Metaphysical naturalism

Metaphysical naturalism is the worldview most contemporary atheist philosophers defend. It is stronger than methodological naturalism (which is a working principle for scientific inquiry) and stronger than mere atheism (which only denies the existence of gods). A metaphysical naturalist denies the existence of any nonphysical entities — souls, ghosts, angels, abstract objects in some readings — not just deities.

The standard argument for metaphysical naturalism is inductive: science has been progressively explaining phenomena that earlier cultures attributed to supernatural agents — disease, weather, mental illness, the origin of species — without ever needing to invoke a nonphysical cause. The track record is one-directional. The naturalist concludes that the most reasonable extrapolation is that any remaining puzzles ("the origin of consciousness," "the fine-tuning of the constants," "why there is something rather than nothing") will eventually be explained naturalistically too, even if the explanations are not yet in hand.

Critics — including most theist philosophers and some atheists — push back in several ways. The hard problem of consciousness (David Chalmers) is offered as a phenomenon that resists physical explanation in principle. The fine-tuning argument (Robin Collins) is offered as evidence the natural order itself requires explanation. Alvin Plantinga's evolutionary argument against naturalism contends that if our cognitive faculties were shaped only by natural selection on survival value, we have no good reason to trust them on questions of metaphysics. Naturalists have published responses to each, and the literature is large.

For a secular reader navigating the philosophy of religion, the most important thing about metaphysical naturalism is that it is a positive worldview making positive claims, not just an absence of belief. "I am an atheist" is silent on whether numbers, moral facts, or qualia are real; "I am a metaphysical naturalist" is not. Knowing which one is on the table prevents most of the bad debates between believers and nonbelievers, where each side responds to a position the other has not actually taken.