The exact implications of naturalism depend on whether the natural sciences are considered an orthodox or heterodox form of knowledge. In the former case, after W. V. Quine, writing in the 1960s, naturalism is often defined as the conversion of philosophical questions to ones in the natural sciences. This sort of naturalist addresses problems of knowledge by looking into the composition of the brain, and problems of morals by examining humanity's biological heritage. Philosophers thus serve, as John Locke described his relationship to his friend Isaac Newton, as “underlabourers” who clear the conceptual obstacles to a properly scientific understanding of the world. When analytic social epistemologists (see analytic social epistemology) such as Alvin Goldman and Philip Kitcher describe themselves as “naturalists”, they mean to accord the natural sciences this level of epistemic privilege.

However, “naturalism” had first been used polemically three centuries earlier against Spinoza to refer to his heretical interpretation of the Bible, which implied that God is one with material reality, and that Creation is simply the self-realization of this single unified substance. However, Lessing, Goethe and other leaders of the eighteenth-century German Enlightenment gave “naturalism” a more positive spin, which made humanity the intellectual vanguard of nature's evolution. This perspective was enthusiastically adopted in the nineteenth and early-twentieth centuries by Ludwig Feuerbach, Karl Marx, Ernst Mach and the pragmatists. It is also present in Fuller's version of social epistemology.