So also with Aristotle. As a naturalist, he is, indeed, purely objective; but when he offers a general explanation of the world, the subjective element introduced by Protagoras and Socrates at once reappears. Simple absolute self-consciousness is for him the highest good, the animating principle of Nature, the most complete reality, and the only one that would remain, were the element of nonentity to disappear from this world. The utter misconception of dynamic phenomena which marks his physics and astronomy can only be accounted for by his desire to give life the priority over mechanical motion, and reason the priority over life. Thus his metaphysical method is essentially identical with the introspective method recommended by Plotinus, and, if fully worked out, might have led to the same results. We cannot, then, agree with Zeller, when he groups the Neo-Platonists together with the other post-Aristotelian schools, on the ground that they are all alike distinguished from Plato and Aristotle by the exclusive attention which they pay to subjective and practical, as opposed to scientific and theoretical interests. It seems to us that such distinctions are out of relation to the historical order in which the different systems of Greek philosophy were evolved. It is not in the substance of their teaching, but in their diminished power of original speculation, that the thinkers who came after Aristotle offer the strongest contrast to their predecessors. In so far as they are exclusively practical and subjective, they follow the Humanists and Socrates. In so far as they combine Socratic tendencies with physical studies, they imitate the method of Plato and Aristotle. Their cosmopolitan naturalism is inherited from the Cynics in the first instance, more remotely from the physiocratic Sophists, and, perhaps, in the last resort, from Heracleitus. Their religion is traceable either to Pythagoras, to Socrates, or to Plato. Their scepticism is only a little more developed than that of Protagoras and the Cyrenaics. But if we seek for some one principle held in common by all these later schools, and held by none of the earlier schools, we shall seek for it in vain. The imitative systems are separated from one another by the same fundamental differences as those which divide the original systems. Now, in both periods, the deepest of all differences is that which divides the spiritualists from the materialists. In both periods, also, it is materialism that comes first. And in both, the transition from one doctrine to the other is marked by the exclusive prominence given to subjective, practical, sceptical, or theological interests in philosophy; by the enthusiastic culture of rhetoric in general education; and by a strong religious reaction in the upper ranks of society.