The theory of evolution, as thus set forth, the theory of the evolution of all from one self-existent immanent principle, is nowadays considered not only as the fullest explanation ever given of the unity and order of the universe, being a system of perfect monism, plainly reasoned out in all its details, but also the only one which, as overcoming any kind of dualism, gives satisfaction to the human mind. For, if one and the self-same principle is not the source of all, existing unity cannot prevail throughout creation. If this one principle is not supposed to be immanent in the world, nature is not explained from itself, but rather is rendered unintelligible; that which is plain and visible in it being accounted for by something unseen and unknown. And, if this one immanent principle is not regarded as absolutely independent and self-existent, it becomes necessary to conceive of the universe as conditioned without perceiving any cause or condition on which it is dependent, and to ascribe the orderly and constant succession of phenomena, not to an agent working according to law, but to arbitrary creative will.