Reduction and Elimination in Philosophy and the Sciences
Reduction and Elimination in Philosophy and the Sciences
Reduction and Elimination in Philosophy and the Sciences
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Expla<strong>in</strong><strong>in</strong>g <strong>the</strong> Bra<strong>in</strong>:<br />
Ruthless <strong>Reduction</strong>ism or Multilevel Mechanisms?<br />
Markus Eronen, Osnabrück, Germany<br />
1. Introduction<br />
In this paper, I will compare <strong>and</strong> criticize two approaches<br />
to reduction <strong>and</strong> explanation <strong>in</strong> neuroscience: metascientific<br />
reductionism <strong>and</strong> mechanistic explanation. I will first<br />
show that <strong>the</strong> traditional models of <strong>in</strong>ter<strong>the</strong>oretic reduction<br />
are unsuitable for neuroscience. Then I will compare John<br />
Bickle’s model of metascientific reductionism <strong>and</strong> Carl<br />
Craver’s model of mechanistic explanation, argu<strong>in</strong>g that<br />
<strong>the</strong> latter has a stronger case, especially when supplemented<br />
with James Woodward’s <strong>in</strong>terventionist account of<br />
causal explanation.<br />
2. Inter<strong>the</strong>oretic reduction<br />
The development of <strong>in</strong>ter<strong>the</strong>oretic models of reduction<br />
started <strong>in</strong> <strong>the</strong> middle of <strong>the</strong> 20 th century, <strong>in</strong> <strong>the</strong> spirit of<br />
logical positivism. The ultimate goal was to show how unity<br />
of science could be atta<strong>in</strong>ed through reductions. In <strong>the</strong><br />
classic model (most importantly Nagel 1961, 336-397),<br />
reduction consists <strong>in</strong> <strong>the</strong> deduction of a <strong>the</strong>ory to be reduced<br />
(T2) from a more fundamental <strong>the</strong>ory (T1). Conditions<br />
for a successful reduction are that (1) we can connect<br />
<strong>the</strong> terms of T2 with <strong>the</strong> terms T1, <strong>and</strong> that (2) with <strong>the</strong> help<br />
of <strong>the</strong>se connect<strong>in</strong>g assumptions we can derive all <strong>the</strong><br />
laws of T2 from T1.<br />
Unfortunately this model fails to account for many<br />
cases that are regarded as reductions. The model is too<br />
dem<strong>and</strong><strong>in</strong>g: it is very hard to f<strong>in</strong>d a pair of <strong>the</strong>ories that<br />
would meet <strong>the</strong>se requirements. Even Nagel’s prime example,<br />
<strong>the</strong> reduction of <strong>the</strong>rmodynamics to statistical mechanics,<br />
is much more complicated than Nagel thought<br />
(see, e.g., Richardson 2007). The classic model also has<br />
problems accommodat<strong>in</strong>g <strong>the</strong> fact that <strong>the</strong> reduc<strong>in</strong>g <strong>the</strong>ory<br />
often corrects <strong>the</strong> <strong>the</strong>ory to be reduced, which means that<br />
<strong>the</strong> <strong>the</strong>ory to be reduced is strictly speak<strong>in</strong>g false. However,<br />
logical deduction is truth-preserv<strong>in</strong>g, so it should not<br />
be possible to deduce a false <strong>the</strong>ory from a true one.<br />
Problems of this k<strong>in</strong>d lead to <strong>the</strong> development of<br />
more <strong>and</strong> more sophisticated models of <strong>in</strong>ter<strong>the</strong>oretic reduction,<br />
<strong>and</strong> f<strong>in</strong>ally to <strong>the</strong> “New Wave reductionism” of P.<br />
S. Churchl<strong>and</strong> (1986), P. M. Churchl<strong>and</strong> (1989) <strong>and</strong> J.<br />
Bickle (1998, 2003, 2006). Due to constra<strong>in</strong>ts of space, I<br />
will not go through <strong>the</strong>se models here. It is sufficient to<br />
po<strong>in</strong>t out one fundamental assumption that underlies all<br />
<strong>in</strong>ter<strong>the</strong>oretic models of reduction, <strong>and</strong> which leads to serious<br />
problems <strong>in</strong> <strong>the</strong> case of psychology <strong>and</strong> neuroscience.<br />
This assumption is that <strong>the</strong> relata of reductions are<br />
exclusively <strong>the</strong>ories, <strong>and</strong> that <strong>in</strong>ter<strong>the</strong>oretic relations are<br />
<strong>the</strong> only epistemically <strong>and</strong> ontologically significant<br />
<strong>in</strong>terscientific relations (see, e.g., McCauley 2007).<br />
However, well-structured <strong>the</strong>ories that could be h<strong>and</strong>led<br />
with logical tools are rare <strong>in</strong> <strong>and</strong> peripheral to psychology<br />
<strong>and</strong> neuroscience. Instead, scientists typically look for<br />
mechanisms as explanations for patterns, effects,<br />
capacities, phenomena, <strong>and</strong> so on (see, e.g., Machamer et<br />
al. 2000 <strong>and</strong> Cumm<strong>in</strong>s 2000). Although <strong>the</strong>re are <strong>the</strong>ories<br />
<strong>in</strong> a loose sense <strong>in</strong> psychology <strong>and</strong> neuroscience, like <strong>the</strong><br />
LTP <strong>the</strong>ory for spatial memory or <strong>the</strong> global workspace<br />
<strong>the</strong>ory, <strong>the</strong>se are not <strong>the</strong>ories that could be formalized,<br />
86<br />
<strong>and</strong> can hardly be <strong>the</strong> start<strong>in</strong>g po<strong>in</strong>ts or results of logical<br />
deductions. Therefore look<strong>in</strong>g at <strong>the</strong> relations between<br />
<strong>the</strong>ories is <strong>the</strong> wrong start<strong>in</strong>g po<strong>in</strong>t, at least <strong>in</strong> <strong>the</strong> case of<br />
psychology <strong>and</strong> neuroscience.<br />
3. Metascientific reductionism<br />
At least partly for <strong>the</strong>se reasons, John Bickle, <strong>the</strong> most<br />
ardent advocate of New Wave reductionism, has taken<br />
some distance from <strong>the</strong> <strong>in</strong>ter<strong>the</strong>oretic models of reduction<br />
<strong>and</strong> now emphasizes look<strong>in</strong>g at <strong>the</strong> “reduction-<strong>in</strong>-practice”<br />
<strong>in</strong> current neuroscience (Bickle 2003, 2006). He calls this<br />
approach “metascientific reductionism” to dist<strong>in</strong>guish it<br />
from philosophically motivated models of reduction that are<br />
typically used <strong>in</strong> philosophy of m<strong>in</strong>d.<br />
The idea is that <strong>in</strong>stead of impos<strong>in</strong>g philosophical<br />
<strong>in</strong>tuitions on what reduction has to be, we should exam<strong>in</strong>e<br />
scientific case studies to underst<strong>and</strong> reduction. We should<br />
look at experimental practices of an admittedly<br />
reductionistic field, characterized as such by its<br />
practitioners <strong>and</strong> o<strong>the</strong>r scientists.<br />
Accord<strong>in</strong>g to Bickle, molecular <strong>and</strong> cellular cognition<br />
– <strong>the</strong> study of <strong>the</strong> molecular <strong>and</strong> cellular basis of cognitive<br />
function – provides just <strong>the</strong> right example. The reductionist<br />
methodology of molecular <strong>and</strong> cellular cognition has two<br />
parts: (1) <strong>in</strong>tervene causally <strong>in</strong>to cellular or molecular<br />
pathways, (2) track statistically significant differences <strong>in</strong><br />
<strong>the</strong> behavior of <strong>the</strong> animals (2006, 425). When this<br />
strategy is successful <strong>and</strong> a m<strong>in</strong>d-to-molecules l<strong>in</strong>kage has<br />
been forged, a reduction has been established. The<br />
cellular <strong>and</strong> molecular mechanisms directly expla<strong>in</strong> <strong>the</strong><br />
behavioural data <strong>and</strong> set aside <strong>in</strong>terven<strong>in</strong>g explanatory<br />
levels (2006, 426). Higher-level psychology is needed for<br />
describ<strong>in</strong>g behavior, formulat<strong>in</strong>g hypo<strong>the</strong>ses, design<strong>in</strong>g<br />
experimental setups, <strong>and</strong> so on, but accord<strong>in</strong>g to Bickle,<br />
<strong>the</strong>se are just heuristic tasks, <strong>and</strong> when cellular/molecular<br />
explanations are completed, <strong>the</strong>re is noth<strong>in</strong>g left for higherlevel<br />
<strong>in</strong>vestigations to expla<strong>in</strong> (2006, 428).<br />
Metascientific reductionism does not require that <strong>the</strong><br />
relata of reductions are formal <strong>the</strong>ories, <strong>and</strong> does not lead<br />
to <strong>the</strong> problem mentioned <strong>in</strong> <strong>the</strong> end of last section.<br />
However, it is not without its share of problems, as I will<br />
show below.<br />
4. Mechanistic explanation<br />
The discrepancies between traditional models of reduction<br />
<strong>and</strong> actual scientific practice <strong>in</strong> psychology, neuroscience<br />
<strong>and</strong> biology have resulted <strong>in</strong> <strong>the</strong> development of alternative<br />
models. One alternative that I have just discussed is<br />
Bickle’s metascientific reductionism. Ano<strong>the</strong>r approach that<br />
has been receiv<strong>in</strong>g more <strong>and</strong> more attention recently is<br />
mechanistic explanation (e.g., Bechtel & Richardson 1993,<br />
Machamer et al. 2000). In this paper I will focus on Carl<br />
Craver’s (2007) recent <strong>and</strong> detailed account of mechanistic<br />
explanation.<br />
The central claim of advocates of mechanistic explanation<br />
is that good explanations describe mechanisms