The Relationship between the Form of the Good and the Foundation of Justice—A Metaphysical Interpretation of Plato’s “Republic”

柏拉图《理想国》通过善的理念的形上学奠基，构建了正义的本原性解释框架。研究表明，城邦正义与灵魂正义的经验定义(各司其职、内在和谐)存在循环论证困境，其合法性必须回溯至善的理念这一终极本原。通过分析“线段喻”与“太阳喻”，本文从形而上学视角解读柏拉图《理想国》中善的理念与正义的奠基关系。指出第四卷正义定义存在循环论证等解释困境，而第六卷揭示善的理念是正义的终极本原。通过解析“线段喻”，阐明善作为存在与认识的终极根据，赋予正义宇宙秩序论意义，为现代社会秩序危机提供启示。Plato’s “Republic” establishes a metaphysical foundation for justice through the Idea of the Good, constructing an ontological framework for its interpretation. This study reveals that the empirical definitions of justice in the polis (“each performing his proper role”) and in the soul (“inner harmony”) encounter circular reasoning, necessitating recourse to the Idea of the Good as their ultimate ground. Through analysis of the “Divided Line” and “Sun” analogies, this paper examines the foundational relationship between the Idea of the Good and justice in the Republic from a metaphysical perspective. It demonstrates how Book IV’s definitions of justice contain unresolved aporia, while Book VI positions the Idea of the Good as justice’s ontological basis. By interpreting the “Divided Line”, the study clarifies the Good’s dual role as the ultimate principle of both being and cognition, endowing justice with cosmic teleological significance, thereby offering insights for addressing modern crises of social order.