universe. If there is more than one, then, although one could define the natural world as
the entire collection of such universes, it would be better to adopt the position that there
is more than one natural world. In this way, metaphysical claims about nature or the
natural world could be restated as claims about our natural world and so would have a
better chance of being justified.
Varieties of Naturalism
If to be natural is to be a part of nature as defined above, then what is naturalism? Here,
of course, there is more than one answer because one can be naturalistic
methodologically or metaphysically or epistemologically. It is often claimed by those
who embrace both science as currently practiced and some form of supernaturalistic
religion that science is naturalistic methodologically but not metaphysically.
“Methodological naturalism” is defined as follows:
Methodological naturalism =df. Scientists should not appeal to supernatural entities
when they explain natural phenomena.
Notice that one can be a methodological naturalist on this definition even if one believes
that it is permissible for scientific explanations to refer to nonnatural entities. One
advantage of this is that some of the abstract entities (e.g., numbers) to which scientific
explanations routinely appeal may very well be nonnatural.
“Metaphysical naturalism” is defined as follows:
Metaphysical naturalism =df. Supernatural entities do not exist.
Notice that, on this definition, one can be a metaphysical naturalist without rejecting the
reality of nonnatural entities. This is important, because, while our knowledge of nature
may provide reason to believe that nothing is supernatural,
end p.279
it provides little basis for the further conclusion that nature is all there is. Notice also that
one can be a metaphysical naturalist without being a materialist or even a physicalist
about the natural world. (This is not to deny, however, that physicalism is very likely
given metaphysical naturalism.) Finally, notice that metaphysical naturalists can accept
the position of philosophers like Thomas Nagel (1986, 25–27) and John Searle (1992, ch.
5) that consciousness is irreducibly subjective, even if, contrary to what Searle (116–24)
contends, this forces them to reject the position that a unified scientific understanding of
nature is possible.
Both metaphysical and methodological naturalism must be distinguished from the various
theses to which philosophers sometimes apply the label “epistemological naturalism” or,
more pejoratively, “scientism,” such as the view that all knowledge is scientific
knowledge; the view that, although nonscientific knowledge is possible, it has a lower