Such an idea can hardly be distinguished from the idea of growth or development; one passes naturally into the other. Thus it is equally proper to say that the third scientific influence, the conception of organism and growth, is dominant in the Leibnizian thought, or that this is swallowed up and absorbed in the grand idea of continuity. The law of animal and vegetable life and the law of the universe are identified. The substance of the universe is activity; the law of the universe is interdependence. What is this but to say that the universe is an organic whole? Its activity is the manifestation of life,--nay, it is life. The laws of its activity reveal that continuity of development, that harmony of inter-relation, which are everywhere the marks of life. The final and fundamental notion, therefore, by which Leibniz interprets the laws of physics and mathematics is that of Life. This is his regnant category. It is "that higher and metaphysical source" from which the very existence and principles of mechanism flow. The perpetual and ubiquitous presence of motion reveals the pulsations of Life; the correlation, the rationality, of these motions indicate the guiding presence of Life. This idea is the alpha and omega of his philosophy. CHAPTER III. THE PROBLEM, AND ITS SOLUTION. Leibniz, like every great man, absorbed into himself the various thoughts of his time, and in absorbing transformed them. He brought into a focus of brilliancy the diffused lights of truth shining here and there. He summed up in a pregnant and comprehensive category the scattered principles of his age. Yet we are not to suppose that Leibniz considered these various ideas one by one, and then patched them into an artificial unity of thought. Philosophies are not manufactured piecemeal out of isolated and fragmentary thoughts; they grow from a single root, absorbing from their environment whatever of sustenance offers itself, and maturing in one splendid fruit of spiritual truth. It is convenient, indeed, to isolate various phases of truth, and consider them as distinct forces working to shape one final product, and as a convenient artifice it is legitimate. But it answers to no process actually occurring. Leibniz never surrendered his personal unity, and out of some one root-conception grew all his ideas. The principles of his times were not separate forces acting upon him, they were the foods of which he selected and assimilated such as were fitted to nourish his one great conception.