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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pled way to demonstrate <strong>the</strong> success or failure of reductions.<br />
What is more, it seems to me that Chalmers’s <strong>and</strong><br />
Jackson’s account fails to ground <strong>the</strong> metaphysical necessity<br />
that, accord<strong>in</strong>g to physicalism, connects physical to<br />
mental states, on relations between concepts, propositions,<br />
or whatever else can become objects of knowledge,<br />
whe<strong>the</strong>r that be a priori or a posteriori. This is because, by<br />
constru<strong>in</strong>g <strong>the</strong> relation of a priori entailment as one between<br />
functions from possible worlds to extensions, <strong>the</strong>ir<br />
account seems to reverse <strong>the</strong> required order of explanation,<br />
analys<strong>in</strong>g a supposedly logical - conceptual relation <strong>in</strong><br />
metaphysical terms, whereas what was be<strong>in</strong>g advertised<br />
orig<strong>in</strong>ally was exactly <strong>the</strong> opposite. To say that knowledge<br />
of <strong>the</strong> complete physical description of <strong>the</strong> world would<br />
allow us to have a priori knowledge of all macroscopic<br />
facts, which is what <strong>the</strong> orig<strong>in</strong>al <strong>the</strong>sis about a priori entailment<br />
<strong>in</strong>cluded, is to say that our underst<strong>and</strong><strong>in</strong>g of <strong>the</strong><br />
terms that we use <strong>in</strong> order to describe <strong>the</strong> world <strong>in</strong> physical<br />
terms, allows us to deduce, without look<strong>in</strong>g at <strong>the</strong> world<br />
any fur<strong>the</strong>r, its complete description <strong>in</strong> macroscopic terms.<br />
But, an essential component of this <strong>the</strong>sis seems to be<br />
that it is our a priori underst<strong>and</strong><strong>in</strong>g of <strong>the</strong> concepts <strong>in</strong>volved<br />
that grounds <strong>the</strong> derivation, not <strong>the</strong> objects that are<br />
referred to by <strong>the</strong>se concepts. In Chalmers’s <strong>and</strong> Jackson’s<br />
account, <strong>the</strong> burden of <strong>the</strong> derivation is transferred to<br />
<strong>the</strong> level of extensions, not <strong>the</strong> way that <strong>the</strong>se extensions<br />
are represented by us. This, <strong>in</strong> my view, renders <strong>the</strong> account<br />
unsuitable to be used <strong>in</strong> explicat<strong>in</strong>g <strong>the</strong> way metaphysically<br />
necessary relations are grounded on logical -<br />
conceptual relations such as that of entailment.<br />
In later work, Jackson tries to accommodate similar<br />
criticisms, by attempt<strong>in</strong>g to reconcile <strong>the</strong> metaphysical<br />
nature of his proposed relation of entailment with <strong>the</strong><br />
apriority that supposedly characterizes it. Thus, he calls<br />
<strong>the</strong> relation of a priori entailment that he endorses de re,<br />
claim<strong>in</strong>g that it is a type of metaphysical necessitation<br />
between properties, not necessitation between sentences<br />
or concepts. Here is <strong>the</strong> relevant def<strong>in</strong>ition that he appeals<br />
to, quoted directly from his paper:<br />
132<br />
P1 a priori necessitates P2 iff one’s grasp of what it<br />
is to be a P1 <strong>and</strong> what it is to be a P2 allows one to<br />
see that if P1 is <strong>in</strong>stantiated <strong>the</strong>n so is P2.<br />
(Jackson 2005, pp. 252-3).<br />
However, I do not th<strong>in</strong>k that this move can serve Jackson’s<br />
argument. It is obvious that, contrary to his pronouncements,<br />
his characterisation of de re a priori necessitation,<br />
by appeal<strong>in</strong>g to our ‘grasp of what it is to be’ a given property,<br />
proceeds via concepts; given this, Jackson clearly<br />
has to suggest a way <strong>in</strong> which <strong>the</strong>se concepts are related.<br />
S<strong>in</strong>ce he repudiates explicit conceptual analyses, he has<br />
to represent <strong>the</strong> relation between <strong>the</strong>m as a relation between<br />
functions, i.e. a priori <strong>in</strong>tensions. But, as has been<br />
argued above, lack<strong>in</strong>g explicit analyses, <strong>the</strong> relation between<br />
<strong>the</strong>se <strong>in</strong>tensions can never be cognitively obvious,<br />
s<strong>in</strong>ce it operates at <strong>the</strong> limit, i.e. as a relation between <strong>the</strong><br />
concepts’ extensions across possible worlds. This cannot<br />
be reasonably thought of as a relation between mental or<br />
l<strong>in</strong>guistic representations; ra<strong>the</strong>r, it seems to be closer to<br />
what he <strong>and</strong> Chalmers would call a metaphysically ‘brute’<br />
one.<br />
But, if <strong>the</strong> commitment of physicalism to a priori<br />
entailment is to be rejected, so that our true high-level<br />
descriptions of <strong>the</strong> world cannot be derived from <strong>the</strong><br />
complete physical story, <strong>the</strong>n how can <strong>the</strong> <strong>the</strong>sis ever be<br />
v<strong>in</strong>dicated? If physical properties fail to account<br />
completely, <strong>in</strong> a fully reductive account, for <strong>the</strong> successful<br />
Physicalism Without <strong>the</strong> A Priori Passage — Harris Hatziioannou<br />
explanations that we give <strong>in</strong> macroscopic terms, <strong>in</strong> what<br />
sense can <strong>the</strong>y be considered superior <strong>in</strong> <strong>the</strong> explanatory<br />
scheme of th<strong>in</strong>gs? A full answer to <strong>the</strong>se questions<br />
certa<strong>in</strong>ly needs a systematic <strong>in</strong>vestigation <strong>in</strong>to <strong>the</strong> relation<br />
between properties that perta<strong>in</strong> to different levels of<br />
explanation. However, I th<strong>in</strong>k that <strong>the</strong> key for accept<strong>in</strong>g<br />
physicalism without an a priori passage is to realize that,<br />
even with<strong>in</strong> <strong>the</strong> doma<strong>in</strong> of physics, <strong>the</strong> descriptions of<br />
complex systems can very rarely be derived <strong>in</strong> an a priori<br />
way from <strong>the</strong> descriptions of <strong>the</strong>ir constituents. The<br />
derivation must necessarily <strong>in</strong>volve idealizations,<br />
simplify<strong>in</strong>g assumptions, approximations, <strong>and</strong> brute<br />
numerical methods, all techniques that rupture <strong>the</strong> smooth<br />
ma<strong>the</strong>matical derivation of properties that perta<strong>in</strong> to more<br />
complex systems, thus render<strong>in</strong>g impossible <strong>the</strong> a priori<br />
passage from one level of description to ano<strong>the</strong>r. The<br />
failure is already apparent <strong>in</strong> <strong>the</strong> classical three-body<br />
problem, which has exact solutions only <strong>in</strong> some restricted<br />
forms. And, of course, it is patently obvious <strong>in</strong> more<br />
complex systems: even know<strong>in</strong>g <strong>the</strong> momentary positions<br />
<strong>and</strong> momenta of all <strong>the</strong> fundamental particles that<br />
comprise an iron atom, say, we have no hope at all of a<br />
priori deduc<strong>in</strong>g, on <strong>the</strong> basis of our best laws of quantum<br />
<strong>the</strong>ory, <strong>the</strong>ir dynamical evolution <strong>in</strong> time. To arrive at <strong>the</strong><br />
physics of such complex systems from <strong>the</strong> physics of more<br />
simple ones, we simply have to resort to methods which<br />
are, at least <strong>in</strong> part, justified by appeal to empirical data.<br />
Physics simply does not have an analytically solvable<br />
equation that describes <strong>the</strong> behaviour of every system that<br />
falls with<strong>in</strong> its scope. In fact it has such equations only for<br />
unrealistic, highly idealized systems, which are<br />
encountered <strong>in</strong> tightly controlled experimental situations<br />
(see Cartwright 1999).<br />
I th<strong>in</strong>k that <strong>the</strong> important po<strong>in</strong>t to keep here is <strong>the</strong><br />
follow<strong>in</strong>g: If <strong>the</strong> passage from simple to complex systems<br />
is not a priori guaranteed even with<strong>in</strong> physics, <strong>the</strong>n we<br />
should not expect that <strong>the</strong> passage from each<br />
neurophysiological to its correspond<strong>in</strong>g mental state will be<br />
thus guaranteed ei<strong>the</strong>r. I am aware that this po<strong>in</strong>t raises<br />
doubts concern<strong>in</strong>g <strong>the</strong> way <strong>in</strong> which an antireductionist<br />
account such as this could support physicalism: if no<br />
smooth reductions are forthcom<strong>in</strong>g, not even with<strong>in</strong> <strong>the</strong><br />
doma<strong>in</strong> of physical <strong>the</strong>ory, how can we ever be confident<br />
that it is <strong>the</strong> physical properties that account for <strong>the</strong> causal<br />
<strong>and</strong> o<strong>the</strong>r characteristics of mental states? I believe that,<br />
just like <strong>in</strong> <strong>the</strong> cases of <strong>the</strong> classical three-body problem<br />
<strong>and</strong> <strong>the</strong> iron atom we have reason to believe that <strong>the</strong><br />
features of <strong>the</strong> world that are responsible for <strong>the</strong> dynamical<br />
evolution of <strong>the</strong>se systems are physical (albeit ones that<br />
cannot be precisely quantified), so <strong>in</strong> <strong>the</strong> case of a<br />
psychological state we have reason to expect that <strong>the</strong><br />
features that are responsible for its causal outcomes are<br />
also physical, even if <strong>the</strong>re is no way to move from <strong>the</strong><br />
physical description to <strong>the</strong> psychological one, except by<br />
appeal<strong>in</strong>g to ‘brute’ a posteriori knowable necessitation.<br />
Thus, we may view <strong>the</strong> psychological description as<br />
captur<strong>in</strong>g, vaguely <strong>and</strong> imprecisely, <strong>the</strong> salient features of<br />
<strong>the</strong> physical system, while at <strong>the</strong> same time expect<strong>in</strong>g that<br />
it will be <strong>the</strong> description of <strong>the</strong> underly<strong>in</strong>g complex physical<br />
state that will ultimately fully account for mental<br />
phenomena, <strong>in</strong> <strong>the</strong> sense of provid<strong>in</strong>g <strong>the</strong> exact sufficient<br />
causes for <strong>the</strong>m, <strong>the</strong> effective mechanisms that are<br />
present <strong>in</strong> <strong>the</strong> world. It is true that we need <strong>in</strong>dependent<br />
arguments to warrant this expectation, but, of course,<br />
plenty of <strong>the</strong>se have already been given <strong>in</strong> <strong>the</strong> literature,<br />
<strong>and</strong> <strong>the</strong>re is no space to discuss <strong>the</strong>m here. I hope at least<br />
that <strong>the</strong>se sketchy suggestions po<strong>in</strong>t towards a viable<br />
underst<strong>and</strong><strong>in</strong>g of a posteriori physicalism.