But Being and Becoming include two great realms: that of “Nature” and that of “Mind,” _i.e._ consciousness and the processes of consciousness. And two apparently fundamentally different branches of knowledge relate to these: the natural sciences, and the mental sciences. If a unified and “natural” explanation is really possible, the beginning and end of all this “reducing to simpler terms” must be to bridge over the gulf between these; but this, in the sense of naturalism, necessarily means that the mental sciences must in some way be reduced to terms of natural science, and that the phenomena, processes, sequences, and laws of consciousness must likewise be made “commensurable” with and be linked on to the apparently simpler and clearer knowledge of “Nature,” and, if possible, be subordinated to its phenomena and laws, if not indeed derived from them. As it is impossible to regard consciousness itself as corporeal, or as a process of movement, naturalism must at least attempt to show that the phenomena of consciousness are attendant and consequent on corporeal phenomena, and that, though they themselves never become corporeal, they are strictly regulated by the laws of the corporeal and physical, and can be calculated upon and studied in the same way. But even the domain of the natural itself, as we know it, is by no means simple and capable of a unified interpretation. Nature, especially in the realm of organic life, the animal and plant world, appears to be filled with marvels of purposefulness, with riddles of development and differentiation, in short with all the mysteries of life. Here most of all it is necessary to “reduce” the “teleological view” to terms of the purely causal, and to prove that all the results, even the evolution of the forms of life, up to their highest expressions and in the minutest details of their marvellous adaptations, came “of themselves,” that is to say, are quite intelligible as the results of clearly traceable causes. It is necessary to reduce the physiological and developmental, and all the other processes of life, to terms of physical and chemical processes, and thus to reduce the living to the not living, and to derive the organic from the forces and substances of inanimate nature. The process of reduction does not stop even here. For physical and chemical processes are only really understood when they can be resolved into the simplest processes of movement in general, when all qualitative changes can be traced hack to purely quantitative phenomena, when, finally, in the mechanics of the great masses, as well as of the infinitely small atoms, everything becomes capable of expression in mathematical terms.