What Plato did for early Greek philosophy, what Numenius did for post-Platonic thought, that Proclus Diadochus, the "Successor," did for Plotinos and his followers. For the first time since Numenius we find again a comparative method. By this time religion and philosophy have fused in magic, and so, instead of a comparative religion, we have a comparative philosophy. Proclus was the first genuine commentator, quoting authorities on all sides. He was sufficient of a philosopher to grasp Neoplatonism as a school of thought; and far from paying any attention to Ammonius, as recent philosophy has done, as source of Neoplatonism, he traces the movement as far as Plutarch, calling him the "father of us all," inasmuch as he introduced the conception of "hypostasis." Evidently, Proclus looked upon this as the centre of Neoplatonic development, and therefore we shall be justified in a closer study of this conception; and we may even say that its historic destiny was a continuation of the main stream of creative Greek philosophy; or, if you prefer, of Platonism, or Noumenianism, or even Plotinian thought. Did Greek philosophy die with Proclus? The political changes of the time forced alteration of dialect and position; but the accumulations of mental achievements could not perish. This again we owe to Proclus. Besides being the first great commentator he precipitated his most valuable achievements in logical form, in analytic arrangement, in the form of crystal-clear propositions, theorems, demonstrations, and corollaries. Such a highly abstract form was inevitable, inasmuch as Numenius had turned away from Aristotelian observation of nature. Just like the Hebrew thinkers, who finally became commentators and abstract theorizers, nothing else was left for a philosophy without connection with experiment, when whittled down by the keenest intellects of the times. This abstract method, still familiarly used by geometry, reappeared among the School-men, notably in Thomas Aquinas. Later it persisted with Spinoza and Descartes. However, rising experimentalism has gradually terminated it, its last form appearing in Kant and Hegel. Kant's "Ding in sich," reached after abstracting all qualities, is only a re-statement of Numenius and Plotinos's "subject," or, definition of matter; and Hegel's dialectic, beginning with Being and Not-being, more definitely proclaimed by Plotinos, goes as far back as the Eleatics and Heraclitus, not to mention Plato. However, Kant and Hegel are the great masters of modern thought; and although at one time the rising tide of materialism and cruder forms of evolution threatened to obscure it, Karl Pearson's "Grammar of Science," generous as it is in invective against Kant and Hegel, in modern terms clinches Berkeley's and Kant's demonstration of the reality of the super-sensual, thus vindicating Plotinos, and, before him, Numenius.