Following a naturalistic approach to metaphysics, this chapter argues that materialism and scientific realism are much more plausible than their major alternatives: idealism and social constructivism. The appropriate philosophical method is to use inference to the best explanation of evidence rather than thought experiments and a priori speculation. Natural philosophy legitimately accepts the existence of objects, properties, relations, changes, events, processes, mechanisms, groups, space, and time. All of these concepts and hypotheses are subject to revision as science and philosophy generate more evidence and alternatives. However, skepticism is appropriate concerning the existence of other entities such as souls, gods, spirits, facts, and group minds. If evidence and inference to the best explanation support the existence of an entity, then we are justified in concluding that it exists.