The purpose of this study is to approach the meaning of knowledge, experience and adult education methods, which are important concepts in adult education, through Plato s Politeia. Plato s Politeia was systematically presented with the composition and content of adult education as well as youth education, and was adult educational significance in terms of education methods such as recollection, dialectics and self-directed learning. According to Plato, the adult learner s knowledge is not just a visible world, such as technology or information, but intelligible world known by intelligence. It is to constantly internalize the uncertain opinions(doxa) that have accumulated so far, leading to a firm perception of reality(idea). Plato thought that all experience was not connected to knowledge, and that knowledge acquired through experience can be true knowledge by experiencing contradictions with existing knowledge. What is needed for this is a dialectical inquiry, and through the process of numerous conversations and exploration, adult learners become a source of powerful action to live a worthwhile life with true knowledge. In this regard, knowledge, experience, and dialectical inquiry processes in adult education are the education itself that is interacted with each other organically.