The present medium of general intelligence and theory in which we live embraces in a way the results of all that has preceded it, of all the steps of culture through which the world has risen. But in this body of intellectual beliefs and ideas with which our single soul is clad,--in this common soil of thought,--the several contributions of the past have been half or even wholly obliterated, and are only the shadows of their old selves. What in a former day was a question of all-engrossing interest has left but a trace: the complete and detailed formations of ancient thought have lost their distinctness of outline, and have shrunk into mere shadings in the contour of our intellectual world. Questions, from which the ancient philosophers could never shake themselves loose, are now only a barely perceptible _nuance_ in the complex questions of the present day. Discussions about the bearings of the 'one' and the 'many,' puzzles like those of Zeno, and the casuistry of statesmanship such as is found in the Politics of Aristotle, have for most people little else than an antiquarian interest. We scarcely detect the faint traces they have left in the 'burning questions' of our own age. We are too ready to forget that the past is never altogether annihilated, and that every step, however slight it may seem, which has once been taken in the movement of intellect, must be traversed again in order to understand the constitution of our present intellectual world. To outward appearance the life and work of past generations have so completely lost their organic nature, with its unified and vital variety, that in their present phase they have turned into hard and opaque atoms of thought. The living forces of growth, as geologists tell us, which pulsed through the vegetables of one period are suspended and put in abeyance: and these vegetables turn into what we call the inorganic and inanimate strata of the earth. Similarly, when all vitality has been quenched or rendered torpid in the structures of thought, they sink into the material from which individuals draw their means of intellectual support. This inorganic material of thought stands to the mind, almost in the same way as the earth and its products stand to the body of a man. If the one is our material, the other is our spiritual _substance_. In the one our mind, as in the other our body, lives, moves, and has its being.