When we forget this and treat any partial experience as though it were the complete and adequate expression of the whole nature of Reality,—in other words, when we try to apply to existence or the universe as a whole conceptions which are only valid for special aspects of existence,—we shall inevitably find ourselves led to contradictory and absurd results. Each partial aspect of a total system can only be ultimately understood by reference to the whole to which it belongs, and hence any attempt to treat the part in abstraction as itself a self-contained whole,—or, in other words, to treat the concepts with which we have to work in dealing with some special aspect of the world of experience as ultimately valid in their application to the whole system,—is bound to issue in contradiction. Again, just because our knowledge of the structure of the system as a whole is so imperfect as it is, our insight into the structure of its constituents is also necessarily limited. Hence it will commonly happen that, even within the limits of their applicability, the special concepts of our various sciences are not, when thought out, free from internal contradiction. For instance, we are led to absurd results when we try, as Materialism does, to interpret the whole system of experience in terms of the concepts used in the purely physical sciences; and again, even in their restricted use as physical categories, these concepts seem incapable of being so defined as to involve no element of contradiction. In both these senses all Appearance implies an element of contradiction; only for an insight which could take in at once the whole system of existence would its details be completely coherent and harmonious. But this does not alter the fact that, so far as our insight into any part of the whole and its connection with other parts is self-consistent, it does convey genuine, though imperfect, knowledge of the whole. Though our detailed insight into the structure of the whole may never reach the ideal of perfect self-consistency, yet it may approximate to that ideal in different degrees, at different stages, or with reference to different aspects. And the closer the approximation the less the modification which our knowledge would require to bring it into complete harmony with itself, and the greater therefore the element of truth about Reality which it contains.