Quining Naturalism

Scientific naturalism is a metaphysical doctrine, a view about what there is, or what we ought to believe that there is. It maintains that natural science should be our guide in matters metaphysical: the ontology we should accept is the ontology that turns out to be required by science. Quine is often regarded as the doyen of scientific naturalists, though the supporting cast includes such giants as David Lewis and J. J. C. Smart. An alternative view offers a causal criterion for ontological commitment: we should be realists about whatever manifests itself in virtue of having effects. In particular, perhaps, we should believe in the existence of whatever figures in good causal explanations of observed phenomena, and of our experiences and beliefs in general. Thus electrons play a role in good causal explanations of our beliefs ‘about electrons’, presumably, and so we should be realists about electrons; but values don’t seem to figure in causal explanations of our evaluative beliefs, so we should not be realists about values. These two criteria for realism are not the same, of course. The first is often thought to provide a reason for doubting that the second is a necessary condition, on the grounds that entities that are not causally efficacious—numbers, perhaps, or possible worlds—may be indispensable to science. There is much agreement, however. Much of what figures in explanations of our beliefs also figures in natural science. All of it does so, as long as explanations of our beliefs are ipso facto scientific explanations. In that case, proponents of second criterion are entitled to regard themselves as strictly more stringent naturalists than their permissive Quinean cousins. David Armstrong calls the causal criterion the Eleatic Principle, and takes it, contra Lewis, to favour fictionalism about possible worlds. Other notable advocates of the Eleatic criterion include Hartry Field, who takes it to provide support for fictionalism about mathematics; and Simon Blackburn, who suggests that it marks the line at which realism should give way to quasi-realism.