But first we must clear the ground a little by considering what it really is that we are to study, and if it be possible to study it at all. Nature-study if it is to be possible must begin, and if it is to be fruitful must end, in something which is not strictly the study of nature, but which we call Philosophy. One of the most brilliant examples of that union of philosophic speculation with nature-study which is so marked a feature of the German thought of our day is H. von Keyserling’s work, The Structure of the World.[14] Keyserling begins by laying it down as a postulate of thinking that “The Universe is a rounded, inwardly coherent Whole.” A postulate of thinking this is indeed, and more than that—it is a postulate of living. If under all the variety and apparent discontinuity of the universe there does not lie _One_ all-pervading and unifying Power, then meditation and action are alike vain, for none can tell the hour when some incursion of the unknown may not shatter our cosmos into chaos, or leave us in a new universe with the edifice of our past experience, the familiar home of the spirit, lying in ruins around us. Every one assumes, consciously or unconsciously, that there is such a Power, that the universe is One, that however mysterious, however little known or understood it may be, it is not essentially deceptive or incalculable. The savage and the philosopher alike assume this, and act upon the assumption. It is perhaps possible not merely to assume but to prove it. For let us try to imagine what would be the case if it were not true. If the Principle, the ultimate Reality of the universe, be not one it must be at least dual. There must be not less than two principles. Now there are only three ways in which these two principles—and what we say will hold good for any greater number—can be related to each other. They must either (1) be identical, or (2) they must be complementary, each possessing something which the other is lacking in, or (3) they must negate each other and be mutually contradictory and exclusive. But two absolutely identical principles, if we can conceive such a thing, are indistinguishable from one. Two or more complementary principles, again, make up, when taken together, but a single whole, as in the Christian Trinity. Therefore if the universe be really dual, its two principles must negate and contradict each other. Now these two hostile principles must either be equal in force or one must be more powerful than the other. In the latter event, seeing that they divide between them the sum total of existence and thus stand in naked and essential antagonism, with no place for evasion, and no auxiliary or modifying forces to call in, it follows of necessity that if one surpassed the other by even the smallest conceivable excess, it must, in eternity, master it and reduce it to impotence. So by this road we come back to unity again. If, however, we