Naturalism is the philosophical viewpoint that natural laws and forces (as opposed to supernatural ones) operate in the universe, and that nothing exists beyond this natural universe, or, if it does, it does not affect the natural universe that we know. Followers of naturalism assert that natural laws are the rules that govern the structure and behaviour of the universe, that the universe is a product of these laws, and that the goal of science is to discover and publish them systematically. Further, this sense of naturalism holds that spirits, deities, and ghosts are not real and that there is no “purpose” in nature.