Open Journal of Philosophy
2012. Vol.2, No.2, 84-88
Published Online May 2012 in SciRes (
Copyright © 2012 SciRes.
Thinking about Physicalism
Ricardo Restrepo
Escuela de Constitucionalismo y Derecho, Instituto de Altos Estudios Nacionales, Quito, Ecuador
Email:, r icardo.restr
Received January 30th, 2012; r evised February 25th, 2012 ; accepted March 11th, 2012
Physicalism, if it is to be a significant thesis, should differentiate itself from key metaphysical contenders
which endorse the existe nce of platonic entitie s, emergent prope rties, Cartes ian souls, angels, and God. Ph y-
sicalism can never be true in worlds where things of these kind s exist. David Papineau, David Spurrett, and
Barbara Montero have recently developed and defended two influential conceptions of physicalism. One
is derived from a conception of the physical as the non-mentally-and-non-biologically identifiable. The
other is derived from a conception of the physical as the non-sui-generis-mental. The paper looks at the
resources available to those conceptions, but argues that each is insufficient to yield a conception of
physicalism that differentiates it from key anti-physicalist positions. According to these conceptions, if we
lived in a world full of things that clearly cannot be physical, we would still live in a physical world. Thus,
such conceptions of physicalism are of little theoretical interest.
Keywords: Physicalism; Papineau; Consciousness; Mental; Causal Closure
Physicalism is the doctrine that everything actual is physical.
To make this precise, Jackson (1994) put it thus: any minimal
physical duplicate of our world is a duplicate simpliciter. This
doctrine seems to be flexible in various respects. For example,
finding out that anti-matter exists does not refute physicalism.
A minimal physical duplicate of our world would contain anti-
matter distributed just as it is in our world. Similarly, were we
to find out that phlogiston does exist after all or that the world
is as Newton theorised, this should not refute physicalism.
Rather, it would simply turn out that a minimal physical dupli-
cate of our world would contain phlogiston or have the proper-
ties Newtonian physics posits. According to our best current
knowledge, of cour se, a minimal physical duplica te of our world
would not contain such items. We can call these things “merely
not actually physical”. To put it in terms of Jackson’s formula,
physicalism allows that there are possible minimal physical
duplicates of some worlds such that they contain things that are
merely not ac t ually physical.
The doctrine of physicalism, however, must have a breaking
point, even if this limit is a fuzzy one. Without a border physic-
calism is completely drained of its theoretical interest. There
must be things physicalism cannot allow—things that clearly
could not exist in a world where physicalism is true. There
must be possible things—we can call these “anti-physical”—
that realize conditions under which physicalism would be false.
No world in which physicalism is true could contain platonic
entities, robustly emergent properties, angels, Cartesian souls,
nor God. In Jackson’s formula, there is no possible minimal
physical duplicate of a world containing anti-physical things. If
our world contained these things, then physicalism would be
In the ideal case, physicalists are not committed to the exis-
tence of anti-physical things. A philosopher might, however,
express commitment to physicalism but also express commitment
to anti-physical things, like platonic entities and God. Such
philosophers hold that except for their selected anti-physical
things, physicalism is true, acknowledging (at times tacitly) that
were matters to be left without positing this exception, they
would be in an unsustainable position.
Ruling out the possibility that any minimal physical dupli-
cate of a world contains an anti-physical thing is thus a neces-
sary condition on any interesting and possibly true conception
of physicalism. In this paper, I ev aluate David Papineau’s (2002),
Spurrett and Papineau’s (1999), and Montero and Papineau’s
(2005) conception of physicalism in these terms. I conclude that
their accounts are not able to meet this theoretical requirement.
Thought: From the Challenge of Consciousness
to the Challenge of Physicalism
One of the central challenges of physicalism is to adequately
deal with consciousness. Papineau (2002) sets himself to this
task in Thinking about Consciousness. The starting point for his
inquiry is the proposition which makes use of the causal argu-
ment for physicalism. Conscious properties seem to have phy-
sical effects. Thus, since every physical effect has a sufficient
physical cause, conscious properties must themselves be physic-
cal. In the context of the philosophy of mind, one is naturally
inclined to ask in response, but what about the “gap”? There
would appear to be a gap between conscious properties and
physical properties in that, for instance, one seems to be able to
know every physical fact about conscious echolocation, but still
not know what it is like to have such experiences (Nagel, 1974);
or that one may know every physical property of seeing red, but
without having seen red for one’s self, there seems to be a
property of seeing red that one does not know (Jackson, 1986).
The apparent gap between physical and conscious properties is
bridged by acknowledging that we can think about one and the
same worldly phenomenon of consciousness in neither mental
nor biological terms. To be physical is to be “identifiable non-
mentally-and-non-biologically”, which is to have the ability to
be referred to “independently of this specifically mental con-
ceptual apparatus” (2002: p. 41). Since conscious properties of
the world can be identified in this way, there is no problem with
them being physical and causal. The apparent gap is merely a
conceptual one because we can refer to everything going on
when a bat has experiences characteristic of echolocation and in
experiences of seeing red with physical concepts; it is just that
experiences can be referred to with mental concepts also. In one
stroke Papineau provides solutions to Kim’s (2005) two “world-
knots” about the mind-body: how conscious properties can be
accommodated within a purely physical world and how mental
properties can be causal. To put it in terms of Jackson’s formula,
Papineau’s (2002) physicalism is the thesis that any minimal
duplicate of the non-mentally-and-non-biologically identifiable
entities of our world is a duplicate simpliciter.
The problem with this thesis is that it fails to differentiate the
metaphysics of physicalism from the metaphysics of relevant
contenders. If our world is a world containing anti-physical
entities, our world would be, by the standards of the considered
conception of physicalism, a physicalist world.
Were platonic entities to exist, they would exist outside space
and time (Balaguer, 2009). These objects are taken to exist even
if the physical world did not, and are non-physical if anything
could be. A world where platonic entities exist, is a world where
anti-physical entities exist. Consider the platonic number 5. It
can be identified without specifically mental or biological con-
cepts. In fact, 5 is not a specifically mental or biological con-
cept. Alternatively, it can be identified as the result of 3 plus 2,
for example. Notice that there is a sense in which the concept of
the number 5 is mental, just like the concept of an electron; but
5 and electrons are not mental concepts in the sense relevant
here. Mental concepts here are solely those concepts which
operate in psychological terms, like belief, sight, and under-
standing. Because platonic numbers can be identified non-
mentally-and-non-biologically, Papineau would say that there is
a minimal physical duplicate of a world, which would have
platonic entities. Were platonic entities to exist in our world,
Papineau would have to say that physicalism is still tru e.
Secondly, emergent mental and vital properties are anti-
physical properties constituting an alternative metaphysics to
physicalism (McLaughlin, 1992). Papineau describes them as
constituting “non-physical causes of motion” (Papineau, 2002:
p. 25). One way of identifying emergent mental properties is as
a species of causes which are “not the vectorial ‘resultants’ of
basic physical forces like gravity and impact, but which ‘emerged’
when matter arranged itself in special ways” (Papineau, 2002: p.
252). But now notice that this way of identifying emergent
mental and vital properties does not make use of specifically
mental concepts; so by Papineau’s standards they would be
bona fide physical properties of the world, and there is a mini-
mal physical duplicate of a world which would contain them.
As Papineau (2002) agrees however, physicalism, a thesis he
endorses, is supposed to be incompatible with emergentism, a
thesis he rejects.
Thirdly, consider the possibility that angels exist. Suppose
that people, whilst alive, are completely identifiable as the re-
sult of certain aggregations of molecules. What happens to
people when they physically die is that they become angels, no
longer coincident with such aggregations of molecules, but
nevertheless up to all sorts of things between Heaven, Hell, and
Earth. Then, those angels can be identified non-mentally-and-
non-biologically as the continuants of the results of certain
aggregations of molecules. This non-mental-and-non-biological
identification opens the possibility, by the applied standards,
for angels to be physical, resulting in the thesis that the exis-
tence of angels is compatible with physicalism, and that there is
a minimal physical duplicate of a world containing angels. But
as everyone knows, if physicalism is a significant metaphysical
thesis, it is incompatible with the existence of angels (Chalmers,
Fourthly, suppose for a moment that Cartesian souls exist.
The Cartesian soul is an entity outside of space which is intrin-
sically ungoverned by the laws of physics and which interacts
causally with certain physical particles (coincident with the
pineal gland).1 Then, the Cartesian soul is non-mentally-
and-non-biologically identifiable as one of the things that in-
teract causally with certain physical particles. Consequently,
by Papineau’s standards, Cartesian souls would be physical if
they existed, and any minimal physical duplicate of that world
would have to contain Cartesian souls in order to be a duplicate
simpliciter. But Cartesian dualism is precisely a core meta-
physical position against which physicalism is defined in the
relevant debate. It should never be the case that a completely
physical world contains Cartesian souls.
Lastly, suppose God sparked the natural universe into exis-
tence 15 billion years ago wi th the Big Bang. The n God would
be non-mentally-and-non-biologically identifiable as the thing
that created the natural world 15 billion years ago. Again, by
Papineau’s standards, God would be physical, and a minimal
physical duplicate of a theist world w ou l d c o nta i n G o d, wh i c h i s
false (Chalmers, 1996).
No minimal physical duplicate of a world could contain pla-
tonic entities, emergent mental and biological properties, angels,
Cartesian souls, or God. If our world contained such things,
physicalism would be false. But Papineau’s theory would fail to
make this judgment. Papineau’s theory of physicalism wrongly
implies that even if platonic entities, emergent mental and bio-
logical properties, angels, Cartesian souls, and God existed in
our world, physicalism would be true.
A possible reply argues that the mentioned anti -physical things
do not exist, and consequently that no identification of them is
truly successful because our concepts of these things do not
pick anything out. So these things are not identifiable in the
first place and are therefore not non-mentally-and-non-bio-
logically identifiable, not physical, and not compatible with
physicalism. Things that do exist, however, are identifiable non-
This idea, however, gets matters confused. The concept of
the physical plays a distinctively important role in physicalist
theory, a theory whose success can be measured by how it in-
teracts with relevant contenders. The concept of the physical is
what gives physicalist doctrine its distinctive ontology. If the
conception of the physical advocated is one that applies to
relevant, possible anti-physical things, even if they do not actu-
1As with platonism, I mean to eschew debate here about Descartes’, as well
as Plato’s,historically accurate metaphysical views. There is debate about
whether these philoso phers corres
ondingly held what goes by the name o
“Cartesian dualism” and “platonism”. For example, Yablo (1990)argues
that Descartes’ relevant conclusions never go beyond asserting non-identity,
and this claim is insufficient for the rejection of physicalism, since someone
who argues that an aggregate of particles at a particular time constitutes but
is not identical with the statue with which it coincides at that time is not
committed to the rejection of physicalism. For a modern version of this
approach see Pereboom (2002), for example. Rather, I mean to refer to the
respective theories “Cartesian dualism” and “Platonism” are typically used
to refer to and which I otherwise specify.
Copyright © 2012 SciRes. 85
ally exist, then the resulting conception of physicalism is trivial
because it has no conditions under which it is false. Physicalism
should be able to mark out a distinctive metaphysical proposal
independently of which is the correct one. Its content should
not effectively be to say that the world is the way it is, whatever
it is like, and nothing more.
Papineau believes that his proposed conception of the physic-
cal “generates a conclusion of great philosophical interest: name-
ly, that all mental states, and in particular all conscious states,
must be identical with non-mentally identifiable states” (2002:
p. 41). However, keeping the mentioned anti-physical things in
mind, we see that anything, even a core anti-physical thing, is
identical with things that are identifiable in this way. Thus, it
cannot be of great philosophical interest that consciousness can
also be identified in this way.
At this point, one might wonder whether the very analytical
strategy of providing a conception of the physical in terms of a
dichotomy in our physical and mental concepts is misguided.
Consider how this strategy could be used to analyse our world,
not in physical terms, but in mental ones.
George is a panpsychist of the idealist type. The main chal-
lenge for him is to account for physical properties, and to meet
it he writes a book called Thinking about the Physical. George
agrees with Papineau that the physical is the non-mentally and
non-biologically identifiable. Employing the strategy of his
opponent, he holds that the mental is the non-physically identi-
fiable. George holds that everything is mental, and his proof
against the physicalist is that anything the physicalist says is
physical, the panpsychist can identify mentally (non-physi-
First, George recalls that in Papineau’s theory, the physical is
that which is non-mentally-and-non-biologically identifiable.
Identification, as Papineau agrees, consists in the mental opera-
tion of referring with applicable concepts. So Papineau refer-
ences the physical in mental terms, and thereby shows us that
the physical is also mentally identifiable.
Second, another example of how the physical can be non-
physically identified can be seen in Papineau’s (2002) history
of the idea of the completeness of the physical, which makes
reference to the principle of conservation of energy. He says,
“It took the genius of the young Hermann von Helmholtz
(1821-1894) to see the connections” (p. 245) between rational
mechanics and Joule’s work, which enabled him to make an
important discovery. This was the discovery of the principle of
conservation of energy. Consequently, one way of identifying
the physical property that is the conservation of energy is
through the use of specifically mental concepts like the discov-
ery of a genius. So, George concludes, everything is mental.
Physical properties are non-physically identifiable and are con-
sequently mental.
Of course, the physicalist might object that in contexts such
as physics classrooms such non-physical identifications do not
satisfy our explanatory needs. George disagrees because quan-
tum mechanics gives him grounds for introducing mental con-
cepts into physics and he points to Mermin (1985) and Stairs
(1990) to make the point that there is plenty of talk of observa-
tion in physics. But George is wise enough to note that not
every explanation with mental terms will satisfy our explana-
tory needs. Rather, he points out that for settings like psychol-
ogy classrooms non-mental terms do not satisfy our explana-
tory needs either, and consequently physical concepts do not
have an explanat o ry edge over mental ones.
The point is not that we cannot refer to the physical using
concepts that are not mental; we evidently can. Rather, the
point is that Papineau himself provides a general way of refer-
ring to physical phenomena in mental terms, and the reason to
call the position physicalist rather than panpsychist becomes
mysterious. In fact, we see that this strategy would incorrectly
count various other core anti-physical worlds as ones where
physicalism is true.
The Physical as the Non-Sui-Generis-Mental
Spurrett and Papineau (1999) and Montero and Papineau
(2005) propose a more outward-looking conception of the
physical: that the physical itself, and physical causes in par-
ticular, are not mental, “ending up with physicalism as the the-
sis that everything that has a non-mental effect must itself be
non-mental” (2005: p. 233). This thesis is taken to be supported
by physiological and other types of empirical investigation
(2005: p. 236). Stoljar (2009) notes the obvious objection that
“if a property is mental and physical” given physicalism and the
existence of the mental, then this view implies the contradiction
that “it will be both mental and non-mental which (of course) it
can’t be!”
Now I agree that the way proponents of this view of physic-
calism formulated it easily misleads upon a quick read. But
Montero and Papineau (2005) avoid the inconsistency of iden-
tifying the mental with the non-mental, by saying that the
“non-mental” is to be interpreted as “non-sui-generis-mental”
(2005: fn. 1) and that non-sui-generis-mental causes are those
things which can be “fully accounted for in terms of non-mental
causes” (Spurrett & Papineau, 1999: p. 26). Mental causes must
consequently be accountable for by individually non-mental
realization elements, which add up to those mental causes. One
natural way of thinking of a mental property is as one which is
realized when certain basic physical properties are combined in
a particular way, much like in the way the property of being a
triangle is realized when certain basic geometrical properties
are put together in a specific way (Jackson, 2006). In the case
of geometry, a basic geometrical property such as a line is not
triangular, just as, for instance, having a negative charge is not
mental. However, one could not consistently claim that a trian-
gle must be identified with the non-triangular, just as one could
not consistently claim that the mental must be identified with
something non-mental. Rather, a mental property may be iden-
tified with a group of basic physical properties assembled in a
certain way just as triangles may be identified with groups of
lines put together in a particular way. It is logically guaranteed
that certain arrangements of lines are triangles. Without contra-
diction, triangles are in this sense not sui generis triangles.
Similarly, given physicalism, it is logically guaranteed that
certain arrangements of physical properties are mental. What
would make them not sui generis mental is that they can be
fully accounted for in terms of properties which are not by
themselves mental. Something would be sui generis mental if it
was mental and could not be accounted for in this way.
One may wonder whether Papineau and Spurrett’s (1999)
and Papineau and Montero’s (2005) view is compatible with
the identity theory (Smart, 1962; Kim, 2005), since certain
physical properties would themselves be mental. According to
the relevant identity theory, the mental property of being in
pain, for instance, would be identical with a property of the
brain, like having c-fibres fire. So that property of the brain
Copyright © 2012 SciRes.
would be mental. Nevertheless, if that property of the brain is
built up from more basic non-mental properties, there would be
no conflict. For instance, having c-fibres fire is built up from
the molecules that compose c-fibres, neurotransmitters, and
charged elements. Such elements are not themselves mental.
Rather, the thing they are organized to compose is.
One way of interpreting the so-called via negativa is provid-
ing a sufficient condition for being physical. But this interpreta-
tion would meet anti-physical things as counterexamples. The
platonic number 3 is not sui generis mental in that it can be
accounted for in completely non-mental terms. Similarly, em-
ergent properties can be fully accounted for in non-mental
terms. Emergent plant life certainly has this ability. Emergent
mental life is just a non-linear effect of basic physical proper-
ties, which after the discovery of the function that relates them,
can be used to make normal scientific predictions (Broad, 1925).
Though they give rise to the mental, there is nothing here that
implies that such basic elements must themselves be mental.
Consequently, emergent mental properties are accounted for by
the non-mental conditions and the non-linear laws that deter-
mine them, and are, consequently, non-sui-generis-mental.
The proponents of this view must mean that it is an aspect of
the physical that it is non-sui-generis-mental. Montero and
Papineau (2005) indicate that this is what they suggest when
they reply to Witmer and Gillet’s (2005) objection that this
conception is prey to Hempel’s dilemma. This dilemma says
that there is no question of physicalism because if we under-
stand it as the view that current physics accounts for everything,
then given the incompleteness and the existence of errors of
current physics, it is false. If the target understanding of physic-
calism implies taking ideal physics to account for everything,
then it follows that we have no idea what we are asserting be-
cause we do not know what ideal physics is like. Given that we
have no other conception of the physical, physicalism is either
false or trivial. Montero and Papineau (2005) respond that their
thesis merely serves to direct attention to the fact that “cur-
rentresearch has so far failed to reveal any sui generis mental
causes, and from this it is reasonable to infer that there aren’t
any such causes” (p. 236). Similarly, when confronted with my
objections, they might argue that they are merely pointing out a
contingent empir ic a l fact about the physical.
There are many things that the physical is not, however. It is
not sui generis Newtonian, nor sui generis phlogiston, nor
Godly, nor sui generis made of ectoplasm, nor sui generis
physiological either since brains and neurons are not funda-
mental entities. Generally, it is not very enlightening to be told
that the physical is not sui generis anything. Papineau and
Montero (2005) say that the physical is not sui generis mental
because they think that the set of statements which characterize
the current empirical understanding of the world includes the
statement that there are not sui generis mental causes. If it is
reasonable to say that since physiological research has not
found sui generis mental causes that, by scientific induction,
causes are not sui generis mental (p. 235), then it is reasonable
to conclude by the same principle that they have the rest of the
characters that current physics posits. Rather than assert the
relatively uninformative conclusion that the fundamental prop-
erties of the universe are probably not mental on the basis of
current research, they could assert the likelihood of the positive
ontology of current research, which contains many causes
whose existence are just as confirmed as the theory that there
are no sui generis mental things.
The richer ontology of this conception of the physical may
sound just like one of the horns of Hempel’s dilemma. Mon-
tero’s and Papineau’s response is essentially that they are talk-
ing about what science has found (or failed to find) and that the
derived understanding is likely to be true. Is the current under-
standing sufficient to completely account for all effects? Mon-
tero and Papineau agree that it is not (p. 235). It is, however, a
richer understanding, which considers more than the assertion
that the cause is not sui generis mental. So if one is willing to
bet on scientific grounds that the physical is not sui generis
mental, one should also be able to bet on similar scientific
grounds on the rest of the statements on the list of current un-
derstanding. This would yield a more complete account of ef-
fects, resulting in a much larger return on the same epistemic
investment. To assert that that the list of complete causes will
be physical, like any physicalist investment, has its risks and
challenges (Cartwight, 2010), but we are assuming here that
physicalism has already taken the risks.
This more positive aspect of the so-called via negativa is,
however, something that we can expect the physicalist theory at
issue to endorse because its proponents think that bits of this
knowledge can be plugged in to substitute the term “physical”
depending on one’s purpose. They say:
We shall make the point that there is more than one way
of understanding ‘physics’. In particular, we shall identify
two plausible completeness theses. Each such thesis can
be plugged into the causal argument, and each then gener-
ates its own version of ‘physicalism’. Which complete-
ness thesis you ought to be interested in depends on the
purpose to which you want to put the causal argument
(Spurrett & Papineau, 1999: p. 25).
So the via negativa is just one of the ways of understanding
the “physical”, a way characterised by the plugging in the
property of lacking a certain property in the physicalist concept-
tion. The strategy even allows one to say positive things about
the physical, namely that it is quantitative (Spurrett & Papineau,
1999: p. 25). This might be largely true, but it is far from an-
swering Hempel’s dile mma.
Further, the fundamental problem for the via negativa re-
mains. It fails to provide a conception of physicalism that does
not imply that if we lived in a world where core anti-physical
things exist, physicalism would still be true. Many possible
anti-physical things, like platonic entities, angels, God and/or
emergent properties are non-sui-generis-mental (and quantita-
tive, since they can be counted). Some minimal non-sui-ge-
neris-mental duplicates of some worlds would thus contain
anti-physical objects. This conception consequently fails to
carve out a distinctive metaphysics for physicalism. Thus, both
conceptions of physicalism analyzed in this paper are far from
yielding the advertised conclusions of great philosophical in-
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