Naturalism is a foundational commitment of both atheism and secular humanism, underlying their further affirmations that this life is the only life and that meaning and morality are human responsibilities. It stands opposed to the theistic and supernaturalist frameworks of the religious traditions, and it aligns with the conviction that belief should follow evidence, since naturalists hold that no reliable evidence points beyond the natural world. The affirmation is presented here as the settled view of those who hold it.
Philosophical naturalism has ancient roots, notably in Epicurus and in the Roman poet Lucretius's De Rerum Natura, On the Nature of Things, which argued at length that the world operates by natural causes without divine intervention and that fear of the gods and of an afterlife causes needless human suffering; the position was revived and given a more explicitly scientific grounding in the twentieth century, notably by the philosopher W. V. O. Quine, whose account of naturalized epistemology argued that philosophy itself should be continuous with, rather than prior to or independent of, the findings of natural science, an influential modern statement of the naturalist position atheists and secular humanists generally draw upon.