"The difficulty involved in the proper and adequate means of describing changes in continuous deformable bodies is the method of differential equations. ... They express mathematically the physical concept of contiguous action. Einstein's Theory of Relativity"

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The measure of our rationality determines the degree of vividness with which we appreciate the needs of other life, the extent to which we become conscious of the real character of our own motives and impulses, the ability to harmonize conflicting impulses in our own life and in society, and the capacity to choose adequate means for approved ends.

— Reinhold Niebuhr