柏拉圖的《泰鄂提得斯》主要在探討知識的定義。但文中，泰鄂提得斯對知識所提出的三個定義，全都被蘇格拉底否決了。最後對話以「無解」作終。本文試圖解釋：這是因為柏拉圖認為舉凡活著的人都是無法真正達臻「知識」的，這表示，我們根本不可能提出對「知識」的恰當定義；然而，這篇對話並不是單純重複所謂「蘇格拉底對知識的否認」，而是在對「λόγος／說明」的知識意涵作更進一步的審思。「λόγος」無法用來定義知識，但豐富的哲學的「λόγος」卻能引領我們，一方面避免把錯誤信念當作知識，另方面持續檢驗信念的真假，朝向永不終止的對知識的探尋。

Plato's ”Theaetetus” is a classic text on defining knowledge. But Socrates refutes Theaetetus' all three attempted definitions of knowledge in the dialogue. The dialogue ends in aporia and does not endorse any definition of knowledge at all. For, in my view, Plato holds that we embodied human beings cannot actually arrive at true knowledge, and this means that we cannot give an adequate definition of knowledge, either. However, this is not simply a Socratic disavowal of knowledge, but a more elaborate reconsideration of the epistemic significance of λόγος. In this paper, I will try to interpret the ”Theaetetus” by exploring the rich meaning of λόγος and its epistemic significance: though the dialogue does not reach a firm definition of knowledge, the whole discussion forms a rich λόγος and reveals a long process of examining beliefs, forming a coherent web of belief and thereby a good attempt of approaching knowledge. To a certain extent, my interpretation seems coherentist. But strictly speaking, it is not a coherence theory of knowledge. For the significance of λόγος is not a successful grasp of knowledge, but to show that what we grasp is not knowledge and thus stimulate a further philosophical inquiry. With the help of λόγος, Plato leads readers on the one hand to avoid mistaking beliefs to be knowledge, and on the other hand, more constructively, to examine beliefs in an endless inquiry into knowledge, such as one conducted by Socrates and Theaetetus in the ”Theaetetus”.