The "efficient cause," that which produces and instigates a movement is only some external change as it accidentally gives a kind of push to an immature, imperfect being and starts it moving toward its perfected or fulfilled form. The final cause is the perfected form regarded as the _explanation or reason_ of prior changes. When it is not taken in reference to the changes completed and brought to rest in it, but in itself it is the "formal cause": The inherent _nature_ or character which "makes" or constitutes a thing _what it is_ so far as it truly _is_, namely, what it is so far as it does not change. Logically and practically all of the traits which have been enumerated cohere. Attack one and you attack all. When any one is undermined, all go. This is the reason why the intellectual modification of the last few centuries may truly be called a revolution. It has substituted a conception of the world differing at every point. It makes little matter at what point you commence to trace the difference, you find yourself carried into all other points. Instead of a closed universe, science now presents us with one infinite in space and time, having no limits here or there, at this end, so to speak, or at that, and as infinitely complex in internal structure as it is infinite in extent. Hence it is also an open world, an infinitely variegated one, a world which in the old sense can hardly be called a universe at all; so multiplex and far-reaching that it cannot be summed up and grasped in any one formula. And change rather than fixity is now a measure of "reality" or energy of being; change is omnipresent. The laws in which the modern man of science is interested are laws of motion, of generation and consequence. He speaks of law where the ancients spoke of kind and essence, because what he wants is a correlation of changes, an ability to detect one change occurring in correspondence with another. He does not try to define and delimit something remaining constant _in_ change. He tries to describe a constant order _of_ change. And while the word "constant" appears in both statements, the meaning of the word is not the same. In one case, we are dealing with something constant in _existence_, physical or metaphysical; in the other case, with something constant in _function_ and operation. One is a form of independent being; the other is a formula of description and calculation of interdependent changes.