Reduction and Elimination in Philosophy and the Sciences

A Metaphysically Moderate Version of Humean Supervenience
Szilárd Koczka, Miskolc, Hungary
Humean Supervenience (HS) is the doctrine that the nomic
features of our world supervenes on the arrangement of
basic, non-nomic properties. David Lewis's motivation in
elaborating HS was to present a view which does not refer
to properties and relations alien to physics, so it is
extremely important for the defender of HS to make it
compatible with current physics. Contrary to Lewis,
philosophers known as necessitarians or governists claim
that laws express necessary relations. These claims
involve an implicit ontological commitment that Lewis
summarizes as follows „...there are more things in heaven
and earth than physics has dreamt of.” (Lewis 1994,474).
Within a non-humean ontological framework there
can be states of affairs which are metaphysically related. A
non-humean approach can be plausible only if the
defenders of this view can put forward a convincing
argument to the point that the very notion of a natural law
involves a non-humean ontology. Whether one can acquire
such an argument is dubious, and as humean analyses do
not require such extra entities to explain the role of laws in
science, it seems that the ontologically less comitted
humean view is the promising one. For the rest of the
paper I will assume that there is no such argument around.
It is clear, that philosophical accounts of scientific
laws appeal to metaphysical intuitions, but there is a
significant difference between invoking intuitions or
metaphysical theories. If one tries to analyse the notion of
scientific laws in terms of his favorite metaphysical theory,
the proposed analysis assumes that the background
metaphysical theory is already accepted. As Lange (2000)
emphasises: without a previously established metaphysical
framework, this kind of approach is unilluminating. But if
we keep in mind that a philosophical account of the natural
laws is to be fitted with scientific practice, then it seems the
weaker metaphysical commitment the philosophical
account has the better. Scientists do not employ fully
developed metaphysical theories, but they surely know
how to work with these laws.
Formulations of Humean Supervenience
Lewis's original formulation of HS can be summarized as
follows: In the actual world, everything supervenes on local
qualities instantiating at certain points of space-time. There
is no difference between two possible worlds without some
difference in these local qualities. As Loewer (1996) points
out, Lewis's motivation was to defend physicalism against
philosophical challenges. Thus HS is motivated by a tendency
to avoid appeal to non-physical entities. However,
Lewis's (1986) own formulation postulates local properties
which seems to contradict current theories in quantum
mechanics. It seems that if our current quantum mechanics
is correct, then we have to abandon the view that there
are local properties at all. Lewis in his (1986,xi) admitted
that his formulation – as a physicalist doctrine – can be
falsified by empirical research, if it excludes the possibility
of his local properties; in this sense HS is at best a contingent
truth.
Loewer argues that for an acceptable doctrine we
need to refine the Humean Supervenience thesis in order
to make it compatible with recent physics. Loewer(1996)
claims that the problem of defining the Humean Base (HB)
on which everything else supervenes can be solved by
appealing to the mathematical apparatus of quantum
physics. According to his solution, the HB can be
characterized as consisting of points of the fundamental
mathematical space which is used by current quantum
mechanics. Earman and Roberts (2005) have some
misgivings about Loewer's version of HS. They argue that
different physical theories use different mathematical
spaces, and there is no uncontroversial way to determine
which mathematical treatment is the fundamental one. If
we try to specify the HB as the fundamental magnitudes of
the best future physical theory HS – without an account of
what makes a theory 'physical' – will be vacuous. It is
possible that future physics postulates several kinds of
entities which are alien to our current theories.
There are two possible answer to the question of
HS's compatibility with recent physical theories: (i)To make
HS compatible with recent physics a neo-humean
philosopher have to define the HB on which everything
else supervenes. As Earman and Roberts emphasize: at
this point our original metaphysical problem turns to be an
epistemological one. (ii)There is a possible alternative to
the epistemological account that Schaffer (2008) has in his
mind while he defends reductionism as a thesis about
mind-and-theory independent reality. He writes: “Causation
and the laws of nature are nothing over and above the
pattern of events, just like a movie is nothing over and
above the sequence of frames.” (Schaffer 2008).
According to his view, we do not need to define precisely
what kind of properties belong to the HB since this
formulation of HS does not concern the subvenient base. It
is important that Schaffer does not even refer to basic
(microphysical) facts. His starting point is the manifest
image, so it does not matter that whether we can define
basic microphysical facts with the help of our best theories.
However this approach relies on the presupposition that
knowledge about mind independent reality can be acquired
via metaphysical inquiry of the manifest image. Behind
these presuppositions is the view that we have knowledge
about the natural laws. This is what I doubt. For a
minimalist viewpoint if it is possible to come out with a
metaphysically less committed approach of nomic notions,
it seems that there are no much reason to hold such a
view. Thus if there is a formulation of (i) which can handle
our philosophical problems about scientific laws, we can
disapprove (ii). My solution relies on a distinction between
natural laws (of which we does not have knowledge) and
scientific laws. I think that the debate can be meaningful
only if we start with the notion of a scientific law and then
try to answer the question as to what philosophically
relevant implications it may have.
Natural laws or scientific laws?
Metaphysical discussions of natural laws assume that
science aims to discover the laws of nature. Consequently,
a metaphysical account of the natural laws can be accepted
only if it can explain the role of the laws in scientific
practice. Non-humeans argue that the notion of scientific
law required by science can only be explained within a
non-humean metaphysical framework. Humeans (e.g.
Loewer 1996) argue that HS does explain the role of the
notion of scientific laws and we do not need non-Humean
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