By Timothy Williamson, The New York Times, September 3, 2011
Many contemporary philosophers describe themselves as naturalists. They mean that they believe something like this: there is only the natural world, and the best way to find out about it is by the scientific method. I am sometimes described as a naturalist. Why do I resist the description? Not for any religious scruple: I am an atheist of the most straightforward kind. But accepting the naturalist slogan without looking beneath the slick packaging is an unscientific way to form one’s beliefs about the world, not something naturalists should recommend.
What, for a start, is the natural world? If we say it is the world of matter, or the world of atoms, we are left behind by modern physics, which characterizes the world in far more abstract terms. Anyway, the best current scientific theories will probably be superseded by future scientific developments. We might therefore define the natural world as whatever the scientific method eventually discovers. Thus naturalism becomes the belief that there is only whatever the scientific method eventually discovers, and (not surprisingly) the best way to find out about it is by the scientific method. That is no tautology. Why can’t there be things only discoverable by non-scientific means, or not discoverable at all? Still, naturalism is not as restrictive as it sounds. For example, some of its hard-nosed advocates undertake to postulate a soul or a god, if doing so turns out to be part of the best explanation of our experience, for that would be an application of scientific method. Naturalism is not incompatible in principle with all forms of religion. In practice, however, most naturalists doubt that belief in souls or gods withstands scientific scrutiny.
What is meant by “the scientific method”? Why assume that science only has one method? For naturalists, although natural sciences like physics and biology differ from each other in specific ways, at a sufficiently abstract level they all count as using a single general method. It involves formulating theoretical hypotheses and testing their predictions against systematic observation and controlled experiment. This is called the hypothetico-deductive method.
One challenge to naturalism is to find a place for mathematics. Natural sciences rely on it, but should we count it a science in its own right? If we do, then the description of scientific method just given is wrong, for it does not fit the science of mathematics, which proves its results by pure reasoning, rather than the hypothetico-deductive method. Although a few naturalists, such as W.V. Quine, argued that the real evidence in favor of mathematics comes from its applications in the natural sciences, so indirectly from observation and experiment, that view does not fit the way the subject actually develops. When mathematicians assess a proposed new axiom, they look at its consequences within mathematics, not outside. On the other hand, if we do not count pure mathematics a science, we thereby exclude mathematical proof by itself from the scientific method, and so discredit naturalism. For naturalism privileges the scientific method over all others, and mathematics is one of the most spectacular success stories in the history of human knowledge.
Which other disciplines count as science? Logic? Linguistics? History? Literary theory? How should we decide? The dilemma for naturalists is this. If they are too inclusive in what they count as science, naturalism loses its bite. Naturalists typically criticize some traditional forms of philosophy as insufficiently scientific, because they ignore experimental tests. How can they maintain such objections unless they restrict scientific method to hypothetico-deductivism? But if they are too exclusive in what they count as science, naturalism loses its credibility, by imposing a method appropriate to natural science on areas where it is inappropriate. Unfortunately, rather than clarify the issue, many naturalists oscillate. When on the attack, they assume an exclusive understanding of science as hypothetico-deductive. When under attack themselves, they fall back on a more inclusive understanding of science that drastically waters down naturalism. Such maneuvering makes naturalism an obscure article of faith. I don’t call myself a naturalist because I don’t want to be implicated in equivocal dogma. Dismissing an idea as “inconsistent with naturalism” is little better than dismissing it as “inconsistent with Christianity.”
Still, I sympathize with one motive behind naturalism — the aspiration to think in a scientific spirit. It’s a vague phrase, but one might start to explain it by emphasizing values like curiosity, honesty, accuracy, precision and rigor. What matters isn’t paying lip-service to those qualities — that’s easy — but actually exemplifying them in practice — the hard part. We needn’t pretend that scientists’ motives are pure. They are human. Science doesn’t depend on indifference to fame, professional advancement, money, or comparisons with rivals. Rather, truth is best pursued in social environments, intellectual communities, that minimize conflict between such baser motives and the scientific spirit, by rewarding work that embodies the scientific virtues. Such traditions exist, and not just in natural science.
The scientific spirit is as relevant in mathematics, history, philosophy and elsewhere as in natural science. Where experimentation is the likeliest way to answer a question correctly, the scientific spirit calls for the experiments to be done; where other methods — mathematical proof, archival research, philosophical reasoning — are more relevant it calls for them instead. Although the methods of natural science could beneficially be applied more widely than they have been so far, the default assumption must be that the practitioners of a well-established discipline know what they are doing, and use the available methods most appropriate for answering its questions. Exceptions may result from a conservative tradition, or one that does not value the scientific spirit. Still, impatience with all methods except those of natural science is a poor basis on which to identify those exceptions.
Naturalism tries to condense the scientific spirit into a philosophical theory. But no theory can replace that spirit, for any theory can be applied in an unscientific spirit, as a polemical device to reinforce prejudice. Naturalism as dogma is one more enemy of the scientific spirit.
Timothy Williamson is the Wykeham Professor of Logic at Oxford University, a Fellow of the British Academy and a Foreign Honorary Member of the American Academy of Arts and Sciences. He has been a visiting professor at M.I.T. and Princeton. His books include “Vagueness” (1994), “Knowledge and its Limits” (2000) and “The Philosophy of Philosophy” (2007).