The spiritualist or idealist believes in a spiritual, which means in a ghostlike and inexplicable, nature of force. The materialist thinkers, on the other hand, are skeptical. A scientific proof of faith or of skepticism does not exist. The materialist has only this advantage over his idealist opponent, that he looks for the transcendental, the nature, the cause, the force, not back of the phenomenon, not outside of matter. But he remains behind the idealist when he ignores the difference between matter and force. The materialist dwells on the actual inseparability of matter and force and does not admit any other reason for a distinction between the two than "an external reason derived from the demand of our mind for systematization." Buechner says in "Nature and Mind," page 66: "Force and matter, separated from one another, are for me nothing but thoughts, fantasies, ideas without any substance, hypotheses which do not exist for any healthy study of nature, because all phenomena of nature are rendered obscure and unintelligible by such a separation." But if Buechner deals with any special department of natural science in a productive way, instead of handling phrases of natural philosophy, his own practice will show him that the separation of forces from matter is not an "external," but an internal, an imminent necessity, by which alone we are enabled to elucidate and understand the phenomena of nature. Although the author of "Force and Matter" chose for his motto: "Now, what I want is--facts," we assure the reader that this device is more a thoughtless word than a serious opinion. Materialism is not so coarse-grained that it wants purely facts. Those facts which Buechner is looking for are by themselves not specifics for his desires. The idealist likewise wants such facts. No student of nature wants mere hypotheses. What all cultivators of the field of science want is not so much facts as explanations or an understanding of facts. Even the materialist will not deny that science, the "natural philosophy" of Buechner not excepted, is more concerned with mental forces than with bodily matter, that it cares more for force than for matter. The separation of force and matter is derived from "the demand of our mind for systematization." Very true! But so does all science emanate from the demand of our reason for systematization.