Since Lucretius is thus identical for us with his poem, and is lost in his philosophy, the antecedents of Lucretius are simply the stages by which his conception of nature first shaped itself in the human mind. To retrace these stages is easy; some of them are only too familiar; yet the very triteness of the subject may blind us to the grandeur and audacity of the intellectual feat involved. A naturalistic conception of things is a great work of imagination,--greater, I think, than any dramatic or moral mythology: it is a conception fit to inspire great poetry, and in the end, perhaps, it will prove the only conception able to inspire it. We are told of the old Xenophanes that he looked up into the round heaven and cried, “The All is One.” What is logically a truism may often be, imaginatively, a great discovery, because no one before may have thought of the obvious analogy which the truism registers. So, in this case, the unity of all things is logically an evident, if barren, truth; for the most disparate and unrelated worlds would still be a multitude, and so an aggregate, and so, in some sense, a unity. Yet it was a great imaginative feat to cast the eye deliberately round the entire horizon, and to draw mentally the sum of all reality, discovering that reality makes such a sum, and may be called one; as any stone or animal, though composed of many parts, is yet called one in common parlance. It was doubtless some prehistoric man of genius, long before Xenophanes, who first applied in this way to all things together that notion of unity and wholeness which everybody had gained by observation of things singly, and who first ventured to speak of “the world.” To do so is to set the problem for all natural philosophy, and in a certain measure to anticipate the solution of that problem; for it is to ask how things hang together, and to assume that they do hang together in one way or another. To cry “The All is One,” and to perceive that all things are in one landscape and form a system by their juxtaposition, is the rude beginning of wisdom in natural philosophy. But it is easy to go farther, and to see that things form a unity in a far deeper and more mysterious way. One of the first things, for instance, that impresses the poet, the man of feeling and reflection, is that these objects that people the world all pass away, and that the place there-of knows them no more. Yet, when they vanish, nothingness does not succeed; other things arise in their stead. Nature remains always young and whole in spite of death at work everywhere; and what takes the place of what continually disappears is often remarkably like it in character. Universal instability is not incompatible with a great monotony in things; so that while Heraclitus lamented that everything was in flux, Ecclesiastes, who was also entirely convinced of that truth, could lament that there was nothing new under the sun.