Abstract

The author argues that there is a sharp contrast between Plato's earlier teleological explanation of nature and his later conception. In the Phaedo Anaxagoras' νοṽς as a teleological principle is rejected, the forms taking its place, in the Philebus the existence of a νοṽς explaining order and finality in nature, is strictly demonstrated. After that nature and consequences of this new doctrine are briefly discussed : the ineffable character of the transcendent cause of the world ; the reduction of the number of the Forms to those of substances in nature ; the causality of νοṽς as an immanent and intermediate one ; the foundation of a mathematical science of nature. Thirdly the author makes an effort to reconstruct the philosophical grounds of this development, starting from the three theses, on which the argumentation of the Philebus is based. 1) νοṽς can only exist in a soul. It is argued that the dynamic conception of soul in the Phaedrus logically leads to the conclusion, that νοṽς also is movement . 2) To explain cosmic order and finality a νοṽς has to be accepted. This new idea occurs for the first time in the Sophistes and in the myth of the Politicus. 3) Cosmic order has a mathematical and astronomical character. This aspect is absent before the Philebus and seems to have been a consequence of Plato's discovery of the regularity in the planitary motions . Finally the author thinks he can indicate in the Sophistes the turning-point in the theory of Forms, as a result of the extension of the notion of being