No matter where you look you will find that every fact in Nature is relatively cause and effect according to the point of view. Thus, if a railroad engine backs into a train of cars it transmits a certain amount of motion to the first car. This imparted motion is again passed on to the next car, and so on. The motion of the first car is, on the one hand, the effect of the impact of the engine, and is, on the other hand, the "cause" of the motion of the second car. And, in general, what is an "effect" in the first car becomes a "cause" when looked at in relation to the second, and what is an "effect" in the second becomes a "cause" in relation to the third. So that even the materialist will agree that "cause" and "effect" are relative terms in dealing with any series of facts in Nature. [Sidenote: A Common Platform for All] A man may be either a spiritualist, believing that the mind is a manifestation of the super-soul, or he may be a materialist, and in either case he may at the same time and with perfect consistency believe, as a practical scientist, that the mind is a "cause" and has bodily action as its "effect." Naturally this point of view offers no difficulties whatever to the spiritualist. He already looks upon the mind or soul as the "originating cause" of everything. [Sidenote: Thoughts Treated as Causes] But the materialist, too, may in accordance with his speculative theory continue to insist that _brain-action_ is the "originating cause" of mental life; yet if the facts show that certain thoughts are invariably followed by certain bodily activities, the materialist may without violence to his theories agree to the great practical value of _treating these thoughts as immediate causes_, no matter what the history of creation may have been. Whatever the brand of your materialism or your religious belief, you can join us in accepting this practical-science point of view as a common platform upon which to approach our second fundamental proposition, that "all bodily activity is caused, controlled and directed by the mind." [Sidenote: Scientific Method with Practical Problems] Ignoring all religious and metaphysical questions, we have, then, to ask ourselves merely: _Can the mind be relied upon to bring about or stop or in any manner influence bodily action? And if it can, what is the extent of the mind's influence?_ In answering these questions we shall follow the method of the practical scientist, whose method is invariably the same whatever the problem he is investigating. This method involves two steps: first, the collection and classification of facts; second, the deduction from those facts of general principles. [Sidenote: Uses of Scientific Laws]