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Mental causation and mental properties
†
M
ICHAEL
E
SFELD
(published in
Dialectica
59
(2005), pp. 5–18)
A
BSTRACT
The aim of this paper is to defend the causal homogeneity of functional, mental properties against Kim’s attack. It is
argued that (a) token identity is sufficient for mental causation, that (b) token identity implies a sort of functional
reduction, but that (c) nonetheless functional, mental properties can be causally homogeneous despite being multiply
realizable: multiple composition is sufficient for multiple realizability, but multiple composition does not prevent the
realizers from having their pertinent effects in common. Thus, the causal exclusion problem provides no argument for
abandoning the position that there are functional, mental properties that are natural kind properties.
1. The causal exclusion problem
The following four principles are a popular way of setting out the mind–body problem. Each
of these principles is plausible taken on its own. But it is difficult to see how they can be true
taken together:
(1)
distinction
: Mental states are distinct from physical states.
(2)
mental causation
: Mental states cause physical states.
(3)
completeness
: For any physical state
p
, insofar as
p
has a cause, it has a complete physical
cause (that is, a sufficient physical cause).
(4)
no systematic overdetermination
: If mental states cause physical states, there is no
systematic overdetermination of the physical states in question by complete physical
causes and additional mental causes.
These four principles imply what is known as the
causal exclusion problem
: given (3) it
seems that physical causes exclude – or at least pre-empt – mental causes.
This paper will only be concerned with the causal exclusion problem. If we conceive
physical states in the last resort as the states that are described by a fundamental and universal
physical theory – such as quantum field theory or general relativity – the causal exclusion
problem touches not only mental causes. It extends to all so-called higher-level causes such as
chemical, geological, biological, and neurobiological causes. If we explain “physical states”
in the above mentioned four principles as “fundamental physical states” (or “microphysical
states” for that matter), we can replace “mental states” with “chemical states”, [6] “biological
states”, etc. The problem thus is a general one. Consequently, the position considered in this
paper concerns not only mental causes, but all so-called higher-level causes.
In order to search for a solution to this problem, it is sufficient to conceive causation as a
relation between individual states (state tokens), one state token causing another state token.
For the sake of sketching out a solution to this problem, it is not necessary to commit us to
one particular view of states: states may be states of substances (continuants), or they may
simply be four-dimensional events (occurrents). It is, however, necessary to adopt a fine-
grained view of state tokens:
let us regard a state token as an instance of a property – that is,
University of Lausanne, Department of Philosophy, CH-1015 Lausanne, Switzerland, Michael-
Andreas.Esfeld@unil.ch.
†
Mental causation and mental properties
2
a property token – occurring at a certain time
. Such a fine-grained conception is
indispensable to capture mental causation: the point at issue is whether an instance of a
mental property (a mental state token) can stand in a causal relation to an instance of a
physical property (a physical state token). For example, the headache of Mary this noon is a
mental state token. The question is whether this state token causes a physical state token such
as Mary’s arm reaching out for an aspirin.
There is no easy solution to this problem: it is not plausible simply to drop any of the four
principles mentioned above. If one abandons (4), one has to maintain that all the effects that
mental causes produce are simultaneously produced by physical causes. For instance, in any
case when my right arm goes up, there are physical laws and initial conditions that yield a
certain probability for a state token of the type right arm going up occurring, and there are
mental causes, distinct from the physical causes that yield the very same probability.
Consequently, the supposition seems to be superfluous that for some physical effects, there
are not only physical causes, but also mental causes (which are distinct from the physical
causes).
1
Mental causation seems to fall victim to Occam’s razor.
If one gives up (3), one runs into a dilemma. Physical causation is tied to laws. There are
physical laws that yield, together with initial conditions, for any physical state of a type
P
a
certain probability of occurring. The one horn of the dilemma is that some physical laws are
false, because they do not indicate the correct probabilities for the occurrence of physical state
tokens of certain types (that is, those states which also have mental causes, the mental causes
being distinct from the physical ones). Physical laws and initial conditions yield a certain
probability for my right arm going up in the next five minutes. (At least if we go down to the
microphysical level, there are strict laws that indicate, given initial conditions, a certain
probability, say, for the changes of movements of atomic particles in my right shoulder
occurring that are necessary for my right arm to go up). If, in the next five minutes, I take the
decision to lift my right arm (mental state token), this decision is a mental cause that raises
the probability for a state token of the type [7] right arm going up occurring, including the
occurrence of the microphysical state tokens that are necessary for my right arm going up in
the given situation. Hence, the physical laws and initial conditions do not indicate the correct
probabilities for physical states of certain types to occur, because they ignore one crucial
factor that enters into the determination of these probabilities, namely mental intentions.
The other horn of the dilemma is to say that there are physical states of certain types to
which physical laws do not apply (namely, the states which also have mental causes). My
body (or a part of it – such as the brain or one particular area of the brain) is a physical system
that interacts with a non-physical system (mental causes) so that it does not come under
physical laws. Note that the problem which the principle of completeness poses for mental
causation is independent of whether or not the physical causes are deterministic or
probabilistic. Hence, the question of whether or not our current basic physical theories contain
irreducibly probabilistic laws is irrelevant to the problem of mental causation.
2
Giving up (2) seems to be a possibility to be envisaged only as a last resort. Mental
causation is a cornerstone of the view of ourselves as thinking and acting beings. If there were
no mental causes, there wouldn’t be any actions, no freedom to act, etc. It is, however, my
1
But see Loewer (2001), Marcus (2001), and Bennett (2003).
2
See Loewer (1996) and Esfeld (2000).
Mental causation and mental properties
3
intention to put down my thoughts that causes my typing this paper, etc. As regards (1), the
multiple realizability of mental states is widely taken to show that mental states are distinct
from physical states.
2. The functionalist solution
There is a standard solution to the problem of mental causation based on functionalism that is
able to accommodate all four mentioned principles in a certain sense. According to
functionalism, mental states are functional states, defined by a causal role. That is to say, a
certain pattern of causes and effects defines a mental state of the type
M
. These include
mental states of other types as well as input states and output states. For instance, to give a
rough idea, a functional definition of pain may include tissue damage as a characteristic cause
and distress and wincing as characteristic effects. According to the mainstream conception of
functionalism, a functional state (or property) is a second order state (or property), namely the
state of being in some – first order – state that fills the causal role in question. The distinction
between first order and second order states is relative: a biological state that realizes a mental
state is a first order state with respect to the mental state, but it may itself be a second order,
functional state with respect to a microphysical state. The first order states that realize a
functional state can be of various sorts: all they need to have in common is to exercise the
causal role in question. Thus, functional states admit of multiple realization by first order
states. [8] For instance, it may be the case that pain is realized by the firing of C-fibres in
humans, but it is realized in another way in octopuses, and it may be realized by states of
silicon chips in Martians. In that case, the realization of pain varies from species to species.
Multiple realizability of a mental type
M
may go even further than that. The type of
physical tokens that realize
M
may vary from individual case to individual case. This may to a
certain extent be true of intentional states: Why should the neural state token that realizes my
belief this morning that grandmothers deserve respect be of the same type as the neural state
token that realizes your belief this morning that grandmothers deserve respect, or the token
that realized my belief of the same type last week?
Realization, thus construed, is a relation between one functional type and many first order
tokens. It is, however, misleading to conceive single first order state tokens as the realizers of
a functional type. In each case, it is rather an arrangement of first order state tokens that
realizes a functional state type.
3
For instance, it is not the firing of C-fibres as such that
realizes pain in humans. Rather, a given token of C-fibres firing realizes a state of the type
pain if and only if this token is suitably related with other brain state tokens so that these
tokens taken together produce a characteristic pain reaction such as wincing. It is therefore
reasonable to conceive realization as a relation between a functional state type and
arrangements of first order state tokens.
The idea hence is this one: mental state types are realized by arrangements of physical state
tokens. On the one hand, because of multiple realizability, mental state types (mental
properties) are distinct from physical state types (physical properties). On the other hand,
since all the mental states that occur in the actual world are realized by arrangements of
physical tokens and since causation is a relation between state tokens, physical causes do not
exclude or pre-empt mental causes.
3
Compare the distinction between “core realizers” and “total realizers” that Shoemaker (1981, section 2)
draws.
Mental causation and mental properties
4
My first claim is that conceiving realization as amounting to identity between mental state
tokens and physical state tokens is sufficient to account for mental causation
. That is to say,
any mental token that there is in the world is identical with an arrangement of physical tokens
(or, at least, constituted by an arrangement of physical tokens).
4
Thus, Mary’s headache this
noon is identical with (or constituted by) a brain state token such as her C-fibres firing this
noon in relation to suitable other brain state tokens (that taken together produce her reaching
out for an aspirin). One may object that Mary’s headache this noon could have been realized
in another way than by that arrangement of physical tokens: if that [9] arrangement of
physical tokens did not occur, her headache could nonetheless have occurred, being realized
in another physical way. However, in that case, Mary would have had another headache-token
this noon – although that headache-token could have been qualitatively indistinguishable from
the one that actually occurred. The identity between tokens is, of course, necessary. What is
contingent is that other tokens of the same type than the actual ones could have occurred.
If a mental token is identical with an arrangement of physical tokens, the effects that the
arrangement in question produces are the effects that the mental token produces. If there is
identity of property tokens, there is no conceptual space left for asking whether the cause
produces an effect in virtue of its mental or in virtue of its physical properties. Mental tokens
cause physical tokens, being identical with physical tokens. Note that a particular
arrangement of physical tokens is a case of the mental type
M
(a mental token) only because it
exemplifies the causal relations – the pattern of causes and effects – that characterize
M
.
Can we do with anything less than token identity? In other words, is the assumption of
token identity not only sufficient, but also necessary in order to account for mental causation,
given completeness (3) and the absence of systematic overdetermination (4)? Stephen Yablo
(1992), to mention one influential argument against token identity, proposes to conceive
realization as a case of the relation between determinables and determinates. Being in a state
of C-fibres firing in suitable relation to other brain states is a way of being in pain – as being
aquamarine is a way of being blue. According to Yablo, there is no identity between a token
of a determinate (such as being aquamarine, or being in a state of C-fibres firing) and a token
of a determinable (such as being blue, or being in a state of pain).
5
Nonetheless, he maintains
that there is no competition for causal efficacy between determinables and their determinates.
However, one can argue that if there is no token identity, determinables and their
determinates do not compete for causal efficacy, simply because tokens of determinables are
at most in some sense causally relevant to the production of effects, but the actual causal work
is done by the tokens of the determinates. Thus, it is the token of C-fibres firing in suitable
relation to other brain state tokens (and not the pain token) that actually produces all the
effects that are characteristic of pain. Establishing this point would of course require further
argument.
6
Nevertheless, it is evident that token identity is sufficient for mental causation – and
arguably also necessary. Jaegwon Kim argues for token identity as a necessary and sufficient
condition for mental causation in his influential book [10]
Mind in a physical world
on the
4
I shall not discuss the distinction between token identity and constitution in this paper. See Poland (1994,
16-18).
5
But see MacDonald & MacDonald (1986, 149-150), who argue that the relation between a token of a
determinate property and a token of a determinable property is identity.
6
See Pineda (2002, 36-40), for an argument against Yablo (1992) along these lines.
Mental causation and mental properties
5
basis of the causal exclusion problem (1998, chapters 2 and 4). In a précis of that book, he
sums up his claim in these words:
If M is to retain its causal status, it must be reducible to P – at least, the given instantiation of M
must be reductively identifiable with the instantiation, on that occasion, of its supervenience or
realization base. (Kim 2002b, 642)
In other words, identity between a given token
m
and a given arrangement of physical tokens
p
is necessary and sufficient to solve the problem of causal exclusion.
3. Functional reduction
The claim of token identity is a sort of reductionism about the mental: all mental tokens that
there are in the actual world are nothing but arrangements of physical tokens. As Kim (1998,
chapter 4) makes clear, functionalism with respect to mental properties allows us to apply the
Ramsey–Lewis method of functional reduction (see Lewis 1970). This method suits well with
token identity. We can briefly characterize it in this way: (1) Let
M
be a functional, mental
type. We define
M
through its relations to other types, that is, relations to other mental types
as well as – physical – inputs and outputs. (2) We replace the concepts that figure in this
definition by free variables. (3) We bind these variables by existential quantification, thus
postulating that there is at least one realization of
M
(this is the Ramsey-sentence of
M
). (4)
We discern realizations of
M
. That is to say, we replace the variables with a description of
realizer states that stand in the appropriate relations. That description no longer contains the
mental concepts figuring in the definition of
M
.
If we assume that any realization of
M
is a physical realization of
M
by an arrangement of
physical tokens, the Ramsey–Lewis method shows us a way to describe any token of
M
in a
physical vocabulary alone. The force of the Ramsey–Lewis method of functional reduction is
evident in the case of the multiple realization of a functional, mental type
M
: this method
shows that and how it is in principle possible to give a physical description of each case of
M
,
however scattered the multiple realization of
M
may be. No extensional equivalence between
mental and physical concepts is required for that reduction.
The Ramsey–Lewis method of functional reduction provides for holism: the definition of
any mental type includes relations to other mental types. Functional reduction therefore does
not imply that it is in principle possible to give a physical description of each mental token
taken separately. It may only be possible to pick out in a physical vocabulary the arrangement
of physical tokens that is identical with a cluster of mental tokens. Holism is widely accepted
with respect to intentional states. Relations to other belief states are constitutive of, for
instance, being [11] in the belief state that grandmothers deserve respect. Consequently, it
may not even in principle be possible to single out a description of physical tokens that are the
realizers of a belief of that type alone on the given occasion. It may even in principle only be
possible to give a physical description of the realizers of the relevant cluster of belief states.
However, in order to avoid an unnecessary complication in setting out the argument of this
paper, I shall ignore this qualification in the following.
What is more, the physical description of a functional token amounts to an explanation of
that token. Why are there tokens of a mental type
M
in the world? Because there are
arrangements of physical tokens that stand in the causal relations that define
M
, that is,
physical tokens which have the causes and effects that are characteristic of
M
. Even if there is
an extreme variety in the physical realizers of
M
, token identity entails psycho-physical laws
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Mental causation and mental properties
†
M
ICHAEL
E
SFELD
(published in
Dialectica
59
(2005), pp. 5–18)
A
BSTRACT
The aim of this paper is to defend the causal homogeneity of functional, mental properties against Kim’s attack. It is
argued that (a) token identity is sufficient for mental causation, that (b) token identity implies a sort of functional
reduction, but that (c) nonetheless functional, mental properties can be causally homogeneous despite being multiply
realizable: multiple composition is sufficient for multiple realizability, but multiple composition does not prevent the
realizers from having their pertinent effects in common. Thus, the causal exclusion problem provides no argument for
abandoning the position that there are functional, mental properties that are natural kind properties.
1. The causal exclusion problem
The following four principles are a popular way of setting out the mind–body problem. Each
of these principles is plausible taken on its own. But it is difficult to see how they can be true
taken together:
(1)
distinction
: Mental states are distinct from physical states.
(2)
mental causation
: Mental states cause physical states.
(3)
completeness
: For any physical state
p
, insofar as
p
has a cause, it has a complete physical
cause (that is, a sufficient physical cause).
(4)
no systematic overdetermination
: If mental states cause physical states, there is no
systematic overdetermination of the physical states in question by complete physical
causes and additional mental causes.
These four principles imply what is known as the
causal exclusion problem
: given (3) it
seems that physical causes exclude – or at least pre-empt – mental causes.
This paper will only be concerned with the causal exclusion problem. If we conceive
physical states in the last resort as the states that are described by a fundamental and universal
physical theory – such as quantum field theory or general relativity – the causal exclusion
problem touches not only mental causes. It extends to all so-called higher-level causes such as
chemical, geological, biological, and neurobiological causes. If we explain “physical states”
in the above mentioned four principles as “fundamental physical states” (or “microphysical
states” for that matter), we can replace “mental states” with “chemical states”, [6] “biological
states”, etc. The problem thus is a general one. Consequently, the position considered in this
paper concerns not only mental causes, but all so-called higher-level causes.
In order to search for a solution to this problem, it is sufficient to conceive causation as a
relation between individual states (state tokens), one state token causing another state token.
For the sake of sketching out a solution to this problem, it is not necessary to commit us to
one particular view of states: states may be states of substances (continuants), or they may
simply be four-dimensional events (occurrents). It is, however, necessary to adopt a fine-
grained view of state tokens:
let us regard a state token as an instance of a property – that is,
University of Lausanne, Department of Philosophy, CH-1015 Lausanne, Switzerland, Michael-
Andreas.Esfeld@unil.ch.
†
Mental causation and mental properties
2
a property token – occurring at a certain time
. Such a fine-grained conception is
indispensable to capture mental causation: the point at issue is whether an instance of a
mental property (a mental state token) can stand in a causal relation to an instance of a
physical property (a physical state token). For example, the headache of Mary this noon is a
mental state token. The question is whether this state token causes a physical state token such
as Mary’s arm reaching out for an aspirin.
There is no easy solution to this problem: it is not plausible simply to drop any of the four
principles mentioned above. If one abandons (4), one has to maintain that all the effects that
mental causes produce are simultaneously produced by physical causes. For instance, in any
case when my right arm goes up, there are physical laws and initial conditions that yield a
certain probability for a state token of the type right arm going up occurring, and there are
mental causes, distinct from the physical causes that yield the very same probability.
Consequently, the supposition seems to be superfluous that for some physical effects, there
are not only physical causes, but also mental causes (which are distinct from the physical
causes).
1
Mental causation seems to fall victim to Occam’s razor.
If one gives up (3), one runs into a dilemma. Physical causation is tied to laws. There are
physical laws that yield, together with initial conditions, for any physical state of a type
P
a
certain probability of occurring. The one horn of the dilemma is that some physical laws are
false, because they do not indicate the correct probabilities for the occurrence of physical state
tokens of certain types (that is, those states which also have mental causes, the mental causes
being distinct from the physical ones). Physical laws and initial conditions yield a certain
probability for my right arm going up in the next five minutes. (At least if we go down to the
microphysical level, there are strict laws that indicate, given initial conditions, a certain
probability, say, for the changes of movements of atomic particles in my right shoulder
occurring that are necessary for my right arm to go up). If, in the next five minutes, I take the
decision to lift my right arm (mental state token), this decision is a mental cause that raises
the probability for a state token of the type [7] right arm going up occurring, including the
occurrence of the microphysical state tokens that are necessary for my right arm going up in
the given situation. Hence, the physical laws and initial conditions do not indicate the correct
probabilities for physical states of certain types to occur, because they ignore one crucial
factor that enters into the determination of these probabilities, namely mental intentions.
The other horn of the dilemma is to say that there are physical states of certain types to
which physical laws do not apply (namely, the states which also have mental causes). My
body (or a part of it – such as the brain or one particular area of the brain) is a physical system
that interacts with a non-physical system (mental causes) so that it does not come under
physical laws. Note that the problem which the principle of completeness poses for mental
causation is independent of whether or not the physical causes are deterministic or
probabilistic. Hence, the question of whether or not our current basic physical theories contain
irreducibly probabilistic laws is irrelevant to the problem of mental causation.
2
Giving up (2) seems to be a possibility to be envisaged only as a last resort. Mental
causation is a cornerstone of the view of ourselves as thinking and acting beings. If there were
no mental causes, there wouldn’t be any actions, no freedom to act, etc. It is, however, my
1
But see Loewer (2001), Marcus (2001), and Bennett (2003).
2
See Loewer (1996) and Esfeld (2000).
Mental causation and mental properties
3
intention to put down my thoughts that causes my typing this paper, etc. As regards (1), the
multiple realizability of mental states is widely taken to show that mental states are distinct
from physical states.
2. The functionalist solution
There is a standard solution to the problem of mental causation based on functionalism that is
able to accommodate all four mentioned principles in a certain sense. According to
functionalism, mental states are functional states, defined by a causal role. That is to say, a
certain pattern of causes and effects defines a mental state of the type
M
. These include
mental states of other types as well as input states and output states. For instance, to give a
rough idea, a functional definition of pain may include tissue damage as a characteristic cause
and distress and wincing as characteristic effects. According to the mainstream conception of
functionalism, a functional state (or property) is a second order state (or property), namely the
state of being in some – first order – state that fills the causal role in question. The distinction
between first order and second order states is relative: a biological state that realizes a mental
state is a first order state with respect to the mental state, but it may itself be a second order,
functional state with respect to a microphysical state. The first order states that realize a
functional state can be of various sorts: all they need to have in common is to exercise the
causal role in question. Thus, functional states admit of multiple realization by first order
states. [8] For instance, it may be the case that pain is realized by the firing of C-fibres in
humans, but it is realized in another way in octopuses, and it may be realized by states of
silicon chips in Martians. In that case, the realization of pain varies from species to species.
Multiple realizability of a mental type
M
may go even further than that. The type of
physical tokens that realize
M
may vary from individual case to individual case. This may to a
certain extent be true of intentional states: Why should the neural state token that realizes my
belief this morning that grandmothers deserve respect be of the same type as the neural state
token that realizes your belief this morning that grandmothers deserve respect, or the token
that realized my belief of the same type last week?
Realization, thus construed, is a relation between one functional type and many first order
tokens. It is, however, misleading to conceive single first order state tokens as the realizers of
a functional type. In each case, it is rather an arrangement of first order state tokens that
realizes a functional state type.
3
For instance, it is not the firing of C-fibres as such that
realizes pain in humans. Rather, a given token of C-fibres firing realizes a state of the type
pain if and only if this token is suitably related with other brain state tokens so that these
tokens taken together produce a characteristic pain reaction such as wincing. It is therefore
reasonable to conceive realization as a relation between a functional state type and
arrangements of first order state tokens.
The idea hence is this one: mental state types are realized by arrangements of physical state
tokens. On the one hand, because of multiple realizability, mental state types (mental
properties) are distinct from physical state types (physical properties). On the other hand,
since all the mental states that occur in the actual world are realized by arrangements of
physical tokens and since causation is a relation between state tokens, physical causes do not
exclude or pre-empt mental causes.
3
Compare the distinction between “core realizers” and “total realizers” that Shoemaker (1981, section 2)
draws.
Mental causation and mental properties
4
My first claim is that conceiving realization as amounting to identity between mental state
tokens and physical state tokens is sufficient to account for mental causation
. That is to say,
any mental token that there is in the world is identical with an arrangement of physical tokens
(or, at least, constituted by an arrangement of physical tokens).
4
Thus, Mary’s headache this
noon is identical with (or constituted by) a brain state token such as her C-fibres firing this
noon in relation to suitable other brain state tokens (that taken together produce her reaching
out for an aspirin). One may object that Mary’s headache this noon could have been realized
in another way than by that arrangement of physical tokens: if that [9] arrangement of
physical tokens did not occur, her headache could nonetheless have occurred, being realized
in another physical way. However, in that case, Mary would have had another headache-token
this noon – although that headache-token could have been qualitatively indistinguishable from
the one that actually occurred. The identity between tokens is, of course, necessary. What is
contingent is that other tokens of the same type than the actual ones could have occurred.
If a mental token is identical with an arrangement of physical tokens, the effects that the
arrangement in question produces are the effects that the mental token produces. If there is
identity of property tokens, there is no conceptual space left for asking whether the cause
produces an effect in virtue of its mental or in virtue of its physical properties. Mental tokens
cause physical tokens, being identical with physical tokens. Note that a particular
arrangement of physical tokens is a case of the mental type
M
(a mental token) only because it
exemplifies the causal relations – the pattern of causes and effects – that characterize
M
.
Can we do with anything less than token identity? In other words, is the assumption of
token identity not only sufficient, but also necessary in order to account for mental causation,
given completeness (3) and the absence of systematic overdetermination (4)? Stephen Yablo
(1992), to mention one influential argument against token identity, proposes to conceive
realization as a case of the relation between determinables and determinates. Being in a state
of C-fibres firing in suitable relation to other brain states is a way of being in pain – as being
aquamarine is a way of being blue. According to Yablo, there is no identity between a token
of a determinate (such as being aquamarine, or being in a state of C-fibres firing) and a token
of a determinable (such as being blue, or being in a state of pain).
5
Nonetheless, he maintains
that there is no competition for causal efficacy between determinables and their determinates.
However, one can argue that if there is no token identity, determinables and their
determinates do not compete for causal efficacy, simply because tokens of determinables are
at most in some sense causally relevant to the production of effects, but the actual causal work
is done by the tokens of the determinates. Thus, it is the token of C-fibres firing in suitable
relation to other brain state tokens (and not the pain token) that actually produces all the
effects that are characteristic of pain. Establishing this point would of course require further
argument.
6
Nevertheless, it is evident that token identity is sufficient for mental causation – and
arguably also necessary. Jaegwon Kim argues for token identity as a necessary and sufficient
condition for mental causation in his influential book [10]
Mind in a physical world
on the
4
I shall not discuss the distinction between token identity and constitution in this paper. See Poland (1994,
16-18).
5
But see MacDonald & MacDonald (1986, 149-150), who argue that the relation between a token of a
determinate property and a token of a determinable property is identity.
6
See Pineda (2002, 36-40), for an argument against Yablo (1992) along these lines.
Mental causation and mental properties
5
basis of the causal exclusion problem (1998, chapters 2 and 4). In a précis of that book, he
sums up his claim in these words:
If M is to retain its causal status, it must be reducible to P – at least, the given instantiation of M
must be reductively identifiable with the instantiation, on that occasion, of its supervenience or
realization base. (Kim 2002b, 642)
In other words, identity between a given token
m
and a given arrangement of physical tokens
p
is necessary and sufficient to solve the problem of causal exclusion.
3. Functional reduction
The claim of token identity is a sort of reductionism about the mental: all mental tokens that
there are in the actual world are nothing but arrangements of physical tokens. As Kim (1998,
chapter 4) makes clear, functionalism with respect to mental properties allows us to apply the
Ramsey–Lewis method of functional reduction (see Lewis 1970). This method suits well with
token identity. We can briefly characterize it in this way: (1) Let
M
be a functional, mental
type. We define
M
through its relations to other types, that is, relations to other mental types
as well as – physical – inputs and outputs. (2) We replace the concepts that figure in this
definition by free variables. (3) We bind these variables by existential quantification, thus
postulating that there is at least one realization of
M
(this is the Ramsey-sentence of
M
). (4)
We discern realizations of
M
. That is to say, we replace the variables with a description of
realizer states that stand in the appropriate relations. That description no longer contains the
mental concepts figuring in the definition of
M
.
If we assume that any realization of
M
is a physical realization of
M
by an arrangement of
physical tokens, the Ramsey–Lewis method shows us a way to describe any token of
M
in a
physical vocabulary alone. The force of the Ramsey–Lewis method of functional reduction is
evident in the case of the multiple realization of a functional, mental type
M
: this method
shows that and how it is in principle possible to give a physical description of each case of
M
,
however scattered the multiple realization of
M
may be. No extensional equivalence between
mental and physical concepts is required for that reduction.
The Ramsey–Lewis method of functional reduction provides for holism: the definition of
any mental type includes relations to other mental types. Functional reduction therefore does
not imply that it is in principle possible to give a physical description of each mental token
taken separately. It may only be possible to pick out in a physical vocabulary the arrangement
of physical tokens that is identical with a cluster of mental tokens. Holism is widely accepted
with respect to intentional states. Relations to other belief states are constitutive of, for
instance, being [11] in the belief state that grandmothers deserve respect. Consequently, it
may not even in principle be possible to single out a description of physical tokens that are the
realizers of a belief of that type alone on the given occasion. It may even in principle only be
possible to give a physical description of the realizers of the relevant cluster of belief states.
However, in order to avoid an unnecessary complication in setting out the argument of this
paper, I shall ignore this qualification in the following.
What is more, the physical description of a functional token amounts to an explanation of
that token. Why are there tokens of a mental type
M
in the world? Because there are
arrangements of physical tokens that stand in the causal relations that define
M
, that is,
physical tokens which have the causes and effects that are characteristic of
M
. Even if there is
an extreme variety in the physical realizers of
M
, token identity entails psycho-physical laws
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