_This_ idea of the unknowable is the root of all materialism; and yet no scientific man, however materialistic his proclivities, treats the unanalysable residuum thus when he meets it in the experiments of his laboratory. On the contrary, he makes this final unanalysable fact the basis of his synthesis. He finds that in the last resort it is energy of some kind, whether as heat or as motion; but he does not throw up his scientific pursuits because he cannot analyse it further. He adopts the precisely opposite course, and realises that the conservation of energy, its indestructibility, and the impossibility of adding to or detracting from the sum-total of energy in the world, is the one solid and unchanging fact on which alone the edifice of physical science can be built up. He bases all his knowledge upon his knowledge of "the unknowable." And rightly so, for if he could analyse this energy into yet further factors, then the same problem of "the unknowable" would meet him still. All our progress consists in continually pushing the unknowable, in the sense of the unanalysable residuum, a step further back; but that there should be no ultimate unanalysable residuum anywhere is an inconceivable idea. In thus realising the undifferentiated unity of Living Spirit as the central fact of any system, whether the system of the entire universe or of a single organism, we are therefore following a strictly scientific method. We pursue our analysis until it necessarily leads us to this final fact, and then we accept this fact as the basis of our synthesis. The Science of Spirit is thus not one whit less scientific than the Science of Matter; and, moreover, it starts from the same initial fact, the fact of a living energy which defies definition or explanation, wherever we find it; but it differs from the science of matter in that it contemplates this energy under an aspect of responsive intelligence which does not fall within the scope of physical science, as such. The Science of Spirit and the Science of Matter are not opposed. They are complementaries, and neither is fully comprehensible without some knowledge of the other; and, being really but two portions of one whole, they insensibly shade off into each other in a border-land where no arbitrary line can be drawn between them. Science studied in a truly scientific spirit, following out its own deductions unflinchingly to their legitimate conclusions, will always reveal the twofold aspect of things, the inner and the outer; and it is only a truncated and maimed science that refuses to recognise both.