xii ACTIVITY AND SUBSTANCE 207 



avu&amp;gt; Kara), wherein all things stream away (TTUVTU pel /cat 

 ov8e.v fj.evet). In spite of the somewhat sinister denial of 

 permanence implied in this addition, Heracliteanism may 

 well have seemed to restore to the universe the life which 

 Eleaticism had made impossible. 



But in Plato the pendulum swings back again to 

 the side of ovcria. Rightly or wrongly, he detected in 

 Heracliteanism consequences which seemed to him fatal 

 to the possibility of knowledge, and instead of seeking 

 to determine the actual limits of the Flux and betaking 

 himself to the practical methods science has since elaborated 

 in order to know it, he preferred to reject Heracliteanism 

 and to propound a revised, and greatly improved, Eleati 

 cism. He points out our need of a TTOV o-rw, which is 

 not swept away in the Flux, of a fixed standard whereby 

 to measure and render knowable the flow of Becoming, 

 and in his theory of Ideas he conceived himself to have 

 supplied this demand. In it plurality is, in a manner, 

 recognised in the plurality of the Ideas, united though 

 they are in the Idea of the Good, while the phenomenal 

 world is admitted not to be wholly illusory, being pera^v 

 rov OVTOS Kal pr) oWo?, intermediate between the Ideas 

 and the principle of impermanence, the mystery of which 

 Plato seems to have thought he could resolve by calling 

 it the Non-Existent. 



In the end, however, the Idea remains the only true 

 reality, and the Idea as such is unchanging Being, out of 

 Space and Time. Hence to call anything, e.g., Pleasure, 

 a Becoming (yevecri,^ is ipso facto to cast a slur upon 

 its reality and to disqualify it for the position of the Chief 

 Good which must be, he thinks, an abiding ousia. 



In Aristotle the tables are once more turned. To 

 Aristotle the real world, i.e., the world whereof we desire 

 an explanation, is after all the world of change in which 

 we move and live, rather than the system of immutable 

 and timeless laws which we devise for its explanation. 

 Hence Plato s changeless ousiai seem to him too distant 

 and divorced to explain the world, A conception of 

 Substance which is to explain the facts of the world must 



