TWO CHALLENGES THAT CATEGORICAL PROPERTIES POSE TO
PHYSICALISM
Robert Schroer
Abstract
What are physical objects like when they are considered independently of their causal
interactions? Many think that the answer to this question involves categorical
properties—properties that make contributions to their bearers that are independent
of any causal interactions those objects may enter into. In this paper, I examine two
challenges that this solution poses to Physicalism. The first challenge is that, given
that they are distinct from any of the scientifically described causal powers that they
happen to convey, categorical properties will not qualify as being ‘physical’
properties. Given the right definition of ‘physical’, this challenge can be overcome. I
argue, however, that the only way we can have a positive grasp of the nature of
categorical properties is via ‘acquaintance’—a non-physical relation. This second
challenge to Physicalism cannot be overcome.1
The Apparent Incompleteness of the Physical Sciences
The physical sciences study how objects behave in various settings and how they
causally interact with one another; they are interested in what objects do, not in what
they are like apart from what they do. Consider, for example, some of the properties
that are the focus of the crown jewel of the physical sciences: physics.
…mass is knowable only by its dynamic effects. Turn up the magnification
and we find things like an electrical charge at a point, or rather varying over a
region, but the magnitude of a field at a region is known only through its
effects on other things in spatial relation to that region. A region with charge
is very different from a region without…It differs precisely in its dispositions
or powers.2
If we assume that the physical sciences capture the essences of the properties they
posit—if, for example, we assume the laws of physics capture the essence of mass—
then the properties posited by the physical sciences will be what, in the current
literature, are known as ‘dispositional properties’—properties whose essences are
exhausted by the causal powers they convey upon their bearers. As a result of its
essence, there is a necessary connection between a given dispositional property and
the powers it conveys; mass, qua dispositional property, conveys the same causal
powers in all possible worlds where it is instantiated.3
The fact that the physical sciences focus on what objects do, and not on what
they are apart from what they do, raises a question:
I would like to thank Brendan O’Sullivan for helpful comments on an earlier draft of this
paper.
2
Simon Blackburn, ‘Filling in Space’, Analysis 50 (1990), p. 63.
3
For similar definitions of ‘dispositional properties’, see John Heil, From an Ontological
Point of View (New York: Oxford University Press, 2003); David Armstrong, ‘Four Disputes
about Properties’, Synthese 144 (2005), p. 309-320; Carl Gillett and Bradley Rives, ‘The
Non-Existence of Determinables: Or, a World of Absolute Determinates as Default
Hypothesis’, Nous 39 (2005), p. 483-504; Jonathan Schaffer, ‘Quiddistic Knowledge’,
Philosophical Studies 123 (2005), p. 1-32; and Alexander Bird, Nature’s Metaphysics
(Oxford: Oxford University Press, 2007).
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1
Reference to the proton is fixed as the thing that causes interactions of a
certain kind, that combines in certain ways with other entities, and so on; but
what is the thing that is doing the causing and combining?4
What are protons like when they are considered independently of the various causal
interactions that they enter into? It’s hard to see how the physical sciences can
answer this question. The fact that the physical sciences seem to give us an
incomplete description of the objects they describe—a description that focuses on
what these objects do, and not on what they are apart from what they do—is what I’ll
call the ‘the Problem of the Apparent Incompleteness of the Physical Sciences’ or ‘the
Problem of Incompleteness’, for short.
This problem has received a lot of discussion.5 Although some want reject the
coherence of Chalmers’ question and argue that physical objects possess only
dispositional properties (as defined above)6, many accept the coherence of the
question and, in an effort to answer it, claim that physical objects have ‘categorical
properties’—properties that make contributions to their bearers that are independent
of the causal interactions into which these objects enter. According to the latter
group, a physical object’s categorical properties are what we should point to when
attempting to answer the question ‘What is the thing doing the causing and
combining?’
For expositional purposes, let’s call anyone who responds to the Problem of
Incompleteness by claiming that at least some of the properties of physical objects are
categorical a ‘Categoricalist’. Categoricalists differ from one another in terms of
what they say about the existence of dispositional properties. Some want to claim that
physical objects possess both dispositional and categorical properties.7 Others, in
contrast, want to claim that physical objects possess only categorical properties.8
According to this second Categoricalist position, the physical sciences use
‘dispositional names’—names that highlight the causal relations that the tokens of
properties partake in—to refer to properties that are, in fact, categorical in nature.
4
David Chalmers, The Conscious Mind (Oxford: Oxford University Press, 1996), p. 153.
The origin of the problem traces back to Hume’s and Berkeley’s arguments that the primary
qualities (i.e. the properties described by the physical sciences) are not enough to ‘fill in’
space. For more recent discussions of the problem, see Bertrand Russell, The Analysis of
Matter (London: Kegan Paul, 1927); David Armstrong, Perception and the Physical World
(London: Routledge & Kegan Paul, 1961); Chalmers, Conscious Mind; Frank Jackson, From
Metaphysics to Ethics (New York: Oxford University Press, 1998); Rae Langton, Kantian
Humility: Our Ignorance of Things in Themselves (Oxford: Oxford University Press, 1998);
Daniel Stoljar, ‘Two Conceptions of the Physical’, Philosophy and Phenomenological
Research 62 (2001), p. 253-270; Daniel Stoljar, Ignorance and Imagination: The Epistemic
Origin of the Problem of Consciousness (Oxford: Oxford University Press, 2006).
6
See, for example, Sydney Shoemaker, ‘Causality and Properties’, in P. van Inwagen (ed.),
Time and Cause (Dordrecht: Reidel Publishing Company, 1980), p. 109-153; Sydney
Shoemaker, ‘Causal and Metaphysical Necessity’, Pacific Philosophical Quarterly 79 (1998),
p. 253-270; Bird, Nature’s Metaphysics.
7
More carefully, some Categoricalists want to claim that physical objects possess both
dispositional and non-dispositional properties. See, for example, Brian Ellis, Scientific
Essentialism (Cambridge: Cambridge University Press, 2001) and George Molnar, Powers: A
Study in Metaphysics (Oxford: Oxford University Press, 2003).
8
See, for example, David Armstrong, A World of States of Affairs (Cambridge: Cambridge
University Press, 1997).
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2
Mass, for instance, is a categorical property that is picked out in virtue of the causal
powers it happens to convey. In virtue of being a non-dispositional property,
however, mass conveys the causal powers it does in concert with the laws of nature
and not solely in virtue of its intrinsic nature. If the laws of nature were different, the
powers conferred by mass would be different as well. Generalizing this last point, we
can say that if a categorical property conveys powers to its bearers, it does so
contingently.
The First Challenge Presented by Categorical Properties
The existence of categorical properties appears to be a threat to Physicalism. The
thesis of Physicalism is often defined in terms of the physical sciences; it is often
defined as the position that everything supervenes upon the properties posited by the
physical sciences. As noted earlier, the physical sciences pick out properties in terms
of the causal powers they convey. But categorical properties have intrinsic natures
that are distinct from the powers they happen to convey. As a result, the physical
sciences will be incapable of describing the intrinsic natures of categorical properties.
This makes it seem like categorical properties will be missed by the physical sciences
which, given the above definition of Physicalism, guarantees that categorical
properties will be non-physical. Let’s call this ‘the First Challenge Presented by
Categorical Properties’.
There are ways of interpreting (or modifying) the definition of Physicalism
that allow a Categoricalist to respond to this challenge. He could, for instance,
maintain that a property counts as ‘physical’ as long as it is referred to by the physical
sciences. So although the physical sciences describe properties in terms of the powers
they convey upon their bearers, it could be that the properties they end up referring to
are, in fact, categorical properties, properties that are only contingently connected
with the aforementioned powers.9
Another option for the Categoricalist is to define physical properties in
ostensive terms. Physical properties could be defined, for example, as the properties
necessary to give a complete account of paradigmatically physical objects (such as
tables and chairs). If categorical properties are included among these properties—as
you might think they would be, given the Problem of Incompleteness—then
categorical properties will count as being ‘physical’.10
The above definitions of Physicalism are controversial. But this is no slight,
for all definitions of Physicalism are controversial, including ones that
straightforwardly appeal to the physical sciences (like the initial definition I sketched
above).11 So when the Categoricalist says, ‘just because categorical properties have
intrinsic natures that cannot be described by the physical sciences doesn’t mean that
they can’t be physical properties’, his supporting argument isn’t relying on an
especially controversial sense of the word ‘physical’.
For additional discussion of this point, see Jackson, From Metaphysics and Stoljar, ‘Two
Conceptions’ and Ignorance.
10
For additional discussion of this point, see (again) Jackson, From Metaphysics and Stoljar,
‘Two Conceptions’ and Ignorance. (In his ‘Two Conceptions’, Stoljar actually gives two
definitions of ‘the physical’—one that appeals to the physical science, another that is
ostensive.)
11
See, for example, Carl Hempel, ‘The Logical Analysis of Psychology’, in H. Feigl and W.
Sellars (eds.), Readings in Philosophical Analysis (New York: Appleton-Century-Crofts,
1949), p. 373-384 and Tim Crane and D.H. Mellor, ‘There is no Question of Physicalism’,
Mind 51 (1990), p 185-206.
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The First Challenge to Physicalism has been blunted. It would be mistake,
though, to think that this is the only way the existence of categorical properties
challenges the thesis of Physicalism. As I will show, the real challenge posed by
these properties resides elsewhere; it rears its head when we attempt to explain how
we can have a positive grasp of the nature of categorical properties.
What does it take to have a positive grasp of categorical properties?
If dispositional properties existed, it would be relatively easy to say what they are
like—all you would need to do is point to their scientifically described causal powers.
(Recall that the essence of a dispositional property is exhausted by such powers.)
Categorical properties, in contrast, are supposed to make contributions to their bearers
that are independent of the various causal interactions involving those objects. (As
we saw earlier, a categorical property can contingently convey causal powers to its
bearers. But describing these powers is not the same thing as describing the essence
of the categorical property that, in concert with the laws of nature, helps to convey
them.) In order for categorical properties to serve as a completely satisfying solution
to the Problem of Incompleteness, we need a positive account of their essences—we
need to know what they are like.
To be clear, some Categoricalists act as though there is nothing we can point
to in order to fill out our conception of categorical properties.12 According to the
proponents of this extreme position, the Problem of Incompleteness reveals that
physical objects possess a kind of property of which we are fated to be ignorant. I
suspect that most defenders of categorical properties, however, will not want to go
this route: all we have seen so far is that the physical sciences are incapable of
revealing the intrinsic nature of categorical properties. It’s not crazy to think that
there may be other ways of learning about properties that will allow us to grasp the
intrinsic nature of categorical properties. (Indeed, we will see later that it is possible
for subjects to grasp the intrinsic nature of categorical properties in another way, but
only at the price of denying Physicalism!)
Where can Categoricalists turn in an attempt to fill out our conception of
categorical properties? Some turn to introspection and point to the intrinsic properties
of experience—i.e. phenomenal properties—to fill out our conception of categorical
properties. Simon Blackburn, for example, claims that ‘categoricity comes with the
subjective view.’13 Similarly, David Chalmers maintains that ‘There is only one class
of intrinsic, nonrelational property with which we have any direct familiarity, and this
is the class of phenomenal properties.’14
Another possibility is that perception allows us to grasp the essence of some
categorical properties. (John Heil, for instance, acts as though one of the best
arguments in favour of categorical properties is that we can see them.15) The idea,
then, is that our perceptual experiences reveal the essence of some of the categorical
properties of the external objects that we see.
This idea is briefly discussed in Jackson, From Metaphysics, under the label ‘Kantian
Physicalism’. Langton, Kantian Humility, develops this idea into an interpretation of Kant’s
noumena.
13
Blackburn, ‘Filling’, p. 65.
14
Chalmers, The Conscious Mind, p. 153. Such suggestions raise the spectre of panpsychism.
I follow Chalmers, The Conscious Mind and Stoljar, Ignorance, however, in thinking that
pointing to phenomenal properties in this context does not inevitably result in panpsychism.
15
See, in particular, Heil, From an Ontological Point.
12
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But how, exactly, does introspection or perception allow us to grasp the
essence of a categorical property? For expositional simplicity, let’s start with the idea
that introspection makes us aware of categorical properties of experience. Earlier, we
defined categorical properties in negative terms: they are non-dispositional properties
in that they make contributions to their bearers that are independent of the causal
interactions that those objects may enter into. Since the essence of a categorical
property is distinct from the powers that it conveys in a given world, it is logically
possible for there to be distinct categorical properties in this world that happen to
convey the same set of powers.16 Suppose, for sake of argument, that this situation
obtains; suppose that there are distinct phenomenal properties—A and A'—that
happen to convey the same powers to the experiences that instantiate them. If
introspective awareness of phenomenal properties is mediated by a causal process, it
follows that we will be unable to introspectively discriminate A from A' for both of
these phenomenal properties are guaranteed to effect us in exactly the same way. It
also follows that we will be unable to introspectively notice a change in our
experience where A is replaced by A'.
Of course, if there are no ‘primed’ phenomenal properties (such as A') in the
actual world, then, in principle, introspection could discriminate all phenomenal
properties from one another and could note all experiential changes from one
phenomenal property to another. But even in this case, the fact that a phenomenal
property like A' is logically possible still means that we don’t have that much of a
positive understanding of the essence of the phenomenal properties that actually exist,
such as A.17
To appreciate this last point, imagine a liquid superficially similar to water
that has a completely different chemical nature, such as Putnam’s XYZ.18 Perception
alone would not be capable of discriminating these liquids from one another. If you
were chemically ignorant and your understanding of water was exclusively
perceptual, the fact that you would not be able to perceptually discriminate H2O from
XYZ would reveal that you don’t have much of a grasp of the essence of water. Now
if XYZ doesn’t exist in your world—if the only clear, tasteless liquid in your world is
H2O—you might be able to perceptually discriminate water from all other actual
liquids. But the fact that there could be a superficially similar liquid that you would
be unable to perceptually discriminate from water still shows that you don’t have
much of a perceptual grasp of the essence of water. Analogously, if your grasp of
phenomenal properties is exclusively introspective, the fact that you would be unable
to introspective discriminate A from A' shows that you do not have much of a grasp
of the categorical essence of A. It doesn’t matter whether there actually is a
phenomenal property in your world answering to the description of A'.
I will call this line of argument ‘the Shoemaker Argument’, for Shoemaker
uses similar considerations to argue that we cannot know about or even refer to
categorical properties.19 (I suspect that Categoricalists who claim that we are fated to
be ignorant of categorical properties have a similar argument in mind.) In response to
Shoemaker, several have pointed out that our failure to grasp the essence of
For more on this point, see Bird, Nature’s Metaphysics.
Cf. John Hawthorne, ‘Causal Structuralism’, in J. Tomberlin (ed.), Philosophical
Perspectives 15 (Malden: Blackwell Publishers, 2001), p. 361-378.
18
Hilary Putnam, ‘The Meaning of “Meaning”’, Minnesota Studies in the Philosophy of
Science 7 (1975), p. 131-193.
19
See Shoemaker, ‘Causality’ and ‘Causal and Metaphysical’.
16
17
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categorical properties does not entail an inability to know about or refer to them.20
That’s why I want to emphasize that, in my hands, the Shoemaker Argument only
establishes that we do not have a full grasp of the categorical nature of phenomenal
properties. It does not establish that we cannot know things about these properties or
that we cannot refer to them.
The Shoemaker Argument assumes that our introspective awareness of
phenomenal properties is facilitated by the effects they have on us. This assumption
invites a response: perhaps our introspective awareness of phenomenal properties is
via a non-causal, direct, and brute cognitive relation (‘acquaintance’) that obtains
between the mind and those properties. If this were the case, we could be directly
acquainted with differences between the intrinsic natures of A and A' even if these
properties happen to convey the same causal powers, for our introspective access to
these properties would not be mediated via their effects upon us. This, in turn, means
Categoricalists can repel the Shoemaker Argument if they maintain that we are
acquainted with the phenomenal properties of our experiences.
We can reach the same conclusion if, instead of pointing to phenomenal
properties, we try to explain what categorical properties are like by appealing to our
perceptual grasp of certain properties of external objects. If these properties of
external objects are categorical, it follows, as a logical possibility, that there could be
two distinct properties of external objects—B and B'—that happen to convey the
same causal powers to their bearers. If perception is a casual process, as many
following H.P. Grice believe, then we will be unable to perceptually discriminate B
from B' or notice a change where an external object lost B and gained B'.21 (This is
just the Shoemaker Argument again, applied this time to properties of external
objects.) If, however, perception involves a non-causal form of awareness of these
categorical properties, the Categoricalist can rebut the Shoemaker Argument and
maintain that we are acquainted with the intrinsic categorical differences between B
and B' despite the fact that both of these properties are guaranteed to lead to the same
effects when instantiated.
Let’s summarize the discussion of this section. To give a completely
satisfying solution to the Problem of Incompleteness, the Categoricalist needs to give
a positive account of what categorical properties are like—an account of what their
intrinsic natures are like, and not just an account of the causal powers they happen to
convey. Since science is of no help with this project, the obvious thing to do is turn to
introspection or perception. As we have seen, though, the only way that either of
these ideas will work is if the Categoricalist appeals to the relation of acquaintance.
In the next section, we will see that this commitment to acquaintance introduces a
second threat to Physicalism.
The Second Challenge Presented by Categorical Properties
As an epistemological notion, ‘acquaintance’ has had its share of problems; there are
concerns about infallible beliefs22, the speckled hen problem23, and the myth of the
See, for example, Schaffer, ‘Quiddistic’ and Bird, Nature’s Metaphysics.
H.P. Grice, ‘The Causal Theory of Perception’, Proceedings of the Aristotelian Society 35
(1961), p. 121-152.
22
See, for instance, David Armstrong, ‘Is Introspection Knowledge Incorrigible?’,
Philosophical Review 72 (1963), p. 417-432.
23
See Roderick Chisholm, ‘The Problem of the Speckled Hen’, Mind 51 (1942), p. 368-373.
20
21
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given24, just to name a few. (Despite these concerns, some people continue to be
drawn to the idea that we are acquainted with intrinsic features of our experiences25
while others—so-called ‘Disjunctivists’ about perception—claim that, in the case of
veridical perception, we are acquainted with mind-independent properties of external
objects.26) Rather than investigate these well-worn objections, I will focus on another
problem that acquaintance raises for the Categoricalist: namely, a commitment to
acquaintance threatens the thesis of Physicalism.
Before beginning, however, I have a confession: strictly speaking, I can’t
prove that if there is such a thing as the relation of acquaintance, it must be a nonphysical relation. But such a conclusion seems likely. To get a sense of the bleak
prospects for a Physicalist account of acquaintance, let’s consider Joseph Levine’s
recent discussion of the possibility.27 One crucial element to the notion of
acquaintance is that it gives us a direct and substantial awareness of its referent. (For
convenience, I’ll assume that the referent in question is an intrinsic property of
experience—i.e. a phenomenal property.) When we are acquainted with a
phenomenal property, the ‘mode of presentation’ of that property does not involve
other properties (this is what makes it ‘direct’), nor is it thin as it would be in the case
where I blindly point in front of myself and think, ‘I wonder what that is?’28 Rather,
when we are acquainted with a phenomenal property, that property serves as its own
substantial mode of presentation.
Levine investigates the prospects of a Physicalist account of acquaintance by
exploring the recent trend among some Physicalists of claiming that phenomenal
concepts contain, as constituents, the very phenomenal properties to which they
refer.29 This can be viewed as a Physicalist-friendly attempt to capture the idea,
central to the notion of acquaintance, that when we introspect a phenomenal property
that property serves as its own substantial mode of presentation.
…when we think of a relation such as acquaintance, with its sense of
immediacy, metaphysical language about ‘sticking the object right in there’
irresistibly comes to mind. But this language is metaphorical. The current
proposal is to solve the problem by taking it literally.30
This is an alternative account of the mechanism of introspective awareness, an
account that does not maintain that we are introspectively aware of a phenomenal
See Wilfred Sellars, ‘Empiricism and the Philosophy of Mind’, Minnesota Studies in the
Philosophy of Science 1 (1956), p. 253-329.
25
See, for instance, David Chalmers, ‘The Content and Epistemology of Phenomenal Belief’,
in Q. Smith and A. Jokic (eds.), Consciousness: New Philosophical Issues (Oxford: Oxford
University Press, 2003), p. 220-272.
26
For discussion of this idea, see the papers in A. Byrne and H. Logue (eds.), Disjunctivism:
Contemporary Readings (Cambridge, MA: The MIT Press, 2009).
27
See Joseph Levine, ‘Phenomenal Concepts and the Materialist Constraint’, in T. Alter and
S. Walter (eds.), Phenomenal Concepts Phenomenal Knowledge (Oxford: Oxford University
Press, 2007), p. 145-166.
28
This example is taken from Joseph Levine, Purple Haze (Oxford: Oxford University Press,
2001), p. 82.
29
See, for example, David Papineau, Thinking about Consciousness (Oxford: Oxford
University Press, 2002) and Ned Block, ‘Max Black’s Objection to the Mind-Body Identity’,
in T. Alter and S. Walters (eds.), Phenomenal Concepts, p. 249-306.
30
Levine, ‘Phenomenal Concepts’, p. 163.
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property in virtue of its effects upon us. The problem, however, is that it is unclear
how the physical presence of a phenomenal property in a phenomenal concept
translates into a direct and substantial cognitive presence. After all, our phenomenal
concepts instantiate lots of different properties...so why it is the case that we are
aware of these particular properties? And why are we aware of these properties in
this very unique and substantial manner? As Levine says
It still smacks of that famous cartoon of the physicist scribbling all these
formulas on the blackboard with one in the middle that says ‘and then a
miracle occurs’. The transition from physical containment to awareness—the
special kind allegedly afforded by phenomenal concepts—is still an
inexplicable transition.31
I’m inclined to follow Levine’s lead on this. I find it utterly mysterious how the
physical relation of containment (or any other non-causal physical relation) could
explain the kind of awareness of phenomenal properties we are supposed to have in
virtue of being acquainted with them. It seems that in order to explain how such a
relation works, we need more resources than that Physicalist can provide; it seems we
need a brute non-physical relation. This is ‘the Second Challenge Presented by
Categorical Properties’, and I don’t see how Categoricalists can overcome it.
Conclusion
In positing the existence of categorical properties—properties whose essences are not
captured by the physical sciences—the Categoricalist appears to threaten the thesis of
Physicalism. As we have seen, this threat can be blunted; given the right definition of
‘the physical’, categorical properties can qualify as being physical properties.
In order to serve as a completely satisfying solution to the Problem of
Incompleteness, however, Categoricalists need a positive account of the nature of
categorical properties. In an effort to fill out our conception of these properties,
Categoricalists could appeal to introspection or perception. The Shoemaker
Argument shows that the only way that introspection or perception could provide this
service is if it involves acquaintance. And in virtue of the commitment to
acquaintance, the threat to Physicalism re-enters the picture. So although the
existence of categorical properties, by itself, does not threaten Physicalism, our
epistemic access to these properties does.
What’s the proper conclusion to draw from all this? Assuming that we want
to retain our Physicalism, should we deny the existence of categorical properties and
instead argue that the Problem of Incompleteness is not a problem after all? Should
we take another look at the Categoricalist position that I earlier dismissed as
‘extreme’, the position that maintains that there are categorical properties but that
have no grasp of their intrinsic nature? Or should we reconsider the very distinction
between dispositional and categorical properties?32 It’s hard to say. But one thing is
for sure: we cannot give a completely satisfying answer to the Problem of
Levine, ‘Phenomenal Concepts’, p. 163.
See, for example, Heil, From an Ontological Point, where it is argued that each individual
property is both dispositional and categorical. For a similar position, see Robert Schroer, ‘Is
There More than One Categorical Property?’, The Philosophical Quarterly 60 (2010), p. 831850. For a discussion of how such an approach addresses the Problem of Incompleteness, see
Robert Schroer, ‘How Far Can the Physical Sciences Reach?’, American Philosophical
Quarterly 47 (2010), p. 253-266.
31
32
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Incompleteness by appealing to categorical properties without seriously threatening
Physicalism.
Arkansas State University
Department of English and Philosophy
P. O. Box 1890
State University, AR 72467
USA
Email: rschroer@astate.edu
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