Reduction and Elimination in Philosophy and the Sciences

Mental Causation and Physical Causation
Lorenzo Casini, Canterbury, Kent, England, UK
1. Introduction
The recent debate between Antony and Kim on the nature
of mental causation offers the possibility to evaluate the
reason underlying two up-to-date physicalist positions:
Kim’s Reductive Physicalism and Antony’s Non-Reductive
Physicalism. Despite differences, both share a common
metaphysical task. They look for a systematic account of
the relations between the physical and the mental, which is
needed, so they say, because higher-level properties can
enter into ‘genuine’ laws only if they inherit the causal
power of ontologically prior lower-level entities. This means
that there could not be regularities concerning mental
states without underlying physical mechanisms. In particular,
only the physical mechanisms at work at the microlevel
can secure and explain the truth of psychological generalisations.
Only at the microlevel, Antony and Kim argue, we
find the entities involved in ‘genuinely’ causal phenomena.
I show that if the paradigmatic feature which the
microphysical is to display is that it conforms to a particular
model of causal production, as Kim explicitly suggests, this
prevents Reductive- and Non-Reductive Physicalism to
achieve their tasks. In fact, certain quantum mechanics’
phenomena cannot be described in terms of causal production.
If we accept a statistical-regularist approach to
describe phenomena in the quantum domain, then quantum
mechanics and psychological phenomena are on a
par with respect to their causal features. The physicalists,
who claim the necessity to account for the mental in physical
terms, is to clarify what peculiar feature microphysical
mechanisms possess, and the mental is to inherit, for psychological
generalisations to be secured and explained.
2. The Metaphysical Picture: Physicalism
and Reductionism
Both Antony and Kim conceive the world as layered, i.e.,
made of different levels organised in a hierarchical structure.
The determining level, the physical bottom level, is
ontologically prior to all the other higher levels, because its
entities stand with those of the higher levels in a partwhole
relation, such as that which occurs between one
oxygen and two hydrogen atoms and a H2O molecule.
However, at each level there are properties which make
their first appearance at that level. For instance, properties
like density or viscosity of H2O molecules were not present
at the lower level of their atomic constituents. In particular,
(i) the entities of psychology, such as sensations and propositional
attitudes, are nothing over physical complexes,
such as patterns of neurons; (ii) each mental property
(e.g.: a toothache, the belief that ‘the water is wet’, etc.) is
a property of some physical entity or system of physical
entities (e.g.: an underlying pattern of neurons). The question,
then, is: How can mental properties have the causal
power they have in a world ultimately constituted by physical
entities and mechanisms?
Antony’s and Kim’s answers, however, are different.
The former does, whereas the latter does not, accept that
systems of lower-level entities can acquire mental properties,
i.e., mental causal powers, which are emergent from
the lower base, and non-ontologically-reducible to it. For
Kim and Antony, a property at a given level is emergent, iff
non-ontologically-reducible to the lower-level property it
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emerges from. For Antony, the properties of the psychological
domain are like H2O with respect to its atomic
constituents. This would legitimate the autonomy of psychology,
whose properties must inherit their causal power
from lower-level physical entities but are not to be reducible
to the properties of these entities, on pain of identifying
psychology with branches of physics. In order to meet
these desiderata, she wants reductive explanation without
ontological reduction. In contrast, Kim claims that psychological
properties do not constitute a proper scientific domain,
given that they can be ontologically reduced to
physical properties. In fact, so he reasons, they are not,
strictly speaking, emergent as H2O is, insofar as they apply
to precisely the same objects as do their realiser properties—i.e.,
mental properties and their realisations are
properties of entities at the same level, and have the same
causal powers (Kim 1998, 82-3). The difference between
their positions depends on whether or not multiple realisability
(MR) holds. According to MR, each mental property
can be realised by many distinct physical properties—
therefore is not identical to any of them. If MR is true, then
no reduction is possible, and psychology is autonomous
(Antony 2007, 154-5).
Kim does not accept the idea that there is in principle
an indefinite number of realisers among the individuals
of the same species or structure type. That is, he challenges
the truth of MR, and claims that a structure-specific
reduction is—in principle—possible, granted that the
physical realisers the psychological properties are reduced
to are sufficiently similar to one another (Kim 1993, 89,
313). Mental properties can be identified with physical
properties which play the same causal role—for each mental
property there is also a physical property which is necessary
and sufficient for the mental property to arise, given
that they are, in fact, one and the same (Kim 2006, 280).
Mental terms which stand for disjunctions of different
physical properties, instead, have no ontological correlates—therefore
no scientific value (Kim 1993, 334-5). As a
consequence of reduction, psychology loses its proper
subject matter, and together its autonomy.
For Antony, in contrast, ontological reduction is impossible
because of MR. In order to vindicate mental causation
as mental and justify the autonomy of psychology,
whilst consistently holding that the physical is ontologically
prior, she advocates the possibility—in principle—of a
reductive explanation of every mental property in terms of
physical properties, such that some physical property is
sufficient but not necessary for a mental property to
emerge. Mental properties are properties of some physical
system or other—therefore ontologically acceptable, and
proper scientific kinds, because they enter into realisationindependent
regularities, i.e., regularities which do not
depend necessarily on one specific physical property (Antony,
Levine 1997, 92-4).
3. Back to Basics
I do not explain the differences between Kim’s model for
ontological reduction and Antony’s model for reductive
explanation. Instead, I stress a fundamental similarity be-