 Naturalists draw a distinction between methodological naturalism, an epistemological principle that limits scientific inquiry to natural entities and laws, and ontological or philosophical naturalism, a metaphysical principle that rejects the supernatural (Forrest 2000). Since methodological naturalism is concerned with the practice of science (in particular, with the kinds of entities and processes that are invoked), it does not make any statements about whether or not supernatural entities exist. They might exist, but lie outside of the scope of scientific investigation. Some authors (e.g., Rosenberg 2014) hold that taking the results of science seriously entails negative answers to such persistent questions into the existence of free will or moral knowledge. However, these stronger conclusions are controversial.