It now only remains in this chapter to speak of the later Platonism. The Old Academy, of which Plato was the founder, limited its labours to the illustration and defence of his doctrines. The Middle Academy, originating with Arcesilaus, born B.C. 316, maintained a warfare with the Stoics, developed the doctrine of the uncertainty of sensual impressions and the nothingness of human knowledge. The New Academy was founded by Carneades, born B.C. 213, and participated with the preceding in many of its fundamental positions. On the one side Carneades leans to scepticism, on the other he accepts probability as his guide. This school so rapidly degenerated that at last it occupied itself with rhetoric alone. The gradual increase of scepticism and indifference throughout this period is obvious enough; thus Arcesilaus said that he knew nothing, not even his own ignorance, and denied both intellectual and sensuous knowledge. Carneades, obtaining his views from the old philosophy, found therein arguments suitable for his purpose against necessity, God, soothsaying; he did not admit that there is any such thing as justice in the abstract, declaring that it is a purely conventional thing; indeed, it was his rhetorical display, alternately in praise of justice and against it, on the occasion of his visit to Rome, that led Cato to have him expelled from the city. Though Plato had been the representative of an age of faith, a secondary analysis of all his works, implying an exposition of their contradictions, ended in scepticism. If we may undertake to determine the precise aim of a philosophy whose representatives stood in such an attitude of rhetorical duplicity, it may be said to be the demonstration that there is no criterion of truth in this world. Persuaded thus of the impossibility of philosophy, Carneades was led to recommend his theory of the probable. "That which has been most perfectly analyzed and examined, and found to be devoid of improbability, is the most probable idea." The degeneration of philosophy now became truly complete, the labours of so many great men being degraded to rhetorical and artistic purposes. It was seen by all that Plato had destroyed all trust in the indications of the senses, and substituted for it the Ideal theory. Aristotle had destroyed that, and there was nothing left to the world but scepticism. A fourth Academy was founded by Philo of Larissa, a fifth by Antiochus of Ascalon. It was reserved for this teacher to attach the Porch to the Academy, and to merge the doctrines of Plato in those of the Stoics. Such a heterogeneous mixture demonstrates the pass to which speculative philosophy had come, and shows us clearly that her disciples had abandoned her in despair. [Sidenote: End of the Greek age of Faith.]