness or triangularity by actually having the sensory hallucination. Nor was it enough for one to apprehend the properties of triangularity or redness in a purely intellectual way. In addition to that intellectual apprehension, the hallucination can add new information in an analogue and non-conceptual form.
Intentionalists can respond by appealing to the Ducasse-Chisholm adverbial theory of perception. When one perceives or hallucinates something red, one is in a state of being-appeared-to-redly. Nothing need actually be red, nor need there be an object that even appears to be red. Instead, it is one's sensory experiencing that is in a state somehow related to redness, perhaps by representing red things or by being the state that normally occurs when veridically perceiving red things or a state that justifies or prompts in a certain way the belief that something is red.
Of course, our sensory representations have a kind of object structure: We are not just appeared to redly; instead we are appeared to red-triangularly, as if we were seeing something red and triangular. In addition, our sensory appearances seem to have a kind of relative location in space. Macbeth's hallucination of the knife is just to the right of a table. Thus, our appearances have a kind of logical and quantificational structure: the appearance of something red and triangular and to the left of something green and circular. In the end, these object-like nodes in the structure of appearance must either be objects that appear to us in certain ways or mere symbols or signs that represent things as being certain ways in relation to us and to one another.
To make sense of this dispute, we will have to distinguish between conceptual and non-conceptual (or digital and analogue) representations. A conceptual or digital representation need not contain something the same or similar properties to the thing represented. Digital storage devices, for example, like computer memory, contain representations that share qualitatively very little in common with the things represented. On the other hand, a non-conceptual or analogue representation, like a map or picture, actually contains something with the same or similar properties to the thing being represented. A map represents a triangular region by containing something triangular or nearly so. It seems that one can learn from a hallucination precisely because it is an analogue representation. In a hallucination one perceives in a sensory way something that is itself red and triangular (or close to being so), in a way that no mere representation or content could be. If hallucinations do involve analogue representations, then while hallucinating we must be aware of something red and triangular. Since there is nothing physical that is red and triangular in the right location, we must be aware of some mental object.
However, Intentionalists have a plausible reply. Analogue representation does not require that the very same properties be realized in the representational medium and the represented object. All that is required is that there be a systematic, one-to-one mapping, an isomorphism, between the properties possessed by the representational objects and those possessed by the represented objects. For example, we can use colors to represent variations in temperature or length to represent acoustic volume. In the same way, it could be that there is nothing red or knife-shaped in our representational system when hallucinating a knife, but only a pattern of neural firings that belongs to a system of patterns isomorphic to the shape and color of external objects. It may be that in hallucination we are in some fashion aware of that pattern of stimulations (giving rise to the illusion of an object of perception), while in fact seeing absolutely nothing.
In fact, we could use the distinction between apprehending and perceiving that we introduced earlier. When we are having a hallucination or are subject to an illusion, we are not perceiving anything, but we may be apprehending a number of abstract objects, including properties and possibilities. The internal representations may fail to correspond to any existing physical object in the environment, but they may still correspond to certain possible situations. By having those internal representations we can gain knowledge of those possibilities. We can learn from what we apprehend even though we do not perceive anything.
Before leaving Intentionalism, we should note that John McDowell (1994) has objected to Intentionalism on the grounds that it, like the Veil of Perception, alienates our minds from the natural world around us. McDowell worries that by placing images or representations in the mind, Intentionalists concede too much to defenders of the Veil. When we perceive something, our minds stand in a direct relation to some external object, a relation not mediated by any supposed internal counterpart. Presently, we consider McDowell's favored solution to the problem of hallucination, Perceptual Dualism.
13.3.1.4 Perceptual dualism.
The term ‘disjunctivism’ has been used for a variety of positions in the philosophy of perception since the 1980s. Our term, ‘Perceptual Dualism’, doesn't fit exactly to this history, but ‘disjunctivist’ seems apt as a description of Perceptual Dualism. Roughly, disjunctivism is the idea that hallucination is a fundamentally different kind of mental state than veridical perception. Perceptual Dualism represents a hybrid position, one agreeing with the Veil of Perception and Indirect Realism in the case of hallucination, and with Unitary Direct Realism in the case of veridical perception. In hallucination, on this view, we perceive only a mental object, and in veridical perception, we directly perceive some extra-mental, physical object.
Perceptual Dualists face a serious problem, however, concerning the location of the purely mental object that we are supposed to perceive when hallucinating. Macbeth's bloody knife seems to be located in space. It is hard to see how Macbeth could perceive the knife as located in front of him if it is a completely unlocated, extra-spatial object. If we are going to suppose that we ordinarily perceive something in hallucinations, then we should assume that our perceptions of these mental objects are mostly accurate.
Perceptual Dualists have several options here. First, they could simply concede that sense data are located “out there” in ordinary space. The experienced parts or properties of one's mind would then, or at least could, be scattered over a fairly large region of space. Suppose, for example, that one has a hallucination of a supernova in the sky. the sense data perceived in such a case would be scattered radically over a huge spatiotemporal region.
Alternatively, Perceptual Dualists could suppose that one perceives the location of objects in two different but coordinated spaces, a private mental space and a public physical or physical-cum-mental space (see Davis 2014). Thus, sense data and physical objects do in fact exemplify different sets of spatial properties, but we are unable to tell by introspection whether we are perceiving an object as being located in private or in public space. The two sets of properties are themselves indistinguishable by introspection. Nonetheless, in cases of veridical perception, we perceive the physical locations of physical objects directly.
To avoid falling into a simple Indirect Realism, Perceptual Dualists must suppose that physical things are located both in public space and in the private spaces of minds that are perceiving them. There is some plausibility for this. For example, the sofa is located to the left of the chair in RCK's private space, but not in objective space (where there is no left or right).
This sort of Perceptual Dualism seems to provide a viable alternative to the Veil of Perception as an account of hallucination. Its main drawback lies in its complexity, when compared with its main competitors, namely, Direct Realism and the Veil. Perceptual Dualists have to propose that two quite different processes are taking place in cases of hallucination and veridical perception, in spite of the fact that they seem, introspectively, to be quite similar.
The Atlas of Reality Page 48
