In text-books of Dynamics and in treatises of Natural Philosophy that is a perfectly legitimate procedure;[4] but when later on we come to philosophise, and to deal with the universe as a whole, we must forgo the ingrained habit of abstraction, and must remember that for a _complete_ treatment _nothing_ must permanently be ignored. So if life and mind and will, and curiosity and mischief and folly, and greed and fraud and malice, and a whole catalogue of attributes and things not contemplated in Natural Philosophy—if these are known to have any real existence in the larger world of total experience, and if there is any reason to believe that any one of them may have had some influence in determining an observed result, then it is foolish to exclude these things from philosophic consideration, on the ground that they are out of place in the realm of Natural Philosophy, that they are not allowed for in its scheme, and therefore cannot possibly be supposed capable of exerting any effective interference, any real guidance or control. [Footnote 4: It is on a similar basis that there is a science of rigid dynamics, with elasticity and fluidity excluded; and thus also can there be a hydrodynamics in which the consequences of viscosity are ignored.] My contention then is—and in this contention I am practically speaking for my brother physicists—that whereas life or mind can neither generate energy nor directly exert force, yet it can cause matter to exert force on matter, and so can exercise guidance and control: it can so prepare any scene of activity, by arranging the position of existing material, and timing the liberation of existing energy, as to produce results concordant with an idea or scheme or intention: it can, in short, "aim" and "fire."