It is not our design to enter at all at large into these views, still less to dispute them, but merely to give the latest and most approved defence of a single point of their position, a point which we submit is the kernel of the whole controversy, and which we believe to be the very Achilles heel and crack in the armor of their panoply of argument—that is, the _Theory of the Absolute_. Demonstrate the possibility of the Absolute, and materialism is impossible; disprove it, and all other philosophies are empty nothings,—_vox et præterea nihil_. Here, and only here, is materialism brought face to face with metaphysics; here is the combat _à l’outrance_ in which one or the other must perish. No one of its apostles has accepted the proffered glaive more heartily, and defended his position with more wary dexterity, than Moleschott, and it is mainly from his work, entitled _Der Kreislauf des Lebens_, that we illustrate the present metaphysics of materialism. Our first question is, What is the test of truth, what sanctions a law? Until this is answered, all assertion is absurd, and until it is answered correctly, all philosophy is vain. The response of the naturalist is: “The necessary sequence of cause and effect is the prime law of the experimentalist—a law which he does not ask from revelation, but will find out for himself by observation.” The source of truth is sensation; the uniform result of manifold experience is a law. Here a double objection arises: first, that the term “a necessary sequence” presupposes a law, and begs the question at issue; and, secondly, that, this necessity unproved, such truth is nothing more than a probability, for it is impossible to be certain that our next experiment may not have quite a different result. Either this is not the road to absolute truth, or absolute truth is unattainable. The latter horn of the dilemma is at once accepted; we neither know, nor can know, a law to be absolute; to us, the absolute does not exist. Matter and force with their relations are there, but what we know of them is a varying quantity, is of this age or the last, of this man or that, dependent upon the extent and accuracy of empirical science; we cannot speak of what we do not know, and we know no law that conceivable experience might not contradict. But how, objects the reader, can this be reconciled with the pure mathematics? Here seem to be laws above experience, laws admitting no exception.