Reduction and Elimination in Philosophy and the Sciences

Physicalism Without the A Priori Passage
Harris Hatziioannou, Athens, Greece
Defenders of a priori entailment hold that physicalism is
committed to the following two theses: first, that all
macroscopic (high-level) facts, including facts about the
mind, are necessitated by the totality of physical (low-level)
facts, and, second, that, granting knowledge of the latter
set of facts, we can deduce the former without needing
any further empirical information. My target in this paper
will be the claim regarding the second commitment of
physicalism. Specifically, I will argue against two different
formulations of the thesis and then conclude with some
suggestions regarding the way in which we may
understand a posteriori physicalism and the determining
relation between low and high-level facts that it posits.
A number of attempts have been made to analyze
the thesis that physicalism is committed to the idea that
physical facts a priori determine all other facts. One prominent
example is David Lewis’s account (Lewis 1972),
which, relying on the Ramsey - Carnap method of defining
theoretical terms, appeals to the functional definability of
high-level terms in order to deduce them from the terms of
the reducing theory. By this procedure, the theoretical
terms in question are understood in terms of the relations
that they hold among each other, as these are expressed
in a vocabulary of which we had prior understanding: they
are explicitly defined as the unique entities, whatever
these may be, that occupy the causal roles specified by
the theory. In the mind/body case, the theory under reduction,
‘folk psychology’, is supposed to include all commonly
known platitudes about the mind, platitudes that are built in
our a priori understanding of these terms. In Lewis’s view,
these platitudes do nothing more than specify the position
of each mental state in the causal nexus in which it partakes;
thus, each mental state can be in principle explicitly
defined in terms of its characteristic causes and effects.
With the expected advancement of science, and when
these same causes and effects are given a physical characterization,
we will be able to identify the states picked by
the two different sets of terms, thus effecting the reduction
of our folk psychological theory of mind to the more comprehensive
physical theory.
Now, Lewis’s method provides a clear picture of the
way in which the a priori entailment of facts about the mind
by physical facts could be understood. Given the functional
definitions, the identification will clearly be the result of a
deductive inference. However, Lewis’s contention that
mental terms can be explicitly defined in terms of their
causal role is hardly convincing, not only to nonphysicalist,
but also to many physicalist philosophers. The
problem with such explicit analyses is threefold: First, they
seem to misconstrue the conventional meaning of such
terms; our concepts picking conscious states have strong
non-causal connotations, so that a functional definition a la
Lewis is bound to miss some part of the meaning we conventionally
associate with them. Second, they ignore the
possibility of multiple realization. There is widespread
agreement, at least since Wittgenstein, that we can find
explicit analyses in terms of necessary and sufficient conditions
only for few of our mental or other everyday concepts:
automobile, life, or belief that X, are all concepts
that seem to be multiply realizable, in the sense that it is
impossible to specify in a finite non-trivial way the conditions
of application that will capture all and only their referents.
The third objection points to the fact that conceptual
analyses such as Lewis’s seem to hold future empirical
research into the nature of mind hostage to a priori meaning
considerations. Raising the widespread platitudes
about the mind to the status of a priori definitions of mental
terms pays no heed to the fact that our concepts evolve
continuously in the light of novel empirical as well as conceptual
developments. The moral to be drawn from the
foregoing considerations, is that the explicit analysis of
mental and other terms that we commonly use in order to
describe the world, and their corresponding concepts, is
something that we cannot aspire to, since any proposed
analysis is likely to miss an essential part of their content.
That same moral has been drawn by Chalmers and
Jackson (Chalmers & Jackson 2001, Chalmers 1996,
Jackson 1998), who have proposed an alternative scheme
for reduction. Their scheme eschews such finite explicit
analyses, being based instead on a priori intensions, which
are understood as functions from possible worlds to extensions,
and that cannot be put into any explicit linguistic
description. These functions are supposed to capture our
implicit knowledge of the application conditions of our concepts,
the kind of knowledge that allows us to judge, on a
case by case basis, whether they apply to a certain situation
or not. So, given a non-trivial neutral description of a
possible world, considered to be the actual world, we can
(ideally) determine the extension of our concepts. For example,
given a description of a world where the salient
transparent, odourless, drinkable etc. liquid (‘the watery
stuff’) in the environment is H2O, the a priori intension of
the concept ‘water’ refers to H2O; given a description of a
world where the watery stuff is XYZ, it refers to XYZ. In
other words, the component of meaning that is a priori
associated with any given term or concept has no explicit
description; it is encompassed in the term’s a priori intension,
the function that determines the term’s extension in
every world considered as actual. Accordingly, no appeal
to explicit analyses needs to be made in accounting for the
relation of a priori entailment that supposedly holds between
low-level and high-level facts: this relation can simply
be analysed as one between functions from possible
worlds to extensions.
Chalmers’s and Jackson’s account thus avoids
Lewis’s questionable commitment to the explicit definability
of theoretical terms. However, the problem is that it seems
to have lost the transparency that characterized Lewis’s
way of analysing the relation of a priori entailment. With
the latter method, the question whether a certain instance
of inter-level reduction succeeds has a clear answer: if the
proposed functional analyses of the respective sets of
terms are in place, then the deductive inference and, consequently,
the inter-level reduction, can be carried through.
Chalmers’s and Jackson’s method, by repudiating explicit
conceptual analyses, has lost this virtue: for any proposed
instance of inter-level reduction, the answer whether it
succeeds or fails lies in the viability of our intuitions regarding
the referents of our concepts in various counteractual
scenarios. But this method is always going to be open to
scrutiny, since a sceptic may appeal to indeterminacy,
different intuitions, or even knowledge deficit, in order to
question a proposed reduction of one theory to another, or
a suggested failure thereof. A priori entailment, understood
as in Chalmers’s and Jackson’s way, gives us no princi-
131