This brief survey of the origin of Greek philosophy will enable us to understand the position of the Eleatics. Regarded collectively, and as a school developing a body of doctrine, they advanced in abstraction beyond any of their predecessors or contemporaries. Whereas other philosophers had sought for the abstract in phenomenal elements, the Eleatics went straight through language to the notion of pure being: even the numbers of Pythagoras were not sufficient for the exigencies of their logic. The unity of being, as the one reality, and the absolute impossibility of not-being, revealed by the consciousness and demonstrated by language in the copula #esti#, forms the groundwork of their dogmatism. How important was the principle thus introduced into the fabric of European thought, is evident to every student of the history of philosophy. It is enough in this place to point out to what extent it has influenced our language through such words as entity, existence, essence. The Eleatics may claim as their own coinage the title of all metaphysics--Ontology, or the Science of Being. In order to make the attitude of these earliest Greek thinkers still more clear, we must return for a moment to Heraclitus, who instituted a polemic against the Eleatic doctrine of Being. He asserted that Being is no more than not-Being. Regarded in itself as an abstraction, Being turns out to be identical with nothing. The relation of Being to not-Being in Becoming formed the central point of his metaphysic, and was enunciated in the axiom, All is flowing, #panta rhei#. Though the Heraclitean polemic was directed against the school at large, it would be in the last degree inaccurate to treat the Eleatic doctrine, as maintained by Xenophanes, Parmenides, Zeno, and Melissus, from the point of view of one consistent system. By so doing not only would the truth of history be violated, but one of the most valuable examples of the growth of thought in Greece would be lost.