Turning to the physical significance of the numbers, we may note that it is these magnitudes which enter into the expression of a distance, hence which serve to define congruence. If we are dealing with a purely amorphous continuum in which no particular definition of congruence or distance is pressed upon us by nature, there can exist no particular distribution of numbers inherent in the continuum. But if, on the other hand, as in the case of space, or, better still, of Einstein’s four-dimensional space-time, a precise definition of practical congruence is imposed upon us by nature—if, in other words, our continuum, in place of being amorphous, possesses a definite metrics or structure—there will exist a -distribution inherent in the continuum, and this distribution will define its metrical field. The same arguments would apply to the structural tensors of curvature of the continuum, namely, to , to and to . If the continuum is amorphous, these structural tensors, together with the ’s that compose them, are meaningless until we have decided upon some theoretical type of congruence of geometry; and even then they represent characteristics of structure that are as conventional as the geometry we have selected. But if, on the other hand, a definite metrics exists in the continuum, then these structural tensors represent curvatures of the continuum, which we may regard as physically existent and no longer as purely conventional. [Pg 99] CHAPTER VIII THE MEANING OF THE WORD RELATIVITY ALL our previous discussions and explanations have been made in order to prepare the ground for Einstein's theory of relativity. However, before we proceed to discuss Einstein’s theory proper, it may be useful to reach a more precise understanding of the scientific meaning of the words “relativity” and “absoluteness.” In traditional philosophy an absolute reality is the primary, self-existing reality, the substance, the true being or the metaphysical reality, whereas a relative reality is a secondary, dependent reality owing its form of being to a relation of the genuinely real.[35] Now, so far as scientific philosophy is concerned, absolute reality is a myth. All we can ever become cognisant of in nature reduces in the final analysis to structure, that is, to relationships. Hence, if we adopt this very general understanding of the word “relativity,” we may anticipate even at this stage that Einstein’s theory can add nothing to our belief in the fundamental relativity of all knowledge. Obviously, then, when physicists speak of absolutes and relatives, they are referring to categories of a nature differing from those of philosophers.