## 1. The Content of Russellian Monism


### 1.1 Three Core Russellian Monist Theses



Russellian monism can be seen as combining three core theses:
*structuralism about physics*, which states roughly that
physics, at least current physics (see section 4.1), describes the
world only in terms of its spatiotemporal structure and dynamics;
*realism about quiddities*, which states that there are
*quiddities*, that is, properties that underlie the structure
and dynamics physics describes; and *quidditism about
consciousness*, which states that quiddities are relevant to
consciousness. We will discuss these theses in turn.



To understand the first core thesis, structuralism about physics,
consider David J. Chalmers's description of how physical theory
characterizes its basic entities:



> 
> 
> ...physical theory only characterizes its basic entities
> *relationally*, in terms of their causal and other relations to
> other entities. Basic particles, for instance, are largely
> characterized in terms of their propensity to interact with other
> particles. Their mass and charge is specified, to be sure, but all
> that a specification of mass ultimately comes to is a propensity to be
> accelerated by certain forces, and so on. Each entity is characterized
> by its relation to other entities, and so on forever. ...The
> picture of the physical world that this yields is that of a giant
> causal flux, but the picture tells us nothing about what all this
> causation *relates*. 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? As Russell (1927a) notes,
> this is a matter about which physical theory is silent. (Chalmers
> 1996: 153)
> 
> 
> 



Chalmers's description expresses structuralism about physics
vividly. But his claim that physical theory characterizes its basic
entities only relationally could be challenged. Shape is usually
counted among an object's non-relational properties (Stoljar
2015). For example, contrast a ball's sphericality, a
non-relational property, with its tendency to roll when pushed, a
relational property. So, if physical theory characterizes its basic
entities partly in terms of their shapes, then Chalmers's claim
might seem doubtful.



Such considerations need not be taken to indicate that structuralism
about physics is false. But they do seem to indicate that the relevant
distinction between structural and non-structural properties--the
one relevant to structuralism about physics--does not align with,
and thus should not be explicated in terms of, the
relational/non-relational distinction. (Henceforth we omit mention of
dynamics because the relevant issues concern structure.)



Structuralism about physics is sometimes formulated in terms of the
distinction between extrinsic and intrinsic properties (Chalmers 1996:
153-155; see the entry
 intrinsic vs. extrinsic properties).
 But those formulations have been challenged on similar grounds: a
ball's sphericality is usually counted among its intrinsic
properties, as are other properties in terms of which physical theory
characterizes its basic entities (Ney 2015; Stoljar 2015). (We will
henceforth use 'extrinsic' and 'relational'
interchangeably, and likewise for 'intrinsic' and
'non-relational'.) It might therefore be preferable to
explicate the structural/non-structural distinction in a different
way.



One approach is to do so by distinguishing between *relatively*
and *absolutely* intrinsic properties (Pereboom 2011:
92-97, 2014, 2015, 2016; for an alternative explication, see
Chalmers 2010: 20, fn. 17; 2013: 256; cf. Alter 2016: 804-09).
Roughly, relatively intrinsic properties are intrinsic properties that
are nothing over and above extrinsic properties, whereas absolutely
intrinsic properties are intrinsic properties that are not relatively
intrinsic. (The relative/absolute intrinsicness distinction derives
from Leibniz and Kant; see Leibniz to De Volder April 1702 [Leibniz G
II, 240; 1969: 526-527]; Kant 1781/1787: A277/B333; Pereboom
1985: 413-23; 1991b; Van Cleve 1988; Langton 1998.)



We can articulate that distinction more precisely in terms of
metaphysical grounding (or, on some conceptions, constitution; see the
entries
 metaphysical grounding
 and
 material constitution)
 where *A* *grounds* (or *constitutes*)
*B* just in case *A* metaphysically necessitates
*B* and *B* exists in virtue of *A*, as follows
(Pereboom 2016):



> 
> 
> *P* is a *relatively intrinsic* property of *X*
> just in case *P* is an intrinsic property of *X* and
> *P* is grounded in extrinsic properties of either *X* or
> parts of *X*.
> 
> 
> 



By contrast,



> 
> 
> *P* is an *absolutely intrinsic* property of *X*
> just in case *P* is an intrinsic property of *X* and
> *P* is not grounded in extrinsic properties of either
> *X* or parts of *X*.
> 
> 
> 



Thus, for example, it seems plausible that a ball's sphericality
is grounded in spatiotemporal relations among its parts (as Leibniz
argued; Leibniz to De Volder April 1702 [G II, 240; 1969:
526-527]; see
 section 2.1
 below) and is therefore merely relatively intrinsic. A similar point
applies to other intrinsic properties described in physics. For
example, although mass would seem to be an intrinsic property of
material entities, in the passage quoted above Chalmers remarks that
in physical theory, "all that a specification of mass ultimately
comes to is a propensity to be accelerated by certain forces, and so
on" (Chalmers 1996: 153). Accordingly, the only aspects of mass
that physical theory describes are relatively, not absolutely,
intrinsic.



Suppose structuralism about physics is explicated such that structural
properties are construed as extrinsic properties or relatively
intrinsic properties. In that case, the thesis is consistent with the
claim that physical theory characterizes its basic entities partly in
terms of its intrinsic properties, as long as those intrinsic
properties are relatively and not absolutely intrinsic. (For further
discussion of structuralism about physics, see
 section 4.1
 below; and the entries
 structuralism in physics
 and
 structural realism.)



The second core Russellian monist thesis, realism about quiddities,
states that there are (instantiated) properties of precisely the sort
about which, according to structuralism about physics, physical theory
is silent: properties that underlie the spatiotemporal structure
physical theory describes. Those properties categorically ground the
most basic physical dispositions that physics describes, in the way a
ball's spherical shape categorically grounds its disposition to
roll when pushed. These underlying properties are often called
*quiddities* (Lewis 2009; Chalmers 2012). They are also called
*inscrutables* (Montero 2010). The latter designation is meant
to indicate something on which many proponents of realism about
quiddities agree: we know little about quiddities beyond the
theoretical roles they are supposed to play.



One might reject realism about quiddities even if one accepts
structuralism about physics. As Chalmers (2013: 254) writes,
"There are respectable structuralist or dispostionalist views of
physics on which physics involves just structure or dispositions all
the way down" (e.g., Ladyman and Ross, with Spurrett and Collier
2007; Ney 2015; cf. Shoemaker 1980; Hawthorne 2001; McKitrick 2003).
But Russellian monists and others (e.g., Lewis 2009) regard such
structuralist or dispositionalist views as implausible. That is
because such views "seem to yield a world devoid of substance or
qualities" (Chalmers 2013 [2015: 254]). A world devoid of
substance or qualities might or might not be possible. But according
to realism about quiddities, the actual world is not like that.



The third core Russellian monist thesis, quidditism about
consciousness, states that quiddities are relevant to consciousness.
More specifically, it states that quiddities are relevant to
*phenomenal* consciousness. For example, consider the feeling
one has when suffering from a painful migraine or when seeing a
brilliantly red sunset. As it is often put, there is *something it
is like* to have a phenomenally conscious experience (Nagel 1974;
see the entry
 consciousness;
 throughout, all references to consciousness refer to phenomenal
consciousness). There is no consensus among Russellian monists on
exactly how quiddities are relevant to consciousness
 (section 4).
 But many claim that phenomenal properties are *constituted* by
quiddities, or by quiddities together with various structural
properties.



One might reject quidditism about consciousness even if one accepts
structuralism about physics and realism about quiddities. For example,
one might combine the latter two theses with a dualist theory on which
quiddities categorically ground the most basic physical dispositions
physics describes but are not relevant to consciousness (perhaps on
this theory consciousness is fundamental and not constituted by
anything). By contrast, according to quidditism about consciousness,
quiddities play both of those roles.



One could identify Russellian monism with the conjunction of all three
core theses, where each thesis could be explicated in different ways,
resulting in different varieties of the theory. For present purposes,
that characterization will suffice (see below, sections 1.2 and 4; for
an alternative characterization, see Pereboom 2011: 89; cf. Alter and
Nagasawa 2012: 71-72.)


### 1.2 Varieties of Russellian Monism



While all Russellian monists maintain that quiddities are relevant to
consciousness
 (section 1.1),
 some construe quiddities themselves as phenomenal properties (Maxwell
1978; Lockwood 1989, 1992; Rosenberg 2004; Strawson 2003, 2006a,b;
Morch 2014; Goff 2015, 2017; cf. Unger 2005). The result is a
variety of Russellian monism known as *Russellian panpsychism*
(Chalmers 2013 [2015: 246-247]). Russellian panpsychism is so
called due to the assumption that phenomenality is ubiquitous: it
occurs everywhere the most basic physical dispositions do. But as a
terminological matter, one might allow that a Russellian monist theory
counts as Russellian panpsychism if it specifies either that *at
least some* of the most basic physical dispositions are underlain
by phenomenal quiddities (Chalmers 2013 [2015: 246]) or that
*all* such dispositions are so underlain (Strawson
2006a,b).)



Panpsychism has a long philosophical history (see the entry
 panpsychism;
 Skrbina 2005), but some find the doctrine incredible (Searle 1997;
but see Chalmers 1997b; Alter and Nagasawa 2012: 90). Here it should
be noted that Russellian panpsychists typically do not construe
quiddities as *macrophenomenal* properties, that is, as
familiar phenomenal properties such as those commonly associated with
feeling pain and seeing red. More often, Russellian panpsychists
construe quiddities as *microphenomenal* properties, that is,
as phenomenal properties of microphysical entities. Microphenomenal
properties might differ radically from the macrophenomenal sort
(Chalmers 1996: 293-297; Strawson 2003, 2006a; Rosenberg 2004:
95). Some Russellian panpsychists construe quiddities as
*cosmophenomenal* properties, that is, phenomenal properties of
the whole cosmos, which might likewise differ radically from
macrophenomenal properties (Goff 2017). So, the sorts of phenomenal
properties that, according to Russellian panpsychism, underlie the
most basic physical dispositions need not be much like any with which
we are familiar. This might make panpsychism more palatable to some
philosophers--though, some argue, if such properties differ
enough from familiar macrophenomenal properties, one might doubt that
they deserve to be called phenomenal at all (Kind 2006).



Another option for Russellian monists is to construe quiddities as
what Chalmers calls *protophenomenal* properties, which he
characterizes as follows:



> 
> 
> ...*protophenomenal* properties are special properties
> that are not phenomenal (there is nothing it is like to have a single
> protophenomenal property) but that can collectively constitute
> phenomenal properties, perhaps when arranged in the right structure.
> (Chalmers 2013 [2015: 259])
> 
> 
> 



The result is a variety of Russellian monism known as *Russellian
panprotopsychism*. Russellian panprotopsychism does not entail
panpsychism. Perhaps only entities in a limited class (e.g., some
states of some animals) have protophenomenal properties that are
arranged in a consciousness-constituting structure. In that case, on
Russellian panprotopsychism consciousness would occur only in those
entities and not elsewhere. There are also hybrid varieties of
Russellian monism, on which some quiddities are phenomenal and others
are protophenomenal (Holman 2008).



Russellian monism is a distinctive theory in the metaphysics of mind.
Nevertheless, it is possible to identify varieties that correspond to
more traditional theories, including physicalism, idealism, neutral
monism, and (despite the name) even dualism (see the entries
 physicalism;
 idealism;
 neutral monism;
 and
 dualism).
 On physicalist Russellian monism, both quiddities and structural
properties are physical (Stoljar 2001; Pereboom 2011, 2014, 2015,
2019; Coleman 2012, 2015; Montero 2015; Morris 2016; Brown 2017). On
idealist Russellian monism, both quiddities and structural properties
are mental (Bolender, 2001; Adams 2007; Schneider 2018; cf. Chalmers
1996: 155). On neutral monist Russellian monism, both quiddities and
structural properties are neutral, where neutral properties are
neither physical nor mental but underlie both physical and mental
properties (Nagel 1986, 1998; cf. Stoljar 2015; Wishon 2016; also see
the discussion of *panqualityism* in the entry
 panpsychism).
 Finally, Russellian monism could be combined with the traditional
(e.g., Cartesian) dualist view that the concrete world includes two
fundamentally distinct sorts of entities, the physical sort and the
mental sort. This can be done by, for example, identifying structural
properties with physical properties and quiddities with certain mental
properties (cf. Chalmers 2010: 135).



Physicalist and neutral monist varieties of Russellian monism are most
naturally understood as forms of Russellian panprotopsychism (Alter
and Coleman 2020b; but see Morris 2016, Brown 2017), whereas idealist
and dualist varieties are most naturally understood as forms of
Russellian panpsychism (Chalmers 2013, Schneider 2018). Much of the
recent literature on Russellian monism focuses on the physicalist
variety, often called *Russellian physicalism* (Montero 2015).
Russellian physicalism is usually presented as an alternative to,
rather than a version of, traditional physicalism. But that might seem
misleading. On many traditional physicalist theories, there are
non-phenomenal properties that can collectively constitute phenomenal
properties, perhaps when arranged in the right
structure--microphysical properties, say. On those theories, such
properties would qualify as protophenomenal properties by the
characterization quoted above from Chalmers 2013 (Papineau 2002:
22-23, fn. 5).



Some traditional physicalist theories conflict with other aspects of
Russellian monism. For example, (physicalist) analytic functionalism
(Armstrong 1968; Lewis 1966, 1972, 1980) conflicts with the Russellian
monist's denial that structural truths alone *a priori*
entail all phenomenal truths (see the entry
 functionalism;
 *phenomenal truths* are truths about consciousness). But other
traditional physicalist theories are not similarly disqualified. For
example, *a posteriori* physicalists also deny that structural
truths alone *a priori* entail all phenomenal truths (see the
entry
 physicalism).
 Nevertheless, in their view, there are non-phenomenal properties that
can collectively constitute phenomenal properties, perhaps when
arranged in the right structure. So, one might wonder why *a
posteriori* physicalism does not qualify as Russellian
physicalism.



Chalmers recognizes this problem. He therefore makes two further
stipulations designed to help distinguish Russellian physicalism from
traditional physicalist theories:



> 
> 
> ...(i) protophenomenal properties are distinct from structural
> properties and (ii) there is an *a priori* entailment from
> truths about protophenomenal properties (perhaps along with structural
> properties) to truths about the phenomenal properties that they
> constitute. (Chalmers 2013 [2015: 260])
> 
> 
> 



Given those further stipulations, *a posteriori* physicalists
would deny that there are protophenomenal properties. Similar
considerations apply to other traditional physicalist theories.
Russellian physicalism is different. (For other ways to distinguish
among varieties of Russellian monism, see
 section 4;
 Alter and Nagasawa 2012; Chalmers 2013; Goff 2017.)


## 2. Russellian Monism in the History of Western Philosophy


### 2.1 Russellian Monism in the Seventeenth through Nineteenth Centuries



One could find views that resemble Russellian monism in certain
respects throughout the history of philosophy. For example,
panpsychism is very old indeed (and not distinctive to the west). But
it is hard to find views approximating full-fledged Russellian monism
before the early modern period. This is not a coincidence: the theory
is closely tied to modern physics, which was first developed during
that era. Yet it did not take long for the theory, or something akin
to it, to emerge. Arguably, Russellian monism can be ascribed to
various early modern figures, including at least Gottfried Wilhelm
Leibniz, Immanuel Kant, and Arthur Schopenhauer.



Leibniz's Russellian monist theory may be found in his critique
of Rene Descartes' theory of matter (Pereboom 2011:
92-97; cf. 1991a,b). In Descartes' theory, material
substance is essentially just extension in three spatial dimensions
(Descartes *Principia Philosophiae*, "Part Two: The
Principles of Material Things" 1644 [1984: v. 1, 223-247;
AT VIII 40-79]; see the entry
 Descartes' physics).
 Leibniz contends that Descartes' theory is unsatisfactory
because, first, the extension of a physical object is (in the
terminology introduced in
 section 1.1,
 which is Kantian (Kant 1781/1787: A277/B333)) a relatively intrinsic
property of it, since it resolves into the plurality, spatial
continuity, and temporal coexistence of its parts, and the extension
of those parts resolves into those extrinsic properties of their
parts, *ad infinitum*; and, second, any real thing, that is,
any actual, concrete entity, cannot possess only extrinsic or
relatively intrinsic properties: it must possess an absolutely
intrinsic property as well. Leibniz writes: "there is no
denomination so extrinsic that it does not have an intrinsic
denomination at its basis" (Leibniz to De Volder April 1702
[Leibniz G II, 240; 1969: 526-527]). In his view, a conception
of the physical world that does not include absolutely intrinsic
properties is in an important sense incomplete. In effect, his
complaint is that Descartes' theory of matter describes only
structure without describing a quiddistic ground for that structure,
or even acknowledging the possibility of or the need for such a
ground.



In Leibniz's view, the absolutely intrinsic properties
underlying real things are at least connected to *primitive
force* (see the entry
 Leibniz's philosophy of physics).
 Primitive force (which can appear to us phenomenally as physical
force) generates a progression from one representation to the next in
a series, in conformity with a law (Leibniz 1698 [1969: 504; 1989:
162-63]; Adams 1994: 352; Jorati 2018). On one interpretation,
primitive forces are the fundamental elements, "the sole
inhabitants of the ground floor" of Leibniz's ontology
(Jorati 2018); thus, the most basic substances, mind-like monads,
"do not have forces, strictly speaking--they are
forces" (Jorati 2018; cf. Adams 1994: 265, 378-379). On
that reading, primitive forces *are* the absolutely intrinsic
properties underlying real things. They might be called Leibnizian
quiddities.



Leibniz might be the first Russellian monist. In his view, all the
properties physics presents are either extrinsic or relatively
intrinsic. This corresponds to structuralism about physics. He
contends there are absolutely intrinsic properties, primitive forces
on one reading, in which those extrinsic properties and relatively
intrinsic properties are grounded. This corresponds to realism about
quiddities. Those quiddities ground all of the other features of
reality, including consciousness generally and macrophenomenal
properties specifically. This corresponds to quidditism about
consciousness. Thus, Leibniz seems to endorse versions of all three
core Russellian monist theses. And because on his view all basic
entities, including Leibnizian quiddities and the extrinsic and
relatively intrinsic properties they ground, are mental, Leibnizian
Russellian monism is a version of Russellian idealism.



Like Leibniz, Kant can be seen as a Russellian monist. Kant endorses a
version of structuralism about physics: "All that we cognize in
matter are nothing but relations. What we call the intrinsic
determinations of it are intrinsic only in a relative
sense..." (1781/1787: A285/B341; Pereboom 1985:
413-23, 1991a,b, 2011: 100-101; Van Cleve 1988; Langton
1998; cf. Holden 2004: 236-263). In material objects we discover
only extrinsic properties and relatively intrinsic properties, never
any properties that are absolutely intrinsic. Indeed, for Kant, matter
itself does not have absolutely intrinsic properties. That is because
he regards matter as "mere appearance". Thus, he writes,
"what it [matter] itself consists in is the mere relation of
something in general to the senses" (1781/1787: A285/B341). If
matter were instead a "thing-in-itself", he implies, then
it would need to have absolutely intrinsic properties. Nevertheless,
in his view all features of appearance, including both matter and
macrophenomenal consciousness, are grounded in things-in-themselves
(or a thing-in-itself) and thus in absolutely intrinsic
properties--a position that suggests both realism about
quiddities and quidditism about consciousness.



Although Kant agrees with Leibniz that there must be absolutely
intrinsic properties for the world to exist as we know it, he differs
with Leibniz about forces. In Kant's view, forces are relational
and thus not absolutely intrinsic (1781/1787: A265/B321; 1786:
498-491). He does not say whether there are Leibnizian primitive
forces. And he denies that we know much about the nature of the
absolutely intrinsic properties that, he thinks, must exist. Such
knowledge would be tantamount to substantive knowledge of
things-in-themselves, and famously he contends that we lack such
knowledge. He could therefore be described as endorsing an
epistemological doctrine that many contemporary Russellian monists
endorse
 (section 1.1):
 we know little about quiddities beyond the theoretical roles they are
supposed to play.



Schopenhauer can be seen as another pre-twentieth century Russellian
monist. In *The World as Will and Representation*, he affirms
what might be described as versions of structuralism about physics and
realism about quiddities. Natural causal explanation, he writes,



> 
> 
> ...really does nothing more than indicate the orderly arrangement
> according to which the states of matter appear in space and
> time... But it affords us absolutely no information about the
> intrinsic nature (*das innere Wesen*) of any one of these
> phenomena. (1818: Vol. 1, Bk. II, sect. 17, par. 5 [1961: 113])
> 
> 
> 



And he implies that those phenomena do indeed have intrinsic natures,
which suggests quidditism about consciousness.



So far, Schopenhauer's view is similar to Kant's. But
Schopenhauer does something Kant would not do. He makes a further
positive proposal about the nature of the absolutely intrinsic
properties that underlie the orderly arrangement indicated by natural
causal explanations. Specifically, in his view *the will* plays
the key role: "indeed the answer to the riddle is given to the
subject of knowledge who appears as an individual, and the answer is
will" (1818: Vol. 1, Bk. II, sect. 18, par. 1 [1961: 115]). The
absolutely intrinsic properties in which the orderly arrangement of
the world of appearance is grounded are volitional--and hence the
title of his famous book *The World as Will and Representation*
(Schopenhauer 1818: Vol. 1, Bk. II, sect. 18, par. 1 [1961: 115]; see
the entry
 Arthur Schopenhauer).



Some find Russellian monism in works by others in the modern period as
well. Rebecca Copenhaver (2020) argues that George Berkeley can be
seen as a Russellian idealist. Cole Mitchell (in correspondence)
reports that there is a version of Russellian panprotopsychism
discussed by Anthony Collins, in the 1707-08 Clarke-Collins
Correspondence.


### 2.2 Russellian Monism in the Twentieth and Twenty-First Centuries



Contemporary Russellian monists often trace their view to
Russell's 1927 *The Analysis of Matter*, which they read
as developing a structuralist account of physics. Indeed, some find in
that book suggestions of not only structuralism about physics but the
other main components of Russellian monism too (Lockwood 1992 [2015:
144-145]; Chalmers 1996: 166). On this interpretation, Russell
there implied that what are now called quiddities might be identified
with what he called *percepts* (Russell 1927a: 402). It has
also been argued that he more explicitly endorsed the eponymous theory
(though not by its current name) in some of his later writings,
including *Human Knowledge: Its Scope and Limits* and *My
Philosophical Development* (Wishon 2015; but see Stubenberg
2015).



Some argue that Russellian monism has historical roots not only in
Russell's writings but also in early twentieth century works by
Arthur Eddington (Kadic 2017; cf. Strawson 2006a). In
Eddington's view, science does not describe what he calls the
*nature* of the entities it posits, which he also refers to as
the *background* of "pointer readings and similar
indications" (Eddington 1928: 252). For instance, he contends,
physics--modern physics, as opposed to the physics of the
"Victorian physicist" for whom "Atoms were tiny
billiard balls..."--describes atoms not in terms of
their natures but rather in terms of pointer readings (Eddington 1928:
259). Thus, like Russell, Eddington seems to affirm a version of
structuralism about physics (or something in the vicinity). Further,
Eddington proposes that atoms, and perhaps everything else physics
describes, might have "something of spiritual nature of which a
prominent characteristic is *thought*" (Eddington 1928:
259). In support of that proposal, he writes,



> 
> 
> But in one case--namely, for the pointer readings of my own
> brain--I have an insight which is not limited to the evidence of
> the pointer readings. That insight shows that they are attached to a
> background of consciousness. Although I may expect that the background
> of other pointer readings in physics is of a nature continuous with
> that revealed to me in this particular case, I do not suppose that it
> always has the more specialized attributes of consciousness.
> (Eddington 1928: 259-260)
> 
> 
> 



Eddington's reflections can be seen as suggestive of either
Russellian panpsychism (Kadic 2017: 46), Russellian
panprotopsychism, or perhaps a hybrid of the two.



In the late twentieth century, Grover Maxwell (1978) and Michael
Lockwood (1989, 1992) each endorse a theory that they attribute to
Russell and is often interpreted as Russellian monism (see, for
example, Chalmers 1996, 2013). Maxwell presents his theory in the
course of defending the mind-brain identity theory (Place 1956; Smart
1959; Lewis 1966; see the entry
 the mind/brain identity theory)
 against Saul Kripke's (1972) influential challenge.
Kripke's challenge concerns how to reconcile that identity
theory with the "apparent contingency of the connection between
the mental state and the corresponding brain state..."
(Kripke 1972 [1980: 152]). Maxwell rejects an assumption on which, he
claims, that challenge relies: the assumption that "we know from
common sense, from physics, from neurophysiology, etc., what brain
events are like" (Maxwell 1978: 134). In his view, those sources
tell us about structural properties but not about brain events'
underlying non-structural properties--a line of reasoning
suggestive of both structuralism about physics and realism about
quiddities. He also seems to endorse something like quidditism about
consciousness. In the case of brain events that are, in his view,
identical to macrophenomenal experiences, he implies that their
underlying non-structural properties might be phenomenal
properties--a claim suggestive of Russellian panpsychism.
Lockwood (1989, 1992) develops a theory similar to Maxwell's,
remarking that it "seems to me the only approach to the
philosophical mind-body problem, currently on offer, that holds
out the slightest promise" (Lockwood 1992 [2015: 145]).



More recent discussions of Russellian monism have followed Maxwell and
Lockwood's lead. The view is advanced as offering a plausible
response not only to Kripke's challenge but also to related
anti-materialist arguments
 (section 3).
 Daniel Stoljar's "Two Conceptions of the Physical"
(2001) is widely considered the classic expression of that idea (see
also Stoljar 2006, 2009, 2014, 2015). The idea is also developed by
Chalmers (1996, 1997a, 2003, 2010: ch. 6, 10) and others (Rosenberg
2004; Alter 2009, 2016; Montero 2010, 2015; Pereboom 2011, 2014, 2015,
2016; McClelland 2013; Brown 2017; Goff 2017). Chalmers (1997a)
introduced the name "Russellian monism," and his work on
the topic has been highly influential. Another main source of the
contemporary interest in Russellian monism is Galen Strawson's
(2003, 2006a,b) seminal work on consciousness and physicalism.



## 3. Arguments for and Objections to Russellian Monism


### 3.1 Arguments for Russellian Monism



Russellian monists usually support their theory by arguing that it has
significant theoretical benefits. We will describe three such
arguments, which appeal to closely related considerations. (For other
arguments for Russellian monism see, for example, Rosenberg 2004;
Strawson 2006a; Goff 2017; Schneider 2018.)



The first argument is based on the claim that Russellian monism
combines theoretical virtues of traditional dualism with those of
traditional physicalism, while avoiding their main drawbacks (Chalmers
2013). The reasoning behind that claim could be stated as follows.
Traditional physicalism has the virtue of allowing consciousness to be
integrated into physical causation. But this comes at the cost of
disregarding or distorting the distinctive features of consciousness.
Traditional dualism avoids that cost. But by separating consciousness
from the physical world, traditional dualism prevents consciousness
from being integrated into physical causation. The latter cost is
famously articulated by Princess Elisabeth of Bohemia, in her
criticism of Cartesian dualism (Elisabeth to Descartes, 21 May, 1643
[1984: v. 3, 218; AT III 665]; see the entry
 Elisabeth, Princess of Bohemia),
 and by related causal arguments for physicalism such as the
following:



> 
> 
> Many effects that we attribute to conscious causes have full physical
> causes. But it would be absurd to suppose that these effects are
> caused twice over. So the conscious causes must be identical to some
> part of those physical causes. (Papineau 2002: 17; cf. Kim 1989,
> 1998).
> 
> 
> 



By contrast, Russellian monism seems to avoid those costs of both
traditional physicalism and traditional dualism. On Russellian monism,
the properties that constitute consciousness--quiddities and
(perhaps) structural properties--play indispensable roles in
physical causation. Consciousness --or at least the components of
consciousness --is thus integrated into physical causation. Yet
the distinctive features of consciousness are neither disregarded nor
distorted. Those features are attributed to quiddities and their
special (e.g., constitutive) relationship to consciousness.



A second argument for Russellian monism is based on the claim that
this theory offers an elegant, unified solution to two distinct
philosophical problems (Lockwood 1989, 1992; Chalmers 1996, 2013
[2015: 254]; Rosenberg 2004; Goff 2017; cf. Russell 1927a, 1927b:
116). One of those problems is how to provide a foundation for the
spatiotemporal structure physics describes. The other is how to
integrate consciousness into physical causation. When considered from
the perspective of a Russellian monist, these two problems seem made
for each other. The requisite foundation of spatiotemporal structure
is provided by (proto)phenomenal quiddities. Because those same
quiddities (partly or wholly) constitute consciousness, consciousness
thereby plays a distinctive role in physical causation--or at
least the components of consciousness play that role. Thus, the
reasoning runs, both problems are solved at once.



A third argument for Russellian monism is based on the claim that
Russellian monism provides a plausible response to anti-materialist
arguments such as the conceivability argument and the knowledge
argument (see the entries
 zombies
 and
 qualia: the knowledge argument
 and Alter 2023). The conceivability argument is often formulated in
terms of a *zombie world* (Chalmers 1996): a physical and
functional duplicate of the actual world but without consciousness. It
is first argued that a zombie world is ideally conceivable, which
means roughly that such a world cannot be ruled out as incoherent by
*a priori* reasoning (Chalmers 2002). It is then argued that
the ideal conceivability of such a world entails its metaphysical
possibility. Finally, it is argued that the metaphysical possibility
of such a world entails that physicalism is false. The knowledge
argument begins with Frank Jackson's (1982, 1986, 1995) case of
Mary, the brilliant scientist in the black-and-white room, who comes
to know the complete physical truth by reading black-and-white science
books and watching science lectures on a black-and-white monitor. If
physicalism were true, Jackson reasons, then Mary would thereby know
everything there is to know about seeing in color: she could deduce
that information from her physical knowledge. But, he claims, this is
not the case. On the contrary, when Mary leaves the room she learns
truths about what it is like to see in color - truths she did
not already know.



According to Russellian monism, those arguments might show that
structure alone does not fully determine (metaphysically necessitate)
the nature or even the existence of consciousness. But it does not
follow that physicalism is false. At most, it follows that
*traditional* physicalist theories are false, because those
theories limit the physicalist's resources to the structural.
*Russellian* physicalism, on which the class of physical truths
includes not only structural truths but quiddistic truths as well, is
not threatened (Stoljar 2001). Further, this anti-structuralist thesis
comports well with the claim that consciousness consists at least
partly in non-structural quiddities--a claim that is central to
Russellian monism generally, not just the physicalist variety
 (section 1).



That response can be developed in different ways, such as rejecting
epistemic premises on which the anti-materialist arguments rely (for
other ways, see Chalmers 2010: 134-135; Pereboom 2011; Alter and
Nagasawa 2012: 83-86). Regarding the conceivability argument,
Russellian physicalists can argue as follows. On reflection, a zombie
world is not ideally conceivable. If such a world initially appears
conceivable, this is because we mistake a zombie world for a
*structural* zombie world: a consciousness-free world that
(minimally) duplicates all of the actual world's structural
features. If there is an ideally conceivable world in the vicinity,
then that world is a structural zombie world. There is no good reason
to accept the ideal conceivability of a full-fledged zombie world,
which would lack consciousness despite duplicating not only the actual
world's structural features but its quiddistic features as well.
Regarding the knowledge argument, Russellian physicalists can argue
that because Mary's black-and-white science lessons leave out
quiddistic information, those lessons teach her only part of the
physical truth. If so, then the truths she learns when she leaves
might be physical. They would be non-structural quiddistic truths but
physical truths nonetheless.


### 3.2 Objections to Russellian Monism



One objection to Russellian monism concerns *the combination
problem*: how do (proto)phenomenal quiddities (or quiddities and
structural properties) combine to constitute macrophenomenal
properties (Seager 1995; Chalmers 2003)? Suppose someone is having a
phenomenally blue experience. If *constitutive* Russellian
monism is true, then the phenomenal blueness of that experience
consists wholly in certain quiddities, perhaps structured in a certain
way (for the distinction between constitutive and non-constitutive
Russellian monism, see Section 4.2). But on many varieties of
Russellian monism, quiddities are micro-level features. On the face of
it, it seems possible that those (or any) micro-level quiddities could
be instantiated without anyone having that (or any)
experience--and that seems possible no matter how they are
structured. If that is possible, then how could phenomenal blueness
consist wholly in (structured) quiddities, as constitutive Russellian
monists hold? Essentially the same problem seems to arise for other
varieties of constitutive Russellian monism, such as those on which
quiddities are construed as cosmophenomenal features (Goff 2009;
Pereboom 2011, 114; Chalmers 2013, 2017).



That is one version of the combination problem, but there are others.
Consider one raised for a version of constitutive Russellian
panspsychism, according to which microphenomenal quiddities, perhaps
together with structural properties, combine to constitute
macrophenomenal properties. The problem can be stated as an objection,
as follows. The constitutive Russellian panpsychist is committed to
the following two claims. First, corresponding to each instance of a
microphenomenal quiddity underlying a physical disposition there is a
unique conscious subject: a microsubject distinct from the
microsubjects that correspond to other such instances of
microphenomenal quiddities. Second, multiple microsubjects
corresponding to microphenomenal quiddities combine to constitute a
single macrosubject. But it is unclear how that second claim could be
true. As William James (1890: 162) suggests, given any group of
subjects and any further subject, it seems possible for the group to
exist without that further subject existing. This is known *the
subject-summing problem* (Goff 2009, 2017; Chalmers 2013, 2017;
Coleman 2014).



Some respond to such combination problems by appealing to a Leibnizian
underrepresentation thesis (Pereboom 2011: 114-115), on which
introspective awareness of phenomenal states fails to represent them
as having microfeatures they do in fact have (Leibniz, *Discourse
on Metaphysics*, SS30 [G IV, 458-59; IV, 574-575];
Pereboom 1991b, 2011: 9, n. 1; cf. Stoljar 2001: 276). Consider the
version of the combination problem stated two paragraphs back,
involving the constitution of phenomenal blueness. On the Leibnizian
underrepresentation thesis, even if one introspects one's
experience as featuring only *noncomplex* phenomenal blueness,
phenomenal blueness might in fact be constituted by an unrepresented
array of (proto)phenomenal quiddities. To support that claim, one
might draw an analogy to a macrophenomenal property that is
constituted by other *macro*phenomenal properties. For example,
a taste experience might appear simple and unconstituted even if in
fact it is constituted by a combination of sweet, sour, salty, bitter,
and umami (as Louis DeRosset has suggested in conversation; see
Pereboom 2011: 115). Likewise, the response continues, perhaps all
macrophenomenal features are constituted by (proto)phenomenal
quiddities, or by quiddities and structural features, which
introspection fails to reveal.



However, that response is only partial. It might show that
introspection alone does not rule out the possibility that
macrophenomenal properties are constituted by quiddities or by
quiddities and structure. But the response does not explain how
macrophenomenal properties might result from such constituents.
Although some explanations have been proposed (e.g., Rosenberg 2004,
2015, Morch 2019), many regard the combination problem for
Russellian monism as unsolved and serious (see the entry
 panpsychism;
 Bruntrup and Jaskolla 2017; Chalmers 2017).



Several other objections to Russellian monism have been raised in the
recent literature, of which we will describe four. The first is
related to the combination problem and applies only to Russellian
panprotopsychism. It is argued that Russellian panprotopsychism faces
the following sort of "revenge" problem. Russellian monism
is motivated partly by its ability to provide plausible responses to
influential anti-physicalist arguments, such as the conceivability and
knowledge arguments
 (section 3.1).
 Those arguments usually begin by attacking allegedly implausible
epistemic commitments of certain traditional physicalist views (such
as analytic functionalism), such as the claim that structural truths
alone *a priori* entail all phenomenal truths. However, some
argue, parallel considerations undermine the Russellian
panprotopsychist's claim that protophenomenal truths and
structural truths together *a priori* entail all phenomenal
truths (Strawson 2006a,b; Goff 2015, 2017). Thus, for example, it is
argued that while still in the black-and-white room Mary can come to
know all the protophenomenal truths just as easily as she can come to
know all the structural truths, and still not thereby be positioned to
know what it is like to see red (for related objections to Russellian
monism, see Cutter 2019, Botin 2023, and Mendelow forthcoming).



In response, some deny that the two *a priori* entailment
claims are on a par (Alter 2018). Mary could come to know any
structural truth while still in the room, the response runs, because
any structural truth can be fully conveyed in the colorless language
of objective science. But protophenomenal properties are
non-structural. So, perhaps some protophenomenal truths cannot be
fully conveyed in such colorless language. If so, then the Russellian
panprotopsychist's *a priori* entailment claim might not
meet the same fate as the one associated with certain traditional
physicalist theories.



A second recent objection, developed by Amy Kind (2015), is that
Russellian monism is unmotivated. The theory is often advanced as
providing insight into the mind-body problem: insight that has
eluded traditional dualists and traditional physicalists
 (section 3.1).
 However, Kind points out, Russellian monism fails to resolve the most
central issue in the debate: whether consciousness is a fundamental
component of the universe. On Russellian panpsychism consciousness is
a fundamental component of the universe, whereas on Russellian
panprotopsychism it is not. Thus, Russellian monism leaves us
"essentially back where we started" (Kind 2015: 420; cf.
Liu 2021, which compares the view to Thomistic hylomorphism and claims
that Russellian monism has similar problems). In response, it has been
argued that this charge misunderstands Russellian monism's aims
(Alter and Coleman 2020a). Russellian monism does not purport to
settle whether consciousness is a fundamental component of the
universe. Rather, the theory is meant to provide a framework in which
that issue (and others) can be more productively addressed--a
framework provided by neither traditional physicalism nor traditional
dualism.



A third recent objection is that Russellian monism, despite its aims,
fails to adequately integrate consciousness into physical causation.
One version of this objection begins with the premise that, on
Russellian monism, a single type of physical disposition might have
been grounded by a distinct quiddity from the quiddity that actually
grounds it (Howell 2015; cf. Robinson 1993). For example, if in the
actual world quiddity Q1 grounds negative charge, then there is a
metaphysically possible world in which a distinct quiddity Q2 grounds
negative charge; the grounding relationship between quiddities and
physical dispositions is in this way metaphysically contingent. If so,
the argument continues, then quiddities (even if they exist) do not
make any distinctive contribution to physical causation. With respect
to physical causation, quiddities are "just along for the causal
ride" (Howell 2015: 34). On another version of the objection,
even if quiddities contribute to physical causation, consciousness
does not thereby inherit any physical efficacy, contrary to what
Russellian monists claim (Robinson 2018; cf. Chan 2020, 2021).



In response to the first version of that objection, on which
quiddities lack physical efficacy, some reject the assumption that any
such conclusion follows from the premise that a single type of
physical disposition might have been grounded by a distinct quiddity
from the quiddity that actually grounds it (Hawthorne 2002, Alter and
Coleman 2020a, 2021). Causal relations, it is argued, do not in
generally hold with metaphysical necessity. So, why must the
relationship between quiddities and dispositions hold with such
necessity, if quiddities are to be physically efficacious? Another
response is to reject the premise that on Russellian monism that
relationship is metaphysically contingent (Chalmers 2013 [2015:
264-265]; Morch 2014, 2019; Gundersen 2015; Kadic
2017; Alter and Coleman 2020a, 2021). In response to the second
version of the objection, on which consciousness does not inherit any
physical efficacy from that of quiddities (even if quiddities partly
or wholly constitute consciousness), one might argue that this charge
is just an instance of a general worry concerning micro-to-macro
causal exclusion, which does not concern consciousness or Russellian
monism specifically. (See the entry
 mental causation;
 Goff 2017: 153-158)



A fourth recent objection to Russellian monism targets the distinction
between the structural and the non-structural. Some argue that this
distinction cannot be explicated in the way that Russellian monism
requires. As noted above
 (section 1.1),
 some have made proposals for how to explicate that distinction. Those
proposals render structuralism about physics consistent with the claim
physics describes some intrinsic properties, thus safeguarding
structuralism about physics from one line of attack. But whether any
of those proposals is fully adequate for the purposes of Russellian
monism is disputed (Stoljar 2015). Other, related objections have been
raised, e.g., that the dispositional/categorical distinction does not
apply to physical properties in the way that Russellian monism implies
(Hiddleston 2019; but see Alter and Pereboom 2023; for other
objections concerning the Russellian monist's
structural/non-structural distinction, see Stoljar 2006, 2009, 2014,
2015; Ney 2015; for responses, see Pereboom 2011, 2014, 2015; Alter
2009, 2016).


## 4. Further Issues


### 4.1 Structuralism about Physics



As noted above
 (section 1.1),
 Russellian monism can be identified with the conjunction of the three
theses: structuralism about physics, realism about quiddities, and
quidditism about consciousness. But one might question whether
Russellian monists are committed to structuralism about physics, at
least if that thesis is understood as saying that physical theory is
*completely* silent on the existence and nature of quiddities.
Given Russellian monism, terms for the basic entities in physical
theory, such as "mass" and "charge", perhaps
*refer* to quiddities, to entities that have quiddities. One
might take that point alone to belie the structuralist's
complete-silence claim. Further, one might wonder, why should
Russellian monists rule out the possibility of physical theory
expressing substantive information about the referents of its terms
(Hawthorne 2002)?



In response, one might argue that physical theory itself is neutral
between a Russellian monist interpretation according to which terms
like "mass" and "charge" refer to quiddities,
and a structuralist interpretation according to which such terms do
not refer to quiddities (Ladyman and Ross, with Spurrett and Collier
2007). That is, one might argue that the commitments of *physical
theory itself*, by contrast with a *metaphysical interpretation
of physical theory*, do not go beyond the structural.
Structuralism about physics could thus be viewed as a thesis only
about physical theory itself. In that case, the considerations
mentioned in the preceding paragraph do not challenge the claim that
Russellian monists are committed to structuralism about physics.



Alternatively, one might give up the claim that Russellian monists are
committed to structuralism about physics (Alter and Pereboom 2023; but
see Brown 2023). What is at the core of Russellian monism, one might
contend, is only that there are quiddities that both underlie
structural features physics describes and are relevant to
consciousness. So, of the three claims we have described as core
Russellian monist theses, perhaps only the second and the third
qualify as such. Or instead, Russellian monists might retain
structuralism about physics but explicate it in a way that is
relatively uncontroversial (or at least less controversial than it
often is), e.g., as a view about *current*physics.


### 4.2 Constitution and Emergence



As noted above
 (section 1.1),
 many Russellian monists claim that macrophenomenal properties are
*constituted by* quiddities, or by quiddities and structure.
But not all do. Instead, some claim that macrophenomenal properties
*emerge from* quiddities, or from quiddities and structure
(Goff 2015), where emergence is taken to be a (diachronic or
synchronic) causal relation.



However, some object that the causal-emergence construal undermines
the claim that on Russellian monism consciousness is integrated into
physical causation (Alter and Nagasawa 2012: 81; Chalmers 2013 [2015:
253-259]). The objection could be stated as follows. On the
causal-emergence construal, there are causal laws connecting
quiddities (or quiddities and structural properties) to
macrophenomenal consciousness: laws that are neither *a priori*
entailed nor metaphysically necessitated by the structural truths that
physical theory describes. In this respect, such laws would be just
like psychophysical laws posited by traditional interactionist
dualism. And it is precisely because of the need to posit such
psychophysical laws that traditional interactionist dualism is charged
with failing to integrate consciousness adequately into physical
causation (Smart 1959). Thus, on the causal-emergence construal, that
charge would apply equally to Russellian monism (but see Goff 2015:
294-97; 2017: Part II *passim*).


### 4.3 Physical Quiddities



Much (though by no means all) of the recent discussion of Russellian
monism focuses on Russellian physicalism, on which quiddities are
physical properties. But there is no well-developed conception of
physical quiddities, or at least none that is widely accepted. This
has prompted speculation as to what such properties might be like.



Derk Pereboom (2011: ch. 5) identifies some candidates for physical
quiddities in the history of philosophy. One comes from the
Aristotelian tradition, on which matter is made up at least partly of
*prime matter*. Prime materiality could be understood as a
physical quiddity that underlies matter, which is structural. On
Thomas Aquinas's (1252-56) Aristotelian view, for
instance, matter consists in extension in three dimensions, i.e.,
*quantity*. But quantity is a form, and in Aquinas's view
a form must inhere in something. That something, he thinks, is prime
matter. Unlike quantity, prime materiality is not (in the terminology
of
 section 1.1)
 a relatively intrinsic property of matter. Instead, it is an
absolutely intrinsic property of matter, and it could be seen as a
physical quiddity (Pereboom 2011: 85, 113). Admittedly, Aquinas held
that prime matter is unintelligible. But other Aristotelians did not
(Pasnau 2009).



Another candidate for a physical quiddity that Pereboom identifies is
due to John Locke (1690). In Locke's conception,
*solidity* is the categorical basis for impenetrability, which
is dispositional. Lockean solidity is "*that which*
hinders the approach of two bodies when they move toward one
another" (Locke 1690: II, iv, emphasis added). Lockean solidity
is also what differentiates matter from space, and is a defining
property of matter. On one plausible interpretation, Pereboom (2011:
97-100) suggests, Locke regards that property as an absolutely
intrinsic property of matter and as a physical quiddity.



A third candidate for physical quiddities, which is similar to Lockean
solidity, may be found in contemporary metaphysics. Many contemporary
metaphysicians accept that there exist non-Humean causal powers (see
the entry
 dispositions).
 Humeans identify causal powers with mere tendencies, which can be
fully explicated by means of subjunctive conditionals such as,
"If an electron were in the vicinity of a proton, it would
attract that proton" (Jacobs 2011). By contrast, non-Humeans
identify causal powers with properties that categorically ground
tendencies--much as Lockean solidity grounds impenetrability.
Such categorical properties are truthmakers for, and not explicable in
terms of, subjunctive conditionals. For example, the causal power of
an electron is a categorical property that makes subjunctive
conditionals such as the one just specified ("If an
electron...") true (Jacobs 2011; cf. Heil 2003, Jaworski
2016). Such truthmakers could be construed as physical quiddities
(Gundersen 2015, Pereboom 2016, 2019).



So, there are at least some candidates for what physical quiddities
might be like (for others, see, e.g., Chalmers 2013 [esp. 2015:
270-274]; Rosenberg 2004; Coleman 2012, 2015). Still, one might
wonder if any of the candidates just described--Aristotelian
prime materiality, Lockean solidity, or non-Humean causal
powers--can serve all of the Russellian physicalist's
purposes. Russellian physicalists argue that positing physical
quiddities safeguards their theory from the conceivability and
knowledge arguments
 (section 3.1).
 But suppose those quiddities are construed as non-Humean causal
powers of physical entities such as electrons. Wouldn't Mary be
in a position to fully understand such powers while she is still in
the room? (Pereboom 2011: 113-114). If so, then the proposed
construal would seem to undermine the Russellian physicalist's
basis for denying that her pre-release physical knowledge is
incomplete. Similarly, one might argue that the proposed construal
would undermine the Russellian physicalist's contention that
while a structural zombie world is ideally conceivable, a full-fledged
zombie world is not. Parallel concerns arise for Aristotelian prime
materiality and Lockean solidity. Even if those properties could be
construed as physical quiddities, they would not appear to facilitate
the Russellian physicalist's objective of providing a plausible
response to the conceivability and knowledge arguments (cf. Botin
2023).


## 5. Final Words



Chalmers writes:



> 
> 
> If we can find a reasonable solution to the combination problem for
> either [Russellian panpsychism or Russellian panprotopsychism], this
> view would immediately become the most promising solution to the
> mind-body problem. (Chalmers 2013 [2015: 274])
> 
> 
> 



Whether or not Chalmers is right about this, many philosophers of mind
believe that Russellian monism merits serious attention.