Monism is a philosophical worldview in which all of reality can be reduced to one “thing” or “substance.” This view is opposed to dualism (in which all of reality is reducible to two substances, e.g., good and evil; light and darkness; form and matter; body and soul) and pluralism (all of reality is comprised of multiple substances). In all of these philosophical views, this article uses the word substance in a technical sense to mean “essence,” or its “thing-ishness”; in other words, something in which properties adhere.