 Different philosophical doctrines travel under the heading of “naturalism.” We can usefully distinguish two broad and important categories: methodological naturalism (or M-naturalism) and substantive naturalism (or S-naturalism) (Leiter 1998; cf. Railton 1990 and Goldman 1994). Naturalism in philosophy is most often a methodological view to the effect that philosophical theorizing should be continuous with empirical inquiry in the sciences. Such a view need not presuppose a solution to the so-called “demarcation problem”—i.e., the problem of what demarcates genuine science from pseudo-science—as long as there remain clear, paradigmatic cases of successful sciences. Some M-naturalists want “continuity with” only the hard or physical sciences; others seek “continuity with” any successful science, natural or social. The latter is probably the dominant strand in philosophy today.