the necessity of such an explanation seemed to him, as it did to them, the deepest ground of a spiritualistic philosophy. On the other hand, his psychological arguments for the immateriality of the soul are drawn from a wider area of experience than theirs, feeling being taken into account no less than thought; instead of restricting himself to one particular kind of cognition for evidence of spiritual power, he looks for it in every manifestation of living personality. In criticising the Stoic system as a whole, the New Academy and the later Sceptics had incidentally dwelt on sundry absurdities which followed from the materialistic interpretation of knowledge; and Plotinus evidently derived some of his most forcible objections from their writings; but no previous philosopher that we know of had set forth the whole case for spiritualism and against materialism with such telling effect. And what is, perhaps, more important than any originality in detail, is the profound insight shown in choosing this whole question of spiritualism _versus_ materialism for the ground whereon the combined forces of Plato and Aristotle were to fight their first battle against the naturalistic system which had triumphed over them five centuries before. It was on dialectical and ethical grounds that the controversy between Porch and Academy, on ethical and religious grounds that the controversy between Epicureanism and all other schools of philosophy, had hitherto been conducted. Cicero and Plutarch never allude to their opponents as materialists. Only once, in his polemic against Colôtes, does Plutarch observe that neither a soul nor anything else could be made out of atoms, but this is because they are discrete, not because they are extended.[446] For the rest, his method is to trip up his opponents by pointing out their inconsistencies, rather than to cut the ground from under their feet by proving that their theory of the universe is wrong.