The method by which Plato eventually found his way out of the sceptical difficulty, was to transform it from a subjective law of thought into an objective law of things. Adopting the Heracleitean physics as a sufficient explanation of the material world, he conceived, at a comparatively early period of his mental evolution, that the fallaciousness of sense-impressions is due, not to the senses themselves, but to the instability of the phenomena with which they deal; and afterwards, on discovering that the interpretation of ideal relations was subject to similar perplexities, he assumed that, in their case also, the contradiction arises from a combination of Being with not-Being determining whatever differences prevail among the ultimate elements of things. And, finally, like Empedocles, he solved the problem of cognition by establishing a parallel between the human soul and the universe as a whole; the circles of the Same and the Other being united in the celestial orbits and also in the mechanism of the brain.[223] It was by an analogous, though, of course, far more complicated and ingenious adjustment, that Hegel sought to overcome the agnosticism which Kant professed to have founded on a basis of irrefragable proof. With both philosophers, however, the sceptical principle was celebrating its supreme triumph at the moment of its fancied overthrow. The dogmatism of doubt could go no further than to resolve the whole chain of existence into a succession of mutually contradictory ideas. If the synthesis of affirmation and negation cannot profitably be used to explain the origin of things in themselves, it has a real and very important function when limited to the subjective sphere, to the philosophy of practice and of belief. It was so employed by Socrates, and, on a much greater scale, by Plato himself. To consider every proposition from opposite points of view, and to challenge the claim of every existing custom on our respect, was a proceeding first instituted by the master, and carried out by the disciple in a manner which has made his investigations a model for every future enquirer. Something of their spirit was inherited by Aristotle; but, except in his logical treatises, it was overborne by the demands of a pre-eminently dogmatic and systematising genius. In criticising the theories of his predecessors, he has abundantly illustrated the power of dialectic, and he has enumerated its resources with conscientious completeness; but he has not verified his own conclusions by subjecting them to this formidable testing apparatus.