Catholic Encyclopedia (1913)/Zeno of Elea
Greek philosopher, born at Elea, about 490 B.C. At his birthplace Xenophanes and Parmenides had established the metaphysical school of philosophy known as the Eleatic School. The chief doctrine of the school was the oneness and immutability of reality and the distrust of sense-knowledge which appears to testify to the existence of multiplicity and change. Zeno's contribution to the literature of the school consisted of a treatise, now lost, in which, according to Plato, he argued indirectly against the reality of motion and the existence of the manifold. There were, it seems, several discourses, in each of which he made a supposition, or hypothesis, and then proceeded to show the absurd consequences that would follow. This is now known as the method of indirect proof, or reductio ad absurdum, and it appears to have been used first by Zeno. Aristotle in his "Physics" has preserved the arguments by which Zeno tried to prove that motion is only apparent, or that real motion is an absurdity. The arguments are fallacious, because as Aristotle has no difficulty in showing, they are founded on on false notions of motion and space. They are, however, specious, and might well have puzzled an opponent in those days, before logic had been developed into a science. They earned for Zeno the title of "the first dialectician," and, because they seemed to be an unanswerable challenge to those who relied on the verdict of the senses, they helped to prepare the way for the skepticism of the Sophists. Besides, the method of indirect proof opened up for the sophist new possibilities in the way of contentious argument, and was very soon developed into a means of confuting an opponent. It is, consequently, the forerunner of the Eristic method, or the method of strife.