A reader poses this question:
Some people argue that the success of science using methodological naturalism is evidence of metaphysical naturalism because, according to them, why would the methods work unless the subject was naturalistic? My question is: do you think this is a fair argument to make?
It depends on what exactly the argument is.
The argument the reader reports is unimpressive. It comes down to saying that the natural sciences are successful because metaphysical naturalism is true. But the success of the sciences in explaining much of what goes on in the natural world is consistent with both the truth and the falsity of metaphysical naturalism. So scientific success does not entail metaphysical naturalism. Does the former provide nondemonstrative evidence of the latter? It is not clear how it could. How could there be empirical evidence of a metaphysical proposition?
Metaphysical naturalism (MN) is the thesis that "all that exists is the space-time world . . . ." The space-time world is the physical world. The thesis, then, is that reality is exhausted by the physical world. The quotation is from David Armstrong.
Now if MN is true (false), then it is presumably necessarily true (false). For it is a metaphysical claim, a claim about the nature of reality. If MN is necessarily true, if true, then it is hard to see how there could be empirical evidence either for it or against it.
Perhaps one could argue as follows:
1. The sciences of nature, physics in particular, have been extremely successful in explaining much about the physical world.
2. This explanatory success, though at present partial, will one day be complete: everything about the physical world will eventually have a natural-scientific explanation, and indeed one that adheres to the constraints of methodological naturalism. (Methodological naturalism is not a thesis or proposition, but an injunction or procedural principle: In explaining natural phenomena, do not invoke as explanantia anything non-natural or supernatural.)
3. If a complete explanation of the physical world and everything in it, including human beings and their cultural artifacts, is achieved by natural-scientific means under the constraints of methodological naturalism, then one would have no good reason not to be metaphysical naturalist.
Therefore
4. One ought to be a metaphysical naturalist.
The problem with this argument is premise (2). It is nothing but a leap of faith. One pins one's hopes on future science, to invoke a widely-bruited battle cry. (And isn't there something utterly bizarre about hoping to be shown to be nothing but a complex physical system? And to be profoundly disappointed if one were shown to have an eternal destiny and the possibility of unending bliss? "Damn! I was so hoping to be nothing but a bag of bones and guts slated for destruction in a few years!")
Not only is (2) a leap of faith and as such something rather unseemly for hard-nosed materialist types to advocate, there is really no chance that natural science operating under the constraints of methodological naturalism and eschewing the sort of panpsychism recently urged by Thomas Nagel, will ever explain in a satisfactory non-question-begging way:
- The very existence of the physical universe
- How life arose from abiotic matter
- How sentience arose from the merely alive
- How self-consciousness -- the ability to deploy thoughtfully the first-person singular pronoun -- arose from the merely alive or from mere sentience
- How intentionality arose from the merely alive
- How something like a first-person perspective is possible, a "view from nowhere," a perspective without which no third-person perspective would be possible and with it the objectivity presupposed by scientific inquiry
- The intrinsic intelligibility of the world which is a presupposition of scientific inquiry
- Where the laws of nature come from
- Why the physical constants have precisely the values they have
- The normativity of reason and how it governs our mental processes
- The applicability of mathematics to natural phenomena: no mathematics, no physics!
- The existence of mathematical objects and the truth of mathematical propositions.
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