Appearance Pluralism, Perception, and Causation
Guy Longworth1
University of Warwick
March 08
1. My aims here are fairly limited. They’re also a little incestuous, since my main
target is the first main chapter of my colleague A. D. Smith’s book The Problem of
Perception. Smith’s book is mainly about a version of the Argument from Illusion
and how he thinks we should respond to that argument. My aims today are the
following. First, I want to sketch the Argument, as Smith appears to understand it,
pausing every so often to worry at some of Smith’s formulations. Second, I want to
focus more closely on a particular sort of response to the Argument, a response that
Smith associates with the early 20th Century movement called New Realism, but
which I think can be detached from that setting. Here, I want to consider what Smith
thinks is wrong with that response, adding some considerations from the work of
Sydney Shoemaker. I won’t be able to respond fully to the complaints pressed by
Smith and Shoemaker, mainly because I’m not yet in a position to mount such a
response. Rather, my aim is limited to pointing to some hoops that someone who
seeks to press their complaints would need to jump through, or push us through,
before it would be clear that there was really something wrong with the broadly New
Realist response to the argument that Smith presents.
Let me say from the outset what I’m not trying to do. First, I’m not trying to argue
that the New Realist type response provides a blanket answer to the Argument from
Illusion. For one thing, even in Smith’s hands, the Argument from Illusion appears to
shade into an Argument from Hallucination. And the New Realist type response to the
Argument from Illusion is implausible as a response to the Argument from
Hallucination. Second, I’m not suggesting that the New Realist type response
provides the optimal, or even a viable, response with respect to any case of illusion.
All I’m attempting here is a sketch of some of the ground over which future dispute
over the standing of the New Realist response should take place. Third, then, I’m not
suggesting that there aren’t other, better objections to the New Realist response than
1
A version of this note was presented at the London Logic and Metaphysics Forum,
March 2008. Thanks to Mark Kaldron, M.G.F. Martin and other members of the
audience on that occasion. Thanks especially to Matthew Soteriou who has done his
utmost to make my engagements with this topic less Naïve.
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those presented by Smith and Shoemaker. I’d be pleased to hear about such objections
in discussion. But my present concern is limited to a particular class of objections.
Finally, I’ll be focusing on visual perception and take no stand about how the issues
discussed here might play out with respect to other forms of perception.
2. Let me begin by sketching Smith’s version of the Argument from Illusion. The
argument is designed to undermine what Smith calls “Direct Realism”, a view
according to which what we see, or what we see directly, includes mind-independent
objects and perhaps mind-independent features or properties of mind-independent
objects. In the first instance, I think “Direct Realism” is supposed to be construed as a
form of Naïve Realism, so to include at least the following two components:
(1) The phenomenal character of our perceptual experience is at least partly
constituted (as I’ll sometimes put it shaped) by objects and properties of which we are
aware in having the perceptual experience.
(2) The objects and properties of which we are aware in having perceptual experience
and that go towards shaping the phenomenal character of our perceptual experience
are mind-independent objects and properties, at least to the extent that they exist
independently of being experienced and are possible objects of experience for
perceivers other than us.
I think that Smith takes Naïve Realism also to include a third component, according to
which the objects and properties that we see play a particular role in determining the
phenomenal character of our visual experience.
(3) The form of awareness involved in the perceptual experience we suffer through
vision, and which shapes the phenomenal character of our experience, is the form
seeing. Thus, the objects and properties that partly determine the phenomenal
character of the perceptual experience involved in our seeing are just the objects and
properties that are seen by us.
Obviously, there is much more to be said in spelling out this type of position. And
there is no reason to expect that all who take themselves to endorse Naïve Realism
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should endorse all components on all spellings out. But the sketch here will do for
present purposes.
Smith’s own response to the Argument from Illusion involves dividing up the objects
and properties that play a role in shaping our experience into, on one hand, those that
go towards determining the phenomenal character of our experience and, on the other
hand, those that we see. He thinks that by drawing that distinction, he is able to
explain phenomenal character by appeal to mind-dependent properties without
thereby threatening the idea that what we see are mind-independent objects and
properties. His idea is that the Argument from Illusion shows that we need minddependent properties to explain the phenomenal character of our perceptual
experience, since there is insufficient variety in the world to explain the various ways
the world appears to us in experience. And he thinks that if those mind-dependent
properties were also the things we see in undergoing perceptual experience, they
would occlude the mind-independent objects and properties that we naively take
ourselves to see. The problem of perception, for Smith, is to explain how there can be
space for his favoured combination of views.
As we’ll see, the New Realist type response takes a slightly different tack. The idea
driving the response is that the objects and properties awareness of which shapes
perceptual experience are mind-independent objects and properties. In order to sustain
that idea, the New Realist appeals to the further idea that the mind-independent world
contains a sufficient plurality of properties to explain the vicissitudes of experience to
which the Argument from Illusion makes appeal. Hence, according to the New Realist
response, there is no need to appeal to a plurality of mind-dependent properties in
order to sustain the first component of Naïve Realism. But I think that the New
Realist can afford to remain neutral about whether the mind-independent properties to
which they appeal in order to explain phenomenal character are properties that we
ordinarily see. The more minimal version of their view is that they are properties of
which we are aware, whether or not our awareness takes the form of seeing them.
So, Smith endorses Naïve Realism (1) and amends Naïve Realism (2) in line with his
distinction between two roles that objects and properties of awareness can play in
shaping experience. And he rejects Naïve Realism (3). The New Realist type
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response, as understood here, endorses Naïve Realism (1) and Naïve Realism (2) and
is neutral with respect to Naïve Realism (3).
3. The crux of the dispute between Smith and his more naïvely realist opponents is the
status of Naïve Realism (1) and Naïve Realism (2). Smith’s version of the Argument
from Illusion is designed to show that at least one of these components must be
revised or rejected and that the favoured revision involves giving up the claim that the
phenomenal character of perceptual experience is shaped by mind-independent
objects and properties. How is the Argument from Illusion supposed to sustain that
trick?
3.1. Let’s begin with the first stage of Smith’s presentation of the Argument,
including his account of what an illusion is (or, rather, what “illusion” will extend
over for purposes of his argument).
Our argument begins…with the premise that perceptual illusion can occur. The
term “illusion” is to be understood here as applying to any perceptual situation
in which a physical object is actually perceived, but in which that object
perceptually appears other than it really is, for whatever reason. [Footnote
omitted] It is therefore irrelevant whether the subject of an illusion is fooled by
appearances or not. (p.23)
This understanding of “illusion” is narrower than some natural understandings, since
we might allow that illusion can strike when no “physical object” is involved. Smith
himself appeals to the possibility of auditory illusions, and one might think that these
involve sounds. Perhaps Smith includes those amongst the physical objects. Or
perhaps he thinks that when one experiences a sound, one typically hears the producer
of the sound, often a physical object. But there are other cases. For instance there
might be illusions involving rainbows, and there might be illusions involving events.
Smith’s understanding of illusion might also be thought broader than (some) ordinary
understandings, as Smith notes:
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For example, the world appears differently to those who are colour-blind and to
those who are not. This involves illusion, in the possibly unnatural sense here
employed. For if I, not being colour-blind, cannot tell red and green things
apart, but you can, at least one of these colours must look different to the two of
us. So, for at least one of us, that colour cannot look the way it really is. (p.23)
3.2. Why is it supposed to follow from a physical object’s looking different to the two
subjects that, for at least one of the subjects, the colour cannot look a way it really is?
Smith’s explains his reason in the following way:
That there “really” is a way the object is “objectively” is a presupposition of the
Direct Realism that is under investigation here, and so will not come up for
discussion. (p.23)
The most important feature of this passage is the claim that “Direct Realism” is
committed to there being a way a perceived object is, however many ways it can
appear to different subjects. Of course, there being a way is consistent with there also
being other ways. But the way this claim appears to function in Smith’s argument
strongly suggests that he intends the quantifier to rule out the possibility of there
being other ways. Otherwise, it would be consistent with the view that the colourblind subject and the non-colour-blind subject are both aware of ways the target
object is, even though those ways are different. The obvious understanding of the
claim then is this: “Direct Realism” presupposes that there is exactly one way a
perceived object really is.
That appears to be a remarkably strong presupposition. Some natural questions at this
point are the following. Is the presupposition tenable, independently of consideration
of illusion (on Smith’s understanding of the latter)? Aren’t there often many ways an
object is, even according to natural scientific descriptions of the object, including
ways described in physics, chemistry, and perhaps biology? Who is the “Direct
Realist” who is supposed to make this presupposition?
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Perhaps Smith’s view can be clarified in the following way. Suppose that there is
exactly one way each physical object is. Then we might suppose that that way will
often include a variety of more specific ways. For instance, the fact that a physical
object is one way—for instance, spherical—appears not to rule out its also being a
different way—for instance, red. In that case, when we say that there is exactly one
way the physical object is, we might mean something like the following. There are a
variety of specific ways the object is, and if we take each of those ways and conjoin
them, we get a maximally specific way the object is. And there is only one such way
the object is.
Smith’s argument would then appear to require something like the following. Each
specific way an object “really” is involves a single dimension of variation. With
respect to each such dimension, there is only one specific location the object can
occupy, so only one specific way the physical object can be. Hence, if it appears to
different subjects to occupy different positions along a single dimension, then at least
one of those appearances must fail to correspond with the way the object is, for the
object can occupy at most one location along any such dimension.
With respect to the present example, the idea would be that there is a single
dimension of colour variation, and that an object can really occupy at most one point
along that dimension. Hence, the way the object really is cannot constitute the way it
appears to both our subjects, since some coloured objects present different colour
appearances to the two subjects.
4. That’s the First Stage of the Argument, summarized by Smith in the following way:
(P1.)
[T]here is no type of physical feature that may not appear differently from the
way it really is to any sense that could possibly perceive it.
From there, we move on to the Second Stage, P2:
(P2)
[From P1] …[W]henever something perceptually appears to have a feature
when it actually does not, we are aware of something that does actually possess that
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feature. So, if you are looking at a white wall, which because of the illumination looks
yellow to you, you are aware of something yellow.
From the perspective of Naïve Realism, as understood here, the following component
of this premise seems more or less incontrovertible. Since phenomenal character is
constituted by the objects and features that we’re aware of, something of which we
are aware must have the features required to constitute the phenomenal character of
the experiences that we enjoy. So, if the phenomenal character of our perceptual
experience is of a type that could only be explained by our awareness of something
with some property, F, then in order to enjoy experience with that character, we must
be aware of something with that property, F. There is a get out clause, since Naïve
Realism is only committed to partial constitution of phenomenal character by objects
and properties of awareness. But the get out clause is in place to allow that general
conditions on experience or ways of experiencing might play a role in shaping
perceptual character, and it would be against the spirit of the account to allow specific
features of specific experiences to have their phenomenal character shaped by minddependent objects or properties. So for present purposes we can allow that the Naïve
Realist will accept P2. However, it does not yet follow that that property must be one
that, in cases of illusion, is not instanced by the mind-independent objects of which
we are aware.
4.2. The Third Stage of the argument is P3:
P3.
…[S]ince the appearing physical object does not possess that feature which,
according to the previous step, we are immediately aware of in the illusory
situation, it is not the physical object of which we are aware in the illusory
situation, it is not the physical object of which we are aware in such a situation;
or, at least, we are not aware of it in the direct, unmediated way in which we are
aware of whatever it is that possesses the appearing feature—that direct way in
which we formerly took ourselves to be generally aware of normal physical
objects. (p.25)
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If we endorse the three premises, as Smith understands them, we appear to be forced
(give or take the get out clause mentioned earlier) to give up Naïve Realism (1) or
Naïve Realism (2), or both. We might worry that all the work is being done by the
first premise, which is in effect the premise that some cases of things looking some
way to us cannot be explained by appeal to mind-independent objects or their
properties. And Smith’s argument to this point does not rule out the following type of
response.
The phenomenal character of our perceptual experience is partly shaped by the
features of things we are aware of. And, where the experience takes the form of visual
perception, those features are mind-independent features. However, they are not
always the features we say that the things we see really possess; sometimes they are
mere appearances. However, that is perfectly consistent with the ways things appear
being mind-independent features, features things would possess whether or not we
became aware of them.
What, if anything, does Smith have to say in response to that type of response to his
argument? Put another way, what argument does Smith have to the effect that some
cases of illusion cannot be explained in line with Naïve Realism (1) and Naïve
Realism (2)? What constraints are there on the range of mind-independent objects and
features that are able to sustain that result?
5. Smith considers a response to his argument at least close to the one just sketched,
attributing it to the New Realist movement that flourished in the United States at the
beginning of the last century. He writes:
A number of philosophers…have attempted to block [the argument] at Stage
Three. The New Realists accept the sense-datum inference: when the tomato
looks black to me, I am aware of something black. They deny, however, that I
am therefore not aware of a normal physical object… For why should not the
blackness that I see be a genuine feature of the tomato? (29)
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Although Smith’s characterisation of New Realism brings that position close to the
sort of response sketched above, there are two points at which it departs slightly from
that sketch.
First, the initial way in which Smith describes New Realism has it committed to
objects’ instancing a variety of colour properties, so that the tomato instances both
redness and also blackness. But the response sketched here is less radical. According
to that response, the tomato instances both the property of appearing red and the
property of appearing black, where that is perfectly consistent with it instancing
neither redness or blackness.
Second, Smith characterises the New Realists as attempting to block his argument at
Stage Three, our P3. But an equally natural view would be that they seek to challenge
the argument at Stage One, our P1, by seeking to reject the idea that illusion is
possible, at least where illusion is understood in the particular way that Smith
recommends. On Smith’s understanding, there are possible illusions that involve
physical objects’ lacking any property corresponding with the way they appear. In
denying the possibility of that sort of illusion, the present response has it that
appearance properties are ways things are, so that the only sort of illusion that is
possible is one involving things not really being a way they appear, despite really
having appearance properties able to shape the phenomenal character of experiences
of that thing.
Smith seems to correct both points in the following passage, while introducing
another optional element to the New Realist type account:
[The New Realists]…were actually engaged in questioning our everyday
conception of physical reality, and replacing it with a picture of physical objects
as extremely complex systems of variegated views and appearances. Reality is
now regarded as being sufficiently rich to allow all the features present in our
varying perceptions to be genuine constituents of physical reality. (30)
The optional element that Smith introduces here is the idea that the ‘variegated views
and appearances’ that are to play a role in constituting the variegated characters of our
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perceptual experiences are to replace, rather than to supplement, those aspects of our
everyday conception of physical reality that involve physical objects and some of
their properties being comparatively stable elements in our experience, by contrast
with the complex systems of appearances elements of which play a more ephemeral
role in shaping our experience.
What, then, does Smith think is wrong with the New Realist style of response? There
are two main strands to his objection, both in the following passage.
Our straightforward understanding of physical objects is replaced in such an
account by a bewildering system of properties from which the fairly stable
everyday characteristics of things can be abstracted only with great ingenuity…
The supposedly physical difference [presented by a single physical object that
presents two appearances to a subject, or subjects] is a difference that makes no
physical difference at all. A merely apparent difference is not, to be sure, wholly
without possible causal consequences. Such consequences are, however,
restricted to causal contexts that involve the psychological realm… The point is
that there is no possible non-psychological, merely physical, situation in which
the supposedly physical difference…counts for anything. This invalidates the
claim that the difference in question is indeed physical. (31)
Let’s leave aside the optional component of the New Realist type response according
to which our straightforward understanding of physical objects is replaced, rather than
supplemented, by a bewildering system of appearance properties. We can then focus
on two broad lines of objection contained in this passage.
The first line of objection is that, if we allow physical objects to bear the required
variety of appearance properties, this is bound to ‘bewilder’ our attempts to see
through their array in order also to perceive the ‘fairly stable…characteristics of
things’.
There are at least two ways of developing this sort of concern, neither of which I want
to spend time on here. The first way takes the form of a challenge to the New Realist
to explain how we are able to perceive objects and the properties they really have in
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the face of the bewildering plurality of appearances. While I think that challenge is a
good one, it is one that would appear to confront most theorists in this area, since
most theorists allow that there is a plurality of appearances and differ only over
whether those appearances are taken to be independent of our experience of them. In
particular, the challenge confronts Smith to the same extent that it confronts the New
Realist.
The second way of developing this type of concern also takes the form of a challenge,
in this case to explain why our awareness of appearances does not serve to screen us
off from objects and their fairly stable characteristics. Since it is possible for
something to appear some way F without being F, we might think that awareness of
the appearance of F is compatible with a failure to be aware of F. In that case, we
might wonder how, in cases where something not only appears F, but also is F, we
can see through the appearance in order to see the instancing of F. Again, I think this
is a good question, but it seems an equally good question for someone who believes
that appearance properties are mind-dependent, so is not of immediate concern in the
present context.
The second line of objection is the one I want to focus on for the remainder of the
talk. According to this second line, the problem is supposed to attend the idea that
appearance properties are “physical”, or perhaps more minimally that such properties
are causally efficacious with respect to what is “physical”. Again, there are a variety
of ways of developing this sort of concern, and I shall focus on only a selection.
A first way of developing the concern is by appeal to the idea that “physical”
properties must have a variety of possible effects. In particular, according to this idea,
“physical” properties must do more than simply affecting the phenomenal character of
perceptual experience.
One way of responding to this development is to point out that, if that is what the
requirements are on “physical” properties, as Smith understands them, then there is no
immediate reason for the Naïve Realist to care about whether the properties that shape
phenomenal character are “physical”. What the Naïve Realist is committed to is only
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that the shaping properties are mind-independent; they have no further commitments
regarding the specific nature of those mind-independent properties.
In fact I don’t think that Smith intends his classification of properties as “physical” to
do that sort of work. Rather, he intends “physical” and “objective” to do the same sort
of work, akin to the work of “mind-independent” as I’m using it. His thought, then, is
that in order for a property to count as mind-independent it must have effects on
things other than our minds.
One response to this development would be to question the requirement. We might
challenge the claim that mind-independence entails the power to affect things other
than the mind. However, we might then find it somewhat mysterious that mindindependent properties could be so limited in their range of effects given that they are
constituted independently of those effects. If we do find that mysterious, then a better
response would be to point out that it appears to be only a contingent feature of
appearance properties that their effects are limited to perceptual experiences. Insofar
as we think of appearance properties as mind-independent we might also think of
them as the sorts of properties that might be detected by a physical machine, perhaps
a machine similar in construction to the physical systems that enable human
experience. Unless there is reason to think that no such machine is possible, its
possibility would seem to underwrite sufficient width of cosmological role for
appearance properties that we can happily view those properties as mind-independent.
Although further discussion is warranted, I predict that the upshot will be
unfavourable to Smith’s case. Either Smith will be forced to appeal to more stringent
conditions on what is to count as mind-independent, or “objective”, or “physical”, at
which point his Naïve Realist opponent will be apt to view those conditions as
optional. Or he will appeal to conditions that the Naïve Realist is independently
disposed to accept, at which point his Naïve Realist opponent will be able to show
that appearance properties can meet those conditions.
It seems to me then that Smith’s argument runs aground at this point. There is no
immediate reason, based upon the premise that they only have impact on experience,
to reject the view that appearance properties are mind-independent. However, there is
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a quite different way of developing this general type of concern by appeal to a
converse premise. Taking this line, Sydney Shoemaker has attempted to argue that
mind-independent appearance properties would, in at least some possible cases, be
precluded from having an impact on experience. It is to his argument that I now turn.
Shoemaker’s argument can be sketched in the following way. We begin by supposing,
in line with Naïve Realism, that there might be two subjects, Jo and Kim, who are so
constructed that, when confronted by a particular type of physical property, P, the
phenomenal character of Jo’s experience is shaped by appearance F and not by
appearance G, while the phenomenal character of Kim’s experience is shaped by
appearance G and not by appearance F. The question at issue is whether the
phenomenal characters of both experiences are shaped by mind-independent
appearance properties, F and G, respectively. Shoemaker argues that whether that is
possible depends upon the specific way in which the difference between Jo and Kim
is explained. In particular, Shoemaker argues that it appears to be possible that the
“proximal effect” on Jo and Kim of the physical property, P, together with whatever
appearance properties it supports, might be the same, consistently with their
experiences having different phenomenal characters. This might be so, for instance, if
the immediate impact on their perceptual systems, perhaps at the retinal surface, is the
same, and the differences in their respective experiences arise as a result of further
processing in the system’s innards. Shoemaker’s idea, in short, is that what I’ll call
the “surface” of the two systems screens off their operative elements—those involving
the system’s innards—from causal interaction with the two appearances. Hence, the
different mind-independent properties are inefficacious in producing the different
experiential effects enjoyed by Jo and Kim. That may be consistent with the
appearance properties being mind-independent. But on Shoemaker’s view, it is not
consistent with their shaping Jo and Kim’s experiences in the way the New Realist
supposes. Hence, if Shoemaker is right, it is not consistent with the scouted response
to Smith’s argument.
I don’t have space to engage in detail with Shoemaker’s argument. Instead, I want to
briefly sketch some hoops that the purveyor of the argument will need to jump
through (or push us through) before the New Realist, or appearance pluralist, need be
troubled by it.
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1. Although we might well believe that there are causal constraints on what can be
perceived, it is not trivial that these constraints apply at the level of experience and
experienced property. The Naïve Realist takes the relevant form of experience,
awareness of a property, to be a type of relation holding between a subject and the
objects or properties of which they are aware. And it is apt to seem mysterious that a
property could cause the holding of a relation between a subject and that property, in
part because causation is often held to involve an independence condition, apparently
failed in the required type of case.
However, Mark Kalderon has a lovely example which at least suggests that there is
nothing immediately problematic about such cases of causation. He has us consider
the power of the wind to cause a weather vane to point in its direction. We could
attempt to question whether Kalderon’s case is really of the required sort. And we
could try to question whether whether the principles governing the case are
guaranteed to hold in the case of awareness. For in the case of awareness, the relations
are supposed to play a constitutive role with respect to experience, while weather
vanes and their directions can be characterised without appeal to the wind.
But a better response would be to shift tack slightly. Instead of using Naïve Realism
in an attempt to argue that causation couldn’t play the constraining role, we might use
it instead as the basis for an argument to the effect that it needn’t play that role. In the
first place, the thought would be that required distinctions between cases of
perception and other cases can be captured by appeal to whether the required
experiential relation holds, without needing additional input from causal conditions.
In the second place, it might be suggested that, insofar as causal conditions are
relevant to whether an experiential relation is in place, those conditions apply at a
lower level, requiring, for instance, that the physical properties that support the
experienced properties interact causally with parts of the physical system that
supports the experience of those properties. At that point, the apparent difficulty for
the Naïve Realist would lapse.
2. Suppose, however, that reason can be provided for a causal condition on awareness
that applies at an appropriate level. The next hoop involves the Naïve Realist’s
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opponent providing reason to think that Jo, Kim and their respective appearance
properties fail to meet that causal condition. If, for instance, the condition is framed in
terms of chained counterfactuals, then there appears to be no immediate reason for
thinking that the fact that Jo and Kim share an experiential surface undermines the
obtaining of those chained counterfactuals.
What appears to be driving Shoemaker’s argument at this point is a more substantive
conception of causal interaction than is supplied by appeal solely to counterfactuals.
Perhaps, for instance, he is appealing to some sort of physical model of causation,
according to which causal interaction involves transfer, or preservation, of some
conserved quantity like energy. Such a model might ground the idea that the systems’
surfaces screen off the appearance properties from experiential effects.
There are two questions to press at this point. The first is, Should we buy the
proposed account of causation? Jonathan Schaffer argues that our ordinary conception
of causation appears happily to allow cases of negative causation, where cessation of
a process sustaining some effect is taken to cause cessation of the effect. One example
of this is where a bullet to the heart is allowed to cause death by inducing cessation of
the process whereby the brain is oxygenated. If Schaffer is right, then we have some
reason for rejecting the type of physical model of causation that appears to be
required by Shoemaker’s argument.
Alternatively, suppose that Schaffer is wrong. The second question is whether we
should retain our initial commitment to there being causal conditions on awareness, so
understood. That is, discovering that causation proper involves energy transfer or
preservation might make us rethink our initial view that causation proper is required
for awareness. Perhaps, for example, for the work the causal condition is required to
do in governing awareness, a merely counterfactual condition is adequate and
causation proper is redundant.
3. Suppose however that those concerns have been addressed. The third hoop for the
opponent of Naïve Realism involves providing a principled reason for restricting the
proximal effect of appearance properties in a way that might show them to be
inefficacious in the production of experience.
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One question here is, Why should we view the effects of experience as being anything
less than the whole system? Shoemaker appears to be motivated by the idea that we
can think of the surface of the experiential system as a point of initial impact, with
effects within the surface transmitted by events involving the surface rather than
events involving the distal precursors of those surface events. But we might question
that conception of causal interaction. In homage to Thompson Clarke, we might ask
whether our conception of causal relations supports answers to questions like “How
much of the operation of the system was caused by the impact of light on its surface?”
Consider an analogy. I might throw a stone at a cup, causing the cup to break. How
much of the cup’s breaking was caused by the initial impact of the stone on its
surface? How much was due instead to the internal structure of the cup? Insofar as we
find questions like this difficult to answer, or even to understand, that is a sign that we
shouldn’t rush to accept the sort of answer Shoemaker thinks that we should give in
the case of perceptual systems.
Suppose, however, that we allow that the immediate effects of the physical object
presented to Jo and Kim are surface effects. Shoemaker’s argument then requires that
those surface effects act as a sort of screen, or bottleneck, with respect to the plurality
of properties we are assuming to be carried by the physical object. His idea at this
point appears to be that, since the surface of each of the systems is of the same type—
perhaps of the same physical type—then it must transmit the same effects into the
system’s innards.
However, it should be obvious that the appearance pluralist will be unwilling to allow
that argument to stand. For the appearance pluralist is already committed to the
possibility of a single physical object, with a single range of physical properties,
carrying a plurality of appearance properties. So a natural response to the latest round
of argument is that it is also possible for the inner surface of the system to carry a
plurality of properties and for it to be the causal impacts of one rather than another of
this plurality that causally explains the different experiences suffered by Jo and Kim.
6. As I said at the start, I haven’t attempted to show that the New Realist, or
appearance pluralist, type of response to the Argument from Illusion is adequate. I
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haven’t even attempted to show that no causal argument of the sort presented by
Smith and by Shoemaker can be used to undermine that type of response. What I hope
to have done is to indicate some points at which more work will be required before
we’re in a position properly to assess appearance pluralist response to the Argument
from Illusion.
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