As would appear from this statement, Aristotle has never fully developed the idea of his absolute spirit, and still less has he harmonized it with the fundamental principles and demands of his philosophy, although many consequences of his system would seem to drive him to this, and numerous principles which he has laid down would seem to prepare the way for it. This idea is unexpectedly introduced in the twelfth book of the Metaphysics simply as an assertion, without being farther and inductively substantiated. It is at once attended with important difficulties. We do not see why the ultimate ground of motion or the absolute spirit must be conceived as a personal being; we do not see how any thing can he a moving cause and yet itself unmoved; how it can be the origin of all becoming, that is of the departing and arising, and itself remain a changeless energy, a principle of motion with no potentiality to be moved, for the moving thing must stand in a relation of passive and active with the thing moved. Moreover, Aristotle, as would follow from these contradictory determinations, has never thoroughly and consistently determined the relation between God and the world. He has considered the absolute spirit only as contemplative and theoretical reason, from whom all action must be excluded because he is perfect end in himself, but every action presupposes an end not yet perfected; we have thus no true motive for his activity in reference to the world. He cannot be truly called the first mover in his theoretical relation alone, and since he is in his essence extra-mundane and unmoved, he cannot once permeate the life of the world with his activity; and since also matter on one side never rises wholly to form, we have, therefore, here again the unreconciled dualism between the Divine spirit and the unmistakable reality of matter. Many of the arguments which Aristotle brings against the gods of Anaxagoras may be urged against his own theory.