But what I have merely described I have not yet understood; I am only preparing to try to understand it. It stands before me enveloped in all its mystery, and I must now begin to attempt to solve it, for describing is not explaining; it is only challenging explanation. The next step is to discover and formulate the laws. For when man sifts out things and processes and follows them out into their changes and stages he discovers the iron regularity of sequences, the strictly defined lines and paths, the inviolable order and connection in things and occurrences, and he formulates these into laws, ascribing to them the idea of necessity which he finds in himself. In so doing he makes distinct progress, for he can now go beyond what is actually seen, he can draw inferences with certainty as to effects and work back to causes. And thus order, breadth of view, and uniformity are brought into his acquaintance with facts, and his science begins. For science does not merely mean acquaintance with phenomena in their contingent or isolated occurrence, manifold and varied as that may be; it is the discovery and establishment of the laws and general modes of occurrence. Without this we might collect curiosities, but we should not have science. And to discover this network of uniformities throughout all phenomena, in the movements of the heavenly bodies and in the living substance of the cell alike, is the primary aim of all investigation. We are still far away from this goal, and it is more than questionable whether we shall ever reach it. But if the goal should ever be reached, if, in other words, we should ever be able to say with certainty what must result if occurrences _a_ and _b_ are given, or what _a_ and _b_ must have been when _c_ occurs, would explanation then have taken the place of description? Or would understanding have replaced mystery? Obviously not at all. It has indeed often been supposed that this would be the case. People have imagined they have understood, when they have seen that “that is always so, and that it always happens in this particular way.” But this is a naïve idea. The region of the described has merely become larger, and the riddle has become more complex. For now we have before us not only the things themselves, but the more marvellous laws which “govern” them. But laws are not forces or impelling causes. They do not cause anything to happen, and they do not explain anything. And as in the case of things so in that of laws, we want to know how they are, whence they come, and why they are as they are and not quite different. The fact that we have described them simply excites still more strongly the desire to explain them. To explain is to be able to answer the question “Why?”