柏拉圖《泰鄂提得斯》201d-206b段落中，當蘇格拉底預備要檢驗「真信念「加上說明」就是知識」這項定義時，他講述並被視了一套類似原子論說法的「夢理論」。這套理論主張：一般事物是由一些最原初的元素組成的。「元素」本身只有名字，無法做進一步的說明；「組合物」是由元素組合而成的，所以可以用其中元素的名稱編織成一套話語，因而可以做進一步的說明。元素無法「加上說明」所以是不可知的；組合物可以「加上說明」所以是可知的。針對這套「夢理論」。蘇格拉底提出一個兩難的問題－「組合物等於它所有的組成元素」或「組合物會在它所有組成元素之外形成另一個單一的觀念」，並分別檢視這兩種可能。在這段討論中，柏拉圖給由「夢理論」分析語言、事物與知識三層面之間的關係，並在這樣的脈絡下，探索了整體是否等於所有的部分、以及類似當代所謂知識基礎論或融貫論的議題，最後否決以「夢理論」解釋「真信念「加土說明」就是生。誠」這定義的說法。而這段對「夢理論」的檢驗，為希臘當時可能有的「整體等問於所有部分」的想法，以及後來一些哲學家所相信的知識基礎論，投下反省與質疑。

In Plato's Theaetetus 201d-206b, when Socrates is ready to crossexamine the definition of knowledge that 'true belief "with an account (logos)" is knowledge,' he states and explores the so-called 'Dream Theory.' According to the theory, things are classified into two kinds complexes and elements. Complexes consist of elements and can be divided into elements, while elements cannot be divided further, just as atoms. For complexes we can have an account, while for elements we can have only bare names. Within the context of that 'true belief "with an account" is knowledge,' complexes are knowable, while elements are not. To examine the theory, Socrates argues in a dilemma whether a complex is the same as all elements within it or a complex has a single form which is something other than all elements within it. Having examined both the horns of the dilemma, Socrates refutes the theory. In this paper, I wish to show Plato's interesting analysis on the relations among language, things and cognition in this passage. In the light of the, I will show his re t1ection on the identification of the whole with its parts, and on the epistemological foundationalism. Further, it will be shown that Plato does not accept the identification of the whole with its parts and would hold a critical view of epistemological foundationalism.