Abstract

“Good” is the central concept in George Edward Moore’s value theory. Moore, who has an influential work on the indefinability of “good” in moral philosophy, published a book in 1903 titled _Principia Ethica_, affirming that the most fundamental question in all Ethics is how “good” is to be defined. For Moore, it is essential to determine the appropriate subject of ethics in a precise sense as the concept of “good”. In _Principia Ethica_, Moore argues that people make mistakes when defining the “good”. According to Moore’s philosophy, “good” makes value prediction possible because it is a non-natural and unique concept. Despite the many theoretical debates among philosophers about the definability of the term good, this article critically examines the “open question argument” and the “naturalistic fallacy” that Moore's rational analysis leads to the conclusion that “good is indefinable”.