Buechner, in his well-known work on "_Force and Matter_," likewise overlooks this point, the same as all prior materialists, because they are as onesidedly insistent on their _matter_ as the idealists are on their _idea_. Quarrel and strife mean confusion, only peace will bring light. The contrast between matter and mind finds its conciliation in the positive outcome of philosophy which teaches that all distinctions must be reasonable, because neither our instrument of thought nor the rest of nature justify any exaggerated distinctions. In order to elucidate the moot question, nothing is required but the insight that ideas which nature develops in the human brain are materials for the work of our understanding, though not materials for the work of our hands. Philosophy has made material efforts to grasp the understanding and its conceptions and is still making them in the same way in which chemistry is working for the understanding of substances and physics for the understanding of forces. Substances, forces, ideas, conceptions, judgments, conclusions, knowledge and perceptions, according to the positive outcome of philosophy, must be regarded as differences or varieties of the same monistic genus. The differentiation of things no more contradicts their unity than their unity contradicts their differentiation. Darwin expanded the conception of "species" and thus contributed to a better understanding of zoology. Philosophy expands the conception of species still far beyond the Darwinian definition in teaching us to consider the species as little generalities and the largest genus, the absolute or the cosmos as the all in one, the all-embracing species. In order to closely connect the worm and the elephant, the lowest and the highest animal, the vegetable and the animal kingdom, the inorganic and the organic, as members of the same species or genus in a reasonable way, we must keep account of the gradations in nature, the transitions, the connecting links and connecting ideas. Embryology, which shows that the life of the highest animal develops through the stages of the animal genus, has greatly promoted the understanding of the common nature of all animals. "The continuity in the natural gradation of things is perfect, because there are no gradations which are not represented, because there are no differences between the various grades which nature does not fill by an intermediary form.... There is no abrupt difference in nature, no metaphysical jump, no vacuum, no gap in the order of the world," says a well-known author of our times whose name I shall not mention, because I wish to base my argument on the acknowledged facts rather than on names of authorities.