=Aristotle’s Starting-Point.= The two early influences in Aristotle’s mental development offer an explanation for his philosophical point of view. These influences were his empirical training in medicine and his conceptual training in the moral ideals of the Academy. Plato had convinced him that if there were to be any true science, it must be founded on concepts that are unchanging. His own scientific training, however, reinforced by the influence of Democritus, made him respect the value of empirical facts. While the philosophical problem for Aristotle was the same as that for Plato, the difference between them was in the main a matter of emphasis due to their different starting-points. Plato started with the refutation of the Protagorean theory of perception, and consequently he emphasized the value of the conceptual world; Aristotle, however, felt that Plato had overestimated the conceptual world, and he emphasized the importance of empirical facts. Both when a member of the Academy and later, he strongly contended against Plato’s evaluation of the world of Ideas, because they so transcended the sense world that they neither explained nor illuminated it. Aristotle’s reaction against Plato’s theory furthermore gives us a more correct notion of what Plato really taught. If conceptions are to enter into knowledge, they must not exist in the clouds of abstraction. He maintained that Plato had increased the difficulty of the problem by adding a second world of entities quite distinct from the world of nature. The same problem that Plato confronted still exists unanswered, said Aristotle. It is the problem of the twofold world. If Ideas are apart from things, we could not know that they existed, we should not be able to know anything about them, nor should we be able to explain the world through them. It is true that Plato, in his later draft, had conceived Ideas to be teleologically related to the physical things, but how could this be if they were apart from things? Thus in his reaction from Plato’s theory of Ideas, Aristotle reëstablished the world of perceptual fact. This is the starting-point of Aristotle.