Metaphysical idealism is the position—going back to the pre-Socratics and brought to fruition by Plato in the ancient world—that what is ultimately real is something nonmaterial and not apparent to the senses. Insofar as God was believed to be both nonmaterial and most real, all Christian philosophers were “idealists,” but the term is usually reserved for those who posited mind or other nonmaterial substances and things as more real than matter in the natural world.