Finality itself, if he keeps the name, does not save him from his error, for finality in his eyes is nothing but an efficient cause projected into the future. So we see him fixing stages, marking periods, inserting means, putting in milestones, continually destroying movement by halting it before his gaze. And we all do the same by instinctive inclination. Our concept of law, in its classical form, is not general: it represents only the law of co-existence and of mechanism, the static relation between two numerically disconnected terms; and in order to grasp evolution we shall doubtless have to invent a new type of law: law in duration, dynamic relation. For we can, and we must, conceive that there is an evolution of natural laws; that these laws never define anything but a momentary state of things; that they are in reality like streaks determined in the flux of becoming by the meeting of contrary currents. "Laws," says Monsieur Boutroux, "are the bed down which passes the torrent of facts; they have dug it, though they follow it." Yet we see the common theories of evolution appealing to the concepts of the present to describe the past, forcing them back to prehistoric times, and beyond the reasoning of today, placing at the beginning what is only conceivable in the mind of the contemporary thinker; in a word, imagining the same laws as always existing and always observed. This is the method which Mr Bergson so justly criticises in Spencer: that of reconstructing evolution with fragments of its product. If we wish thoroughly to grasp the reality of things, we must think otherwise. Neither of these ready-made concepts, mechanism and finality, is in place, because both of them imply the same postulate, viz. that "everything is given," either at the beginning or at the end, whilst evolution is nothing if it is not, on the contrary, "that which gives." Let us take care not to confound evolution and development. There is the stumbling-block of the usual transformist theories, and Mr Bergson devotes to it a closely argued and singularly penetrating criticism, by an example which he analyses in detail. ("Creative Evolution", chapter i.) These theories either do not explain the birth of variation, and limit themselves to an attempt to make us understand how, once born, it becomes fixed, or else through need of adaptation they look for a conception of its birth. But in both cases they fail. "The truth is that adaptation explains the windings of the movement of evolution, but not the general directions of the movement, still less the movement itself. The road which leads to the town is certainly obliged to climb the hills and go down the slopes; it adapts itself to the accidents of the ground; but the accidents of the ground are not the cause of the road, any more than they have imparted its direction." ("Creative Evolution", pages 111-112.)