“状況”の変化と“もの自身”の変化 : プラトン『テアイテトス』 (154B〜155D) における背丈比べのパラドクスの哲学的意味 (第五百五十號記念特集號)

Abstract

In the course of discussion of Theaetetus' definition that knowledge is perception, Plato interpolates some puzzles about what we call 'relations' of size and number (Theaetetus 154B-155D) , which have been variously interpreted by commentators. Some regard them as unreal problems due to Plato's failure to understand the nature of relational terms or 'incomplete predicates' (a type of interpretation originating from B. Russell, followed by R. C. Cross & A. D. Woozley, C. Kirwan, J. M. McDowell, etc.) ; others consider them, conversely, to be indicating a definite advance of Plato's thought on the relational concepts when compared with his treating the similar problem in the Phaedo 102B-103A (H. Jackson, F. M. Cornford, W. D. Ross, etc.). Rejecting all these interpretations as incompatible with what is stated in the texts concerned, this paper takes the puzzles, in accordance with the way they are presented in the passage, to be expressing the view that (in one of the example cases given there) Socrates really becomes smaller when a new comparison with growing Theaetetus is made, in spite of the fact that nothing is taken away from his stature: the latter fact has, in its own right, nothing to do with his 'becoming smaller'. This way of looking at the change (e. g. 'becoming smaller') , which is stated in the context as a consequence of the Protagorean theory of perception, may apparently contradict common sense, but in itself it has good reason to be conceived as the correct view of change of a thing's property: a thing χ does change in respect of its property, F-ness, if it is put in a different condition or situation relevant to that F-ness. Moreover (so it is pointed out in the paper) , the alternative view that is rejected in the passage, namely the common-sense view that Socrates' 'becoming larger' or 'becoming smaller' is due to the fact that some measure of length is added, or taken away from, his stature, is a view of exactly the same kind as the one which is rejected by Socrates (Plato), according to the important Phaedo passage (96A-102A), in the course of his arriving at the theory of Forms. The crucial reason why Socrates (Plato) has been led to hold the theory of Forms, accoding to that passage, is that he has become definitely unsatisfied with the thinking that it is because some addition is made to the original bulk that a thing becomes larger: it is not because of that, he says, but just because of the Large itself, that a thing becomes larger, and so with other properties. We can thus see quite well why the argument in the puzzles passage in the Theaetetus has every appearance of being seriously meant; for, Plato is there looking again into, and virtually re-affirming, the very line of thought in which his theory of Forms originates. With this in mind, the present writer traces the relevant passages from the Phaedo through the Parmenides to identify the real difficulty Plato has most seriously realized about the way of describing the theory of Forms, and, by identifying it as arising from an ontological commitment to the priority of individual thing ('this something'), which is implied in the 'participation' idioms, the writer then proceeds to try to throw further light on the important significance, for the develpment of Plato's philosophy and for the solution of that difficulty in particular, of the content of the puzzles passage and the theory of perception in which the puzzles are interpolated in the Theaetetus.