If you don’t believe in anything supernatural – gods, ghosts, immaterial souls and spirits – then you subscribe to naturalism, the idea that nature is all there is. The reason you’re a naturalist is likely that, wanting not to be deceived, you put stock in empirical, evidence-based ways of justifying beliefs about what’s real, as for instance exemplified by science. You probably (and rightly) hold that such beliefs are usually more reliable and more objective than those based in uncorroborated intuition, revelation, religious authority or sacred texts. Kept honest by philosophy and critical thinking, science reveals a single manifold of existence, what we call nature, containing an untold myriad of interconnected phenomena, from quarks to quasars. Nature is simply what we have good reason to believe exists.

Taken from “Meming Naturalism”