《理想國》第六、七卷的主題，尤其是整個第六卷，通常被視為是一個知識論的討論，其中最主要的兩個談論即是線段譬喻與洞穴譬喻，因此如何正確地分別解讀兩者，並將兩者放在一個整全的框架下來理解，即是理解柏拉圖《理想國》知識論最重要的課題。通過本文的討論我們似乎可以看到，柏拉圖把知識與存有與真理連結在一起，並且存有與真理即是相互說明的概念，因此真理即是透過認識活動掌握那個對於存有者的存有之揭示（理念），因此認識能力即是瞭解存有，亦即「由靈魂的眼睛看」。而這個對於存有者的存有之認識活動要能夠獲得實踐，必須仰賴善的理念作為施力者，給予認識者去認識的能力、並將真理賦予給可認識者（理念），兩者在真理作為那個使得存有者的存有可以顯現的力量在認識活動中結合在一起，由此可認識者作為某個「真的」，而分有了真理。於此善的理念作為知識與真理的原因、並由此亦為所有者的存有的終極原因，但善的理念並非垂手可得，我們必須付出努力才可以獲致，獲致的方式是我們必須藉由辯證術與哲學的研究，逐步地自以肉體之眼所見的世界，上登到靈魂的眼睛所注視的純理性世界。 柏拉圖在這裡做了一個很仔細的關於知識要求的描述，以兩個不同的類比—線段和洞穴，去說明達致這個最高的原理原則的路徑，他先在線段譬喻中對知識種類與其對應的靈魂從屬狀態做區分與定義，然後在洞穴譬喻中，由人類在其本性上未受教育的最初狀態，和經過教育或啟發後不同的狀態，來解釋教育、或靈魂必須向上攀升的重要性。 經由對於兩個譬喻以及其他相關的概念之解析，我們將可以發現，柏拉圖在《理想國》中提出的真理觀，清楚地指出了存有者與其存有間有一個連結的關係，在真理作為解蔽性的意義中為心靈所掌握，於此對存有的揭示越多、則越真（越「沒有-遮蔽」），其遮蔽的程度越少；但另方面他又明確地排拒那些在存有者的領域中被他描述為「涉及感知與意見的」，並一再地指出上昇之旅除了「前往、趨近存有」外，亦在於排除感知的影響，在這個意義下，他特別強調數理知識的中介作用，並指出數理圖形與數字的抽象作用，可以幫助靈魂向存有趨近。但持平而論，柏拉圖仍為我們指引出一條通往存有的道路，並將《理想國》的知識論以一個完整的存有論的連結關係展現給我們（雖然不無理論上的困難），要求著我們將「真理」的本質與「存有」緊密結合起來，而哲學研究的目的與任務則明確地被定義為對存有的追問，以及將存有與真理之光帶回到「世界」中。 / The theme of the sixth and seventh Book of Plato’s "Republic", especially the whole sixth Book, is usually considered to be the discussion of the knowledge problem (or the epistemology) ; among them there are two main paragraphs about this issue, they are the divided-line simile and cave simile, so how to understand those two similes separately, and at the same time place them under one whole structure to interpret them correctly, namely is the most important task to understand the knowledge problem of Plato's " Republic ". Through the discussion of this thesis, we could see that Plato connected knowledge together with Being and Truth, and Being and Truth are the concepts which explain each other; so Truth is through knowing activity to grasp the revealing of the beings’ Being (Idea), to know is understanding Being, such as 'seeing by eyes of soul'. And to exercise this knowing activity of the beings’ Being, must be dependent on the Idea of Good as the empowerment, offer the power for the Knower to know, and offer Truth to the Knowable (idea) to be known, the two (the Knower and the Knowable) in Truth as the power that makes the beings’ Being shown connect together in the knowing activity, thus the Knowable been regarded as something ' true', and participated Truth. Hence the idea of Good as the cause of Knowledge and Truth, and also as the ultimate cause of the Being of the all beings, but to reach the Idea of Good is not a easy thing, we must endeavor really hard to obtain the Idea of Good. The way to obtain it is that we have to by means of the research of Dialectic and philosophy, ascend step by step from the world seen by bodily eyes, to the purely rational world seen by soul’s eyes. Plato made a very careful description of knowledge requirement here, with two different similes – divided Line and cave, to interpret the route led to this supreme principle. He first discriminates and defines the classification of knowledge and their corresponding subordinated soul states in the divided line simile, then in the cave simile, he brings up the primitive uneducated state of the human nature, and the different states after educated or enlightened, to explain the importance of education or the upward journey of soul. Via the analysis of two similes and other relevant concepts, we could discover, the Truth View which Plato puts forward in " Republic ", clearly states there is a relation linked between beings and Being, grasped by the mind in the Truth as the Unhiddenness; therefore the more revealing of Being, the truer (more ' un- hidden'), and the less its degree hidden is. But on the other hand he distinctly discards those which he described as ‘involved sensual perception and opinion’ in the field of beings, and constantly points out the upward journey not only about 'going to and close to the Being’, also about discarding the influence of sensual perception. Thus he especially emphasizes the intermediate position of mathematical knowledge, and point out that the abstract function of the mathematical figures and numbers could help soul come toward Being. But generally speaking, Plato still leads us to the road toward Being, and shows us the epistemology of "Republic" with one intact ontology interrelation (though there are still some difficulties in his theory), therefore forces us to integrate the essence of ‘Truth’ and ‘Being’ closely; in this way the purpose and task of philosophic study are clearly defined as the questioning of Being, and bringing the light of Being and Truth back to 'the World'.