our right to believe in the OMOs that the indirect realists claim we're never directly aware of.
2.41 One way to develop the first line of response would be to consider a crude reliabilist response. A reliabilist about justification thinks that beliefs are justified iff they are the outputs of reliable processes, processes that produce a sufficiently high ratio of true to false beliefs.9 Notice that the arguments adduced thus far have been silent on the question as to whether experience reliably leads to a high ratio of true to false beliefs. Suppose that it does. Suppose further, as seems plausible, that when we form our perceptual beliefs, we believe non‐inferentially in external objects and believe non‐inferentially that they have certain features (e.g. color, shape, location, etc.). If this is compatible with indirect realism, maybe indirect realism isn't so bad. The process that takes sense data as input and spits out a perceptual belief as output might generate a sufficiently good truth ratio even if the IOAs are distinct from OMOs. Imagine we were primed to believe that a thing is present whenever we observed a shadow. We take it we all agree that the inference from the observation of a shadow to the presence of a thing is a reliable one even if the shadow cast is distinct from the thing we observe.
2.42 One way to develop the second line of response is to consider the possibility of acquiring evidence that connects IOAs to OMOs that goes beyond the evidence provided by a single experience. The indirect realist might grant that we have better evidence to believe things about IOAs than OMOs but still insist that over time we get good enough evidence to believe that OMOs resemble IOAs in certain salient ways. They might try to model justification and knowledge concerning OMOs on familiar examples of scientific inference from the observed to the unobserved. Here's Frank Jackson (1977):
Consider a familiar example, the Molecular theory of gases. The Molecular theory of gases explained the various experimentally observed properties of gases … and enabled the prediction of new properties which were subsequently experimentally verified. On this basis and prior to the direct observation of molecules, it became universally accepted that gases are made up of sub‐microscopic particles (molecules). And similar remarks apply to the whole development of the atomic theory in all its forms.
(1977, p. 143)
The lesson that Jackson wants us to draw from these cases is that we should be open to the idea that we can learn about that which we cannot directly observe by observing distinct things directly. This includes knowledge of the sub‐microscopic and of the external world.
2.43 Although these points suggest that we shouldn't dismiss indirect realism too swiftly, problems nonetheless remain for the view. Let's briefly consider two related ones that bring out some perplexities of the view that may have thus far flown under the radar. And on this score, let's think again about Price's cricket ball. According to the indirect realist, when you see the ball there are two distinct objects of awareness:
IOA: the immediate object of awareness is sense data, something distinct from every perceptible material object and something that has all the properties it appears to have.
OMO: the cricket ball, which is an ordinary material object. It is distinct from the IOA and it only potentially has the properties that it appears to have. If the subject's experience is veridical, it will share some of the properties of the IOA. If not, it might not.
On this approach, if the experience of the OMO is veridical, a subject will be aware of two things that are white and round, a sense data and a cricket ball.
2.44 The first odd feature of indirect realism we want to bring out is that the view implies that there are two distinct round and white things. One of these is located where the cricket ball is. (Why? Because one of these things, the OMO, is the cricket ball.) What about the IOA? Where is it? Well, the Argument from Hallucination tells us that it could continue to exist and continue to be just as round and just as white if, say, neuroscientists destroyed the cricket ball but stimulated your brain in such a way that your conscious experience continued just as it would when seeing the ball under normal conditions. In this case of hallucination, there would be no white and round thing left where the cricket ball was. At least, we cannot find anything round and white there. So, where could it be? One natural thought at this juncture is to say the white and round IOA is “in the head” of the person having the experience. However, this answer begins to look less viable on further inspection. Just suppose that the neuroscientists take the suggestion seriously, cut the person open, and discover there is nothing white and round there, either. Of course, you press back and say that what you meant was that the white and round IOA is “in the mind” of the perceiver, not literally in the head. In taking this line, though, consider what you'd be committed to: you'd be committed to the idea that there could exist white things and round things that exist in the world even if we destroy every white material object and every round material object. This seems quite weird, doesn't it? How could there be round things that exist if there are no round material objects?
2.45 The second oddity has to do with location. We sometimes suffer from perceptual illusions where things are closer than they appear. How do indirect realists account for this? Easily! They offer the account just sketched and say that the experience is illusory because the location of the IOA differs from the location of the OMO. (Remember that this is generally how they account for illusion. The Phenomenal Principle tells us that whenever it appears there is something F, the subject is aware of something that is F. The indirect realists say that this bearer of F‐ness is sense data and that it is distinct from every OMO.) Thus, as W.H.F. Barnes (1944) notes, indirect realists cannot plausibly deny that sense data have the properties they appear to have:
The sensum theory was devised to overcome the difficulty that we sometimes seem to be directly aware of some property in an object even though this property is not really present and is incompatible with others which are present. Sensa really have those properties which objects only appear to have. The chief convenience of the theory in fact is that it provides a home for every quality, real or apparent, which is experienced, and it does so by attributing to every such quality the status of a particular existent. If sensa could appear to have properties which they do not really have, the sensum theory would be bankrupt.10
The problem here is that the indirect realists cannot plausibly claim that sense data have the spatial properties we attribute to them.
2.46 Suppose you and a friend both see the wall and it appears yellow to your friend but white to you. It follows from the Phenomenal Principle that there is a sense datum where the wall appears to be to your friend that is yellow and a sense datum where the wall appears to be to you that is white. Since the wall appears to your friend to be in the very place it appears to you to be, it would follow that there is at one place and one time an object that is completely white and an object that is completely yellow. A single location cannot be occupied by an object that is completely white and completely yellow,11 so it appears that the Phenomenal Principle must be mistaken.
2.47 It is possible to veridically perceive the location of an object, so it should be possible for the immediate object of your friend's awareness to be located in just the spot that yours is. If the immediate object of your friend's awareness occupies that region and is yellow, yours cannot be white. And yet it must be, according to the Phenomenal Principle.
2.48 Price once suggested that sense data occupy a “special kind of space.” A sense datum that you're aware of might be spatially related to another sense datum that you're aware of, but they don't occupy “public space,” as he puts it.12
