The aim of this article is to show a part of Plato's view of knowledge lying in the first part of the Theaetetus. How to interpret ousia in the final refutation(184-186)is crucial to that aim. Many commentators, including Corn ford, have construed basically that Plato argued here the judgement of psyche (soul) about percepts or a matter of proposition, on the grounds that sentences in<S is P>form that have percept-Subjects are found at 185A9, 11-12, B2, 4-5. Such a tendency of studying Plato's text is increasing in power nowadays. [Interpretation I]. But I doubt whether 'judgement' or<S is P>proposition is the question at issue or a primary matter here. I think ousia is 'nature'(physis)in the meaning of 'that which is F' answering to a question 'What is F?', and offer an interpretation of the text. [Interpretation II]. Our text is as follows : A(1) 185A8-B6 : <S is P>propositions are found as contents(objects)of thinking (considering, judging). A(2) 185B7-E2 : soul's own thinking of ta koina about<S>. [185E3-186A1]: division of soul's thinking and objects into two types. B186A2-B10 : soul's own thinking of ousia of〜(P) [about<S>?]. [Interpretation I] The grounds of reading 'judgement' or<S is P>proposition in our text throughout are that Text A(1), A(2)and B are equivalent to one another, i. e. A(2)is a mere paraphrase of A(1), so : A(1)thinking of<S is P> =B thinking of ousia of〜(P)about<S> [Interpretation II] About Text A : α) The aim of introducing the 'about'(peri)-phrase into Text A is originally to affirm that ta koina are imperceptible in any way. cf. 184E8-185A7. In fact, after A(1) =exemplification of ta koina, Socrates' question is whether we have such an organ as grasps ta koina as well as in the case of sense-perception. The 'about'-phrase strengthens, formally, Socrates' rhetrical question, and still has the original form and role. And here the stress is on 'what is it that thinks ta koina about<S>?', not on 'thinking of ta koina about <S>'. β) Plato seems to be indifferent to (S) in the 'about'-phrase. Except their first introduction, names of Sound/Colour are never indicated afterwards, and Sound/Colour are dissolved into 'everything' soon after. Besides, a (somewhat strange)question of 185B9-10 suggests the formality of, and Plato's indifference to, <S>. Addition of such a formal phrase is also based on the fact that ta koina means, literally, 'they are thought of as common to a pair of things, and many or all things'. So, it doesn't matter if <S> is indefinite. Thus, it is reasonable from α)β) above that no 'about'-phrase is found at [185E3-186A1]. It was dismissed its post. For these the same reasons, no thinking or judgement of a specified<S>is told in A(2), and A(2)is not a mere paraphrase of A(1). About Text B : 'To everything' (epi panton 186A3)doesn't mean the same thing as 'about'-phrase in Text A in the meaning of<S> in the formula <S is P> , but rather, 'every F' we experience as 'appearance' (phantasia 152C1). It is said at 186B6-9 that soul tries to judge by for itself(1)ousia of the hard and the soft, (2)the oppositeness of the both to each other, and again(3) ousia of the oppositeness, returning to them and comparing them one another. We should notice that a pair of opposite things, not a single one, is told at 186B2-4. When we perceive a pair of opposite things at the same time, we pay attention to the opposite characters themselves, not the things that have them. Of course, we may also see, touch... and judge the pair things that have the characters in each case, but this way of judging(thinking)is excluded from Text B. Besides, other

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