According to Michael Rea, naturalism is a combination of a method and an assumption. Methodologically, naturalism is the attempt to understand the world through the natural sciences. The assumption, which, theoretically at least, can be overturned at any moment, is that everything that exists is material. The assumption can, in principle, be overturned at any moment because natural sciences don’t claim to have all data at their fingertips. Fairies could be found at the bottom of an English garden and God might appear from behind a far off planet, but neither of these events seems plausible given only the data that the natural sciences have produced so far. Rea defines…