Natural science is very well aware of this. It calls its previous descriptions “merely historical,” and it desires to supplement these with ætiology, causal explanation, a deeper interpretation, that in its turn will make laws superfluous, because it will penetrate so deeply into the nature of things that it will see precisely why these, and not other laws of variation, of development, of becoming, hold sway. This is just the meaning of the “reductions” of which we have already spoken. For instance, in regard to crystal formation, “explanation” will have replaced description only when, instead of demonstrating the forms and laws according to which a particular crystal always and necessarily arises out of a particular solution, we are able to show why, from a particular mixture and because of certain co-operating molecular forces, and of other more primary, more remote, but also intelligible conditions, these forms and processes of crystallisation should always and of necessity occur. If this explanation were possible, the “law” would also be explained, and would therefore become superfluous. From this and similar examples we can learn at what point “explanation” begins to replace description, namely, when processes resolve themselves into simpler processes from the concurrence of which they arise. This is exactly what natural science desires to bring about, and what naturalism hopes ultimately to succeed in, thereby solving the riddle of existence. But this kind of reduction to simpler terms only becomes “explanation” when these simpler terms are themselves clear and intelligible and not merely simple; that is to say, when we can immediately see why the simpler process occurs, and by what means it is brought about, when the question as to the “why” is no longer necessary, because, on becoming aware of the process, we immediately and directly perceive that it is a matter of course, indisputable, and requiring no proof. If this is not the case, the reduction to simpler terms has been misleading. We have only replaced one unintelligibility by another, one description by another, and so simply pushed back the whole problem. Naturalism supposes that by this gradual pushing back the task will at least become more and more simple, until at last a point is reached where the riddle will solve itself, because description becomes equivalent to explanation. This final stage is supposed to be found in the forces of attraction and repulsion, with which the smallest similar particles of matter are equipped. Out of the endlessly varied correlations of these there arise all higher forms of energy and all the combinations which make up more complex phenomena.