For proof of the first proposition, "nothing exists," Gorgias attached himself to the school of the Eleatics, especially to Zeno. Zeno had taught that in all multiplicity and motion, that is to say, in all existence, there are irreconcilable contradictions. Zeno was in no sense a sceptic. He did not seek for contradictions in things for the sake of the contradictions, but in order to support the positive thesis of Parmenides, that only being is, and that becoming is not at all. Zeno, therefore, is to be regarded as a constructive, and not merely as a destructive, thinker. But it is obvious that by emphasizing only the negative element in his philosophy, it is possible to use his antinomies as powerful weapons in the cause of scepticism and nihilism. And it was in this way that Gorgias made use of the dialectic of Zeno. Since all existence is self-contradictory, it follows that nothing exists. He also made use of the famous argument of Parmenides regarding the origin of being. If anything is, said Gorgias, it must have had a beginning. Its being must have arisen either from being, or from not-being. If it arose from being, there is no beginning. If it arose from not-being, this is impossible, since something cannot arise out of nothing. Therefore nothing exists. The second proposition of Gorgias, that if anything exists it cannot be known, is part and parcel of the whole Sophistic tendency of thought, which identifies knowledge {118} with sense-perception, and ignores the rational element. Since sense-impressions differ in different people, and even in the same person, the object as it is in itself cannot be known. The third proposition follows from the same identification of knowledge with sensation, since sensation is what cannot be communicated. The later Sophists went much further than Protagoras and Gorgias. It was their work to apply the teaching of Protagoras to the spheres of politics and morals. If there is no objective truth, and if what seems true to each individual is for him the truth, so also, there can be no objective moral code, and what seems right to each man is right for him. If we are to have anything worth calling morality, it is clear that it must be a law for all, and not merely a law for some. It must be valid for, and binding upon, all men. It must, therefore, be founded upon that which is universal in man, that is to say, his reason. To found it upon sense-impressions and feelings is to found it upon shifting quicksands. My feelings and sensations are binding upon no man but myself, and therefore a universally valid law cannot be founded upon them. Yet the Sophists identified morality with the feelings of the individual. Whatever I think right is right for me. Whatever you think right is right for you. Whatever each man, in his irrational self-will, chooses to do, that is, for him, legitimate. These conclusions were drawn by Polus, Thrasymachus, and Critias.