Reductionism does not have quite the same hold in philosophy of science that it once did, having been subjected to powerful attack not only from Cartwright, but from Paul Feyerabend, John Dupré, and many others. (I discuss the anti-reductionist literature in detail in Aristotle’s Revenge.) Still, the idea that whatever is real is somehow ultimately nothing more than what can in principle be described in the language of a completed physics exerts a powerful hold on many. Cartwright cites James Ladyman and Don Ross as adherents of this view, and Alex Rosenberg is another prominent advocate. As Cartwright notes, in contemporary writing about science, the lure of reductionism is especially evident in discussions of the purported implications of neuroscience for topics like free will.
Cartwright
sets the stage for her discussion by quoting a famous passage from physicist
Sir Arthur Eddington’s book The
Nature of the Physical World:
I have settled down to the task of
writing these lectures and have drawn up my chairs to my two tables. Two tables!
Yes; there are duplicates of every object about me – two tables, two
chairs, two pens…
One of them has been familiar to me
from earliest years. It is a commonplace
object of that environment which I call the world. How shall I describe it? It has extension; it is comparatively
permanent; it is coloured; above all it is substantial… [I]f you are a plain commonsense man, not too
much worried with scientific scruples, you will be confident that you
understand the nature of an ordinary table…
Table No. 2 is my scientific table…
It does not belong to the world previously mentioned – that world which
spontaneously appears around me when I open my eyes... My scientific table is
mostly emptiness. Sparsely scattered in
that emptiness are numerous electric charges rushing about with great speed;
but their combined bulk amounts to less than a billionth of the bulk of the
table itself…
There is nothing substantial about my second table. It is
nearly all empty space – space pervaded, it is true, by fields of force, but
these are assigned to the category of “influences”, not of “things”. (pp.
xi-xiii)
Now, reductionism
holds that in some sense the first table is really “nothing but” the second
table – or even that the first table does not, strictly speaking, really exist
at all, and that only the second table does (though philosophers typically
characterize the latter sort of view as eliminativist rather than
reductionist).
Reduced reductionism
The first
consideration Cartwright raises to illustrate how problematic reductionism is
concerns the way reductionists have, over the last few decades, repeatedly had
to qualify their claims. The ambitions
of reductionism have, you might say, been greatly reduced. Bold type-type
reductionism gave way first to a weaker token-token
reductionism, and then to yet weaker supervenience
theories.
Type-type
reductionist theories hold that each type
of feature described at some higher-level science can be identified with some type of feature described at a
lower-level science, and ultimately at the level of physics. Perhaps the best-known theory of this kind is
the original mind-brain identity theory,
which holds that every type of psychological state (the belief that it is
raining, the belief that it is sunny, the desire for a cheeseburger, the fear
that the stock market will crash, etc.) can be identified with some specific
type of brain process. A stock example
from the physical sciences would be the claim that temperature is identical to
mean kinetic energy.
As
Cartwright notes, one problem with this sort of view is that it is difficult to
find plausible cases of successful type-type reductions beyond such stock
examples. Another is that the stock
examples themselves are not in fact unproblematic. “Reduction” claims seem really to be eliminativist
claims after all. For example, given the
so-called reduction of temperature, it’s not that what we’ve always understood
to be temperature is really just mean kinetic energy. It’s that what we’ve always understood to be
temperature is not real after all (or exists only as a quale of our experience
of the physical world, rather than something there in the physical world
itself) and all that really exists is mean kinetic energy instead.
A problem
with supposing otherwise is that the laws that govern the features of some
higher-level description and the laws that govern the features of some allegedly
corresponding lower-level description can yield conflicting predictions. One way to think about this – though not
Cartwright’s own example – is in terms of Donald
Davidson’s view that descriptions at the psychological level are not
law-governed in the way that the materialist supposes that descriptions at the
neurological level are. Hence, even if a
brain event of a certain type is strictly predictable, the corresponding mental
event will not be. Given this sort of
mismatch, there is pressure on the type-type reductionist to treat the
higher-level description as not strictly true.
An
especially influential consideration that led philosophers to abandon type-type
reductionism is the “multiple realizability” problem – the fact that
higher-level features can be “realized in” more than one type of lower-level
feature, so that there is no smooth mapping of higher-level types on to
lower-level types of the kind an ambitious reductionist project aims for. In the case of the mind-brain identity
theory, the problem is that the same mental state (believing that it is
raining, say) could plausibly be associated with different types of brain
process in different people, or even in the same person at different
times. Or consider how an economic
property like being one dollar can be
realized in paper currency, in metal currency, or as an electronic record of
one’s bank account balance.
This led
philosophers to embrace less ambitious token-token
reductionist theories. The idea here is
that even if types of feature at a
higher level cannot be smoothly correlated with types of feature at a lower level, nevertheless every token or individual instance of a feature
at the higher level can be identified with some token or individual instance of
a lower-level feature. For example, this particular instance of believing that it’s raining is identical
with that particular instance of a
certain type of brain process.
As
Cartwright notes, however, token reductions in fact tend to yield, after all, type
reduction claims of a sort. An example
would involve disjunctive types at
the lower level of description. For
instance, a token reductionist view of mind-brain relations may entail that a
type of mental state like believing that
it is raining is identical to a “type” of neural property defined as being in brain state of type B1 OR being in
brain state of type B2 OR being in brain state of type B3 OR… And this will, in turn, open up the
possibility of a conflict between what the laws that govern the higher-level
description entail and what the laws that govern the lower-level description
entail.
If it is
objected that disjunctive “types” of the kind just described seem artificial, that
is certainly plausible. But the problem,
as Cartwright notes, is that this illustrates how identifying what counts as a
plausible type is going to require detailed metaphysical analysis, and cannot
be read off the science, as the reductionist supposes.
In any
event, token-token reductionism gave way in turn to talk of supervenience. The basic idea here is that phenomena at some
higher level of description A supervene
on phenomena at some lower level of description B just in case there could not be any difference at what happens at
level A without some corresponding
difference in what happens at level B.
But exactly
what this amounts to is not obvious, and debating the meaning of supervenience
has, Cartwright complains, been a bigger concern of philosophers than
explaining exactly why anyone should believe in it in the first place. (More on this in a moment.) As its vagueness indicates, supervenience entails
an even weaker claim than token-token reduction. Though, in recent years, there has been a lot
of heavy going about “grounding,” which, Cartwright notes, is stronger than
supervenience. The idea is that all
facts are “grounded” in the facts described at the level of physics, in the
sense that whatever happens at the higher levels is “due to” what happens at
the lower, physics level. But here too, why suppose this is the case?
Groundless grounding
Where the
claim that everything supervenes on the level described by physics is
concerned, Cartwright says, there are three basic reasons given for it, none of
them well worked out or convincing.
First, there is a leap from the fact that the lower-level features
described by physics affect what
happens at the higher levels, to the conclusion that those features by themselves
entirely fix what happens at the
higher levels. This is simply a non sequitur.
Second,
there is a leap from the supposition that successful reductions have been
carried out in a handful of cases, to
the conclusion that reductionism is in
general true. But this too is a non sequitur (and on top of that, the
premise is questionable). Third, there
is the claim that physicalistic reductionism is in fact the method applied
within science. But this, Cartwright
argues, is simply not true to the facts of actual scientific practice.
“Grounding”
accounts of reduction suppose that the level described by physics is the sole cause of what happens at the higher
levels, and also that it is in no way itself caused by what happens at the
higher levels. These claims too, argues
Cartwright, are not supported by actual scientific practice.
Here she
appeals in part to recent work in the philosophy of chemistry, in which two
general lines of anti-reductionist argument have been developed. The first and more ambitious of them argues
that chemistry as a discipline rests on classificatory and methodological
assumptions that are simply sui generis
and make the features of the world it uncovers irreducible to those uncovered
by physics. The second does not rule out
reductions a priori, but argues on a
case by case basis that purported reductions have not in fact successfully been
carried out. (I discuss this work in
philosophy of chemistry at pp. 330-40 of Aristotle’s
Revenge.)
But it is
not just that chemistry and other higher-level sciences are not in fact “all
physics” at the end of the day. As
Cartwright emphasizes, “even physics isn’t all physics.” For one thing, “physics” covers a range of
branches, theories, and practices, not all of which have been reduced to the most
fundamental theories. For another, even
the fundamental theories themselves are not fully compatible with each other,
the notorious inconsistency between quantum mechanics and the general theory of
relativity being a longstanding and still unresolved problem. She adds:
The third and to me most important
point is that in real science about real systems in the real world, for
predictions and explanations of even the purest of physics results, physics
must work in cooperation with a motley assembly of other knowledge, from other
sciences, engineering, economics, and practical life. (p. 110)
Cartwright
then goes on to describe in detail the Stanford Gravity Probe B
project as an illustration of the vast quantity of theoretical knowledge and
practical know-how that are necessary in order to apply and test abstract physical
theory, yet cannot itself be reduced to such theory. This recapitulates a longtime theme in
Cartwright’s work over the decades, viz. that the mathematical models and laws
of physics are idealized and simplified abstractions
from concrete physical reality, and do not themselves constitute or capture
concrete physical reality.
In short,
reductionism, Cartwright judges, is poorly defined and poorly argued for. Its lingering prestige is unearned.
I’ve mainly
just summarized Cartwright’s arguments here, since I sympathize with them and
they supplement those that I develop in Aristotle’s
Revenge. They give us, though, only
her case against the views she
opposes, rather than the positive account she’d put in place of them, which is
described later in the book. More on
that in a later post.
Related
reading:
Dupré
on the ideologizing of science
Scientism:
America’s State Religion