There is no especial need here to trace the historical development of these two problems or enter upon a discussion of religious or philosophical questions. Our immediate interest in the mind and its relationship to the body is not because we want to be assured of the salvation of our souls after death. _We want to know all we can about the reality and certainty and character of mental control of bodily functions because of the practical use we can make of such knowledge in this life, here and now._ [Sidenote: Spiritualist, Materialist and Scientist] The practical scientist has nothing in common with either spiritualists, soul-believers, on the one hand, or materialists on the other. So far as the mortality of the soul is concerned, he may be either a spiritualist or a materialist But spiritualism or materialism is to him only an intellectual pastime. It is not his trade. In his actual work he seeks only practical results, and so confines himself wholly to the actual facts of human experience. The practical scientist knows that as between two given facts, and _only_ as between these two, one may be the "cause" of the other. But he is not interested in the "creative origin" of material things. He does not attempt to discover "first" causes. [Sidenote: Science of Cause and Effect] The practical scientist ascribes all sorts of qualities to electricity and lays down many laws concerning it without having the remotest idea as to what, in the last analysis, electricity may actually be. He is not concerned with ultimate truths. He does his work, and necessarily so, upon the principle that for all practical purposes he is justified in using any given assumption as a working hypothesis if everything happens just as if it were true. The practical scientist applies the term "cause" to any object or event that is the invariable predecessor of some other object or event. For him a "cause" is simply any object or event that may be looked upon as forecasting the action of some other object or the occurrence of some other event. The point with him is simply this, Does or does not this object or this event in any way affect that object or that event or determine its behavior? [Sidenote: Causes and "First" Causes]