what could justify treating this system differently other than an assumption that
metaphysical naturalism is true—that there is nothing outside of nature that can affect it.
Despite the apparent strength of considerations like these, some philosophers have argued
for the opposite position. For example, O'Connor (1997, 26–27) claims that
methodological naturalism promotes the quest for truth for two reasons. First, by making
appeals to the supernatural off-limits, it forces scientists to persist in their search for
naturalistic explanations, even when the prospects for such explanations seem very dim.
And such persistence has in the past borne fruit. In short, methodological naturalism is
valuable because it promotes the goal of understanding reality as far as possible in
natural terms. Second, methodological naturalism enables theologians and others
offering nonnatural accounts of natural phenomena to be sure that any such account is
forced to face its strongest competitor. Underlying these two reasons is the idea that a
division of labor between science and theology is desirable. Both disciplines attempt to
understand natural events, but science seeks natural explanations, while theology pursues
supernatural explanations. In this way, our chances of discovering the truth are, according
to O'Connor, maximized. A third reason for believing that methodological naturalism
promotes the goal of understanding nature is offered by Alvin Plantinga (1997, 150–52),
an opponent of methodological naturalism. Following Duhem, he suggests that science
makes progress because of its universality—because scientists
end p.291
manage to cooperate. But such universality is possible only if scientists avoid employing
or presupposing in their theories metaphysical claims that are not shared by other
scientists.
None of these three reasons is conclusive. To begin with, surely the most they show is
that appeals to the supernatural should be a last resort, or that some science but not
necessarily all science should be constrained by methodological naturalism (Plantinga
1997, 152). Either way, sufficient cooperation among scientists would take place and
sufficient effort would be made to find naturalistic explanations. Thus, the worry that,
without an absolute prohibition on appeals to the supernatural in scientific explanations,
proponents of supernaturalistic explanations would not confront their strongest
competitors is unrealistic. It is also unrealistic to claim, as O'Connor does (compare
McMullin 1991, 57–58), that there is nothing wrong with restricting science to the natural
because others can pursue supernaturalist theories. Such a division of labor lowers the
chances of anyone having the interdisciplinary expertise that would be necessary to
pursue certain lines of inquiry. For example, it is unlikely that theologians without
extensive training in science would be able to assess the promise of any serious
supernaturalistic explanation of the origin of life. For presumably, such an explanation
would be a great deal more complicated than “God made it so,” and evaluating any such
explanation, no matter how simple, will require the ability to evaluate the best competing
naturalistic explanations.